Hideto Matsuyama

Analysis of solute diffusion in poly(vinyl alcohol) hydrogel membrane

Abstract Measurement of diffusion and partitioning of solutes having molecular weights ranging 180–66000 in PVA gel membranes with various crosslinking degree were carried out. With increasing solute size or decreasing number of average molecular weight between crosslinks of the membranes, both the solute permeability and partition coefficient decreased. In spite of similar solute sizes, the more hydrophilic solute ribonuclease showed higher permeability and partition coefficient than the less hydrophilic α-lactalbumin, probably due to interaction with the hydrophilic PVA. The solute diffusion through swollen gel membrane was analyzed by the equation based on free volume theory. In this analysis equation, the partition coefficient, which is defined as the ratio of solute concentration in gel membrane standardized by water volume in the membrane to that in bulk solution, was introduced as the probability of a diffusing species finding a mesh with a volume of at least the solute size. The efficiency of the proposed analysis equation was confirmed by the experimental results of the effects of solute size and water volume fraction in the membrane.

Membrane formation via phase separation induced by penetration of nonsolvent from vapor phase. II. Membrane morphology

Phase separation of poly(vinylidene fluoride) dimethylformamide solution was induced by the penetration of water vapor, and the porous membrane was formed. As the humidity in the gas phase increased, membrane morphology changed in the order of dense, porous (cellular), and lacy-like structures. At the higher humidity condition, spherical bead structure was observed, which is likely to be crystalline spherulite. With the increase of the initial polymer concentration, less pores were formed in the case of the lower humidity of 20%, whereas more distinguished spherical structures were formed in the case of higher humidity of 40%. The obtained membrane morphologies were discussed based on both the calculated composition paths during the process and the phase diagram.

Membrane formation and structure development by dry-cast process

Abstract The various types of porous membranes were prepared by dry-cast process in several cellulose acetate/acetone/nonsolvent systems. The nonsolvents used were 2-methyl-2,4-pentanediol, hexanol and octanol. Because of the high boiling points of the nonsolvents used in this work, only the solvent (acetone) evaporated during the membrane formation. The effects of the nonsolvent weight fraction in the cast solution, the polymer weight fraction, membrane thickness and kinds of the nonsolvents on the membrane structures were studied. As the nonsolvent weight fraction increased, the membrane morphology changed in the order of entirely dense, asymmetric and entirely porous structures. The increase in the polymer weight fraction and the decrease in the membrane thickness suppressed the asymmetric structures. These kinds of nonsolvents significantly influenced the membrane morphology. In order to understand the change of the obtained membrane structures, the phase diagrams for ternary systems were clarified experimentally and theoretically. Moreover, the mass transfer process was analyzed and the changes in the polymer volume fractions during the membrane formation were simulated. Based on both these thermodynamic and kinetic properties, the membrane structures obtained were discussed in detail. The asymmetrc structures obtained in this work were found to be attributable to the kinetic difference in the increase rates of the polymer fractions across the binodal line.

Membrane formation via phase separation induced by penetration of nonsolvent from vapor phase. I. Phase diagram and mass transfer process

The isothermal phase diagram for poly(vinylidene fluoride)/dimethyl formamide/water system was derived. The binodal and spinodal were calculated based on the Flory–Huggins theory and the calculated binodal was approximately in agreement with the experimental data of the cloud points. The isothermal crystallization line was also obtained according to the theory of melting point depression. Mass transfer of the three components during membrane formation by the precipitation from the vapor phase has been analyzed. During this process, phase separation of the polymer solution is induced by the penetration of water vapor in the solution. The calculated result on the changes of the cast film weights indicated the good agreement with the experimental data. The time-course of the polymer concentration profile in the film was calculated for various cases of different humidity of the vapor phase and different initial polymer concentration.

Phase separation mechanism during membrane formation by dry-cast process

Phase separation mechanisms during the membrane formation by dry-cast process were investigated by light scattering in the cellulose acetate/dimethylformamide (DMF)/2-methyl-2,4-pentanediol system. Phase separation occurred by spinodal decomposition (SD) when paths of the composition changes due to the evaporation of DMF were close to the critical point in the phase diagram. Characteristic properties of the early stage of SD such as an apparent diffusion coefficient and an interface periodic distance were obtained from the Cahn theory. Phase separation occurred by nucleation and growth (NG) when paths of the composition changes were far from the critical point. SEM observation confirmed that the membrane formed by the SD mechanism had interconnected structure, whereas that by the NG mechanism had the closed cell porous structure.

