The tubular morphology of intracellular membranous compartments is actively maintained through in... more The tubular morphology of intracellular membranous compartments is actively maintained through interactions with motor proteins and the cytoskeleton. Moving along cytoskeletal elements, motor proteins exert forces on the membranes to which they are attached, resulting in the formation of membrane tubes and tubular networks. To study the formation of membrane tubes by motor proteins, we developed an in vitro assay consisting of purified kinesin proteins directly linked to the lipids of giant unilamellar vesicles. When the vesicles are brought into contact with a network of immobilized microtubules, membrane tubes and tubular networks are formed. Through systematic variation of the kinesin concentration and membrane composition we study the mechanism involved. We show that a threshold concentration of motor proteins is needed and that a low membrane tension facilitates tube formation. Forces involved in tube formation were measured directly with optical tweezers and are shown to depend only on the tension and bending rigidity of the membrane. The forces were found to be higher than can be generated by individual motor proteins, indicating that multiple motors were working together to pull tubes. We propose a simple mechanism by which individual motor proteins can dynamically associate into clusters that provide the force needed for the formation of tubes, explaining why, in contrast to earlier findings [Roux, A., Cappello, G., Cartaud, J., Prost, J., Goud, B. & Bassereau, P. (2002) Proc. Natl. Acad. Sci. USA 99, 5394-5399], motor proteins do not need to be physically linked to each other to be able to pull tubes.
The properties and performance of a recently developed thin film nanocomposite (TFN), with inorga... more The properties and performance of a recently developed thin film nanocomposite (TFN), with inorganic nanoparticles incorporated in the active layer, and standard thin film composite (TFC) spiral wound seawater desalination reverse osmosis (RO) membranes were assessed by comparison on the scale of 4040 and 8040 membrane modules. Scanning electron microscopy with energy-dispersive X-ray spectroscopy, contact angle-, and ζ-potential measurements did not show large differences between TFN membranes and a TFC membrane (SW30HRLE). Small scale pilot tests (4040 elements) showed that the TFN had a factor two higher water permeability than the TFC. Salt rejection was similar, but the TFC showed slightly better rejection of NDMA and glycerol. Larger scale pilot tests (multiple 8040 elements) confirmed the nearly twofold higher water permeability for the TFN as compared to aged TFC membranes (SW30XHR). However, the boron rejection of the TFN was lower than that of the aged TFC. Furthermore, an...
The adsorption of mixed micelles of poly(4-(2-amino hydrochloride-ethylthio)-butylene)- block-pol... more The adsorption of mixed micelles of poly(4-(2-amino hydrochloride-ethylthio)-butylene)- block-poly(ethylene oxide), PAETB 49- b-PEO 212 and poly(4-(2-sodium carboxylate-ethylthio)-butylene)- block-poly(ethylene oxide), PCETB 47- b-PEO 212 on solid/liquid interfaces has been studied with light, X-ray, and neutron reflectometry. The structure of the adsorbed layer can be described with a two-layer model consisting of an inner layer formed by the coacervate of the polyelectrolyte blocks PAETB 49 and PCETB 47 ( approximately 1 nm) and an outer layer of PEO 212 blocks ( approximately 6 nm). The micelles unfold upon adsorption forming a rather homogeneous flat layer that exposes its polyethylene oxide chains into the solution, thus rendering the surface antifouling after modification with the micelles.
ABSTRACT Complex coacervate core micelles form in aqueous solutions from poly(acrylic acid)-block... more ABSTRACT Complex coacervate core micelles form in aqueous solutions from poly(acrylic acid)-block-poly(acrylamide) (PAAxPAAmy, x and y denote degree of polymerization) and poly(N,N-dimethyl aminoethyl methacrylate) (PDMAEMA150) around the stoichiometric charge ratio of the two components. The hydrodynamic radius, Rh, can be increased by adding oppositely charged homopolyelectrolytes, PAA140 and PDMAEMA150, at the stoichiometric charge ratio. Mixing the components in NaNO3 gives particles in highly aggregated metastable states, whose Rh remain unchanged (less than 5% deviation) for at least 1 month. The Rh increases more strongly with increasing addition of oppositely charged homopolyelectrolytes than is predicted by a geometrical packing model, which relates surface and volume of the particles. Preparation in a phosphate buffer ¿ known to weaken the electrostatic interactions between PAA and PDMAEMA ¿ yields swollen particles called complex coacervate core micro-emulsions (C3-Es) whose Rh increase is close to that predicted by the model. These are believed to be in the stable state (lowest free energy). A two-regime increase in Rh is observed, which is attributed to a transition from more star-like to crew-cut-like, as shown by self-consistent field calculations. Varying the length of the neutral and polyelectrolyte block in electrophoretic mobility measurements shows that for long neutral blocks (PAA26PAAm405 and PAA39PAAm381) the -potential is nearly zero. For shorter neutral blocks the -potential is around -10 mV. This shows that the C3-Es have excess charge, which can be almost completely screened by long enough neutral blocks.
