Showing papers on "Membrane published in 2004"
TL;DR: This review critically analyzes what is known of phase behavior and liquid-liquid immiscibility in model systems and compares these data with what isknown of domain formation in cell membranes.
Abstract: Views of how cell membranes are organized are presently changing. The lipid bilayer that constitutes these membranes is no longer understood to be a homogeneous fluid. Instead, lipid assemblies, termed rafts, have been introduced to provide fluid platforms that segregate membrane components and dynamically compartmentalize membranes. These assemblies are thought to be composed mainly of sphingolipids and cholesterol in the outer leaflet, somehow connected to domains of unknown composition in the inner leaflet. Specific classes of proteins are associated with the rafts. This review critically analyzes what is known of phase behavior and liquid-liquid immiscibility in model systems and compares these data with what is known of domain formation in cell membranes.
1,615 citations
TL;DR: An array of aligned carbon nanotubes (CNTs) was incorporated across a polymer film to form a well-ordered nanoporous membrane structure, which was confirmed by electron microscopy, anisotropic electrical conductivity, gas flow, and ionic transport studies.
Abstract: An array of aligned carbon nanotubes (CNTs) was incorporated across a polymer film to form a well-ordered nanoporous membrane structure This membrane structure was confirmed by electron microscopy, anisotropic electrical conductivity, gas flow, and ionic transport studies The measured nitrogen permeance was consistent with the flux calculated by Knudsen diffusion through nanometer-scale tubes of the observed microstructure Data on Ru(NH3)6(3+) transport across the membrane in aqueous solution also indicated transport through aligned CNT cores of the observed microstructure The lengths of the nanotubes within the polymer film were reduced by selective electrochemical oxidation, allowing for tunable pore lengths Oxidative trimming processes resulted in carboxylate end groups that were readily functionalized at the entrance to each CNT inner core Membranes with CNT tips that were functionalized with biotin showed a reduction in Ru(NH3)6(3+) flux by a factor of 15 when bound with streptavidin, thereby demonstrating the ability to gate molecular transport through CNT cores for potential applications in chemical separations and sensing
1,302 citations
TL;DR: Functionalised carbon nanotubes are able to cross the cell membrane and to accumulate in the cytoplasm or reach the nucleus without being toxic for the cell up to 10 µM.
1,041 citations
TL;DR: The synthesis of well-defined porous carbon films involves four steps: monomer-block copolymer film casting, structure refining through solvent annealing, polymerization of the carbon precursor, and carbonization.
Abstract: The synthesis of well-defined porous carbon films involves four steps: (1) monomer-block copolymer film casting, (2) structure refining through solvent annealing, (3) polymerization of the carbon precursor, and (4) carbonization. The resulting films, such as that depicted, have potential as separation membranes, chemical sensors, and catalysts.
784 citations
TL;DR: Results showed that CS increased the permeability of the OM and IM and ultimately disrupted bacterial cell membranes, with the release of cellular contents, due to electrostatic interaction between NH(3)(+) groups of CS acetate and phosphoryl groups of phospholipid components of cell membranes.
767 citations
TL;DR: A polymer with a rigid, randomly contorted molecular structure, incorporating fused rings connected by spiro-centres, may be precipitated or cast from solution to give microporous powders and membranes stable up to temperatures of 350°C, with apparent surface areas > 600m2
Abstract: A polymer with a rigid, randomly contorted molecular structure (see Figure), incorporating fused rings connected by spiro-centres, may be precipitated or cast from solution to give microporous powders and membranes stable up to temperatures of 350 °C, with apparent surface areas > 600 m2 g–1. Organophilic membranes may be formed, as demonstrated by the separation of phenol from water by pervaporation.
762 citations
TL;DR: A comprehensive review of NF in water treatments is presented in this paper, including a review of the applications of NF as well as in the pretreatment process for desalination; the mechanism and minimization of NF membrane fouling problems; and theories for modelling and transport of salt, charged and noncharged organic compounds in NF membranes.
