This paper reports the properties of highly oriented nanocomposite tapes based on isotactic PP an... more This paper reports the properties of highly oriented nanocomposite tapes based on isotactic PP and needle-like sepiolite nanoclay, obtained by a solid state drawing process. The intrinsic 1D character of sepiolite allows its exploitation in 1D objects, such as oriented polymer fibres and tapes, where it can be uniaxially oriented upon drawing. A synergistic increase in mechanical properties is presented for highly drawn tapes (l 20) and low filler loadings ( 2.5 wt.-%), which can not be simply explained by micromechanical composite models. Instead, mechanical properties are intimately related to the dispersion state of the nanoclays in PP, the rheological properties of the nanocomposites and the polymer morphology.
ABSTRACT Using X-ray diffraction we have determined the structure factor of pure iodine and of a ... more ABSTRACT Using X-ray diffraction we have determined the structure factor of pure iodine and of a number of dilute mixtures of KI in I2. We show that these liquids exhibit short-range orientational order, adjacent molecules being orient- ed more or less parallel. The intramolecular bond length in pure liquid iodine is 2·70±0·01 Å, intermediate between the bond lengths of gaseous and solid iodine. Upon addition of KI the bond length increases, while the distances to atoms in the second and third shell decrease. These effects are related to recent high-pressure diffraction measurements on solid iodine.
The processing of semi-crystalline polymers such as polyethylene (PE) involves the shaping of the... more The processing of semi-crystalline polymers such as polyethylene (PE) involves the shaping of the molten material in moulds and dies by injection moulding methods or film blowing and fibre spinning techniques. 1 Once processed, the polymer shape is stabilised via ...
The lipid and keratin structure of pig stratum corneum has been elucidated by small-and wide-angl... more The lipid and keratin structure of pig stratum corneum has been elucidated by small-and wide-angle X-ray structures of human and mouse sc have been elucidated.
Ceramides were isolated from the pig stratum corneum (SC) and mixed in varying molar ratios with ... more Ceramides were isolated from the pig stratum corneum (SC) and mixed in varying molar ratios with either cholesterol or with cholesterol and free fatty acids. The phase behavior of the mixtures was studied by small-(SAXD) and wide-angle (WAXD) X-ray diffraction. Ceramides alone did not exhibit a long range ordering. Upon addition of cholesterol to ceramides, lamellar phases were formed and a hexagonal lateral packing was detected similar to that seen in intact SC. At a cholesterol/ceramide molar ratio of 0.1, only one reflection at 5.9 nm was observed. At a cholesterol/ceramide molar ratio of 0.2, three reflections corresponding to 12.3, 5.56, and 4.26 nm appeared. The reflections were based on two phases. Increasing the cholesterol/ceramide ratio to 0.4, the peak positions were slightly shifted. The diffraction pattern revealed the presence of two lamellar phases with periodicities of 12.2 and 5.2 nm, respectively. The positions of the peaks remained unchanged when the cholesterol/ceramide ratio was increased up to 1.0. At a cholesterol/ceramide molar ratio of 2.0, the intensity of various peaks based on the 12.2 nm phase decreased in intensity. The phase behavior of the cholesterol/ceramide mixtures in a ratio between 0.4 and 1.0 was very similar to that found in intact pig SC in which two lamellar phases with periodicities of 6.0 and 13.2 nm are present. Our data further indicate that the formation of the 5.2 nm lamellar phase requires a higher cholesterol content than the formation of the 12.2 nm lamellar phase. Furthermore, when the relative amount of cholesterol is very high, the 5.2 nm phase is the most pronounced one. Addition of free fatty acids increased the solubility of cholesterol, indicating the role free fatty acids may play for the skin barrier function. The phase behavior of cholesterol/ceramide/fatty acid mixtures was found to be dependent on the chain length of fatty acids used. Namely, addition of short-chain free fatty acids (C14-Cl8) did not change the periodicity of the 12.2 and 5.2 nm phases, but induced the formation of an additional 4.2 nm phase. In the presence of long-chain free fatty acids (C16-C26), the periodicity of the lamellar phases was slightly increased (to 13.0 and 5.3 nm, respectively) but no additional 4.2 nm phase was formed. I These results indicate that the lipid phase behavior of the cholesterol/ceramide/free fatty acid mixtures closely mimics that of the intact stratum corneum only in the presence of long-chain free fatty acids.-Bouwstra, J. A, G. S. Gooris, K. Cheng, A. Weerheim, W. Bras, and M. Ponec. Phase behavior of isolated skin lipids. J. Lipid Res. 1996. 37: 999-101 1.
