Modulating artificial membrane morphology: pH-induced chromatic transition and nanostructural transformation of a bolaamphiphilic conjugated polymer from blue helical ribbons to red nanofibers.

Design and characterization of helical ribbon assemblies of a bolaamphiphilic conjugated polymer and their color-coded transformation into nanofibers are described. An L-glutamic acid modified bolaamphiphilic diacetylene lipid was synthesized and self-assembled into right-handed helical ribbons with micron scale length and nano scale thickness under mild conditions. The ribbon structures were further stabilized by polymerizing well-aligned diacetylene units to form bisfunctional polydiacetylenes (PDAs). Transitions from flat sheets to helical ribbons and tubes were observed by transmission electron microscopy. The helical ribbons appear to originate from the rupture of flat sheets along domain edges and the peeling off between stacked lipid layers. These results point to the applicability of chiral packing theory in bolaamphiphilic supramolecular assemblies. Contact mode atomic force microscopy observations revealed that high order existed in the surface packing arrangement. Hexagonal and pseudorectangular packings were observed in flat and twisted regions of the ribbons, respectively, suggesting a correlation between microscopic morphologies and nanoscopic packing arrangements. The tricarboxylate functionalities of the bolaamphiphilic lipid provide a handle for the manipulation of the bisfunctional PDAs' morphology. Increasing solution pH caused the fraying of helical ribbons into nanofibers accompanied by a sharp blue-to-red chromatic transition. A dramatic change in circular dichroism spectra was observed during this process, suggesting the loss of chirality in packing. A model is proposed to account for the pH-induced morphological change and chromatic transition. The color-coded transition between two distinct microstructures would be useful in the design of sensors and other "smart" nanomaterials requiring defined molecular templates.     

Using breath figure patterns on structured substrates for the preparation of hierarchically structured microsieves

Microsieves are advanced filtration membranes characterized by a uniform pore size, a high pore density, and a thickness smaller than the pore diameter. The uniform pore size provides a high selectivity; the small thickness gives rise to a high flux and allows efficient removal of any filter cake by backflushing. However, microsieves are sensitive to mechanical stress. Thus, they need either an external macroporous support or a hierarchical structure that provides an integrated supportive structure. We prepare microsieves with a hierarchical pore structure by creating breath figure patterns within layers of solutions of polymers in a volatile solvent that are spread out on top of structured supports. For the formation of breath figure patterns, the volatile solvent is evaporated in a moist atmosphere. This cools the surface to such an extent that dew droplets form on the thin film, partially penetrate into the layer, and create a concave imprint in the final solid polymer layer. This procedure is usually done on flat surfaces; in our case the spreading of the polymer solution is done on a support decorated with protrusions. In this procedure, the dew droplets touch the protrusions of the structured support before the polymer solution vitrifies. At the same time, the trenches of the structured substrate are filled with polymer much deeper than the penetration depth of the dew droplets. After the separation of the vitrified layer from the substrate, we obtain thin polymer membranes with a hierarchical structure consisting of an ultrathin active separation layer with submicrometer pores and a supporting layer with larger pores.     

Spherical foam growth in Al alloy melt

The ultra light metal structure, realizing the light-ness and multifunction of structural material, has a bright future in high-tech and civil fields and is be-coming one of the hotspots in developed countries in 21 century[1―8]. Preparing Al foam by mel…     

Mobility of protein through a porous membrane

The electrophoretic mobility of proteins in membrane pores has been investigated experimentally. When the size of the protein is small relative to the pore size, the protein mobility is identical to the free protein mobility. As the pore radius approaches the protein radius the mobility of the protein is significantly reduced. This phenomenon has been explained in terms of electrokinetic theory. Using a method of reflections, and taking into account the effect of the back-flow, an approximation has been developed for the average mobility in a closed system of a spherical particle moving under electrophoresis parallel to the axis of a cylindrical pore. This approximation assumes that the surface potential of the particle is low, and is valid for arbitrary double layer thickness relative to particle size, provided that there is minimal overlap between the double layers at the pore surface and around the particle. It is also predicted that when the protein and the membrane have surface potentials of the same sign, there can be a significant increase in protein mobility for medium-sized pores.     

