| 1. |
- Antunes, Filipe, et al.
(författare)
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A rheological investigation of the association between a non-ionic microemulsion and hydrophobically modified PEG. Influence of polymer architecture
- 2003
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 215:1-3, s. 87-100
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Tidskriftsartikel (refereegranskat)abstract
- ydrophobically modified polymers (HM-P) typically behave as thickeners in a wide range of systems. The thickening effect in an aqueous solution of this kind of polymer depends on intermolecular hydrophobic associations and also on chain entanglements if the polymer concentration is significantly above the overlap concentration. In the present investigation a rather short end-capped polymer has been investigated at concentrations that are significantly below the overlap concentration. Despite the rather low polymer concentration, polymer chains were connected into a three-dimensional network by using microemulsion droplets as cross-linking points. The simple structure of the solution simplifies interpretations of results since chain entanglements can be expected to be of low importance and only intermolecular hydrophobic associations have to be considered. In particular the rheological response is in most cases well characterized by one single relaxation time and, then, the solution can be rationalized withi the framework of the Maxwell model. We have found that the length of the polymer chain's hydrophobic end-groups, as well as the temperature, have a large influence on dynamics of the system, while the length of the hydrophilic mid-block has a relatively small significance. On the other hand, the connectivity in the system depends critically on the microemulsion concentration. Thus, a maximum was found in viscosity as a function of volume fraction, interpreted as being due to a decrease in crosslink lifetime. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 2. |
- Antunes, Filipe, et al.
(författare)
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Network formation of catanionic vesicles and oppositely charged polyelectrolytes. Effect of polymer charge density and hydrophobic modification
- 2004
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:11, s. 4647-4656
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Tidskriftsartikel (refereegranskat)abstract
- In nonequimolar solutions of a cationic and an anionic surfactant, vesicles bearing a net charge can be spontaneously formed and apparently exist as thermodynamically stable aggregates. These vesicles can associate strongly with polymers in solution by means of hydrophobic and/or electrostatic interactions. In the current work, we have investigated the rheological and microstructural properties of mixtures of cationic polyelectrolytes and net anionic sodium dodecyl sulfate/didodecyldimethylammonium bromide vesicles. The polyelectrolytes consist of two cationic cellulose derivatives with different charge densities; the lowest charge density polymer contains also hydrophobic grafts, with the number of charges equal to the number of grafts. For both systems, polymer-vesicle association leads to a major increase in viscosity and to gel-like behavior, but the viscosity effects are more pronounced for the less charged, hydrophobically modified polymer. Evaluation of the frequency dependence of the storage and loss moduli for the two systems shows further differences in behavior: while the more long-lived cross-links occur for the more highly charged hydrophilic polymer, the number of cross-links is higher for the hydrophobically modified polymer. Microstructure studies by cryogenic transmission electron microscopy indicate that the two polymers affect the vesicle stability in different ways. With the hydrophobically modified polymer, the aggregates remain largely in the form of globular vesicles and faceted vesicles (polygon-shaped vesicles with largely planar regions). For the hydrophilic polycation, on the other hand, the surfactant aggregate structure is more extensively modified: first, the vesicles change from a globular to a faceted shape; second, there is opening of the bilayers leading to holey vesicles and ultimately to considerable vesicle disruption leading to planar bilayer, disklike aggregates. The faceted shape is tentatively attributed to a crystallization of the surfactant film in the vesicles. It is inferred that a hydrophobically modified polyion with relatively low charge density can better stabilize vesicles due to formation of molecularly mixed aggregates, while a hydrophilic polyion with relatively high charge density associates so strongly to the surfactant films, due to strong electrostatic interactions, that the vesicles are more perturbed and even disrupted.
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| 3. |
- Benjamins, Jan-Willem, et al.
(författare)
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Ellipsometry studies of nonionic surfactant adsorption at the oil-water interface
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:1, s. 149-159
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Tidskriftsartikel (refereegranskat)abstract
- In the presented study we have developed and implemented a methodology for ellipsometry measurements at liquid interfaces that makes it possible to determine the amount adsorbed without assumptions of refractive index or thickness of the adsorbed layer. It was demonstrated that this is possible by combined measurements from different aqueous phases, H2O and D2O, which were shown to have sufficiently different refractive indices. The methodology was tested by studying adsorption of two types of nonionic poly(ethylene glycol) alkyl ether surfactants, CnH2n+1(OC2H4)(m)OH or CnEm at the decane-aqueous interface, where C12E5 was adsorbed from the oil phase and C18E50 from the aqueous phase. The observed plateau values of the adsorbed amounts were 1.38 and 0.93 Mg/M-2 for C12E5 and C18E50, respectively, which is in agreement with the corresponding values of 1.49 and 1.15 Mg/M-2 obtained from applying the Gibbs equation to interfacial tension data for the same systems. We will briefly discuss the adsorption behavior in relation to the molecular structure of the surfactant and the phase behavior of the oil - surfactant- aqueous systems in relation to our experimental results.
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| 4. |
- Benjamins, Jan-Willem, et al.
(författare)
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Formation of a liquid crystalline phase from phosphatidylcholine at the oil-aqueous interface
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:7, s. 2804-2810
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption of phospholipid (1,2-dioleoyl-sn-glycero-3-phosphatidylcholine) and formation of a surface phase at the oil-water interface has been followed by using ellipsometry. The properties of the interfacial phase were found to depend strongly on whether phospholipid was added to the oil phase or to the aqueous phase as liposomal structures. In the latter case a monolayer formed, while if the phospholipid was supplied from the oil phase a lamellar phase appeared at the interface. The effect on the stabilizing surface phase of a surface-active protein (P-lactoglobulin) was also investigated. The observations are important for understanding stabilizing properties of surface-active compounds commonly used to stabilize emulsions. In addition it has been demonstrated that ellipsometry can be used to study the initial process when a two-phase system consisting of a water and an oil phase is transformed into a three phase system or eventually to a one-phase system.
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| 5. |
- Benjamins, Jan-Willem, et al.
(författare)
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New experimental setup to use ellipsometry to study liquid-liquid and liquid-solid interfaces
- 2002
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 18:16, s. 6437-6444
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Tidskriftsartikel (refereegranskat)abstract
- Different types of optical light guides were constructed and tested to enable convenient multiple angle of incidence ellipsometry, on solid and liquid interfaces in liquid solutions. Two light guides are needed on an ellipsometer, one to guide the incoming light and one to guide the light that is reflected at the test surface, and therefore one light guide was mounted on the laser arm and one on the detector arm of the ellipsometer. With this arrangement the optical windows automatically adjust to always be perpendicular to the direction of the light independent of the angle of incidence. The purpose with these light guides is to facilitate the passage of light through the air/solution interface. A thorough theoretical and experimental analysis of optical errors introduced by such light guides is presented. This discussion includes the effect of multiple reflections between and within the windows of the light guides' On the basis of this analysis a new ellipsometry setup with light guides, consisting of glass tube's with glued end windows, was developed. This setup makes it possible to perform accurate measurements in almost any type of measuring cell at any angle of incidence.