Back Cover: A novel approach for producing more uniform, intact beads by electrospinning a self-a... more Back Cover: A novel approach for producing more uniform, intact beads by electrospinning a self-assembled block copolymer (BCP) solution is demonstrated. This approach allows a relatively high polymer concentration to be used, yet with a low degree of entanglement between polymer chains due to microphase separation of the BCP in a selective solvent system. Further details can be found in the article by L. Wang,* P. D. Topham, O. O. Mykhaylyk, H. Yu, A. J. Ryan, J. P. A. Fairclough, and W. Bras on page 1437.
Introduction The use of reducible supports has been largely applied on deNOx 3-way catalysis. Int... more Introduction The use of reducible supports has been largely applied on deNOx 3-way catalysis. Interesting activities from catalysts using perovskite support were reported from literature for the selective reduction of NO into nitrogen for mobile sources and stationary sources [1,2] suggesting that perovskite could be envisaged as an alternative to ceria zirconia supports. Previous studies have evidenced surface and structural changes on Pd-LaCoO3 systems in the course of the NO+H2 reaction in excess oxygen [3] . In parallel to support reconstruction, the stabilization of oxidic palladium species was characterized by XPS with an unusual binding energy of 337.2eV after stabilization at high temperature in lean conditions [3,4] . This binding energy value was higher than PdO phase (336.2 eV). Uenishi et al [5] have proposed the migration of palladium species inside the framework of the perovskite on a LaFe0.95Pd0.05O3 system after high temperature thermal treatment in oxidizing atmosph...
Polymer beads have attracted considerable interest for use in catalysis, drug delivery, and photo... more Polymer beads have attracted considerable interest for use in catalysis, drug delivery, and photo-nics due to their particular shape and surface morphology. Electrospinning, typically used for producing nanofibers, can also be used to fabricate polymer beads if the solution has a sufficiently low concentration. In this work, a novel approach for producing more uniform, intact beads is presented by electrospinning self-assembled block copolymer (BCP) solutions. This approach allows a relatively high polymer concentration to be used, yet with a low degree of entanglement between polymer chains due to microphase separation of the BCP in a selective solvent system. Herein, to demonstrate the technology, a well-studied polystyrene-poly(ethylene butylene)-polystyrene triblock copolymer is dissolved in a co-solvent system. The effect of solvent composition on the characteristics of the fibers and beads is intensively studied, and the mechanism of this fiber-to-bead is found to be dependent on microphase separation of the BCP.
ABSTRACT The dark conglomerate (DC) phase exhibited by a bent-core liquid crystal shows remarkabl... more ABSTRACT The dark conglomerate (DC) phase exhibited by a bent-core liquid crystal shows remarkable properties including an electric-field tunable chiral domain structure and a large (0.045) reduction of refractive index, while maintaining an optically dark texture when observed under crossed polarizers. A detailed investigation of the system is presented, leading to a model that is fully consistent with the experimental observations. It reports the observation of two distinct regimes in the DC phase: a higher temperature regime in which the periodicity measured by small angle x-ray scattering decreases slightly (0.5%) and a lower temperature regime where it increases considerably (16%). Also, the paper discusses the unusual electric-field-induced transformations observed in both the regimes. These changes have threshold fields that are both temperature and frequency dependent, though the phenomena are observed irrespective of device thickness, geometry, and the alignment layer. The electro-optic behavior in the DC phase corresponds to a number of structural changes leading to unusual changes in physical properties including a small (1%) increase in periodicity and a doubling of the average dielectric permittivity. We propose a model of the DC phase where in the ground state the nanostructure of the phase exhibits an anticlinic antiferroelectric organization. Under an electric field, it undergoes a molecular rearrangement without any gross structural changes leading to an anticlinic ferroelectric order while keeping the overall sponge-like structure of the DC phase intact.
The structure of human stratum corneum was investigated with small-angle x-ray scattering (SAXS).... more The structure of human stratum corneum was investigated with small-angle x-ray scattering (SAXS). At room temperature the scattering curve was characterized by a strong intensity at low scattering vector (Q−1) and two complicated diffraction peaks originating from a lamellar structure of the lipids. The lamellar lipid structure in the stratum corneum transformed to a disordered structure between 65° and 75°C,
The effect of a series of alkyl-azones (N-alkylazocycloheptane-2-one) on the structure of human s... more The effect of a series of alkyl-azones (N-alkylazocycloheptane-2-one) on the structure of human stratum corneum has been studied by small angle X-ray scattering. Treatment with alkyl-azones having alkyl chains greater than six carbons in length resulted in the disordering of the lamellae in the stratum corneum. The results could be correlated with those obtained by thermal analysis. The remaining thermal transition after treatment with longer alkyl chain azones is probably due to the lipids associated with the proteins.