Grand canonical Monte Carlo simulation of argon adsorption at the surface of silica nanopores: effect of pore size, pore morphology, and surface roughness

Argon adsorption (77 K) in atomistic silica nanopores of various sizes and shapes has been studied by means of grand canonical Monte Carlo simulations (GCMC). We discuss the effects of confinement (pore size), pore morphology (ellipsoidal, hexagonal, constricted pore), and surface texture (rough/smooth) on the thickness variation of the adsorbed film with pressure onto the disordered inner surface of porous materials (usually called t-plot or t-curve). We show that no confinement effect occurs when the diameter of the regular cylindrical pore is larger than 10 nm. For pores smaller than 6 nm, we find that the film thickness increases as the pore size decreases. We show that the adsorption isotherm in the rough pore can be described as the sum of an adsorbed amount similar to that found for a smooth pore (of the same radius) and a constant contribution due to atoms "trapped" in the infractuosities of the rough surface which act as a microporous texture. Simulation snapshots for Ar adsorption in hexagonal and ellipsoidal smooth pores indicate that at low pressures the gas/adsorbate interface retains memory of the pore shape and becomes cylindrical prior to the capillary condensation of the fluid in the pore. The film thickness in the hexagonal pore is close to that obtained for a cylindrical pore having a similar dimension. By contrast, we find that the film thickness for an ellipsoidal pore is always larger than that for an equivalent cylindrical pore (having the same length and volume but a circular section). We show that this effect strengthens as the pore size decreases and/or the pore asymmetry increases. Ar adsorption in a cylindrical constricted pore shows that the presence of the narrower part considerably modifies the adsorption mechanism. Finally, we report GCMC simulations of Ar adsorption (77 K) on a plane silica reference substrate for different intermolecular potentials. We discuss the effect of the interaction on the shape of the adsorption isotherm and compare our results with experiments.     

Tuning the optical properties of mesoporous TiO2 films by nanoscale engineering

The optical properties of spin-coated titanium dioxide films have been tuned by introducing mesoscale pores into the inorganic matrix. Differently sized pores were templated using Pluronic triblock copolymers as surfactants in the sol-gel precursor solutions and adjusted by varying the process parameters, such as the polymer concentration, annealing temperature, and time. The change in refractive index observed for different mesoporous anatase films annealed at 350, 400, or 450 °C directly correlates with changes in the pore size. Additionally, the index of refraction is influenced by the film thickness and the density of pores within the films. The band gap of these films is blue-shifted, presumably due to stress the introduction of pores exerts on the inorganic matrix. This study focused on elucidating the effect different templating materials (Pluronic F127 and P123) have on the pore size of the final mesoporous titania film and on understanding the relation of varying the polymer concentration (taking P123 as an example) in the sol-gel solution to the pore density and size in the resultant titania film. Titania thin film samples or corresponding titanium dioxide powders were characterized by X-ray diffraction, cross-section transmission electron microscopy, nitrogen adsorption, ellipsometery, UV/vis spectrometry, and other techniques to understand the interplay between mesoporosity and optical properties.     

Control of the morphology of electrodeposited three-dimensional copper foam by tuning the pressure

Three-dimensional(3D) copper foams have been formed by electrodeposition at different nitrogen pressures and examined by scanning electron microscopy.The results indicate that an increase in system pressure leads to a decrease of the pore size of the copper foam due to the suppressed coalescence of hydrogen bubbles,while the thickness of the copper foam increases with decreasing pressure.Also,the walls around the pores on the copper foam consist of copper dendrites,and the copper dendrites are made up of copper grains with sizes less than 1 μm.The average sizes of the copper grains decrease with increasing system pressure.It has been demonstrated that copper foams with controllable 3D structure formed by electrodeposition at different pressures are comparable to those obtained by electrodeposition at normal pressure in the presence of specific additives.     