711 citations
TL;DR: Physical and functional attributes for recently developed Nafion ® products that satisfy emerging fuel cell requirements are reviewed in this article, including stronger, more durable membranes, and polymer dispersions of higher quality and consistency for catalyst inks and film formation.
695 citations
Book•
01 Jan 2004
TL;DR: The Statistical Mechanics of Membranes and Interfaces (D Nelson) Interfaces: Fluctuations, Interactions and Related Transitions (M E Fisher) Equilibrium statistical mechanics of Fluctuating Films and Membrane (S Leibler) The Physics of Microemulsions and Amphiphilic Monolayers (D Andelman) Properties of Tethered Surfaces (Y Kantor) Theory of the Crumpling Transition as mentioned in this paper.
Abstract: The Statistical Mechanics of Membranes and Interfaces (D Nelson) Interfaces: Fluctuations, Interactions and Related Transitions (M E Fisher) Equilibrium Statistical Mechanics of Fluctuating Films and Membranes (S Leibler) The Physics of Microemulsions and Amphiphilic Monolayers (D Andelman) Properties of Tethered Surfaces (Y Kantor) Theory of the Crumpling Transition (D Nelson) Geometry and Field Theory of Random Surfaces and Membranes (F David) Statistical Mechanics of Self-Avoiding Crumpled Manifolds (B Duplantier) Anisotropic and Heterogeneous Polymerized Membranes (L Radzihovsky) Fixed-connectivity Membranes (M Bowick) Triangulated Surface Models of Fluctuating Membranes (G Gompper & D Kroll)
626 citations
TL;DR: In this article, the fundamental aspects of separations by pervaporation through zeolite membranes are reviewed, and examples of the selectivities and fluxes obtained are presented, including the effects of coverage, competitive adsorption, heat of adaption, molecular sizes, temperature, membrane structure, non-zeolite pores, concentration polarization and support resistance on transport and separations.
608 citations
TL;DR: In this paper, the development and evaluation of acid doped polybenzimidazole (PBI) membranes are reviewed, covering polymer synthesis, membrane casting, acid doping, physicochemical characterization and fuel cell testing.
Abstract: Proton exchange membrane fuel cell (PEMFC) technology based on perfluorosulfonic acid (PFSA) polymer membranes is briefly reviewed. The newest development in alternative polymer electrolytes for operation above 100 °C is summarized and discussed. As one of the successful approaches to high operational temperatures, the development and evaluation of acid doped polybenzimidazole (PBI) membranes are reviewed, covering polymer synthesis, membrane casting, acid doping, physicochemical characterization and fuel cell testing. A high temperature PEMFC system, operational at up to 200 °C based on phosphoric acid-doped PBI membranes, is demonstrated. It requires little or no gas humidification and has a CO tolerance of up to several percent. The direct use of reformed hydrogen from a simple methanol reformer, without the need for any further CO removal, has been demonstrated. A lifetime of continuous operation, for over 5000 h at 150 °C, and shutdown-restart thermal cycle testing for 47 cycles has been achieved. Other issues such as cooling, heat recovery, possible integration with fuel processing units, associated problems and further development are discussed.
TL;DR: The fabrication of freestanding monolithic uniform macroscopic hollow cylinders having radially aligned carbon nanotube walls, with diameters and lengths up to several centimetres are reported, which may allow them to compete with ceramic- and polymer-based separation membranes used commercially.
Abstract: Over the past decade of nanotube research, a variety of organized nanotube architectures have been fabricated using chemical vapour deposition. The idea of using nanotube structures in separation technology has been proposed, but building macroscopic structures that have controlled geometric shapes, density and dimensions for specific applications still remains a challenge. Here we report the fabrication of freestanding monolithic uniform macroscopic hollow cylinders having radially aligned carbon nanotube walls, with diameters and lengths up to several centimetres. These cylindrical membranes are used as filters to demonstrate their utility in two important settings: the elimination of multiple components of heavy hydrocarbons from petroleum-a crucial step in post-distillation of crude oil-with a single-step filtering process, and the filtration of bacterial contaminants such as Escherichia coli or the nanometre-sized poliovirus ( approximately 25 nm) from water. These macro filters can be cleaned for repeated filtration through ultrasonication and autoclaving. The exceptional thermal and mechanical stability of nanotubes, and the high surface area, ease and cost-effective fabrication of the nanotube membranes may allow them to compete with ceramic- and polymer-based separation membranes used commercially.