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| 6. |
- Björklund, Sebastian, et al.
(författare)
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A water gradient can be used to regulate drug transport across skin
- 2010
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Ingår i: Journal of Controlled Release. - : Elsevier. - 0168-3659 .- 1873-4995. ; 143:2, s. 191-200
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Tidskriftsartikel (refereegranskat)abstract
- At normal conditions there is a substantial water gradient over the skin as it separates the water-rich inside of the body from the dry outside. This leads to a variation in the degree of hydration from the inside to the outside of skin and changes in this gradient may affect its structure and function. In this study we raise the question: How do changes in the water gradient across skin affect its permeability? We approach this problem in novel diffusion experiments that permit strict control of the gradient in the chemical potential of water and hence well-defined boundary conditions. The results demonstrate that a water gradient can be used to regulate transport of drugs with different lipophilic characteristics across the skin barrier. It is shown that the transport of metronidazole (log Po/w=0.0) and methyl salicylate (log Po/w=2.5) across skin increases abruptly at low water gradients, corresponding to high degrees of skin hydration, and that this effect is reversible. This phenomenon is highly relevant to drug delivery applications due to its potential of temporarily open the skin barrier for transdermal drug delivery and subsequently close the barrier after treatment. Further, the results contribute to the understanding of the occlusion effect and indicate the boundary conditions of the water gradient needed to make use of this effect
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| 7. |
- Björklund, Sebastian, et al.
(författare)
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Glycerol and urea can be used to increase skin permeability in reduced hydration conditions
- 2013
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Ingår i: European Journal of Pharmaceutical Sciences. - : Elsevier. - 0928-0987 .- 1879-0720. ; 5:50, s. 638-645
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Tidskriftsartikel (refereegranskat)abstract
- The natural moisturizing factor (NMF) is a group of hygroscopic molecules that is naturally present in skin and protects from severe drying. Glycerol and urea are two examples of NMF components that are also used in skin care applications. In the present study, we investigate the influence of glycerol and urea on the permeability of a model drug (metronidazole, Mz) across excised pig skin membranes at different hydrating conditions. The degree of skin hydration is regulated by the gradient in water activity across the membrane, which in turn depends on the water activity of the formulation in contact with the skin membrane. Here, we determine the water activity of all formulations employed using an isothermal calorimetric method. Thus, the gradient in water activity is controlled by a novel experimental set-up with well-defined boundary conditions on both sides of the skin membrane. The results demonstrate that glycerol and urea can retain high steady state flux of Mz across skin membranes at dehydrating conditions, which otherwise would decrease the permeability due to dehydration. X-ray diffraction measurements are performed to give insight into the effects of glycerol and urea on SC molecular organization. The novel steady state flux results can be related to the observation that water, glycerol, and urea all affect the structural features of the SC molecular components in a similar manner.
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| 8. |
- Brogard, M., et al.
(författare)
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A new standardized lipolysis approach for characterization of emulsions and dispersions
- 2007
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 308:2, s. 500-507
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Tidskriftsartikel (refereegranskat)abstract
- A new standardized lipolysis approach is presented where the focus is on the initial rate of lipolysis. An advantage is that data obtained in this way reflect degradation before growing amounts of lipolysis products retard the process. The method can be used to rank different lipase substrates. In particular, the method can be used to obtain information about the susceptibility to degradation of various emulsions and dispersions that are used in technical applications. We present how the method is standardized to facilitate comparison of various substrates. This involves (i) lipase substrate in excess, i.e., the amount of lipase is rate limiting, and (ii) expressing rate of degradation relative to that of a reference substrate, tributyrin. Under such conditions, with the amount of lipase substrate held constant, an increase in enzymatic activity will generate a proportional increase in the lipolysis rate. This enables comparison of results obtained from different enzyme batches and corrects for day-to-day variability. Examples illustrating the potential of the method to discriminate and rank different lipase substrates with regard to enzymatic degradation are presented. (c) 2006 Elsevier Inc. All rights reserved.
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| 9. |
- Esteban, Isabel, et al.
(författare)
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Incorporation of substituted acrylamides to the lamellar mesophase of Aerosol OT
- 2006
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 299:1, s. 378-387
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Tidskriftsartikel (refereegranskat)abstract
- The structure and stability of the lamellar liquid crystal formed by the surfactant sodium bis-2ethylhexyl sulfosuccinate (AOT) in water is perturbed by small amounts of the substituted acrylamides N-isopropyl, N,N-diethyl, N-acryloylmorpholine, and N,N-dimethyl methacrylamide, as revealed by small angle X-ray scattering (SAXS), deuterium NMR, and microscopy. These molecules are water soluble and stay mostly in the water layers between lamellae, but a small fraction of them (5-19%) are incorporated into the AOT bilayers, thereby producing dramatic changes. Both, the degree of anisotropy in the water molecules hydrating AOT (quadrupolar splitting in H-2 NMR) and the long period spacing between lamellae (SAXS), decrease with addition of this molecules at low concentrations, which is attributed to the lower average headgroup, density at the AOT/water interface when the acrylamide is incorporated. The strength of these perturbations depends on the acrylamide, and goes in parallel with the hydrophobic character of the alkyl side groups in its molecule, which suggests that the acrylamides incorporated to the bilayer enter into contact with the lipophilic tails of the AOT molecule. An interaction with the hydrated heads of AOT is also suggested in the particular case of N-isopropylacrylamide. On increasing the molecule concentration an incipient melting of the lamellar phase towards an isotropic solution takes place, first at the microscopic level, then macroscopic. Near this phase transition, the ordered domains lose the random orientation prevailing at lower acrylamide concentrations, and adopt a preferred orientation, perpendicular to the magnetic field. (c) 2006 Elsevier Inc. All rights reserved.
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| 10. |
- Imberg, Anna, 1973-
(författare)
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On Phase Behaviours in Lipid/Polymer/Solvent/Water Systems and their Application for Formation of Lipid/Polymer Composite Particles
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A new kind of lipid/polymer composite particle, consisting of a biodegradable polymer matrix with well-defined lipid domains, has been created. The lipid used is the water-swelling lipid monoolein (MO), which forms a reversed bicontinuous cubic diamond structure in aqueous solutions. The polymer is poly(d,l-lactide-co-glycolide) (PLG), which degrades into water-soluble monomers through hydrolysis. This new particle might be a good alternative for encapsulation of active substances intended to be released over a longer period of time, i.e. sustained/retained/controlled release.To prepare such particles can be difficult. Suitable phase behaviour and a solvent with the right properties are needed. For this reason, the phase behaviours of several different lipid/polymer/solvent/water systems have been explored. From the phase behaviour of a suitable system (i.e. MO/PLG/ethyl acetate/water), a route for formation of lipid/polymer composite particles has been deduced. Particles have been formed and distinct, water-swelling, lipid domains have been confirmed by characterization by means of confocal laser scanning probe microscopy (CLSM). The sample preparation process has been automated and a method based on using a robotic liquid handler has been developed. Phase diagrams have been determined by examination of macroscopic behaviours and the microstructures of the phases have been studied by small- and wide-angle X-ray scattering (L3, V2, Lα, L), nuclear magnetic resonance self-diffusion (L, L3), viscosimetry (L) and rheology (L). Several different theoretical models have been applied for interpretation of the results. For example, the swelling of the reversed bicontinuous cubic phases and the sponge phase have been modelled by applying the theory of infinite periodical minimal surfaces, the sponge phase has been shown to be bicontinuous according to the theory of interconnected rods and the phase behaviour of the polymer has been described by the Flory-Huggins theory. The main focus of this work (4/5) concerns phase studies in multicomponent systems from a physical-chemical point of view.