Effects of the juxtaposition of carbonaceous slit pores on the overall transport behavior of adsorbed fluids

It is a common approximation in the modeling of adsorption in microporous carbons to treat the pores as slit pores, whose walls are considered to consist of an infinite number of graphitic layers. In practice, such an approximation is appropriate as long as the number of graphitic layers in the wall is greater than three. However, it is understood that pore walls in microporous carbons commonly consist of three or fewer layers. As well as affecting the solid--fluid interaction within a pore, such narrow walls permit the interaction of fluid molecules through the wall, with consequences for the adsorption characteristics. We consider the effect that a distributed pore-wall thickness model can have on transport properties. At low density we find that the only significant deviation in the transport properties from the infinite pore-wall thickness model occurs in pores with single-layer walls. For a model of activated carbons with a distribution of pore widths and pore-wall thicknesses, the transport properties are generally insensitive to the effects of finite walls, in terms of both the solid-fluid interaction within a pore and fluid-fluid interaction through the pore walls.     

Improvement of the Derjaguin-Broekhoff-de Boer theory for the capillary condensation/evaporation of nitrogen in spherical cavities and its application for the pore size analysis of silicas with ordered cagelike mesopores

In a previous work, we proposed an improvement of the Derjaguin-Broekhoff-de Boer (DBdB) theory for capillary condensation/evaporation in open-ended cylindrical mesopores. In this paper, we report a further extension of this approach to the capillary condensation/evaporation of nitrogen in siliceous spherical cavities. The main idea of this improvement is to employ the Gibbs-Tolman-Koenig-Buff equation to predict the variation of the surface tension in spherical mesopores. In addition, the statistical film thickness (the so-called t-curve), which is evaluated accurately on the basis of adsorption isotherms measured for MCM-41 materials, is used instead of the originally proposed t-curve to take into account the excess chemical potential due to the surface forces. It is shown that the aforementioned modifications of the original DBdB theory that was refined by Ravikovitch and Neimark have significant implications for the pore size analysis of cagelike mesoporous silicas. To verify the proposed improvement of the DBdB pore size analysis (IDBdB), two series of FDU-1 samples, which are well-defined cagelike mesoporous materials (composed of siliceous spherical cavities interconnected by short necks), were used for the evaluation of the pore size distributions (PSDs). The correlation between the spinodal condensation point in the spherical pores predicted by the nonlocal density functional theory (NDFT) developed by Ravikovitch and Neimark and that predicted by the IDBdB theory is very good in the whole range of mesopores. This feature is mirrored to the realistic PSD characterized by the bimodal structure of pores computed from the IDBdB theory. As in the case of open-ended cylindrical pores, the improvement of the classical DBdB theory preserves its simplicity and simultaneously ensures a significant improvement of the pore size analysis, which is confirmed by the independent estimation of the average pore size by the NDFT and the powder X-ray diffraction method.     

Effect of membrane parameters on the size and uniformity in preparing agarose beads by premix membrane emulsification

Agarose microbeads were prepared by premix membrane emulsification with Shirasu-Porous Glass (SPG) membrane and Polyethylene (PE) membrane. The effects of membrane parameters, including pore size, pore size distribution, contact angle between membrane surface and the water phase, shape of pore opening and membrane thickness on size and uniformity of agarose beads were investigated in this study. The results showed that pore size distribution and shape of pore opening did not affect the emulsification results apparently within a wide range in premix membrane emulsification, not as the result in general emulsification. The contact angle between the water phase and the membrane surface must be large enough to obtain uniform-sized agarose beads in both direct membrane emulsification and premix membrane emulsification. The results also showed that the membrane pore size and thickness affected the size distribution of emulsion. Thicker membrane resulted in more uniform and smaller emulsion when the number of pass through membrane is controlled. There was a linear relationship between the number average diameter of agarose beads and membranes pores size in premix membrane emulsification. Agarose beads with diameters from 3.06 to 9.02 μm were prepared by controlling membranes pore size. The ratio of the number average diameter of agarose beads to membrane pore diameters was found to be 0.486.     

