| 1. |
- Aulin, Christian, 1980-, et al.
(författare)
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Buildup of polyelectrolyte multilayers of polyethyleneimine and microfibrillated cellulose studied by in situ dual-polarization interferometry and quartz crystal microbalance with dissipation
- 2008
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:6, s. 2509-2518
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Tidskriftsartikel (refereegranskat)abstract
- Polyethyleneimine (PEI) and Microfibrillated cellulose (MFC) have been used to buildup polyelectrolyte multilayers (PEM) on silicone oxide and silicone oxynitride surfaces at different pH values and with different electrolyte and polyelectrolyte/colloid concentrations of the components. Consecutive adsorption on these surfaces was studied by in situ dual-polarization interferometry (DPI) and quartz crystal microbalance measurements. The adsorption data obtained from both the techniques showed a steady buildup of multilayers. High pH and electrolyte concentration of the PEI solution was found to be beneficial for achieving a high adsorbed amount of PEI, and hence of MFC, during the buildup of the multilayer. On the other hand, an increase in the electrolyte concentration of the MFC dispersion was found to inhibit the adsorption of MFC onto PEL The adsorbed amount of MFC was independent of the bulk MFC concentration in the investigated concentration range (15-250 mg/L). Atomic force microscopy measurements were used to image a MFC-treated silicone oxynitride chip from DPI measurements. The surface was found to be almost fully covered by randomly oriented microfibrils after the adsorption of only one bilayer of PEI/MFC. The surface roughness expressed as the rms-roughness over 1 ÎŒm2 was calculated to be 4.6 nm (1 bilayer). The adsorbed amount of PEI and MFC and the amount of water entrapped by the individual layers in the multilayer structures were estimated by combining results from the two analytical techniques using the de Feijter formula. These results indicate a total water content of ca. 41% in the PEM.
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| 2. |
- Bäverbäck, P, et al.
(författare)
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Structural properties of β-dodecylmaltoside and C12E 6 mixed micelles
- 2009
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:13, s. 7296–7303-
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Tidskriftsartikel (refereegranskat)abstract
- Mixed micelles formed in aqueous solutions of nonionic surfactants n-dodecyl-hexaethylene-glycol (C12E6) and n-dodecyl-β-D-maltoside (C12G2) have been studied using small-angle neutron and X-ray scattering (SANS and SAXS) and static light scattering (SLS). Apparent micelle molar masses obtained with SLS were analyzed with a model taking into account both micelle growth and interference effects. The analysis shows that pure C12G2 forms small globular micelles whereas C12E6 and the mixtures form elongated micelles of much higher molar mass. The elongated micelles grow with increased concentration according to mean-field theory, and the masses are larger for increasing amounts of C12E6. To describe the SANS and SAXS data for C12E6 and the mixtures, it was necessary to employ a model with coexisting spherical and spherocylindrical micelles. The SANS and SAXS data were fitted simultaneously using this model with core-shell particles and molecular constraints. All mixtures, as well as pure C12E6, can be described by this model, demonstrating the coexistence of spherical and cylindrical micelles. The spherical micelles are the same size in all samples, whereas the cylindrical micelles grow in length with the fraction of C12E6 in the samples, as well as with concentration, in agreement with the SLS analysis. The mass fraction of surfactant in cylindrical aggregates also increases with the fraction of C12E6 and with overall concentration. The analysis of the SAXS and SANS data for pure C12G2 shows that the micelles are disk-shaped. The presence of elongated micelles in pure C12E6 and in the mixtures demonstrates that the behavior of the mixtures is dominated by C12E6.
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| 3. |
- Claesson, Per, et al.