TL;DR: F Fouling by NOM was investigated by employing several innovative chemical and morphological analyses that support the notion that membrane roughness may be considered as a more important factor in membrane fouling by controlling interaction between molecules and the membrane surface, compared to the hydrophobic/hydrophilic character of membranes.
TL;DR: In this paper, a review of ion exchange membranes by radiation-induced graft copolymerization of polar and functional monomers onto non-polar polymeric films and fibers is presented.
TL;DR: In this paper, the removal mechanisms of four natural steroid hormones (estradiol, estrone, testosterone, and progesterone) by nanofiltration (NF) membranes were investigated.
Abstract: The removal mechanisms of four natural steroid hormones-estradiol, estrone, testosterone, and progesterone-by nanofiltration (NF) membranes were investigated. Two nanofiltration membranes with quite different permeabilities and salt retention characteristics were utilized. To better understand hormone removal mechanisms, the membrane average pore size was determined from retention data of inert organic solutes of various molecular weights and a pore transport model that incorporates steric (size) exclusion and hindered convection and diffusion. Results indicate that, at the early stages of filtration, adsorption (or partitioning) of hormones to the membrane polymer is the dominant removal mechanism. Because the adsorptive capacity of the membrane is limited, the final retention stabilizes when the adsorption of hormones into the membrane polymer has reached equilibrium. At this later filtration stage, the overall hormone retention is lower than that expected based solely on the size exclusion mechanism. This behavior is attributed to partitioning and subsequent diffusion of hormone molecules in the membrane polymeric phase, which ultimately results in a lower retention. Hormone diffusion in the membrane polymeric matrix most likely depends on the size of the hormone molecule, hydrogen bonding of hormones to membrane functional groups, and hydrophobic interactions of the hormone with the membrane polymeric matrix.
TL;DR: It is reported that active Rac1 binds preferentially to low-density, cholesterol-rich membranes, and specificity is determined at least in part by membrane lipids.
Abstract: Translocation of the small GTP-binding protein Rac1 to the cell plasma membrane is essential for activating downstream effectors and requires integrin-mediated adhesion of cells to extracellular matrix. We report that active Rac1 binds preferentially to low-density, cholesterol-rich membranes, and specificity is determined at least in part by membrane lipids. Cell detachment triggered internalization of plasma membrane cholesterol and lipid raft markers. Preventing internalization maintained Rac1 membrane targeting and effector activation in nonadherent cells. Regulation of lipid rafts by integrin signals may regulate the location of membrane domains such as lipid rafts and thereby control domain-specific signaling events in anchorage-dependent cells.
TL;DR: In this article, single-walled carbon nanotube (SWNT) reinforced polymer composite membranes have been fabricated using the electrospinning technique using the nanofibers with a diameter in the range 50−100 nm.
Abstract: Single-walled carbon nanotube (SWNT) reinforced polymer composite membranes have been fabricated using the electrospinning technique. Nanofibers with a diameter in the range 50−100 nm were obtained by electrospinning SWNT-filled polystyrene composites. TEM observations revealed incorporation of small SWNT bundles oriented parallel to the nanofiber axis. As-prepared (AP) and ester (EST) functionalized SWNTs have been electrospun with polyurethane (PU) to demonstrate the effect of the chemical functionalization of SWNTs on the mechanical properties of SWNT-reinforced composites. The tensile strength of EST-SWNT-PU membranes is enhanced by 104% as compared to electrospun pure polyurethane membranes, while an increase of only 46% was achieved incorporating AP−SWNT in the polyurethane matrix. The tangent moduli of AP- and EST-SWNT-PU membranes were found to be respectively 215% and 250% higher than the control polyurethane membranes.
