| 1. |
- Tehrani, Ali, 1976, et al.
(author)
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Micelle growth of cationic gemini surfactants studied by NMR and by time-resoved fluorescence quenching
- 2013
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 405, s. 145-149
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Journal article (peer-reviewed)abstract
- The micelle growth of a series of five cationic gemini surfactants has been investigated by time-resolved fluorescence quenching (TRFQ) and by two NMR techniques, line width analysis and diffusometry. The surfactant series was designed such that the effect of a number of variables could be assessed: length of the spacer unit, presence of ester bonds in the tails close to the head groups, and presence of a hydroxyl group in the spacer. For the gemini with long spacer, the micelles remained relatively small in size upon an increase of the concentration. The gemini surfactants with short spacer, on the other hand, showed a considerable micellar growth as the concentration was raised. It is of particular interest that the relatively simple line width analysis of one dimensional H-1 NMR spectra gave qualitatively the same results as the more sophisticated TRFQ and NMR diffusometry techniques.
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| 2. |
- Yaghini, Negin, 1976, et al.
(author)
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Effect of water on the transport properties of protic and aprotic imidazolium ionic liquids - an analysis of self-diffusivity, conductivity, and proton exchange mechanism
- 2014
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 16:20, s. 9266-9275
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Journal article (peer-reviewed)abstract
- In this paper we report on the transport properties of protic and aprotic ionic liquids of the imidazolium cation (C(2)C(1)Im(+) or C(2)HIm(+)) and the TFSI- or TfO- anion as a function of added water. We observe that the self-diffusion coefficient of the ionic species increases upon addition of water, and that the cation diffuses faster than the anion in the entire water concentration range investigated. We also observe that the overall increase of anionic and cationic diffusion coefficients is significant for C(2)HImTfO while it is rather weak for C(2)C(1)ImTFSI, the former being more hydrophilic. Moreover, the difference between cationic and anionic self-diffusivity specifically depends on the structure of the ionic liquid's ions. The degree of ion-ion association has been investigated by comparing the molar conductivity obtained by impedance measurements with the molar conductivity calculated from NMR data using the Nernst-Einstein equation. Our data indicate that the ions are partly dissociated (A(imp)/A(NMR) in the range 0.45-0.75) but also that the degree of association decreases in the order C(2)HImTfO > C(2)HImTFSI approximate to C(2)C(1)ImTfO > C(2)C(1)ImTFSI. From these results, it seems that water finds different sites of interaction in the protic and aprotic ionic liquids, with a strong preference for hydrogen bonding to the -NH group (when available) and a stronger affinity to the TfO anion as compared to the TFSI. For the protic ionic liquids, the analysis of H-1 NMR chemical shifts (upon addition of H2O and D2O, respectively) indicates a water-cation interaction of hydrogen bonding nature. In addition, we could probe proton exchange between the -NH group and deuterated water for the protic cation, which occurs at a significantly faster rate if associated with the TfO anion as compared to the TFSI.
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| 3. |
- Abrahamsson, Christoffer, 1984, et al.
(author)
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Magnetically induced structural anisotropy in binary colloidal gels and its effect on diffusion and pressure driven permeability
- 2014
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In: Soft Matter. - 1744-683X .- 1744-6848. ; 10:24, s. 4403-4412
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Journal article (peer-reviewed)abstract
- We report on the synthesis, microstructure and mass transport properties of a colloidal hydrogel selfassembled from a mixture of colloidal silica and nontronite clay plates at different particle concentrations. The gel-structure had uniaxial long-range anisotropy caused by alignment of the clay particles in a strong external magnetic field. After gelation the colloidal silica covered the clay particle network, fixing the orientation of the clay plates. Comparing gels with a clay concentration between 0 and 0.7 vol%, the magnetically oriented gels had a maximum water permeability and self-diffusion coefficient at 0.3 and 0.7 vol% clay, respectively. Hence the specific clay concentration resulting in the highest liquid flux was pressure dependent. This study gives new insight into the effect of anisotropy, particle concentration and bound water on mass transport properties in nano/microporous materials. Such findings merit consideration when designing porous composite materials for use in for example fuel cell, chromatography and membrane technology.
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| 4. |
- Almgren, Mats, et al.