Wetting of regularly structured gold surfaces

In this study we report results for a systematic study of the wetting of structured gold surfaces formed by electrodeposition through monolayer templates of close-packed uniform submicrometer spheres. Removal of the template after deposition leaves a regular hexagonal array of sphere segment pores where the depth of the pores and, thus, the topography of the surface are controlled by the thickness of gold deposited through the template. We find that, as the thickness of the porous film increases up to the radius of the pores, the apparent contact angle for water on the surface increases from 70 degrees on the flat surface to more that 130 degrees , and then with increasing thickness above the radius of the pores the apparent contact angle decreases back toward 70 degrees . We show that these changes in the apparent contact angle agree with the model of Cassie and Baxter for nonwetted surfaces even though the gold itself is hydrophilic. We also show that the apparent contact angle is independent of the diameter of the pores over the range 400-800 nm. This is the first reported example showing the change of a hydrophilic surface (theta; < 90 degrees ) into a hydrophobic surface (theta; > 90 degrees ) purely by control of the surface topography. The role of the pore shape and size in stabilizing the nonwetting (Cassie-Baxter) droplet on the surface is discussed.     

Penetration into three-dimensional complex porous structures

The short-term uptake of a fluid by porous media is important in a number of processes, such as in coating and printing operations. We present a new model to predict short-term absorption into real pore geometries taking into account fluid properties, surface forces, and the complex pore geometry. Two assumptions are made to reduce the complexity of the situation: (1) the flow resistance between pores can be estimated from pore geometry or air permeability measurements, and (2) the volume of fluid in the constrictions between pores is small. Pores can be connected in any manner and can be in any arrangement. The absorption rates predicted by the model are compared to experimental values obtained with coating layers of plastic, kaolin, and calcium carbonate pigments. These coatings are characterized in terms of void fraction, pore size, contact angle, and permeability. The comparison is good for water and inks when the air permeability of the porous layer is used to determine the average resistance to flow in the sample. These resistance values are close to the values obtained from pore geometries estimated from particle packing simulations.     

Hydrodynamic thickness of petroleum oil adsorbed layers in the pores of reservoir rocks

The hydrodynamic thickness delta of adsorbed petroleum (crude) oil layers into the pores of sandstone rocks, through which the liquid flows, has been studied by Poiseuille's flow law and the evolution of (electrical) streaming current. The adsorption of petroleum oil is accompanied by a numerical reduction in the (negative) surface potential of the pore walls, eventually stabilizing at a small positive potential, attributed to the oil macromolecules themselves. After increasing to around 30% of the pore radius, the adsorbed layer thickness delta stopped growing either with time or with concentrations of asphaltene in the flowing liquid. The adsorption thickness is confirmed with the blockage value of the rock pores' area determined by the combination of streaming current and streaming potential measurements. This behavior is attributed to the effect on the disjoining pressure across the adsorbed layer, as described by Derjaguin and Churaev, of which the polymolecular adsorption films lose their stability long before their thickness has approached the radius of the rock pore.     

