Effect of porosigen on the swelling behavior and drug release of porous N‐isopropylacrylamide/poly(ethylene glycol) monomethylether acrylate copolymeric hydrogels

A series of porous thermoreversible hydrogels were prepared from N‐isopropylacrylamide (90 mol %) and poly(ethylene glycol) methylether acrylate (10 mol %), which was derived from poly(ethylene glycol) monomethylether, N,N′‐methylenebisacrylamide, and porosigen, or poly (ethylene glycol) (PEG) with different molecular weights (MWs). The influence of pore volume in the gel on the physical properties, swelling kinetics, and solute permeation from these porous gels was investigated. The results show that the surface areas, pore volumes, and equilibrium swelling ratios for the porous gels increased with increasing MW of PEG, but the shear moduli and effective crosslinking densities decreased with increasing MW of PEG. The results from the dynamic swelling kinetics show that the transport mechanism was non‐Fickian. The diffusion coefficients of water penetrating into the gels increased with increasing pore volume of the gels. In addition, we also studied solute permeation through the porous gel controlled by temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5490–5499, 2006     

Current-time behaviour for copper electrodeposition. I. Theoretical analysis based on a surface diffusion model

The form of the current-time transients for copper electrodeposition from copper sulphate solutions have been calculated based on a surface diffusion model. The transient was greatly affected by whether the ad-species diffusing across the surface was ad-atom Cu⁰ or ad-ion Cu⁺, and by the surface coverage by the ad-species. The results imply that it is possible to experimentally test the applicability of the surface diffusion model to copper electrodeposition, to identify the ad-species (Cu⁰ or Cu⁺), to estimate the surface coverage and to calculate the parameters related to surface diffusion,D/l ² andi ₀/c ₀.     

Model simulation and analysis of surface diffusion of liquids in porous solids

A general mathematical model for the rates of adsorption of solutes from a liquid by porous solids in a batch system has been derived. The model includes external mass transfer, pore volume accumulation and diffusion, adsorption using nonlinear isotherms, and surface diffusion. Numerical solutions and parametric plots were obtained.The presence of surface diffusion has a large effect on increasing rates of adsorption for slightly and highly adsorbing solutes. External mass transfer controls the rate for small values of the mass transfer coefficient. Appreciable errors can occur if pore diffusion is neglected for the slightly adsorbing case with little error for the highly adsorbing case. Internal concentration profiles show marked differences for slightly and highly adsorbing solutes.     

Performance evaluation of porous electrocatalysts via normalization of the active surface

When comparing the rate of electrochemical processes at different porous electrocatalysts a surface normalization should be used. It is shown for the case of methanol oxidation at PtRu layers electrodeposited on gold substrates that substantially different data are obtained for current, mass spectrometry signals and integrated IR band intensities of the products, with and without normalization of the catalyst surface used. Using stripping of saturated CO coverage as a normalization tool, cyclic voltammograms, on line MS and in situ FTIR spectroscopy give reasonable agreement of catalytic activity towards methanol oxidation.On leave from: Departamento de Química, Universidade Federal do Pará, Rua Augusto Correa S/N, Belém, Pará, Brazil     

Computational simulation of surface diffusion in porous materials

The application of the converging—divergeing pore model, previously developed for the simulation of structural effects on the diffusion of nonadsorbed gases in porous media, to surface transport is described. Good agreement with experimental results reported for surface diffusion of propane and neopentane on a molybdenum sulfide structure is demonstrated in the limit of low surface coverage. At higher coverages, some deviation is seen to occur, but this is more probably due to the inadequacy of Fickian diffusivity correlations under such conditions than to the model itself. A brief comparison with corresponding parallel-path model correlations is also given.     

ADSORPTION IN POROUS SOLIDS HAVING BIMODAL PORE SIZE DISTRIBUTION

The effect of micropore diffusion, macropore diffusion and adsorption on the transient uptake of porous solids having bimodal pore size distribution (for example, zeolites) is theoretically investigated in this paper. Two models commonly used in the literature—the pore diffusion model and the surface diffusion model— are considered and their equivalence is discussed. The bimodal diffusion model equations are solved analytically by using a generalized integral transform method. The solutions for the micropore, macropore concentrations and the fractional uptake are presented. Since two different processes control the transient uptake, the asymptotic solutions for micropore diffusion control case and macropore diffusion control case are obtained by using perturbation methods, so that these asymptotic solutions can be compared with that when these two processes equally contribute to the transient uptake.     