(author)
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Nonideal Mixed Micelles of Fluorinated and Hydrogenous Surfactants in Aqueous Solution. NMR and SANS Studies of Anionic and Nonionic Systems
- 2010
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In: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 26:8, s. 5355-5363
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Journal article (peer-reviewed)abstract
- Contrast variation SANS and F-19 chemical shifts were measured for three mixed equimolar micelle systems: sodium perfluorooctanoate (SPED) and sodiumdecylsulfate (SDeS) in 200 mM NaCl, lithium perlluorononanate LiPFN) and lithium dodecylsulfate (Li DS) in 200 mM LiCl, and a nonionic system C8F17C2H4(OC2H4)(9) and C12H25(OC2H4)(8) in water, all at 25 C. The chemical shift measurements allow the calculation of the average fraction of nearest neighbors of each kind around the reporter group (the trifluoromethyl group). A preference for like neighbors were found in all systems, smallest in the SDeS/SPFO system and largest in the nonionic system, but in all cases substantially smaller than expected at critical conditions. From the SANS measurements the width of the micelle composition distribution was obtained. For the ionic systems similar values were obtained, showing a broadening compared to ideal mixtures, but not broad enough for demixing or clearly bimodal distributions. In the nonionic system the width was estimated as sigma = 0.18 and 0.22 using two different evaluation methods. These values suggest that the system is close to critical conditions. The lower value refers to a direct modeling of the system, assuming an ellipsoidal shape and a Gaussian composition distribution. The modeling showed the nonionic mixed micelles to be prolate ellipsoids with axial ratio 2.2 and an aggregation number larger than 100. whereas the two ionic systems fitted best to oblate shapes (axial ratios 0.8 and 0.65 for SDeS/SPFO and LiDS/LiPFN. respectively) and aggregation numbers of 60 for both.
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| 5. |
- Andersson Trojer, Markus, 1981, et al.
(author)
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Charged microcapsules for controlled release of hydrophobic actives. Part III: The effect of polyelectrolyte brush- and multilayers on sustained release
- 2013
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 15:17, s. 6153-6165
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Journal article (peer-reviewed)abstract
- Poly(methyl methacrylate) microspheres have been prepared by the internal phase separation method using either of the three conventional dispersants poly(vinyl alcohol) (PVA), poly(methacrylic acid) (PMAA), or the amphiphilic block copolymer poly(methyl methacrylate)-block-poly(sodium methacrylate). The block copolymer based microsphere, which has a polyelectrolyte brush on the surface, was surface modified with up to two poly(diallyldimethylammonium chloride)-poly(sodium methacrylate) bilayers. The microspheres were loaded with the hydrophobic dye 2-(4-(2-chloro-4-nitrophenylazo)-N-ethylphenylamino)ethanol (Disperse Red 13) and its release from aqueous dispersions of microspheres with the different surface compositions was measured by spectrophotometry. The burst fraction, burst rate and the diffusion constant were determined from a model combining burst and diffusive release. Out of the three dispersants, the block copolymer gave the slowest release of the dye, with respect to both burst release and diffusive release. A very pronounced further reduction of the diffusion constant was obtained by applying polyelectrolyte multilayers on top of the microspheres. However, the diffusion constant was very weakly dependent on further polyelectrolyte adsorption and one polyelectrolyte bilayer appeared to suffice.
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| 6. |
- Andersson Trojer, Markus, 1981, et al.
(author)
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Encapsulation of actives for sustained release
- 2013
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 15:41, s. 17727-17741
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Research review (peer-reviewed)abstract
- Encapsulation of actives in miniature reservoirs, called microcapsules, is used for protection and in particular controlled release of the active. Regarding controlled release applications, the most common function of the microcapsule is to sustain or extend the release of the active. A number of encapsulation methodologies are available including; internal phase separation, interfacial polymerization, formation of multiple emulsions, Layer-by-Layer adsorption of polyelectrolytes and soft templating techniques, all of which are reviewed in this Perspective. The choice of method depends on the nature of the active (hydrophilic/hydrophobic, size, physical state) and on the intended release rate and release profile. Ways to manipulate the release of the active by tailoring the physicochemical properties of the microcapsule are reviewed. Moreover, appropriate diffusion models are introduced to describe the release profile from a variety of microcapsule morphologies, including Fickian diffusion models and Brownian motion, and the meaning and the misuse of the term ``zero-order release'' are briefly discussed.
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| 7. |
- Bergek, Jonatan, 1984, et al.
(author)
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Controlled release of microencapsulated 2-n-octyl-4-isothiazolin-3-one from coatings: Effect of microscopic and macroscopic pores
- 2014
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In: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 1873-4359 .- 0927-7757. ; 458:1, s. 155-167
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Journal article (peer-reviewed)abstract
- To keep a painted facade protected from mold and algae, anti-growth agents are mixed in the coating. These biocides are small molecules with a high diffusivity inside the soft polymeric coating matrix resulting in a premature loss of protection. A promising improvement can be achieved by encapsulation of the biocide in micro-sized containers and thereby reducing the release rate from the coating. In this study, the biocide 2-n-octyl-4-isothiazolin-3-one (OIT) has been encapsulated by various formulation routes and the release has been studied with regard to different conditions. It was found that an exceptionally low interfacial tension between OIT and water practically prevents any formulation of core-shell particles. However, polymeric monoliths of OIT and poly(methyl methacrylate) could be formulated by the internal phase separation method. OIT release studies from these microspheres revealed formulation-dependent microscopic porosity where the chosen evaporation path of volatile solvent significantly alters the diffusion coefficient of the biocide in the microsphere. Dense microstructure with low diffusivity was given when the poly(methyl methacrylate) was provided time or heat for complete polymer relaxation. The microscopic porosity was evaluated within a framework of applied diffusion models to the experimental data. In an applied perspective, microspheres could offer a value for sustained release of OIT from coatings. In this work, we found a considerable decrease in release rate from dry-film coatings with encapsulated OIT compared to freely dispersed OIT. In addition, macroscopic porosity in the coating, i.e. the porosity in the binder material, was proven to be crucial for the diffusivity. It was shown that macroscopic porosity heavily depends on the drying time of the coating where longer drying times of several weeks gave a substantial decrease in macroscopic porosity and release rate of OIT.