With light scattering titrations, we show that complex coacervate core micelles (C3Ms) form from ... more With light scattering titrations, we show that complex coacervate core micelles (C3Ms) form from a diblock copolymer with a polyelectrolyte block and either an oppositely charged polyelectrolyte, a diblock copolymer with an oppositely charged polyelectrolyte or a mixture of the two. The effect of added salt and pH on both types of C3Ms is investigated. The hydrodynamic radius of mixed C3Ms can be controlled by varying the percentage of oppositely charged polyelectrolyte or diblock copolymer. A simple core-shell model is used to interpret the results from light scattering, giving the same trends as the experiments for both the hydrodynamic radii and the relative scattering intensities. Temperature has only a small effect on the C3Ms. Isothermal titration calorimetry shows that the complexation is mainly driven by Coulombic attraction and by the entropy gain due to counterion release.
ABSTRACT The properties and performance of a recently developed thin film nanocomposite (TFN), wi... more ABSTRACT The properties and performance of a recently developed thin film nanocomposite (TFN), with inorganic nanoparticles incorporated in the active layer, and standard thin Film composite (TFC) spiral wound seawater desalination reverse osmosis (RO) membranes were assessed by comparison on the scale of 4040 and 8040 membrane modules. Scanning electron microscopy with energy-dispersive X-ray spectroscopy, contact angle-, and zeta-potential measurements did not show large differences between TFN membranes and a TFC membrane (SW30HRLE). Small scale pilot tests (4040 elements) showed that the TFN had a factor to higher water permeability as the TFC. Salt rejection was similar, but the TFC showed slightly better rejection of NDMA and glycerol. Larger scale pilot tests (multiple 8040 elements) confirmed the nearly twofold higher water permeability for the TFN as compared to aged TFC membranes (SW30XHR). However, the boron rejection of the TFN was lower than that of the aged TFC. Furthermore, an indirect comparison showed that the flux for the virgin TFN would be about 1.4 Limes that for the virgin TFC.
This paper describes the results of experiments performed in a high-recovery system to elucidate ... more This paper describes the results of experiments performed in a high-recovery system to elucidate the silica scaling phenomenon and characterize the scaling. In this research, cation exchange pretreatment is used to reduce Ca, Ba, and Mg levels to prevent scaling during subsequent nanofiltration (NF) and reverse osmosis (RO) filtration, in which RO is fed with NF concentrate. In a pilot
Current Opinion in Colloid & Interface Science, 2005
In this review we present an overview of the developments of (self-)assembly of linear block copo... more In this review we present an overview of the developments of (self-)assembly of linear block copolymers containing one or more polyelectrolyte blocks in aqueous solution. Different micellar structures and phase behaviour are described. The role of inter- and intramolecular complex coacervation is emphasised. Recent developments in applications of assembly of polyelectrolyte-containing copolymers are presented.
ABSTRACT The trans membrane pressure (TMP) increase due to fouling of an Al2O3 microfiltration (M... more ABSTRACT The trans membrane pressure (TMP) increase due to fouling of an Al2O3 microfiltration (MF) membrane by particles and natural organic matter in different water types is studied. Removal of non-purgeable organic carbon (NPOC), turbidity and UV extinction by MF was found to be about < 10% for water with a very low turbidity (0.14 FNU). For water with a more representative turbidity (3.6–12 FNU) and varying NPOC level (3 or 15 mg/L), removal rates were comparable to literature values: 23% for NPOC and UV, and > 98% for turbidity. The TMP increase due to irreversible fouling is mostly determined by the presence of particles, whereas the amount of NPOC appears to be irrelevant. NPOC seems to be responsible for reversible fouling that can be removed by backwashing.The effect of pretreatment by anion exchange (AIEX) and coagulation on the performance and TMP increase due to fouling was investigated for Noardburgum lake water. The AIEX pretreatment removes > 80% of NPOC, turbidity and UV extinction.For both types of pretreatment reversible fouling is decreased, but irreversible fouling is increased. Especially the AIEX pretreatment leads to a TMP increase due to irreversible fouling, even though most of the NPOC and particles are removed and never reach the MF membrane.