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| 11. |
- Karlberg, Maria, et al.
(författare)
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Hydrophobically modified ethyl(hydroxyethyl)cellulose as stabilizer and emulsifying agent in macroemulsions
- 2005
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 262:1-3, s. 158-167
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Tidskriftsartikel (refereegranskat)abstract
- Stability, droplet diameter and viscosity of o/w macroemulsions of olive oil stabilized with lecithin from soybean and different types of polymers have been investigated. The stabilizing polymers were non-ionic cellulose ethers, both with and without hydrophobic groups grafted onto the polymer backbone. Emulsions without polymers showed essentially no stability against creaming. Unmodified polymers provided limited stability, while hydrophobically modified versions of the polymers improved the stability dramatically. The viscosity of emulsions stabilized by hydrophobically modified polymers was significantly increased compared with aqueous solutions of the polymers alone, suggesting network formation including both polymers and emulsion droplets. It was also found that dilution had virtually no effect on the droplet diameters of emulsions stabilized with hydrophobically modified cellulose ethers and that coalescence was effectively opposed. (c) 2005 Elsevier B.V. All rights reserved.
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| 12. |
- Karlberg, Maria, et al.
(författare)
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Mixed solutions of hydrophobically modified graft and block copolymers
- 2004
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 236:1-3, s. 159-164
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Tidskriftsartikel (refereegranskat)abstract
- Phase separation temperatures and viscosities of dilute and semidilute aqueous mixtures of hydrophobically modified graft and block copolymers have been studied. The graft copolymer was hydrophobically modified ethyl(hydroxyethyl)cellulose (HM-EHEC), and the block copolymers were hydrophobically modified poly(ethylene glycol) (HM-PEG) with diblock (DB) or triblock (TB) structures, i.e., modified at one or both ends, respectively. For comparison, viscosity measurements were made also on mixtures of TB with HM-HEC, and on systems where one of the polymers was unmodified (i.e. HM-EHEC/PEG or TB/EHEC). All results indicate mixed hydrophobic associations between graft and block copolymers. Moderate viscosity enhancements were found on addition of HM-PEG to HM-EHEC, and the effects were larger for TB than for DB. The viscosity changes were quite sensitive to the concentration of HM-EHEC. (C) 2004 Elsevier B.V. All rights reserved.
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| 13. |
- Karlson, L, et al.
(författare)
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A rheological investigation of the complex formation between hydrophobically modified ethyl (hydroxy ethyl) cellulose and cyclodextrin
- 2002
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Ingår i: Carbohydrate Polymers. - 0144-8617. ; 50:3, s. 219-226
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Tidskriftsartikel (refereegranskat)abstract
- The thickening effect of a hydrophobically modified polymer in an aqueous solution is dependent on intermolecular hydrophobic associations, and if the polymer concentration is significantly above the overlap concentration also on chain entanglements. In this investigation we have added different cyclodextrins (CD) in order to decouple hydrophobic polymer-polymer associations via inclusion complex formation with the polymer hydrophobic tails. Both size and hydrophobicity of the cavity of the CD-molecules were found to have an effect on the process. In addition, the influence of chemical structure of the polymer hydrophobic tails was investigated. Either a linear C-14-chain or a more bulky nonylphenol group was used. The viscosity as a function of CD-concentration first decreased strongly, and then attained a constant value. At excess CD the viscosity became virtually the same as in a solution of the unmodified parent polymer, provided that complex formation was not sterically bindered. This suggests that all hydrophobic links, originating from the hydrophobic modification process, which influence the theology could be deactivated. On the other hand, with combinations where the complex formation was hindered to a certain degree the initial decrease was less accentuated, and also, the viscosity leveled out at a significantly higher value. In an attempt to rationalize the data a simple model based on the assumption that each complex formed deactivates one theologically active link was used. In combination with the Langmuir adsorption model the number of complexes as a function of CD concentration could be obtained. This model also gave a value of the complex formation constant. Furthermore, in solutions where all hydrophobic links could be deactivated the results from the model suggested that all polymer hydrophobic tails were originally active in forming the network. (C) 2002 Elsevier Science Ltd. All rights reserved.
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| 14. |
- Karlson, L, et al.
(författare)
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Complex formed in the system hydrophobically modified polyethylene glycol/methylated alpha-cyclodextrin/water. An NMR diffusometry study
- 2003
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 228:1-3, s. 171-179
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Tidskriftsartikel (refereegranskat)abstract
- In aqueous solutions hydrophobically modified polyethylene glycol (HM-PEG) forms a transient polymer network held together by intermolecular hydrophobic associations. In the present investigation we have used NMR-diffusometry to study how the addition of methylated alpha-cyclodextrin (M-alpha-CD) influences the polymer network. The addit on of M-alpha-CD resulted in an increased mean self-diffusion of HM-PEG, DHM-PEG, which is referred to a degradation of the polymer network when hydrophobic associations are disrupted due to complex formation between the hydrophobic groups of HM-PEG and M-alpha-CD. Addition of small amounts of M-alpha-CD results in a dramatic increase in DHM-PEG. Upon further addition of M-a-CD the increase in DHM-PEG is less dramatic and at excess M-alpha-CD, DHM-PEG levels off and equals the mean self-diffusion coefficient for unmodified PEG with the same molecular weight. The suggested interpretation is that the addition of the first molecules of M-alpha-CD mainly reduces the probability for hydrophobic associations inter-connecting different clusters of polymer micelles whereas at higher M-alpha-CD concentrations a disengagement of the individual clusters into separate HM-PEG molecules becomes important. (C) 2003 Elsevier B.V. All rights reserved.
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| 15. |
- Karlson, L, et al.
(författare)
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Cyclodextrins in hydrophobically modified poly(ethylene glycol) solutions: Inhibition of polymer-polymer associations
- 2002
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 18:23, s. 9028-9034
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Tidskriftsartikel (refereegranskat)abstract
- in an aqueous solution of a hydrophobically, end-modified poly(ethylene glycol) polymer, HM-PEG, the thickening effect is dependent on intermolecular hydrophobic associations and the formation of a network structure. In the present investigation cyclodextrin, CD, has been added to an aqueous HM-PEG solution and a decrease in Newtonian viscosity has been followed. The decreased viscosity refers to polymer-polymer associations becoming less numerous when complexes between polymer hydrophobic tails and CD become more frequent; CD-decorated polymer hydrophobic tails have no possibility of contributing to the network. It was found that deactivation of the first few hydrophobic tails has very large consequences for the viscosity. A termination of a fraction as small as 10% (or below) of the total amount of polymer hydrophobic tails may reduce viscosity to a level almost corresponding to that of the unmodified parent polymer. This can be understood by taking into account that a solution of a HM-PEG polymer is, expected to be inhomogeneous with large concentration fluctuations and that the viscosity is likely to be strongly decreased by reducing the probability of hydrophobic associations responsible for connecting different blusters. The effect of CD on rheology is very different for different architectures of hydrophobically modified polymer, in particular between graft copolymers and end-capped ones. This can be understood from the differences in network structure.