This paper reports the properties of highly oriented nanocomposite tapes based on isotactic PP an... more This paper reports the properties of highly oriented nanocomposite tapes based on isotactic PP and needle-like sepiolite nanoclay, obtained by a solid state drawing process. The intrinsic 1D character of sepiolite allows its exploitation in 1D objects, such as oriented polymer fibres and tapes, where it can be uniaxially oriented upon drawing. A synergistic increase in mechanical properties is presented for highly drawn tapes (l 20) and low filler loadings ( 2.5 wt.-%), which can not be simply explained by micromechanical composite models. Instead, mechanical properties are intimately related to the dispersion state of the nanoclays in PP, the rheological properties of the nanocomposites and the polymer morphology.
ABSTRACT Using X-ray diffraction we have determined the structure factor of pure iodine and of a ... more ABSTRACT Using X-ray diffraction we have determined the structure factor of pure iodine and of a number of dilute mixtures of KI in I2. We show that these liquids exhibit short-range orientational order, adjacent molecules being orient- ed more or less parallel. The intramolecular bond length in pure liquid iodine is 2·70±0·01 Å, intermediate between the bond lengths of gaseous and solid iodine. Upon addition of KI the bond length increases, while the distances to atoms in the second and third shell decrease. These effects are related to recent high-pressure diffraction measurements on solid iodine.
The processing of semi-crystalline polymers such as polyethylene (PE) involves the shaping of the... more The processing of semi-crystalline polymers such as polyethylene (PE) involves the shaping of the molten material in moulds and dies by injection moulding methods or film blowing and fibre spinning techniques. 1 Once processed, the polymer shape is stabilised via ...
The lipid and keratin structure of pig stratum corneum has been elucidated by small-and wide-angl... more The lipid and keratin structure of pig stratum corneum has been elucidated by small-and wide-angle X-ray structures of human and mouse sc have been elucidated.
Ceramides were isolated from the pig stratum corneum (SC) and mixed in varying molar ratios with ... more Ceramides were isolated from the pig stratum corneum (SC) and mixed in varying molar ratios with either cholesterol or with cholesterol and free fatty acids. The phase behavior of the mixtures was studied by small-(SAXD) and wide-angle (WAXD) X-ray diffraction. Ceramides alone did not exhibit a long range ordering. Upon addition of cholesterol to ceramides, lamellar phases were formed and a hexagonal lateral packing was detected similar to that seen in intact SC. At a cholesterol/ceramide molar ratio of 0.1, only one reflection at 5.9 nm was observed. At a cholesterol/ceramide molar ratio of 0.2, three reflections corresponding to 12.3, 5.56, and 4.26 nm appeared. The reflections were based on two phases. Increasing the cholesterol/ceramide ratio to 0.4, the peak positions were slightly shifted. The diffraction pattern revealed the presence of two lamellar phases with periodicities of 12.2 and 5.2 nm, respectively. The positions of the peaks remained unchanged when the cholesterol/ceramide ratio was increased up to 1.0. At a cholesterol/ceramide molar ratio of 2.0, the intensity of various peaks based on the 12.2 nm phase decreased in intensity. The phase behavior of the cholesterol/ceramide mixtures in a ratio between 0.4 and 1.0 was very similar to that found in intact pig SC in which two lamellar phases with periodicities of 6.0 and 13.2 nm are present. Our data further indicate that the formation of the 5.2 nm lamellar phase requires a higher cholesterol content than the formation of the 12.2 nm lamellar phase. Furthermore, when the relative amount of cholesterol is very high, the 5.2 nm phase is the most pronounced one. Addition of free fatty acids increased the solubility of cholesterol, indicating the role free fatty acids may play for the skin barrier function. The phase behavior of cholesterol/ceramide/fatty acid mixtures was found to be dependent on the chain length of fatty acids used. Namely, addition of short-chain free fatty acids (C14-Cl8) did not change the periodicity of the 12.2 and 5.2 nm phases, but induced the formation of an additional 4.2 nm phase. In the presence of long-chain free fatty acids (C16-C26), the periodicity of the lamellar phases was slightly increased (to 13.0 and 5.3 nm, respectively) but no additional 4.2 nm phase was formed. I These results indicate that the lipid phase behavior of the cholesterol/ceramide/free fatty acid mixtures closely mimics that of the intact stratum corneum only in the presence of long-chain free fatty acids.-Bouwstra, J. A, G. S. Gooris, K. Cheng, A. Weerheim, W. Bras, and M. Ponec. Phase behavior of isolated skin lipids. J. Lipid Res. 1996. 37: 999-101 1.