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| 8. |
- Boissier, Catherine, 1972, et al.
(author)
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Study of Pharmaceutical Coatings by Means of NMR Cryoporometry and SEM Image Analysis
- 2012
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In: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 1520-6017 .- 0022-3549. ; 101:7, s. 2512-2522
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Journal article (peer-reviewed)abstract
- Nuclear magnetic resonance (NMR) cryoporometry and scanning electron microscopy (SEM) image analysis have been used to investigate the size and shape distribution of pores in pharmaceutical coatings. The coatings were made from a mixture of hydroxypropylcellulose (HPC) and ethylcellulose (EC). Upon solvent evaporation from a solution consisting of both the polymers, a solid polymer film is formed, which after removal of the water-soluble HPC consists of a skeleton of EC. A change in the amount of HPC enables modification of the water permeability through the films. By means of NMR cryoporometry, the presence of small pores (radius below 400 nm) was revealed with no significant change in the pore size distribution (PSD) as the HPC content in the films were changed. NMR cryoporometry showed the presence of channels of a characteristic 30-nm length scale in the films that contained more than 22% HPC. Below this threshold, the lack of interconnecting channels seems to prevent complete HPC dissolution and thereby the water permeability. SEM image analysis showed pore sizes that ranged from hundreds of nanometers up to few micrometers. Above the 22% threshold, further increase of HPC in the films resulted in an increased pore volume and wider PSD.
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| 9. |
- Chen, Guo, 1969, et al.
(author)
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A Porosimetric Mapping of Breadcrumb Structures by Differential Scanning Calorimetry and Nuclear Magnetic Resonance
- 2013
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In: Food Biophysics. - : Springer Science and Business Media LLC. - 1557-1858 .- 1557-1866. ; 8:3, s. 209-215
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Journal article (peer-reviewed)abstract
- Ice crystals in frozen bread are substantially shaped by the complex pore structures of crumb. In this study we inspected the breadcrumb porosity of ice-filled pores from the profiles of ice crystals mapped by differential scanning calorimetry and nuclear magnetic resonance. Two types of wheat bread containing different amounts of dietary fiber and sugar were studied after frozen storage at -18 A degrees C for 3 weeks. Both pore sizes and pore size distributions were derived via comparing the measurements to those of water-saturated mesoporous silica (MCM-41 C18) with a well-defined pore size distribution. Good consistency was shown for the crumb pore structures obtained using the two techniques. Both bread types featured broad nanometer ranges of pore sizes characterized with largely bimodal size distributions. Besides, the frozen high-fiber bread displayed a higher proportion of large pores and a broader pore size distribution than the high-sugar bread. By comparing such pore size distributions with those obtained previously for the corresponding fresh bread, it can be concluded that structural differences between the two bread types were produced during the frozen storage, manifesting the disparate freezing performances of bread with different formulations.
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| 10. |
- Enejder, Annika, 1969, et al.
(author)
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Chemical release from single PMMA microparticles monitored by CARS microscopy
- 2011
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In: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. Multiphoton Microscopy in the Biomedical Sciences XI; San Francisco, CA; 23-25 January 2011. - : SPIE. - 1605-7422. - 9780819484406 ; 7903
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Conference paper (other academic/artistic)abstract
- Microparticles loaded with antigens, proteins, DNA, fungicides, and other functional agents emerge as ideal vehicles for vaccine, drug delivery, genetic therapy, surface- and crop protection. The microscopic size of the particles and their collective large specific surface area enables highly active and localized release of the functional substance. In order to develop designs with release profiles optimized for the specific application, it is desirable to map the distribution of the active substance within the particle and how parameters such as size, material and morphology affect release rates at single particle level. Current imaging techniques are limited in resolution, sensitivity, image acquisition time, or sample treatment, excluding dynamic studies of active agents in microparticles. Here, we demonstrate that the combination of CARS and THG microscopy can successfully be used, by mapping the spatial distribution and release rates of the fungicide and food preservative IPBC from different designs of PMMA microparticles at single-particle level. By fitting a radial diffusion model to the experimental data, single particle diffusion coefficients can be determined. We show that release rates are highly dependent on the size and morphology of the particles. Hence, CARS and THG microscopy provides adequate sensitivity and spatial resolution for quantitative studies on how single-particle properties affect the diffusion of active agents at microscopic level. This will aid the design of innovative microencapsulating systems for controlled release.
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