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| 16. |
- Lafitte, Géraldine, et al.
(författare)
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Diffusion of nutrients molecules and model drug carriers through mucin layer investigated by magnetic resonance imaging with chemical shift resolution
- 2007
-
Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0022-3549. ; 96:2, s. 258-263
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic resonance imaging (MRI) with chemical shift resolution is a recent extension of MRI and it provides information about species resolved molecular transport on the macroscopic scale in complex systems. In this contribution, we show that by using this novel method, one can predict the behavior of drug and food molecules when they are in contact with the mucosal layer in the gastrointestinal tract. For the first time, the transport properties of a mixture of nutrients (i.e., a solution of ethanol and glucose) and of a model drug carrier (i.e., an equimolar solution of cationic and nonionic surfactants) through a mucin gel have been investigated. This study shows that transport properties of the diffusing molecules through a mucin gel are dependent on their size and physicochemical properties. In addition, we show that mucin gel acts as an efficient selective barrier. It favors the disintegration of mixed micelles of nonionic and cationic surfactants by stopping the diffusion of cationic surfactants with slightly affecting the diffusion of the nonionic surfactants. (c) 2006 Wiley-Liss, Inc.
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| 17. |
- Lafitte, Géraldine, et al.
(författare)
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Mixtures of mucin and oppositely charged surfactant aggregates with varying charge density. Phase behavior, association, and dynamics
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:16, s. 7097-7104
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Tidskriftsartikel (refereegranskat)abstract
- The nonionic surfactant Tween80 is a commonly used excipient in drug formulations containing an active substance with low aqueous solubility. Model drug vehicles with varying charge density were obtained by mixing Tween80 (PS-80) with the cationic surfactant Tetradecyltrimethylammonium chloride (TTAC), thus forming mixed micelles. The micelles were mixed with the negatively charged polyelectrolyte mucin, which is a component in the protective mucus layer covering epithelial cell linings. Depending on the composition of the mixture, complex-formation could be followed by precipitation. Using X-ray diffraction, it was found that the precipitate contained a lamellar phase with properties sensitive to the proportion of PS-80. Higher amounts of PS-80 were found to oppose phase separation. Further analysis in the one-phase region, or alternatively of the supernatant of two-phase samples, by H-1 NMR, HPLC, and diffusion measurements with PGSE-NMR led to the conclusions that at low proportion of PS-80 aggregates composed of mixed (PS-80 and TTAC) micelles and mucin were formed, whereas increased concentrations of PS-80 favored the dissolution of the precipitate and limited the interactions between mixed micelles and the polymer.
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| 18. |
- Lafitte, Géraldine, et al.
(författare)
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PFG-NMR diffusometry: A tool for investigating the structure and dynamics of noncommercial purified pig gastric mucin in a wide range of concentrations
- 2007
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Ingår i: Biopolymers. - : Wiley. - 0006-3525 .- 1097-0282. ; 86:2, s. 165-175
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Tidskriftsartikel (refereegranskat)abstract
- For the first time, Pulsed Field Gradient-Nuclear Magnetic Resonance, a powerful noninvasive tool for studying the dynamics and structure of complex-gels, has been used to measure diffusion of probe molecules in aqueous solutions/gels of noncommercial purified pig gastric mucin (PGM), in a concentration range up to 5 wt%. Complementary data were obtained from rheology measurements. The combination of techniques revealed a strong pH dependency of the structure of the PGM samples while changes in concentration, ionic strength, and temperature appeared to induce less pronounced alterations. Viscosity was found to vary in a nonmonotonous way with pH, with the more viscous solutions found at intermediate pH. We propose that this finding is due to a reduced charge density at lower pH, which is expected to continuously increase the relative importance of hydrophobic associations. The results suggest a loose network of expanded fully charged PGM molecules woth considerable mobility at neutral pH (pH 7.4). At intermediate pH (pH 4), a three-dimensional expanded network is favored. At pH 1, the charge density is low and microphase seperation occurs since hydrophobic associations prevail. This leads to the formation of clusters concentrated in PGM molecules seperated by regions depleted in PGM. The results obtained increase our knowledge about the gastric mucosal layer, which in vivo contains mucin in the same concentration range as that of the samples investigated here. (c) 2007 Wiley Periodicals, Inc.
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| 19. |
- Lafitte, Géraldine, et al.
(författare)
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Transport properties and aggregation phenomena of polyoxyethylene sorbitane monooleate (polysorbate 80) in pig gastrointestinal mucin and mucus
- 2007
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 23:22, s. 10933-10939
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Tidskriftsartikel (refereegranskat)abstract
- The aqueous environment in the gastrointestinal tract frequently requires solubilization of hydrophobic drug molecules in appropriate drug delivery vehicles. An effective uptake/absorption and systemic exposure of a drug molecule entails many processes, one being transport properties of the vehicles through the mucus layer. The mucus layer is a complex mixture of biological molecules. Among them, mucin is responsible of the gel properties of this layer. In this study, we have investigated the diffusion of polyoxyethylene sorbitane monooleate (polysorbate 80), a commonly used nonionic surfactant, in aqueous solution, in mucin solutions at 0.25 and 5 wt %, and in mucus. These measurements were done by using the pulsed field gradient spin echo nuclear magnetic resonance (PGSE-NMR) technique. We conclude that polysorbate 80 is a mixture of non-surface-active molecules that can diffuse freely through all the systems investigated and of surface-active molecules that form micellar structures with transport properties strongly dependent on the environment. Polysorbate 80 micelles do not interact with mucin even though their diffusion is hindered by obstruction of the large mucin molecules. On the other hand, the transport is slowed down in mucus due to interactions with other components such as lipids depots. In the last part of this study, a hydrophobic NMR probe molecule has been included in the systems to mimic a hydrophobic drug molecule. The measurements done in aqueous solution revealed that the probe molecules were transported in a closely similar way as the polysorbate 80 micelles, indicating that they were dissolved in the micellar core. The situation was more complex in mucus. The probe molecules seem to dissolve in the lipid depots at low concentrations of polysorbate 80, which slows down their transport. At increasing concentration of polysorbate 80, the diffusion of the probe molecules increases indicating a continuous dissolution of hexamethyldisilane in the core of polysorbate 80 micelles.
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| 20. |
- Lundberg, Dan, 1975, et al.