Back Cover: A novel approach for producing more uniform, intact beads by electrospinning a self-a... more Back Cover: A novel approach for producing more uniform, intact beads by electrospinning a self-assembled block copolymer (BCP) solution is demonstrated. This approach allows a relatively high polymer concentration to be used, yet with a low degree of entanglement between polymer chains due to microphase separation of the BCP in a selective solvent system. Further details can be found in the article by L. Wang,* P. D. Topham, O. O. Mykhaylyk, H. Yu, A. J. Ryan, J. P. A. Fairclough, and W. Bras on page 1437.
Introduction The use of reducible supports has been largely applied on deNOx 3-way catalysis. Int... more Introduction The use of reducible supports has been largely applied on deNOx 3-way catalysis. Interesting activities from catalysts using perovskite support were reported from literature for the selective reduction of NO into nitrogen for mobile sources and stationary sources [1,2] suggesting that perovskite could be envisaged as an alternative to ceria zirconia supports. Previous studies have evidenced surface and structural changes on Pd-LaCoO3 systems in the course of the NO+H2 reaction in excess oxygen [3] . In parallel to support reconstruction, the stabilization of oxidic palladium species was characterized by XPS with an unusual binding energy of 337.2eV after stabilization at high temperature in lean conditions [3,4] . This binding energy value was higher than PdO phase (336.2 eV). Uenishi et al [5] have proposed the migration of palladium species inside the framework of the perovskite on a LaFe0.95Pd0.05O3 system after high temperature thermal treatment in oxidizing atmosph...
Polymer beads have attracted considerable interest for use in catalysis, drug delivery, and photo... more Polymer beads have attracted considerable interest for use in catalysis, drug delivery, and photo-nics due to their particular shape and surface morphology. Electrospinning, typically used for producing nanofibers, can also be used to fabricate polymer beads if the solution has a sufficiently low concentration. In this work, a novel approach for producing more uniform, intact beads is presented by electrospinning self-assembled block copolymer (BCP) solutions. This approach allows a relatively high polymer concentration to be used, yet with a low degree of entanglement between polymer chains due to microphase separation of the BCP in a selective solvent system. Herein, to demonstrate the technology, a well-studied polystyrene-poly(ethylene butylene)-polystyrene triblock copolymer is dissolved in a co-solvent system. The effect of solvent composition on the characteristics of the fibers and beads is intensively studied, and the mechanism of this fiber-to-bead is found to be dependent on microphase separation of the BCP.
ABSTRACT The dark conglomerate (DC) phase exhibited by a bent-core liquid crystal shows remarkabl... more ABSTRACT The dark conglomerate (DC) phase exhibited by a bent-core liquid crystal shows remarkable properties including an electric-field tunable chiral domain structure and a large (0.045) reduction of refractive index, while maintaining an optically dark texture when observed under crossed polarizers. A detailed investigation of the system is presented, leading to a model that is fully consistent with the experimental observations. It reports the observation of two distinct regimes in the DC phase: a higher temperature regime in which the periodicity measured by small angle x-ray scattering decreases slightly (0.5%) and a lower temperature regime where it increases considerably (16%). Also, the paper discusses the unusual electric-field-induced transformations observed in both the regimes. These changes have threshold fields that are both temperature and frequency dependent, though the phenomena are observed irrespective of device thickness, geometry, and the alignment layer. The electro-optic behavior in the DC phase corresponds to a number of structural changes leading to unusual changes in physical properties including a small (1%) increase in periodicity and a doubling of the average dielectric permittivity. We propose a model of the DC phase where in the ground state the nanostructure of the phase exhibits an anticlinic antiferroelectric organization. Under an electric field, it undergoes a molecular rearrangement without any gross structural changes leading to an anticlinic ferroelectric order while keeping the overall sponge-like structure of the DC phase intact.
The structure of human stratum corneum was investigated with small-angle x-ray scattering (SAXS).... more The structure of human stratum corneum was investigated with small-angle x-ray scattering (SAXS). At room temperature the scattering curve was characterized by a strong intensity at low scattering vector (Q−1) and two complicated diffraction peaks originating from a lamellar structure of the lipids. The lamellar lipid structure in the stratum corneum transformed to a disordered structure between 65° and 75°C,
The effect of a series of alkyl-azones (N-alkylazocycloheptane-2-one) on the structure of human s... more The effect of a series of alkyl-azones (N-alkylazocycloheptane-2-one) on the structure of human stratum corneum has been studied by small angle X-ray scattering. Treatment with alkyl-azones having alkyl chains greater than six carbons in length resulted in the disordering of the lamellae in the stratum corneum. The results could be correlated with those obtained by thermal analysis. The remaining thermal transition after treatment with longer alkyl chain azones is probably due to the lipids associated with the proteins.
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Papers by Wim Bras