Organic Liquid Impregnation Behavior into Nanofibrous Membranes: Quantitative Analysis of the Effects of Structural Parameters.

This paper reports the effects of structural parameters on organic liquid impregnation behavior into nanofibrous (NF) polymer membranes. The NF membranes were prepared from organic liquidphilic polymers, poly(amide-imide)s (PAIs), by electrospinning. The impregnation velocity of the organic liquid, ethylmethylcarbonate, into the as-spun PAI NF membranes with diameters ranging from 400 to 900 nm was approximately 10-20 times higher than that into commercial cellulose nonwoven membranes. Our theoretical analyses based on the Kozeny-Carman equation and multivariate statistics clearly indicate that in addition to the porosity of the membranes, the variation in fiber diameter as well as the average fiber diameter is a crucial factor for controlling the liquid impregnation behavior.

Surface morphology and biological activity of protein thin films produced by electrospray deposition.

Protein thin films were prepared by the electrospray deposition (ESD) method from aqueous solutions of alpha-lactalbumin (alpha-LA) at different concentrations, and their surface morphologies and biological activities were characterized. The surface morphologies of the deposited films were observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM and AFM images showed that the film surfaces had a fine porous structure, in which the pore diameters ranged from 40 to 600 nm. The biological activities of the cross-linked protein films were tested by the mechanochemical method. The response to calcium ion (Ca(2+)) demonstrated that the biological activity of the films was preserved. These results indicate that the ESD method is potentially useful for the fabrication of active protein thin films. The freestanding protein thin films prepared by ESD and postdeposition cross-linking provide novel options for protein-based biomaterials.

Effect of proton concentration on membrane potential across a weak amphoteric polymer membrane.

An amphoteric membrane consists of both positively and negatively fixed charge groups chemically bound to the polymer chains. If the external solution is changed from alkali to acid, it is possible to obtain an experimental result in which the membrane potential changes from positive to negative through the isoelectric point. It was characterized by examining the relationship between membrane potential and proton concentration (pH) obtained from both experimental and theoretical considerations. The Nernst-Planck flux equation and the Donnan equilibrium theory were also solved for a four-component system combined with the dissociation constant, in order to discuss the pH dependence of membrane potential in a weak amphoteric membrane by comparing the experimental results with the calculated results. It was proven that the calculated results substantially deviated from the theoretical results despite a similar tendency. Such a deviation was caused by the fact that the original theory disregarded the activity coefficient and the ionic mobility, which were dependent on the fixed charge concentration in a membrane. The original theoretical model was modified by adding the effect of a fixed charge group to the activity coefficient and ionic mobility. The calculated results using the modified model explained well the experimental results if the parameter called charge effectiveness, phi, was introduced into the equations. Introduction of phi into the prediction of membrane potential was already done by Kobatake et al. in a system of a strong polyelectrolyte monopolar membrane/salt aqueous solution. In this study, it was proved that phi can also be introduced into a weak amphoteric polymer membrane/salt aqueous solution system. Finally it was also concluded that the Donnan equilibrium and the Nernst-Planck flux equation were still applicable for examining the transport phenomena for the system of a weak amphoteric charged membrane and electrolyte solutions at various pH.