Modeling growth of organized nanoporous structures by anodic oxidation

Nanostructured porous oxides are produced by anodic dissolution of several metals. A scaling approach is introduced to explain pattern nucleation in an oxide layer, and a related microscopic model shows oxide growth with long nanopores. The scaling approach matches the time of ion transport across the thin oxide layer, which is related to metal corrosion, and the time of diffusion along the oxide/solution (OS) interface, which represents the extension of oxide dissolution. The selected pattern size is of order (dD(S)/v(O))(1/2), where d is the oxide thickness, v(O) is the migration velocity of oxygen ions across the oxide, and D(s) is the diffusion coefficient of H(+) ions along the oxide/solution interface. This result is consistent with available experimental data for those quantities, predicts the increase of pore size with the external voltage, and suggests the independence of pore size with the solution pH. Subsequently, we propose a microscopic model that expresses the main physicochemical processes as a set of characteristic lengths for diffusion and surface relaxation. It shows a randomly perturbed OS interface at short times, its evolution to pore nucleation and to stable growth of very long pores, in agreement with the mechanistic scenario suggested by two experimental groups. The decrease of the size of the walls between the pores with the interface tension is consistent with arguments for formation of titania nanotube arrays instead of nanopores. These models show that pattern nucleation and growth depend on matching a small number of physicochemical parameters, which is probably the reason for the production of nanostructured porous oxides from various materials under suitable electrochemical conditions.     

Adsorbate layering in narrow-pore materials

The conditions of layering of adsorbate molecules in porous systems with characteristic sizes of from 1 to 50–100 nm are discussed. The porous systems contain both very narrow pores, in which interaction potentials of pore walls overlap, and comparatively broad pores without overlapping of surface potentials. Three pore size intervals are distinguished. In the first interval, no adsorbate layering occurs, the second interval is characterized by capillary condensation with critical parameters different from their volume values, and, in the third interval, capillary condensation conditions are almost the same as in the volume adsorbtive phase. Criteria of the characteristic pore sizes of different geometries are formulated; the criteria correspond to small volumes in which first-order phase transitions are absent. The boundary between the first and second pore size regions is observed experimentally as the disappearance/appearance of hysteresis loops in adsorption-desorption isotherms measured under strictly equilibrium conditions as the size of pores decreases/increases. A nonuniform distribution of the surface potential is shown to be responsible for the multiplicity of local regions in porous media with their own vapor-liquid coexisting phases. The spinodal transitions in adsorption-desorption in pores can occur between various local regions. An analysis is performed in terms of the lattice gas model with short-range Lennard-Jones interaction of adsorbate molecules with each other and adsorbent walls.     

Magnetic nanoparticles entrapped in siliceous mesocellular foam: a new catalyst support

γ-Fe(2)O(3) nanoparticles were formed inside the cage-like pores of mesocellular foam (MCF). These magnetic nanoparticles showed a uniform size distribution that could be easily controlled by the MCF pore size, as well as by the hydrocarbon chain length used for MCF surface modification. Throughout the entrapment process, the pore structure and surface area of the MCF remained intact. The resulting magnetic MCF facilitated the immobilization of biocatalysts, homogeneous catalysts, and nanoclusters. Moreover, the MCF allowed for facile catalyst recovery by using a simple magnet. The supported catalysts exhibited excellent catalytic efficiencies that were comparable to their homogeneous counterparts.     

The role of pore size and structure on the thermal stability of gold nanoparticles within mesoporous silica

Highly dispersed gold particles (<2 nm) were synthesized within the pores of mesoporous silica with pore sizes ranging from 2.2 to 6.5 nm and different pore structures (2D-hexagonal, 3D-hexagonal, and cubic). The catalysts were reduced in flowing H2 at 200 degrees C and then used for CO oxidation at temperatures ranging from 25 to 400 degrees C. The objective of this study was to investigate the role of pore size and structure in controlling the thermal sintering of Au nanoparticles. Our study shows that sintering of Au particles is dependent on pore size, pore wall thickness (strength of pores), and pore connectivity. A combination of high-resolution TEM/STEM and SEM was used to measure the particle size distribution and to determine whether the Au particles were located within the pores or had migrated to the external silica surface.     