(författare)
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Studies on the Interactions Between Mucin and Surfactant Aggregates Containing the Cationic Surfactant Dodecyl Betainate
- 2009
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Ingår i: Journal of Dispersion Science and Technology. - : Informa UK Limited. - 1532-2351 .- 0193-2691. ; 30:6, s. 920-928
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Tidskriftsartikel (refereegranskat)abstract
- The interactions of surfactant aggregates containing the cationic, cleavable surfactant dodecyl betainate (DB) with mucin are investigated. The aggregates were either mixed micelles of DB and the nonionic surfactant PS-80 in different ratios or a dispersion of the commercial self-emulsifying drug-delivery formulation Sandimmun Neoral charged with DB. It is found that for the surfactant aggregates to show any notable interactions with mucin these must have a high positive charge density. Also presented are results from Ussing chamber experiments, which suggest that DB has a limited impact on the integrity and the barrier function of the intestinal epithelium.
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| 21. |
- Maleki, Atoosa, et al.
(författare)
-
Effect of pH on the association behavior in aqueous solutions of pig gastric mucin
- 2008
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Ingår i: Carbohydrate Research. - : Elsevier BV. - 1873-426X .- 0008-6215. ; 343:2, s. 328-340
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Tidskriftsartikel (refereegranskat)abstract
- In this study, dynamic light scattering (DLS), turbidity, and rheo-small angle light scattering (rheo-SALS) methods have been utilized to examine the impact of pH (1 <= pH <= 7) on aqueous solutions of noncommercial purified pig gastric mucin. The asymmetric flow field-flow fractionation (AFFFF) measurements established that the mucin sample has a high molecular weight and is polydisperse. DLS measurements on dilute solutions of mucin disclosed large interchain aggregates at pH 2, where the polymer has a low charge density or is uncharged. At lower or higher values of pH, mucin is charged and the tendency of forming interpolymer complexes is affected. In the semidilute concentration regime, pronounced junction zones (`lumps' of polymer) are evolved and a heterogeneous connected network is formed at pH 2, whereas the association structures are disintegrated (smaller `lumps') at lower or higher pH values due to electrostatic repulsive interactions, and a more homogeneous network is evolved. The DLS and viscosity results at pH 1 indicate the development of a fragmented network, composed of contracted chains that are decorated by some positive charges. The effect of shear flow on the structure of semidilute solutions of mucin was investigated with the aid of rheo-SALS methods. The scattered intensity revealed a strong upturn at low values of the wave vector (q) for mucin solutions at pH 2 and pH 4, which suggests the evolution of large association domains. At these pH values, a flow-induced anisotropy in the 2D SALS patterns in the form of elliptical shapes was observed at high shear rates.
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| 22. |
- Mele, Stefania, et al.
(författare)
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Phase behavior in the biologically important oleic acid/sodium oleate/water system
- 2018
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Ingår i: Chemistry and Physics of Lipids. - : Elsevier. - 0009-3084 .- 1873-2941. ; 211, s. 30-36
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Tidskriftsartikel (refereegranskat)abstract
- The phase behavior in the oleic acid/sodium oleate/normal saline (0.15M NaCl aqueous solution) system has been determined. For this purpose visual inspection of samples between crossed polarizers, and Small Angle X-ray diffraction was used to identify the various phases and their unit cell dimensions. A rich phase behavior was observed for the ternary system, featuring reverse micellar, micellar cubic, hexagonal, and cubic phases, and large regions with lamellar phases. As expected the ratio the 'oleic acid/sodium oleate' determines the pH and as a consequence the phase behavior. The results could be modeled by an extended Henderson-Hasselbalch (HH) equation, which takes into account the electrostatic potential at the aqueous lipid interface. The knowledge obtained is important for understanding the lipolysis of triglycerides, as the phase behavior of the end-product of the reaction regulates how well the insoluble product can be dispersed and consequently the kinetics of the process.
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| 23. |
- Pacios, Isabel E, et al.
(författare)
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Fragmentation of the lamellae and fractionation of polymer coils upon mixing poly(dimethylacrylamide) with the lamellar phase of aerosol OT in water
- 2005
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 109:50, s. 23896-23904
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Tidskriftsartikel (refereegranskat)abstract
- The lamellar mesophase formed by surfactant 1,4-bis(2-ethylhexyl) sodium sulfosuccinate (AOT) in deuterated water is mixed with poly(dimethylacrylamide) (PDMAA) polymers of low molecular weight ((M) over bar (n) = (2-20) x 10(3)). The mixtures separate into microphases (lamellar plus isotropic polymer solution). Their microstructures are studied by microscopy, small-angle X-ray scattering (SAXS), and deuterium NMR (2 H NMR). According to SAXS, the lamellar phase fractionates the molecular weight distribution of the polymer, by dissolving only chains with coil sizes smaller than the thickness of the water layers between lamellae, and keeping larger chains segregated from the lamellar phase. The fraction of polymer that is segregated from the lamellar phase grows with (M) over bar (n) of the polymer. In H-2 NMR, there are two signals, a quadrupolar doublet (water molecules hydrating the anisotropic lamellar phase contribute to this doublet) and a singlet (water molecules in the isotropic polymer solution contribute to this singlet). These two signals are deconvoluted to analyze the phases. Mixing with the polymer produces the partial dispersion of the lamellar phase into small fragments (microcrystallites). The structure of these microcrystallites is such that they conserve the regular long period spacing of the macrophase, and are thus identified in SAXS, but they are smaller than the minimum size required to produce quadrupolar splitting (about 4 mu m), and therefore, in H-2 NMR, they contribute to the singlet. H-2 NMR can thus not distinguish between small microcrystallites and an isotropic polymer solution segregated from the lamellar phase; instead small microcrystallites are detected as an apparent increase of the isotropic solution. The degree of dispersion produced by the polymer in the lamellar phase is correlated 4 with the degree of segregation that the polymer suffers. Thus, much greater dispersion into microcrystallites is produced by the higher (M) over bar (n) polymers than by the lower (M) over bar (n) polymers (in the range covered by the present samples, although with a much higher molecular weight sample (3 x 10(6)) that is totally segregated no such microcrystallites were detected).
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| 24. |
- Pacios, I E, et al.