TL;DR: An innovative fabrication of compliant nanocomposite membranes with nanoscale thickness showing extraordinary sensitivity and dynamic range is reported on, which makes them candidates for a new generation of membrane-based sensor arrays.
Abstract: Highly sensitive sensor arrays are in high demand for prospective applications in remote sensing and imaging. Measuring microscopic deflections of compliant micromembranes and cantilevers is developing into one of the most versatile approaches for thermal, acoustic and chemical sensing. Here, we report on an innovative fabrication of compliant nanocomposite membranes with nanoscale thickness showing extraordinary sensitivity and dynamic range, which makes them candidates for a new generation of membrane-based sensor arrays. These nanomembranes with a thickness of 25–70 nm, which can be freely suspended over large (hundred micrometres) openings are fabricated with molecular precision by time-efficient, spin-assisted layer-by-layer assembly. They are designed as multilayered molecular composites made of a combination of polymeric monolayers and a metal nanoparticle intralayer. We demonstrate that these nanocomposite membranes possess unparalleled sensitivity and a unique autorecovering ability. The membrane nanostructure that is responsible for these outstanding properties combines multilayered polymer/nanoparticle organization, high polymer-chain orientation, and a pre-stretched state.
TL;DR: In this article, the fabrication aspects of carbon membranes, which can be divided into six steps: precursor selection, polymeric membrane preparation, pretreatment of the precursor, pyrolysis process, post-treatment of pyroglyzed membranes and module construction.
TL;DR: In this paper, the limitations of per-fluorinated polymer electrolyte membranes to low temperature were discussed and an exhaustive presentation and complementary discussions on various aspects of works done recently on the developments of composite membranes for polymeric electrolyte fuel cell (PEFC) applications were presented.
TL;DR: In this paper, the authors compared the physiochemical properties of Nafion 115 and a composite membrane of Zirconium phosphate (∼25 ¼wt.%) and found that the composite membrane has a greater rigidity that accounts for its improved fuel cell performance.
TL;DR: Particular focus is put on cholesterol's ability to promote a special membrane phase, the liquidordered phase, which is unique for cholesterol (and other higher sterols like ergosterol) and absent in membranes containing the cholesterol precursor lanosterol.
Abstract: Cholesterol (or other higher sterols such as ergosterol and phytosterols) is universally present in large amounts (20-40 mol%) in eukaryotic plasma membranes, whereas it is universally absent in the membranes of prokaryotes. Cholesterol has a unique ability to increase lipid order in fluid membranes while maintaining fluidity and diffusion rates. Cholesterol imparts low permeability barriers to lipid membranes and provides for large mechanical coherence. A short topical review is given of these special properties of cholesterol in relation to the structure of membranes, with results drawn from a variety of theoretical and experimental studies. Particular focus is put on cholesterol's ability to promote a special membrane phase, the liquid-ordered phase, which is unique for cholesterol (and other higher sterols like ergosterol) and absent in membranes containing the cholesterol precursor lanosterol. Cholesterol's role in the formation of special membrane domains and so-called rafts is discussed.
TL;DR: The results strongly indicate the necessity for the paradigm shift of the concept on the plasma membrane: from the two-dimensional fluid continuum model to the compartmentalized membrane model in which its constituent molecules undergo hop diffusion over the compartments.
TL;DR: A novel method to form a hybrid membrane composed of silica–surfactant nanocomposite and a porous alumina membrane, by which size-selective transport of molecules across the membrane becomes possible.
Abstract: A mesoporous membrane composed of nanochannels with a uniform diameter has a potential use for precise size-exclusive separation of molecules. Here, we report a novel method to form a hybrid membrane composed of silica-surfactant nanocomposite and a porous alumina membrane, by which size-selective transport of molecules across the membrane becomes possible. The nanocomposite formed inside each columnar alumina pore was an assembly of surfactant-templated silica-nanochannels with a channel diameter of 3.4 nm; the channel direction being predominantly oriented along the wall of the columnar alumina pore. Molecules could be transported across the membrane including the silica-surfactant nanocomposite with a capability of nanometre-order size-exclusive separation. Our proposed membrane system has a potential use not only for separation science, but also catalysis and chip technologies.