Pore wall thickness and interpore influence on adsorption of alkanes in carbons using explicit pore models

In modeling of activated carbons, the pores are often assumed to be slit-shaped formed of a constant number of graphene layers. X-ray diffraction studies show that micropores are formed between stacks of different numbers of graphene layers. In this study, we investigate, through the grand canonical Monte Carlo method, the influence on the adsorbed alkanes densities of pore walls with different graphene layers thickness and the related interpore adsorbate interaction when the pore wall has only one graphene layer. All studies of thickness and interpore interaction to date were performed using the Steele 10-4-3 potential model. Instead of Steele model, we propose explicit models made up of graphene layers of discrete carbon atoms. We also investigated the sensitivity of the system to the cut-off and solid-fluid parameter. With our explicit model we found that the influence of the number of carbon layers is not significant for n>2 as previously observed by Steele model??DFT studies. The system was also insensitive to cut-off and well deep parameter variations. A new pore model with an extra dummy graphene wall was proposed to investigate the interpore interaction. The interpore interaction study with the alkanes series C1 to C4 shows that the retention capacity of heavier alkanes is the same whether for activated carbons with few layers (stronger interpore interaction) as for carbons with two or more layers (stronger solid-fluid interaction) assuming negligible surface mediation. The explicit models proposed can be successfully used in the elaboration of virtual porous carbon models to reproduce wall thickness and interpore adsorbate interactions phenomena.     

生物质碳材料的孔道分析

生物质碳材料的孔道类型和孔径大小制约着材料有效的活性位点数量,影响材料的性能。孔道分类又是孔径分析的前提条件。因此,建立孔道分类的方法非常有意义。随着生物质碳材料的深入研究,研究者对其孔道分析的要求逐渐提高。他们用实际的吸脱附等温线与IUPAC规范中的吸脱附等温线进行匹配,来分类生物质碳材料的孔道。然而实际的吸脱附等温线具有不规则性,难以匹配IUPAC规范中的吸脱附等温线。所以,本文提出了孔隙率和比表面积占有率的孔道分类新方法。自制生物质碳材料,运用物理吸附仪和TEM (Transmission electron microscope)对其进行表征,采用BET方程（Brunauer-Emmett-Teller）、t-plot方法(Thickness-plot)、DFT方法（Non-local Density Functional Theory）、BJH（Barrett Joyner and Halenda）方法对其孔道进行分析。研究表明,采用孔隙率和比表面积占有率对其进孔道分类,可以准确的定义出微孔生物质碳材料、介孔生物质碳材料和微介孔生物质碳材料。本文用标准样品对孔隙率和比表面积占有率的孔道分类新方法进行论证,结果一致。因此,本文提出的孔隙率和比表面积占有率的孔道分类新方法准确可靠,实用性高。     

THE RESEARCH AND APPLICATION OF COLLOID AS LUBRICANTS

Foam generated by sparging of aqueous solutions of the block copolymers P85 (PEO₂₆‐PPO₃₉‐PEO₂₆), F88 (PEO₁₀₃‐PPO₄₀‐PEO₁₀₃), F127 (PEO₉₉‐PPO₆₅‐PEO₉₉), and L64 (PEO₁₃‐PPO₃₀‐PEO₁₃), has been characterized by foam volume measurements. Uniform wet foam formed, which, after drainage of the major part of the liquid, transformed to polyhedral dry foam. Conductance jumps across the foam column indicated that structural changes occur at a certain liquid fraction. The dry foams of P85 were less stable than those of F88 and F127. The latter copolymers showed similar foam stability over a period of one hour. The L64 foam was very unstable. It is suggested that the stability of the dry foams is determined by the resistance to rupture of the foam films. Foam stability is discussed in relation to earlier studies on surface rheology and to the thickness of thin foam films. A general relationship for all PEOx‐PPOy‐PEOx block copolymers between the dilatational modulus and the foam stability could not be found. However, the ability to form thick adsorption layers, accompanied by steric repulsive forces across foam films, appears to be a general foam‐stabilizing factor. Surface diffusion coefficients of a fluorescent probe in single‐block copolymers foam films are also reported for a brief discussion on Gibbs‐Marangoni stabilization.