(författare)
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Association between Polyelectrolytes and Oppositely Charged Surfactants in Bulk and at Solid/Liquid Interfaces
- 2007
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Ingår i: Colloid Stability and Application in Pharmacy. - Weinheim : Wiley-VCH Verlagsgesellschaft. ; , s. 337-395
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Mixtures of polyelectrolytes and oppositely charged surfactants find applications in many processes and products that are used in our daily life. Such systems also show many interesting features from a scientific point of view. Due to the combined technological relevance and scientific challenge, considerable research efforts have been made in this area in recent years. This has resulted in new theoretical approaches, the development of simulation methods and new experimental techniques and, of course, a large body of new findings. Together, these efforts have increased the understanding significantly, especially during the last 5 years. This chapter reviews some aspects of this topic, focusing on bulk association and association at solid/liquid interfaces. The review is focused on developments during the 21st century, even though in some cases a historical perspective is also offered.
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| 4. |
- Gilanyi, Tibor, et al.
(författare)
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Adsorption of alkyl trimethylammonium bromides at the air/water interface
- 2008
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 317:2, s. 395-401
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Tidskriftsartikel (refereegranskat)abstract
- A number of features of the adsorption of alkyl trimethylammonium bromides with n(c) = 10, 12, 14, and 16 at the air/water interface were studied. First, the adsorption isotherms were calculated front experimental surface tension vs concentration curves by means of the Gibbs equation. Second, a novel method was used to estimate the adsorption free energy change. From the analysis of these data it was concluded that the hydrophobic driving force for the adsorption first increases with increasing adsorbed amount and then levels off in a plateau, which holds true for all four homologues. This peculiar behavior was interpreted by the formation of a thin liquid-like alkane film at the air/water interface once a certain adsorbed amount is exceeded. The hydrophobic contribution to the standard free energy change of adsorption was compared with those values previously determined for alkyl sulfate homologues. This comparison suggests that the alkyl trimethylammonium type surfactants behave as if their alkyl chain was approximately one methylene group shorter than those of the corresponding alkyl sulfates.
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| 5. |
- Hantal, Gyorgy, et al.
(författare)
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Counterion and surface density dependence of the adsorption layer of ionic surfactants at the vapor-aqueous solution interface : A computer simulation study
- 2007
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 111:7, s. 1769-1774
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Tidskriftsartikel (refereegranskat)abstract
- To test the validity of currently used adsorption theories and understand the origin of the lack of their ability of adequately describing existing surface tension measurement data, we have performed a series of molecular dynamics simulations of the adsorption layer of alkali decyl sulfate at the vapor/aqueous solution interface. The simulations have been performed with five different cations (i.e., Li(+), Na(+), K(+), Rb(+), and Cs(+)) at two different surface concentrations (i.e., 2 mu mol/m(2) and 4 mu mol/m(2)). The obtained results clearly show that the thickness of the outer Helmholtz plate, a key quantity of the various adsorption theories, depends on two parameters, that is, the size of the cations and the surface density of the anionic surfactant. Namely, with increasing surface concentration, the electrostatic attraction between the two, oppositely charged, layers becomes stronger, leading to a considerable shrinking of the outer Helmholtz plate. Furthermore, this layer is found to be thicker in the presence of larger cations. The former effect could be important in understanding the anomalous shape of the adsorption isotherms of alkali alkyl sulfate surfactants, while the second effect seems to be essential in explaining the cation specificity of these isotherms.
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| 6. |
- Moglianetti, Mauro, et al.
(författare)
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Interaction of sodium dodecyl sulfate and high charge density comb polymers at the silica/water interface
- 2009
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 5:19, s. 3646-3656
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Tidskriftsartikel (refereegranskat)abstract
- The structures of interfacial layers formed from mixtures of comb polymers, comprising a high charge density cationic backbone and poly(ethylene oxide) (PEO) side-chains, with the anionic surfactant sodium dodecyl sulfate (SDS) at the silica/water interface, have been determined using neutron reflectivity measurements. The use of mixtures in which only the isotopic composition of the surfactant is changed has made it possible to determine the interfacial volume fraction profiles for both the polymer and the surfactant. For the polymer with 90% of the segments charged and 10% of the segments carrying PEO side-chains, there are four regimes of interfacial behavior with increasing surfactant composition of the bulk solution. First there is adsorption of surfactant to the polymer-covered surface, then, slightly above polymer charge stoichiometry, there is adsorption of near-neutral polymer/surfactant complexes followed by the adsorption of polymer/surfactant aggregates, with a well-defined internal structure. If the concentration of SDS is increased directly from below polymer charge stoichiometry to above the cmc, micelles or polymer/micelle complexes interact with the pre-existing polymer layer. Increasing the fraction of segments carrying PEO side-chains to 25% suppresses the formation of charge-neutral polymer/surfactant complexes at the interface. There is an increase in the adsorption of surfactant, which interacts with the pre-existing layer of polymers. This results in the surface aggregation of SDS and a swelling of the PEO side-chains from a mushroom to a brush-like configuration.