Influence of ultrasound on diffusion through skin/leather matrix

Leather is a unique porous material, which is composed of a three-dimensional weave of tanned collagen fibre bundles. Collagen is a fibrous protein well organized in the formation of skin as building block. This paper studies the use of ultrasound in improving the diffusion process through porous skin/leather matrix. A diffusion model for leather processing has been proposed taking into account of pore characteristics in leather. Dye diffusion experiments have been carried out with leather and powdered leather to show the influence of ultrasound under two different diffusion conditions. Apparent diffusion coefficient (D) of dye through leather matrix has been calculated from the experimental dye uptake data. The results indicate that the use of ultrasound could achieve, 16.2 and 8.56 times improvement in D value for leather at 50 °C and 30 °C, respectively as compared to 2.99 and 1.55 times for powdered leather. Scanning electron microscopy (SEM) analysis of leather has also been performed which shows that fibre structure and morphology are not affected by the use of ultrasound. This study throws some light on enhanced transport through porous materials of complex nature such as skin/leather using ultrasound.     

Multifunctional porous membranes with antibacterial properties

Abstract

The paper describes the results of research on obtaining porous membranes produced from polylactide fibers (PLA) by electrospinning, additionally modified with gentamicin antibiotic (GM) at the stage of preparing a spinning solution to provide bactericidal properties. Both solid (1^oPNF) and porous (2^oPNF 3^oPNF) polymer fibers were obtained, and the control of fiber porosity was achieved using various solvent systems: dichloromethane (DCM), dimethylformamide (DMF), chloroform (CHL) and dimethyl sulfoxide (DMSO). Three types of fibers differing in morphology (fiber diameter) and mean pore size were obtained. Physicochemical properties of porous and solid drug-containing fibers were examined, determining their surface free energy (SFE) and wetting angle (CA), and the effectiveness of modification with the drug was confirmed in spectroscopic studies (FTIR-ATR). Antibacterial activity of the prepared drug-modified nonwovens was confirmed by the disk diffusion method against Gram-negative Escherichia coli bacteria strain. The results of tests have shown that depending on the type of solvents used at the electrospinning stage, porous fibers can be obtained from polylactide. The addition of gentamicin affected antibacterial properties, and the pore size determined the rate of drug release monitored by the ion coupled plasma method (ICP).     

Adsorption and diffusion of Pb(II) on the kaolinite(001) surface: A density-functional theory study

The adsorption and diffusion of Pb(II) atom on the hydroxylated (001) surface of kaolinite were investigated using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics was systematically studied for a wide range of coverage Θ [from 0.11 to 1.0 monolayers (ML)] and adsorption sites. The most stable among all possible adsorption sites was the two-fold bridge site followed by the one-fold top site, and the adsorption energy increased with the coverage, thus indicating the higher stability of surface adsorption and a tendency to the formation of Pb(II) islands (clusters) with increasing coverage. Moreover, the energy barrier for diffusion of Pb(II) atom between the one-fold top and the two-fold bridge adsorption sites on kaolinite(001) surface was 0.23 (0.31) eV, implying that the Pb(II) atom is prone to diffusing on kaolinite(001) surface. The other properties of the Pb(II)/kaolinite(001) system including the different charge distribution, the lattice relaxation, and the electronic density of states were also studied and discussed in detail.     

Superhydrophobic polyvinylidene fluoride/graphene porous materials

We demonstrated a simple method to produce superhydrophobic polyvinylidene fluoride (PVDF)/graphene porous materials. The hybrid PVDF/graphene gel was formed by the diffusion of non-solvent (methanol or water) into PVDF/graphene suspension in N,N-dimethylformamide (DMF). By carefully replacing DMF in aged gels by water, gel samples were freeze-dried to produce skinless porous materials. This drying method effectively avoids pore-shrinkage because of the capillary force in the drying process of gels, giving porous materials with high specific surface area and surface roughness. Furthermore, compared with pure PVDF porous materials, the addition of small amount of graphene in hybrid gels not only influences the crystallization of PVDF, but also leads to a dramatically morphology change which significantly increases their surface roughness in nanoscale, thus generating superhydrophobic porous PVDF/graphene materials.     

Hydrophilic and hydrophobic poly(l‐lactic acid) films by building porous topological surfaces

Surface wettability of thin films is significant for their functional properties. Poly(l ‐lactic acid) (PLLA) is proposed as film matrix for building porous topological surfaces. By controlling the dope composition and ambient conditions, the films with ordered pores at micrometer scale are obtained. The results demonstrate that the hydrophilic or hydrophobic surface can be realized by building the porous topological surfaces. Increasing polymer concentration can lead to decreased pore size. The transition behavior of surface pores from discrete bowl‐like to interconnected honeycomb‐like structure with the increasing humidity is observed. The contact angle of top surface of film is higher than that of bottom surface, which verified the different roughness performance. The morphology and scale of topological structure are markedly related with the template effect of water droplets. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44572.     