The tubular morphology of intracellular membranous compartments is actively maintained through in... more The tubular morphology of intracellular membranous compartments is actively maintained through interactions with motor proteins and the cytoskeleton. Moving along cytoskeletal elements, motor proteins exert forces on the membranes to which they are attached, resulting in the formation of membrane tubes and tubular networks. To study the formation of membrane tubes by motor proteins, we developed an in vitro assay consisting of purified kinesin proteins directly linked to the lipids of giant unilamellar vesicles. When the vesicles are brought into contact with a network of immobilized microtubules, membrane tubes and tubular networks are formed. Through systematic variation of the kinesin concentration and membrane composition we study the mechanism involved. We show that a threshold concentration of motor proteins is needed and that a low membrane tension facilitates tube formation. Forces involved in tube formation were measured directly with optical tweezers and are shown to depend only on the tension and bending rigidity of the membrane. The forces were found to be higher than can be generated by individual motor proteins, indicating that multiple motors were working together to pull tubes. We propose a simple mechanism by which individual motor proteins can dynamically associate into clusters that provide the force needed for the formation of tubes, explaining why, in contrast to earlier findings [Roux, A., Cappello, G., Cartaud, J., Prost, J., Goud, B. & Bassereau, P. (2002) Proc. Natl. Acad. Sci. USA 99, 5394-5399], motor proteins do not need to be physically linked to each other to be able to pull tubes.
The properties and performance of a recently developed thin film nanocomposite (TFN), with inorga... more The properties and performance of a recently developed thin film nanocomposite (TFN), with inorganic nanoparticles incorporated in the active layer, and standard thin film composite (TFC) spiral wound seawater desalination reverse osmosis (RO) membranes were assessed by comparison on the scale of 4040 and 8040 membrane modules. Scanning electron microscopy with energy-dispersive X-ray spectroscopy, contact angle-, and ζ-potential measurements did not show large differences between TFN membranes and a TFC membrane (SW30HRLE). Small scale pilot tests (4040 elements) showed that the TFN had a factor two higher water permeability than the TFC. Salt rejection was similar, but the TFC showed slightly better rejection of NDMA and glycerol. Larger scale pilot tests (multiple 8040 elements) confirmed the nearly twofold higher water permeability for the TFN as compared to aged TFC membranes (SW30XHR). However, the boron rejection of the TFN was lower than that of the aged TFC. Furthermore, an...
The adsorption of mixed micelles of poly(4-(2-amino hydrochloride-ethylthio)-butylene)- block-pol... more The adsorption of mixed micelles of poly(4-(2-amino hydrochloride-ethylthio)-butylene)- block-poly(ethylene oxide), PAETB 49- b-PEO 212 and poly(4-(2-sodium carboxylate-ethylthio)-butylene)- block-poly(ethylene oxide), PCETB 47- b-PEO 212 on solid/liquid interfaces has been studied with light, X-ray, and neutron reflectometry. The structure of the adsorbed layer can be described with a two-layer model consisting of an inner layer formed by the coacervate of the polyelectrolyte blocks PAETB 49 and PCETB 47 ( approximately 1 nm) and an outer layer of PEO 212 blocks ( approximately 6 nm). The micelles unfold upon adsorption forming a rather homogeneous flat layer that exposes its polyethylene oxide chains into the solution, thus rendering the surface antifouling after modification with the micelles.
ABSTRACT Complex coacervate core micelles form in aqueous solutions from poly(acrylic acid)-block... more ABSTRACT Complex coacervate core micelles form in aqueous solutions from poly(acrylic acid)-block-poly(acrylamide) (PAAxPAAmy, x and y denote degree of polymerization) and poly(N,N-dimethyl aminoethyl methacrylate) (PDMAEMA150) around the stoichiometric charge ratio of the two components. The hydrodynamic radius, Rh, can be increased by adding oppositely charged homopolyelectrolytes, PAA140 and PDMAEMA150, at the stoichiometric charge ratio. Mixing the components in NaNO3 gives particles in highly aggregated metastable states, whose Rh remain unchanged (less than 5% deviation) for at least 1 month. The Rh increases more strongly with increasing addition of oppositely charged homopolyelectrolytes than is predicted by a geometrical packing model, which relates surface and volume of the particles. Preparation in a phosphate buffer ¿ known to weaken the electrostatic interactions between PAA and PDMAEMA ¿ yields swollen particles called complex coacervate core micro-emulsions (C3-Es) whose Rh increase is close to that predicted by the model. These are believed to be in the stable state (lowest free energy). A two-regime increase in Rh is observed, which is attributed to a transition from more star-like to crew-cut-like, as shown by self-consistent field calculations. Varying the length of the neutral and polyelectrolyte block in electrophoretic mobility measurements shows that for long neutral blocks (PAA26PAAm405 and PAA39PAAm381) the -potential is nearly zero. For shorter neutral blocks the -potential is around -10 mV. This shows that the C3-Es have excess charge, which can be almost completely screened by long enough neutral blocks.