TL;DR: The PVA/Sulfosuccinic acid (SSA)/silica hybrid polyvinyl alcohol (PVA)/SiO 2 hybrid membranes containing sulfonic acid groups were fabricated from different SSA contents.
TL;DR: Protein-depleted membranes demonstrated changes in thickness of up to 5 Å, suggesting that (i) membrane proteins rather than cholesterol modulate the average bilayer thickness of eukaryotic cell membranes, and (ii) proteins and lipids are not naturally hydrophobically matched in some biological membranes.
Abstract: A biological membrane is conceptualized as a system in which membrane proteins are naturally matched to the equilibrium thickness of the lipid bilayer. Cholesterol, in addition to lipid composition, has been suggested to be a major regulator of bilayer thickness in vivo because measurements in vitro have shown that cholesterol can increase the thickness of simple phospholipid/cholesterol bilayers. Using solution x-ray scattering, we have directly measured the average bilayer thickness of exocytic pathway membranes, which contain increasing amounts of cholesterol. The bilayer thickness of membranes of the endoplasmic reticulum, the Golgi, and the basolateral and apical plasma membranes, purified from rat hepatocytes, were determined to be 37.5 ± 0.4 A, 39.5 ± 0.4 A, 35.6 ± 0.6 A, and 42.5 ± 0.3 A, respectively. After cholesterol depletion using cyclodextrins, Golgi and apical plasma membranes retained their respective bilayer thicknesses whereas the bilayer thickness of the endoplasmic reticulum and the basolateral plasma membrane decreased by 1.0 A. Because cholesterol was shown to have a marginal effect on the thickness of these membranes, we measured whether membrane proteins could modulate thickness. Protein-depleted membranes demonstrated changes in thickness of up to 5 A, suggesting that (i) membrane proteins rather than cholesterol modulate the average bilayer thickness of eukaryotic cell membranes, and (ii) proteins and lipids are not naturally hydrophobically matched in some biological membranes. A marked effect of membrane proteins on the thickness of Escherichia coli cytoplasmic membranes, which do not contain cholesterol, was also observed, emphasizing the generality of our findings.
TL;DR: In this paper, a molecular-sieve DDR type zeolite membrane with an aperture of 0.36 × 0.44 nm was formed on a porous alumina substrate by hydrothermal process.
TL;DR: In this article, Sulfonated aromatic poly(ether ether ketones) (S-PEEKs) based membranes have been evaluated for fuel cell applications by determining the degree of sulfonation, water swelling, proton conductivity, methanol diffusivity and thermal stability.
TL;DR: In this article, crosslinked polyvinyl alcohol (PVA) membranes were synthesized by varying the amount of sulfosuccinic acid (SSA) in order to achieve desirable proton conductive properties for fuel cell applications.
TL;DR: In this paper, a physical model of polyelectrolyte membranes is developed that is semiphenomenological and takes into account Schroeder's paradox, and two different transport mechanisms are presented and discussed.
Abstract: In this paper, a physical model is developed that is semiphenomenological and takes into account Schroeder's paradox. Using the wealth of knowledge contained in the literature regarding polymer-electrolyte membranes as a basis, a novel approach is taken in tying together all of the data into a single coherent theory. This approach involves describing the structural changes of the membrane due to water content, and casting this in terms of capillary phenomena. By treating the membrane in this fashion, Schroeder's paradox can be elucidated. Along with the structural changes, two different transport mechanisms are presented and discussed. These mechanisms, along with the membrane's structural changes, comprise the complete physical model of the membrane. The model is shown to agree qualitatively with different membranes and different membrane forms, and is applicable to modeling perfluorinated sulfonic acid and similar membranes. It is also the first physically based comprehensive model of transport in a membrane that includes a physical description of Schroeder's paradox, and it bridges the gap between the two types of macroscopic models currently in the literature.