(författare)
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Nanometric sieving of polymer coils by a lamellar liquid crystal: Surfactant AOT and polydimethylacrylamide
- 2005
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 38:5, s. 1949-1957
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Tidskriftsartikel (refereegranskat)abstract
- The liquid crystal formed by surfactant AOT/water mixtures in its lamellar mesophase at a spacing between lamellae, d, equal to 8 nm, is mixed with poly(dimethylacrylamide) (PDMAA) polymers of low molecular weight in the range M-n= 2-20 x 10(3); the polymers are synthesized by living radical polymerization. The lowest molecular weights do not affect d significantly, indicating that the polymer coils penetrate inside the lamellar phase and dissolve in the water layers. With higher molecular weights, d decreases with added polymer, this decrease being stronger as the molecular weight of the polymer is higher, and the mixture becomes microheterogeneous. This indicates that the higher-molecular-weight polymers are segregated in a separate microphase that partially deswells the lamellae and that this segregation increases with the molecular weight of the polymer. The law, which governs the deswelling of lamella with added polymer, is deduced assuming that a fraction of each polymer can dissolve in the lamellar phase, while the rest of the polymer is segregated from it. This latter fraction is then obtained for each polymer simply by fitting to this law the experimental d as function of polymer concentration. It is proposed that the reason for this fractionation of polymer is that the lamellar structure acts as a grating which sieves the polymer coils according to their size relative to d, chains with molecular weight above a certain cutoff value, determined by d, being excluded from the interlamellar space. The fraction of chains excluded from the lamellae is calculated comparing the experimental molecular weight distributions (from SEC) of the polymers with the cutoff values determined by d. The results show that the polymer samples synthesized here cover the whole spectrum of behaviors, from almost total penetration to almost total exclusion. Both this method of cutting off the molecular weight distribution according to d and the other method of fitting d to the law for lamellar deswelling give similar results for the fraction of polymer that is segregated from the lamellae.
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| 25. |
- Pacios, Isabel E, et al.
(författare)
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Polyelectrolyte-surfactant complexes with long range order.
- 2008
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 319:1, s. 330-337
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Tidskriftsartikel (refereegranskat)abstract
- Mixtures of carboxymethyl cellulose (CMC) or hydrophobically modified CMC with an oppositely charged surfactant (benzyldimethyltetradecylammonium chloride) in water were prepared. When the global polymer concentration is 0.18% by weight and the surfactant content is high enough, a precipitate with hexagonal order is formed. The precipitate composition shows practically constancy in its water content and a slight diminution in polymer concentration when the global surfactant content is varied between 0.9 and 23 wt%. The lattice parameter in this phase decreases when the polymer/surfactant ratio in the phase increases; this variation is faster with CMC than with the hydrophobically modified CMC. In this way electrostatic and hydrophobic interactions are far from being additive. From the extrapolation to infinite dilution, the global interaction seems to depend on the substitution degree in the polymer. Additionally, the comparison between the radius at the polar-apolar interface in the cylinders and the lattice parameter as a function of polymer/surfactant ratio in the hexagonal phase is compatible with some of the alkyl chains belonging to the hydrophobically modified CMC being present in the aqueous zone.
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| 26. |
- Pacios, I E, et al.
(författare)
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Polymerization of N,N-dimethylacrylamide in Aerosol OT-water mixtures: from lamellae to segregation
- 2003
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 218:1-3, s. 11-20
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Tidskriftsartikel (refereegranskat)abstract
- The polymerizable N,N-dimethylacrylamide (DMAA) is added to the lamellar liquid crystalline system formed by the anionic surfactant Aerosol OT and water. Small angle X-ray scattering, gives the same bilayer thickness and hydrophilic group cross-sectional area as without DMAA, and an environment sensitive fluorescent probe indicates that DMAA is likely to be in the water layers between the AOT bilayers. This shows that the structure of the AOT bilayer in the lamellar phase is not affected by DMAA. However, DMAA induces instability of the lamellar phase, and a second phase, an isotropic solution, appears for larger DMAA contents The effect of DMAA in stabilizing this phase with respect to lamellae is much larger than that expected from a simple dilution with water. Furthermore, there is a combined influence of temperature and DMAA concentration on the coexistence of the lamellar and the isotropic phases. When an initiator is added and the monomer polymerizes the tendency to phase separate increases strongly. The lamellar spacing after polymerization is below the value predicted by the global AOT/H2O ratio. This indicates that the polymer segregates from the AOT phase and that the lamellar phase is osmotically compressed by the polymer rich phase. (C) 2003 Elsevier Science B.V. All rights reserved.
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| 27. |
- Pacios, IE, et al.
(författare)
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Equilibrium between poly(NN-dimethylacrylamide) and the lamellar phase of aerosol OT/water
- 2002
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 106:19, s. 5035-5041
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Tidskriftsartikel (refereegranskat)abstract
- A mixed amphiphilic system composed of the anionic surfactant Aerosol OT (AOT), in water forming a lamellar phase, to which is added a neutral noninteracting polymer, poly(N,N-dimethylacrylamide), is studied experimentally by SAXS, H-2 NMR, and microscopy, in a range of surfactant and polymer compositions. Addition of the polymer produces a decrease in the lamellar spacing, the decrease by the polymer being almost twice that produced by an equal volume of AOT. Microscopy reveals heterogeneity, but no macroscopic phase separation occurs. H-2 NMR detects that on increasing the polymer concentration some water is in an isotropic environment. It is inferred that the presence of the polymer induces a microscopic phase separation into a polymer-rich isotropic phase and a surfactant-rich lamellar phase, and this is tested theoretically by calculating the osmotic pressures in these two phases. In the lamellar phase, the effect of electrostatic, undulation, van der Waals, and hydration forces on the AOT bilayer is considered; in the isotropic phase, the osmotic contribution of the polymer is considered. These two pressures correlate well, supporting theoretically the hypothesis of the two phases in equilibrium.
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| 28. |
- Pacios, IE, et al.
(författare)
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In situ polymerization of N,N-dimethylacrylamide in aerosol OT-water: Modified lamellar structure and multiphase separation
- 2002
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:20, s. 7553-7560
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Tidskriftsartikel (refereegranskat)abstract
- N,N-Dimethylacrylamide is polymerized in the lyotropic surfactant system containing Aerosol-OT (AOT) and water. The polymerization is thermally initiated with AIBN, which allows a homogeneous initiation in this very viscous mixture. The starting mixture contains a lamellar liquid crystalline phase and an isotropic phase in equilibrium. After the polymerization, new phases develop which appear to have a lamellar structure, even if originated from the initial isotropic phase. More phases appear after the polymerization, and they are lamellar, since the phase behavior shifts toward the lamellar region when the monomer is consumed. Once the polymer is formed in situ, it segregates from the lamellae and forms an isotropic microphase which does not macroscopically separate. The appearance of this polymer-rich phase modifies the structure of the lamellar mesophase by partially deswelling it. This gives a shorter lamellar spacing. The law that expresses how the AOT-H2O spacing is contracted by the polymer is deduced from the equilibrium between the two (lamellar and isotropic) microphases. All the macroscopic final phases contain polymer, although in different proportions. The molecular weight of the polymer is the same in all phases. The presence of AOT in the medium has no influence on the resulting tacticity, which is the same as that for a polymer obtained in pure water.
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| 29. |
- Pacios, IE, et al.
(författare)
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The effect of poly (N,N-dimethylacrylamide) on the lamellar phase of Aerosol OT/water
- 2002
-
Ingår i: Colloid and Polymer Science. - : Springer Science and Business Media LLC. - 0303-402X .- 1435-1536. ; 280:6, s. 517-525
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Tidskriftsartikel (refereegranskat)abstract
- The effect of a water-soluble uncharged polymer on the stability of the lamellar phase of the Aerosol OT (AOT)/water system is studied. The lamellar phase still exists when water is replaced by an aqueous solution of poly(N,N-dimethylacrylamide) (Rapproximate to4x10(2) Angstrom). Since the coil dimensions are (much) larger than the thickness of the water layers (d(w)approximate to51 Angstrom), the polymer molecules do not enter the lamellar phase. Instead segregation in small domains occurs, and in equilibrium with the AOT-rich phase another separate phase containing the polymer is formed. The polymer-rich phase exerts an osmotic pressure that reduces the water content in the AOT-rich phase, and by compression the repeat distance is reduced.