NONUNIFORM STEADY STATES IN SYSTEMS OF INTERACTING CATALYST PARTICLES. THE CASE OF NEGLIGIBLE INTERPARTICLE MASS TRANSFER COEFFICIENT

The effect of micropore diffusion, macropore diffusion and adsorption on the transient uptake of porous solids having bimodal pore size distribution (for example, zeolites) is theoretically investigated in this paper. Two models commonly used in the literature—the pore diffusion model and the surface diffusion model— are considered and their equivalence is discussed. The bimodal diffusion model equations are solved analytically by using a generalized integral transform method. The solutions for the micropore, macropore concentrations and the fractional uptake are presented. Since two different processes control the transient uptake, the asymptotic solutions for micropore diffusion control case and macropore diffusion control case are obtained by using perturbation methods, so that these asymptotic solutions can be compared with that when these two processes equally contribute to the transient uptake.     

Oxygen Diffusivities and Surface Exchange Coefficients in Porous Mullite/Zirconia Composites Measured by the Conductivity Relaxation Method

Oxygen diffusivities and surface exchange coefficients in various porous mullite/zirconia composites were measured at oxygen partial pressures ranging from 20.2 to 2.02 kPa using the conductivity relaxation method. However, the oxygen diffusivities in porous high-zirconia composites could not be determined because of the predominant surface exchange reaction. Oxygen diffusivities and surface exchange coefficients in low-zirconia composites increased with the zirconia content, while the surface exchange coefficients in high-zirconia composites were approximately constant. A percolation threshold of the surface exchange coefficients occured at ∼40 vol% zirconia for porous zirconia/mullite composites. The oxygen diffusivities in porous low-zirconia composites were independent of the oxygen partial pressure, implying that oxygen diffusion in these composites was related to the migration of oxygen vacancies, whose concentration was independent of the oxygen partial pressure. The surface exchange coefficients of high-zirconia composites decreased with increasing oxygen partial pressure. Finally, it was inferred that the rate-limiting step for oxygen surface exchange could be the charge-transfer process.     

茴香醚在葡萄糖基多孔碳材料上缓释机理

选择葡萄糖为碳源制备了一种多孔碳材料,对材料进行孔隙结构表征,研究材料孔隙结构对茴香醚脱附扩散机制的影响。应用重量法测定茴香醚在不同吸附剂上的脱附动力学曲线,建立扩散系数D_e估算模型,然后计算出茴香醚在吸附剂上的扩散系数D_e（t）-q（t）关系曲线,根据扩散系数值的大小划分扩散机理区域,讨论吸附剂的孔隙结构对茴香醚在吸附剂材料上扩散机制的影响。研究结果表明,所制备样品的比表面积可达1133～3153 m²·g⁻¹,茴香醚在吸附剂上的吸附量可达到1050 mg·g⁻¹;茴香醚香料分子在3种材料上的脱附扩散都经历了一般扩散、Knudsen扩散和表面扩散。吸附剂的孔隙结构对茴香醚香料分子在材料上的脱附扩散机制有影响,其微孔比例越高,茴香醚分子在此吸附剂上以表面扩散机制进行脱附所占比例越高。茴香醚分子在3种吸附剂上的脱附均以Knudsen扩散和表面扩散为主,约占78%～83%。本研究成果对于指导香料物质缓释材料的制备具有实际指导和借鉴意义。     

Correlations between pore structure parameters and gas permeability of corundum porous materials

Corundum porous materials with different contents of calcium hexaluminate formed in situ were prepared using pure calcium aluminate cement as the calcium source. The surface fractal dimensions of the porous materials were calculated based on the experimental data of mercury intrusion. Correlations between pore structural parameters and the permeability coefficients k₁ and k₂ of the porous materials were then studied based on the grey system theory. The results showed that pores in the corundum porous materials have great fractal characteristics. The surface fractal dimension was a significant pore structural parameter that reflected the complexity of pore shape, pore surface, and pore-size distribution, which had the maximum correlation coefficient with the permeability of this type of porous materials. The apparent porosity and pore-size distribution had relatively high correlation coefficients to the permeability as well. Increasing the apparent porosity and the volume percentage of larger pores, and decreasing the volume percentage of smaller pores all benefited the permeability of the porous materials. In addition, the mean pore size and median pore size showed lower correlation coefficients to the permeability—especially for porous materials with a wide pore-size distribution.     