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| 7. |
- Shovsky, Alexander V., et al.
(författare)
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Formation and stability of soluble stochiometric polyelectrolyte complexes: Effects of charge density and polyelectrolyte concentration
- 2009
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Ingår i: Journal of Dispersion Science and Technology. - : Informa UK Limited. - 0193-2691 .- 1532-2351. ; 30:6, s. 980-988
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Tidskriftsartikel (refereegranskat)abstract
- Sterically stabilized polyelectrolyte complexes with stoichiometric composition between oppositely charged synthetic polyelectrolytes carrying strong ionic groups and significantly different molecular weights have been prepared. Poly(sodium styrenesulfonate) (NaPSS) was used as polyanion and a range of brush copolymers with various molar ratio (X = 1, 0.75, 0.5, 0.25) of the poly-methacryloxyethyl trimethylammonium chloride poly(METAC) and the nonionic poly (ethylene oxide) methyl ether methacrylate poly(PEO45MEMA) were used as polycations. Formation and stability of PECs have been investigated by dynamic and static light scattering (LS), turbidity and electrophoretic mobility measurements as a function of polyelectrolyte solution concentration and charge density of the cationic polyelectrolyte. The data obtained suggest that the PEO45- rich systems, NaPSS/PEO45MEMA:METAC-25 and NaPSS/PEO45MEMA: METAC-50, form small, water-soluble, molecular complexes having nonspherical shape. The PEO45-poor NaPSS/PEG45MEMA:METAC-75 form turbid colloidal dispersions, whereas insoluble PECs were revealed for the PEO45-free NaPSS/METAC system. The aggregation level of the PEO45-poor systems is mainly controlled by the concentration of the component solutions used for the preparation of PECs, whereas the aggregation of PEO45-rich nanoparticles is prevented by means of steric stabilization. Electrophoretic mobility data indicate a close to charge neutral state of the generated polyelectrolyte complexes.
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| 8. |
- Shovskyy, Oleksandr, 1978-, et al.
(författare)
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Formation and Stability of Water-Soluble Molecular Polyelectrolyte Complexes : Effects of Charge Density, Mixing Ratio and Polyelectrolyte Concentration
- 2009
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:11, s. 6113-6121
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Tidskriftsartikel (refereegranskat)abstract
- The formation of complexes with stoichiometric (1:1) as well as nonstoichiometric (2:1) and (1:2) compositions between oppositely charged synthetic polyelectrolytes carrying strong ionic groups and significantly different molecular weights is reported in this contribution. Poly(sodium styrenesulfonate) (NaPSS) was used as polyanion, and a range of copolymers with various molar ratios of the poly(methacryloxyethyltrimethylammonium) chloride, poly(METAC), and the nonionic poly(ethylene oxide) ether methacrylate, poly(PEO45MEMA), were used as polycations. Formation and stability of PECs have been investigated by dynamic and static light scattering (LS), turbidity, and electrophoretic mobility measurements as a function of polyelectrolyte solution concentration, charge density of the cationic polyelectrolyte, and mixing ratio. The data obtained demonstrate that in the absence of PEO45 side chains the 100% charged polymer (polyMETAC) formed insoluble PECs with PSS that precipitate from solution when exact stoichiometry is achieved. In nonstoichiometric complexes (1:2) and (2:1) large colloidally stable aggregates were formed. The presence of even a relatively small amount of PEO45 side chains (25%) in the cationic copolymer was sufficient for preventing precipitation of the formed stoichiometric and nonstoichiometric complexes. These PEC’s are sterically stabilized by the PEO45 chains. By further increasing the PEO45 side-chain content (50 and 75%) of the cationic copolymer, small, water-soluble molecular complexes could be formed. The data suggest that PSS molecules and the charged backbone of the cationic brush form a compact core, and with sufficiently high PEO45 chain density (above 25%) molecular complexes are formed that are stable over prolonged times.