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| 30. |
- Sparr, Emma, et al.
(författare)
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A Water Gradient can be used to Regulate Drug Transport across Skin - A Responding Membrane
- 2010
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Ingår i: Biophysical Journal. - : Cell Press. - 0006-3495 .- 1542-0086. ; 98:3, suppl 1, s. 627a-627a
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- At normal conditions there is a substantial water gradient over the skin as it separates the water-rich inside of the body from the dry outside. This leads to a variation in the degree of hydration along the skin and changes in this gradient may affect the structure and function of skin. In this study we raise the question: How do changes in the water gradient across skin affect its permeability? We approach this problem in experiments that permit strict control of the gradient in the chemical potential of water. The results demonstrate that an external water gradient can be used to regulate transport of drugs across the skin. It is shown that the permeability of the skin barrier increases abruptly at low water gradients, corresponding to high degrees of skin hydration, and that this effect is reversible. This phenomenon is highly relevant to drug delivery applications due to its potential of temporarily opening the skin barrier for transdermal delivery of drugs and subsequently closing the barrier after treatment. The results are explained on basis that the skin is a responding membrane, for which small changes in the environment can lead to major changes in membrane structure, which in turn affect its transport properties. We have in parallel theoretical modeling and experimental studies in model systems shown how a water gradient across multilayer lipid membrane can be used as a regulating mechanism to control the barrier properties. These principles are here applied to the barrier of stratum corneum, the upper layer of the human skin, where it can provide an explanation for the experimental findings that a water gradient can be used to regulate drug transport across the skin.
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| 31. |
- Svensson, Olof, et al.
(författare)
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Interactions between chitosan-modified particles and mucin-coated surfaces
- 2008
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier Inc.. - 0021-9797 .- 1095-7103. ; 2:325, s. 346-350
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Tidskriftsartikel (refereegranskat)abstract
- Lipid-based particles (Cubosome® particles) were surface-modified by chitosan and the ratio between particles and chitosan was optimized to minimize the free chitosan concentration in the dispersion. The modified particles were characterized by electrophoretic measurements and the pH dependence of the zeta potential could be directly related to the protonation of chitosan. Interaction between the modified particles and mucin-coated silica surfaces were subsequently investigated in situ by ellipsometry to assess the mucoadhesive properties at physiologically relevant conditions. The result showed that a substantial amount of modified particles was adsorbed to mucin-coated silica surfaces at both pH 4 and pH 6, probably due to electrostatic interactions between amino groups in chitosan and negatively charged groups in mucin. Furthermore, the amount of bound particles decreased by less than 15% upon rinsing indicating relatively strong interactions. This investigation demonstrates that ellipsometry is a useful tool to study mucoadhesive properties of particles in the submicrometer range. Moreover, the novel chitosan-modified particles may be of interest for mucosal drug delivery applications.
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| 32. |
- Svensson, Olof, et al.
(författare)
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Interactions between Drug Delivery Particles and Mucin in Solution and at Interfaces
- 2008
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24, s. 2573-2579
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Tidskriftsartikel (refereegranskat)abstract
- Cubosome particles were produced by fragmenting a cubic crystalline phase of glycerol monooleate and water in the presence of a stabilizing poly(ethylene oxide)-based polymer. The aim of our investigation was to study the interaction between these particles and mucin to gain information on how they would perform as a vehicle for mucosal drug delivery. Particle electrophoresis was used to investigate the interactions between particles and mucin in solution, and ellipsometry was utilized to study the interactions between particles and mucin-coated silica surfaces. The interaction studies were performed at relevant physiological conditions, and the pH and ionic strength were varied to gain more information about the driving forces for the interaction. The results from electrophoretic measurements showed that mucin in solution adsorbed to the particles at pH 4, whereas at pH 6 no clear interaction was detected. From ellipsometric measurements it was evident that the particles adsorb reversibly to a mucin-coated silica surface at pH 4, while no adsorption of particles could be detected at pH 6. The overall conclusion is that the interaction between these particles and mucin is weak and pH-dependent. These findings are in agreement with other investigations of the interactions between mucin and poly(ethylene oxide) chains.
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| 33. |
- Thuresson, Krister, et al.
(författare)
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Binding of SDS to Ethyl(hydroxyethyl)cellulose. Effect of Hydrophobic Modification of the Polymer
- 1996
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Ingår i: Journal of Physical Chemistry. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 100:12, s. 4909-4918
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Tidskriftsartikel (refereegranskat)abstract
- The binding of SDS to cellulose polymers in the semidilute concentration regime has been studied by means of NMR, ion-selective electrode, and a time-resolved fluorescence technique. Two polymers have been used, differing only in a low degree of hydrophobic modification of one of them. NMR self-diffusion and activity measurements show that the binding of SDS to the nonmodified polymer has a fairly pronounced critical aggregation concentration (cac), while binding to the hydrophobically modified polymer is less cooperative up to a concentration of about the cac in the nonmodified polymer/SDS system. NMR T-2 relaxation and fluorescence studies indicate that surfactants bound to the hydrophobically modified polymers in the noncooperative regime have slow dynamics compared to micellized surfactants, to surfactants bound to the unmodified polymer, and to surfactants bound to the hydrophobically modified polymer in the cooperative regime. Furthermore, in the non-cooperative regime the fluorescence studies imply that the SDS aggregation number of the mixed micelles is low and that the number of hydrophobic zones is invariant with respect to the surfactant concentration.
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| 34. |
- Thuresson, Krister, et al.
(författare)
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Clouding of a cationic hydrophobically associating comb polymer
- 2002
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 201:1-3, s. 9-15
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Tidskriftsartikel (refereegranskat)abstract
- A novel cationic hydrophobically associating comb polymer, containing poly(oxyethylene) chains in the back-bone, is described and investigated with respect to the aqueous solubility by cloud point measurements. Cloud points were investigated as a function of polymer charge, poly(oxyethylene) chain length and concentrations of added NaCl and could be interpreted in terms of the aqueous behavior of poly(oxyethylene) chains, general electrostatic effects, salting-out effects for nonionic polymer chains and polymer association. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 35. |
- Thuresson, Krister, et al.
(författare)
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Effect of Hydrophobic Modification of a Nonionic Cellulose Derivative on the Interaction with Surfactants. Phase Behaviour and Association.K. Thuresson, B. Lindman,The Journal of Physical Chemistry, submitted.