Monte-Carlo simulations of surface and gas phase diffusion in complex porous structures

A new procedure for estimating surface diffusivities and tortuosities within realistic models of complex porous structures is reported. Our approach uses Monte-Carlo tracer methods to monitor mean-square displacements for molecules restricted to wander on pore walls within model random mesoporous solids typical of those used as adsorbents, heterogeneous catalysts, and porous membranes. We consider model porous solids formed from initial packings of spheres with unimodal, Gaussian, or bimodal distributions of size; changes in pellet porosity are achieved by increasing microsphere radii and by randomly removing spheres from highly densified packings in order to simulate densification and coarsening, respectively. Geometric tortuosities for the surface phase reached large values at void fractions near 0.04 and 0.42 for densified solids; the surface tortuosity gave a minimum value of 1.9 at a void fraction of ∼0.26. These high tortuosities correspond to percolation thresholds for the void and solid phases, which in turn reflect packing densities at which each phase becomes discontinuous. Surface tortuosities for coarsened solids at low void fractions were similar to those in densified solids; however, at void fractions above ∼0.3, surface tortuosities of coarsened solids increased only gradually with void fraction, because coarsening retains significant overlap among spheres at void fractions above those giving disconnected solids in densified structures. Simulations of bulk diffusion within voids were used to compare the transport properties and connectivity of the void space with those of surfaces that define this void space. Surface and void tortuosities were similar, except for void fractions near the solid percolation threshold, because unconnected solid particles interrupt surface connectivity but not gas phase diffusion paths. Surface and void tortuosities were also similar for channels within linear chains of overlapping hollow spheres as both tortuosities increased with decreasing extent of sphere overlap. These simulations provide a basis for estimates of surface and void tortuosities, which are essential in the interpretation and extrapolation of diffusion rates in complex porous media. Surface and void diffusivity estimates differed significantly from those obtained from lattice and capillary models of complex porous structures.     

Self-diffusion in solutions of carboxylated acrylic polymers as studied by Pulsed Field Gradient NMR. 2. Diffusion of macromolecules

The diffusion constants of carboxylated acrylic copolymers in isopropanol (IPA) have been investigated using the PFG NMR technique. A range of compositions of butyl methacrylate and methacrylic acid random copolymers (BMA–MAA 100/0 through to 60/40 in 10 mol% steps) have been studied. The polymer diffusivity is two orders of magnitude slower than that for the solvent. A maximum value of G _max = 10 T/m for the gradient pulse was used to suppress solvent signal and to measure the low value of the self-diffusion coefficient for the polymers. Polymer diffusion studies at different diffusion times showed that the diffusion constant decreased with increasing diffusion time. The influence of the concentration on the polymer aggregation in solution and the influence of the BMA/MAA molar ratio on the diffusion constants of the polymer have been studied. The diffusion constant for the polymer at long diffusion times increased with mol% BMA which is similar to the short diffusion time studies. The data obtained have been discussed using published results and models for “anomalous diffusion” of macromolecules in polymer solutions.     

Characteristics of surface concentration distribution due to irreversible adsorption in a one-pulse TAP experiment

The distribution of occupied surface coverage after a TAP one-pulse experiment with an irreversible adsorption process in spherical porous catalyst pellets was theoretically analyzed. Analytical expressions for the surface coverage for different reactor configurations, i.e., one-zone and three-zone reactors were determined. It was found that the intraparticle profiles of the surface coverage have the same shape for all catalyst pellets at different reactor axial coordinates. The analytical expression for describing the intraparticle profile of the surface coverage divided by the surface coverage at the pellet outermost is a function of the Thiele modulus and is the same for both reactor configurations. This explains the applicability of the effectiveness factor to calculate the gas conversion for the first order irreversible adsorption/reaction in TAP transient conditions. In addition, for each reactor configuration, the shape of all the profiles of the surface coverage along the reactor axial coordinate for different pellet radial coordinates is the same and is a function of gas conversion. The shape of the interparticle profile of the surface coverage is also the same as that in the non-porous case for the same gas conversion.     

Boundary-Layer Structure with Hydrogen Combustion with Different Injection Intensities

Results of numerical simulation of the influence of intensity of hydrogen injection through a porous surface in the case of hydrogen burning in the boundary layer are presented. Turbulent characteristics of the flow were simulated using the k–epsiv; turbulence model with Chien's modification for low Reynolds numbers. The diffusion model (infinitely large burning rate) was used to describe the chemical reaction process, but the difference in diffusion coefficients of different substances was taken into account. A comparison of injection with and without combustion shows that the presence of a heat-release front delays the laminar–turbulent transition and significantly deforms the profiles of density and viscosity of the gas mixture. As the injection velocity increases, the flame front is shifted from the porous surface toward the outer edge of the boundary layer. The contributions of injection itself and combustion to reduction of skin friction are analyzed. Key wrds: boundary layer, combustion, porous injection, heat and mass transfer, friction.