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| 9. |
- Tonigold, Katrin, et al.
(författare)
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Effects of Aggregates on Mixed Adsorption Layers of Poly(ethylene imine) and Sodium Dodecyl Sulfate at the Air/Liquid Interface
- 2009
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:7, s. 4036-4046
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Tidskriftsartikel (refereegranskat)abstract
- We have exploited the spatial and kinetic resolution of ellipsometry to monitor the lateral movement of inhomogeneous patches of material in mixed adsorption layers of poly(ethylene imine) and sodium dodecyl sulfate at the air/liquid interface. We show that the choice of sample preparation methods can have a profound effect on the state of the interface for chemically equivalent samples. The extent of aggregation in the bulk solution on relevant time scales is affected by specific details of the polymer/surfactant mixing process, which produces varying numbers of aggregates that can become trapped in the interfacial layer, resulting in an enhanced and fluctuating ellipsometry signal. It can be beneficial to apply the surface-cleaning method of aspiration prior to physical measurements to remove trapped aggregates through the creation of a fresh interface. At low pH, the ellipsometry signal of samples prepared with surface cleaning is remarkably constant over a factor of >500 in the bulk composition below charge equivalence, which is discussed in terms of possible adsorption mechanisms. At high pH, through observing temporal fluctuations in the eflipsometry signal of samples prepared with surface cleaning, we reveal two important processes: there is the spontaneous adsorption of aggregates >0.2 mu m in diameter into the interfacial layer, and with time there is the fusion of smaller aggregates to generate new large surface aggregates. We attribute the favorability of the adsorption and fusion processes at high pH to reduced electrostatic barriers resulting from the low surface charge density of the aggregates. It is inappropriate in this case to consider the interface to comprise a homogeneous adsorption layer that is in dynamic equilibrium with the bulk solution. Our work shows that it can be helpful to consider whether there are macroscopic particles embedded in molecular layers at the air/liquid interface for systems where there is prior knowledge of aggregation in the bulk phase.
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| 10. |
- Varga, Imre, et al.
(författare)
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Effect of graft density on the nonionic bottle brush polymer/surfactant interaction
- 2009
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:19, s. 11383–11389-
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Tidskriftsartikel (refereegranskat)abstract
- The effect of graft density on the interaction of nonionic bottle brush polymers with an anionic surfactant (sodium dodecyl sulfate) was investigated. The graft density of 45 units long poly(ethylene oxide) (PEO) side chains was varied in a wide range (30, 50, 75, 90, and 100%) on a methacrylate type polymer backbone. The surfactant binding isotherms were determined by the potentiometric method in the presence of 0.1 M sodium bromide. It was found that due to the grafting of the PEO chains to a polymer backbone the surfactant binding becomes significantly suppressed. The amount of bound surfactant at the critical micelle concentration (cmc) decreases almost 2 orders of magnitude compared to the binding on a linear PEO having a similar molecular weight. The binding of the surfactant was found to occur in cooperative fashion, though the critical aggregation concentration (cac) of the binding was found surprisingly small. This result was interpreted in terms of the surfactant aggregation numbers that were found much smaller in the case of the bottle brush polymers than in the case of linear PEOs due to the steric crowding of the grafted PEO chains. To confirm the results of the binding isotherm measurements, steady-state fluorescence probe (pyrene) measurements as well as static and dynamic light scattering measurements were performed.
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