- 1997
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 101:33, s. 6460-6468
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Tidskriftsartikel (refereegranskat)abstract
- Phase separation studies have been carried out concerning the addition of different surfactants to systems containing either ethyl(hydroxyethyl)cellulose (EHEC) or the hydrophobically modified analogue (HM-EHEC). The polymer concentration was kept constant at 1 g polymer/100 g of water (1 w/w%), while the surfactant concentration was varied. In the polymer/sodium dodecyl sulfate (SDS) systems, which were studied in more detail, phase diagrams were obtained in the presence of various concentrations of inert salt. Moreover, the phase behavior of the HM-EHEC/SDS system showed no marked changes by purification of the surfactant or by contamination with decanol. It was shown that the SDS binding to EHEC was cooperative and could be described in the framework of a closed association model, while for HM-EHEC a two-step binding model had to be used to get a proper description of the binding. In the noncooperative part of the HM-EHEC binding isotherm, the binding showed similarities to the adsorption of SDS on a hydrophobic surface and could be described by a Langmuir adsorption model. From the binding isotherms for SDS, binding isotherms for ionic surfactants with varying chain length could be calculated from simple assumptions. These isotherms give a basis for the interpretation of the phase diagrams. For the ionic surfactants, the phase behavior could be rationalized by considering the polymer/surfactant complex to possess polyelectrolyte characteristics. The observations were discussed in terms of an attractive hydrophobic interaction and a repulsive electrostatic force. Addition of nonionic surfactants was discussed by observing that generally a pair of a nonionic polymer and a nonionic surfactant segregates. However, with HM-EHEC there is an extra attractive hydrophobic interaction due to the presence of polymer hydrophobic tails which can serve as nucleation sites for the surfactants.
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| 36. |
- Thuresson, Krister, et al.
(författare)
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Effect of Hydrophobic Modification on Phase Behaviour and Rheology in Mixtures of Oppositely Charged Polyelectrolytes
- 1996
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Ingår i: Langmuir. - 0743-7463. ; 12:2, s. 530-537
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Tidskriftsartikel (refereegranskat)abstract
- Phase behavior and rheology of polymer mixtures comprising aqueous solutions of oppositely charged polyelectrolytes are investigated. Emphasis is put on the effects of hydrophobic modification of the polymers and addition of salt. The associative phase separation usually observed when mixing oppositely charged polyelectrolytes is effectively prevented over a large miscibility region for the hydrophobically modified polymers. Also, in the extended one-phase region, the viscosity is 3-4 orders of magnitude higher for mixed polyelectrolyte systems compared to that observed for either one of the polymers. Addition of ordinary electrolytes to the mixture decreases the viscosity strongly, and at higher electrolyte contents a phase separation is induced. A mechanism explaining the observations is proposed.
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| 37. |
- Thuresson, Krister, et al.
(författare)
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Effect of Surfactant on Structural and Thermodynamic Properties of Aqueous Solutions of Hydrophobically Modified Ethyl(hydroxyethyl)cellulose
- 1995
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 11:10, s. 3730-3736
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Tidskriftsartikel (refereegranskat)abstract
- Solution properties of ethyl(hydroxyethyl)cellulose (EHEC) and a hydrophobically modified analogue (HM-EHEC) in water in the presence of various amounts of sodium dodecyl sulfate (SDS) have been investigated by cloud point (CP) measurements, titration microcalorimetry, and static light scattering. The CP experiments revealed that the hydrophobically modified polymer is less soluble than the unmodified EHEC at low concentrations of SDS, while at higher surfactant concentrations the solubility properties of the two polymers are practically the same. The resulting enthalpic titration curves from the calorimetric measurements on 0.25% polymer solutions at 25 degrees C consist of a pronounced endothermic peak (moderate SDS concentration) followed by a shallow exothermic one at higher surfactant concentrations. The prominent endothermic peak observed for both systems indicates a strong polymer-surfactant interaction. From the shape of the curves, the onset of the saturation stage of the binding process was estimated to be 20 mm for both polymers. The degree of surfactant binding to the polymer was found, at moderate SDS concentrations, to be the same for EHEC and HM-EHEC. The light-scattering results for both the EHEC/ SDS and HM-EHEC/SDS systems revealed a decreasing angular dependence of the reduced inverse scattered intensity function S(0)S(q) (q is the wave vector) with increasing surfactant concentration. It is observed at moderate levels of surfactant addition that the correlation length xi decreases more strongly for the EHEC/SDS system than for the HM-EHEC/SDS system. By plotting the static light scattering data in the form S(xi)/S(0) versus the dimensionless parameter q xi a universal picture emerged. In the regime q xi > 1, the power law S(q) similar to q(-1.6) was observed for both systems.
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| 38. |
- Thuresson, Krister
(författare)
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Solution properties of a hydrophobically modified polymer
- 1996
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The influence of hydrophobic modification on solution properties of water-soluble polymers in the semi-dilute regime have been studied. The nonionic ethyl(hydroxyethyl)cellulose (EHEC) and its hydrophobically modified analogue (HM-EHEC) are used as model substances. Interactions between the polymer molecules in solution and a third component are investigated, and in particular the influence of the surfactant sodium dodecylsulfate (SDS). The polymer/SDS complex formation is investigated by using several techniques (phase behaviour, rheology, calorimetry, DS- sensitive electrode, NMR, and light scattering and fluorescence techniques). This combination of methods gives thermodynamic information on the complex formation, as well as information about the dynamics of the polymer/surfactant complex. In a binary, semi-dilute, HM-EHEC solution the hydrophobic tails associate in clusters with an average of ten tails. These 'pre-formed' micelles act as nucleation sites for other molecules that contain hydrophobic moieties. The number of mixed micelles, and the strengths of the inter polymeric bonds which they give rise to, control both microscopic properties (as chain motions) and macroscopic behaviour (as rheology and phase behaviour). Experimental phase studies with hexanol as a third component were compared with model calculations in a modified Flory-Huggins approach. By assuming that hydrophobic modification causes enhanced association with the polymer semi-quantitative agreement was found. The associative phase separation that is usually observed in mixtures of two oppositely charged polyelectrolytes is effectively prevented by hydrophobic modification of both polyelectrolytes; a highly viscous phase is formed.
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| 39. |
- Thuresson, Krister, et al.
(författare)
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The association between a non-ionic microemulsion and hydrophobically modified PEG. A rheological investigation
- 2004
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Ingår i: 15th Meeting of the European Colloid and Interface Society (ECIS) (Progress in Colloid and Polymer Science Vol.123). - 3540005536 ; 123, s. 40-43
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Konferensbidrag (refereegranskat)abstract
- The thickening effect of a hydrophobically modified polymer in an O/W microemulsion is investigated. The hydrophobically modified polymer is a triblock copolymer, alkyl end-capped poly(ethylene glycol) and the microemulsion is based on a non-ionic surfactant, pentaethylene oxide dodecyl ether (C12E5) and decane. The rheological properties vary strongly with microemulsion droplet volume fraction, with temperature and with end-caps of the polymer. Particularly interesting are a maximum in viscosity as a function of droplet volume fraction, a decrease in cross-link life-time and very strong temperature dependences. These can be understood on the basis of interdroplet distances and interactions
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