With light scattering titrations, we show that complex coacervate core micelles (C3Ms) form from ... more With light scattering titrations, we show that complex coacervate core micelles (C3Ms) form from a diblock copolymer with a polyelectrolyte block and either an oppositely charged polyelectrolyte, a diblock copolymer with an oppositely charged polyelectrolyte or a mixture of the two. The effect of added salt and pH on both types of C3Ms is investigated. The hydrodynamic radius of mixed C3Ms can be controlled by varying the percentage of oppositely charged polyelectrolyte or diblock copolymer. A simple core-shell model is used to interpret the results from light scattering, giving the same trends as the experiments for both the hydrodynamic radii and the relative scattering intensities. Temperature has only a small effect on the C3Ms. Isothermal titration calorimetry shows that the complexation is mainly driven by Coulombic attraction and by the entropy gain due to counterion release.
ABSTRACT The properties and performance of a recently developed thin film nanocomposite (TFN), wi... more ABSTRACT The properties and performance of a recently developed thin film nanocomposite (TFN), with inorganic nanoparticles incorporated in the active layer, and standard thin Film composite (TFC) spiral wound seawater desalination reverse osmosis (RO) membranes were assessed by comparison on the scale of 4040 and 8040 membrane modules. Scanning electron microscopy with energy-dispersive X-ray spectroscopy, contact angle-, and zeta-potential measurements did not show large differences between TFN membranes and a TFC membrane (SW30HRLE). Small scale pilot tests (4040 elements) showed that the TFN had a factor to higher water permeability as the TFC. Salt rejection was similar, but the TFC showed slightly better rejection of NDMA and glycerol. Larger scale pilot tests (multiple 8040 elements) confirmed the nearly twofold higher water permeability for the TFN as compared to aged TFC membranes (SW30XHR). However, the boron rejection of the TFN was lower than that of the aged TFC. Furthermore, an indirect comparison showed that the flux for the virgin TFN would be about 1.4 Limes that for the virgin TFC.
This paper describes the results of experiments performed in a high-recovery system to elucidate ... more This paper describes the results of experiments performed in a high-recovery system to elucidate the silica scaling phenomenon and characterize the scaling. In this research, cation exchange pretreatment is used to reduce Ca, Ba, and Mg levels to prevent scaling during subsequent nanofiltration (NF) and reverse osmosis (RO) filtration, in which RO is fed with NF concentrate. In a pilot
Current Opinion in Colloid & Interface Science, 2005
In this review we present an overview of the developments of (self-)assembly of linear block copo... more In this review we present an overview of the developments of (self-)assembly of linear block copolymers containing one or more polyelectrolyte blocks in aqueous solution. Different micellar structures and phase behaviour are described. The role of inter- and intramolecular complex coacervation is emphasised. Recent developments in applications of assembly of polyelectrolyte-containing copolymers are presented.
ABSTRACT The trans membrane pressure (TMP) increase due to fouling of an Al2O3 microfiltration (M... more ABSTRACT The trans membrane pressure (TMP) increase due to fouling of an Al2O3 microfiltration (MF) membrane by particles and natural organic matter in different water types is studied. Removal of non-purgeable organic carbon (NPOC), turbidity and UV extinction by MF was found to be about < 10% for water with a very low turbidity (0.14 FNU). For water with a more representative turbidity (3.6–12 FNU) and varying NPOC level (3 or 15 mg/L), removal rates were comparable to literature values: 23% for NPOC and UV, and > 98% for turbidity. The TMP increase due to irreversible fouling is mostly determined by the presence of particles, whereas the amount of NPOC appears to be irrelevant. NPOC seems to be responsible for reversible fouling that can be removed by backwashing.The effect of pretreatment by anion exchange (AIEX) and coagulation on the performance and TMP increase due to fouling was investigated for Noardburgum lake water. The AIEX pretreatment removes > 80% of NPOC, turbidity and UV extinction.For both types of pretreatment reversible fouling is decreased, but irreversible fouling is increased. Especially the AIEX pretreatment leads to a TMP increase due to irreversible fouling, even though most of the NPOC and particles are removed and never reach the MF membrane.
Uploads
Papers by Bas Hofs