Kinetic studies of thermally induced phase separation in polymer–diluent system

Thermally induced phase separation was studied by the light scattering in polypropylene/methyl salicylate system. Data could be well fitted with the linear Cahn theory for spinodal decomposition (SD) in the early stage of phase separation. Characteristic properties of the early stage of SD, such as an apparent diffusion coefficient and an interphase periodic distance, were obtained. The periodic distance ranged from 3 μm to 4 μm. The growth of the phase-separated structure obeyed power-law scaling in the later stage, and the structure factor could be scaled into a universal time-independent form. Domain sizes obtained from the light-scattering measurements were consistent with the optical microscope measurements.

Diffusive permeability of ionic solutes in charged chitosan membrane

The permeabilities of three kinds of solutes with similar sizes such as anionic benzenesulfonic acid, neutral styrene glycol, and cationic theophylline in the chitosan membrane were investigated. The chitosan membrane becomes cationic below its pKa value. Benzenesulfonic acid showed the highest permeability, whereas theophylline showed the lowest, although these solutes have almost the same size. This can be explained by the electrostatic attraction or repulsion between the solute and the membrane instead of the size exclusion effect. The permeabilities of benzenesulfonic acid and theophylline increased and decreased, respectively, with the decrease of pH from 7.4 to 4.0 because of the increase of the charge density of the membrane. Thus, the selectivity of benzenesulfonic acid to theophylline increased and reached about 30 at pH 4.0, in contrast to the selectivity of nearly unity in poly(vinyl alcohol) (PVA) membrane. The partition coefficients for three solutes showed the similar tendencies to those in the permeabilities. Contrary to the results of the permeabilities, the partition coefficients increased with the increase of the degree of the crosslinking in the membrane. This is probably due to the increase of the electrostatic interaction between the solute and the membrane brought about by the smaller mesh size and also due to the increase of the bound water fraction in the membrane.

Effect of membrane preparation conditions on solute permeability in chitosan membrane

Chitosan membrane was prepared in various conditions and diffusive permeabilities of theophylline and vitamin B12 were investigated. The membrane preparation procedure consists of dissolving chitosan in acid solution, cast on the glass plate, drying the dope solution, and immersion of the plate in the gelating agent. Effects of the kinds of acids to dissolve chitosan, chitosan concentration, drying time of the dope solution, and the kinds of the gelating agent on the membrane structure and performance were studied in detail. With increasing the chitosan concentration, the solute permeability decreased, while the selectivity of theophylline to vitamin B12 increased. The membrane changed from the wholly porous structure to the asymmetric structure by the increase of the chitosan concentration. Furthermore, the use of ethanol as the gelating agent brought about the wholly porous structure with the high permeability and the low selectivity. The asymmetric structure and the wholly dense structure were obtained in the cases of the gelating agents, such as aqueous NaOH solution and dimethyl sulfoxide (DMSO), respectively. Thus, the membrane structure can be controlled by the kinds of gelating agent.

Kinetics of droplet growth in the metastable region in cellulose acetate/acetone/nonsolvent system

Abstract The kinetics of droplet growth in the metastable region were investigated in cellulose acetate/acetone/nonsolvent system. The results obtained by the dynamic light scattering apparatus indicated that the droplet diameter d increased with time t in the relation of d 3 ∝ t in all cases. From the detailed consideration on the slope values in these relations, it was concluded that the droplet growth mechanism in this system was coalescence mechanism rather than Ostwald ripening mechanism. The direct observation of the freeze-dried polymer solution by SEM was not contradictory to this conclusion. The initial stage of droplet growth was investigated by the stopped-flow apparatus. The experimental results on the turbidities showed that the droplets grew in the relation of d 3 ∝ t as well as the results by the light scattering.

Separation of Ethyl Ester of Docosahexaenoic Acid by Facilitated Transport Membrane with High Stability

The selective transport of the ethyl ester of docosahexaenoic acid (DHA-Et) was studied in the facilitated transport system where feed phase, membrane phase, and receiving phase had the same ethanol diluent. The carrier of DHA-Et was Ag+, and a Nafion membrane was used as the support so that Ag+ was immobilized in the support by electrostatic force. DHA-Et was sufficiently transported in this system due to the swelling of Nafion by ethanol, while the methyl ester of linoleic acid was hardly transported in a Nafion membrane containing aqueous Ag+ solution (membrane solution). DHA-Et, which has six carbon—carbon double bonds, was transported fairly faster than the ethyl ester of oleic acid which has one double bond with a selectivity of about 10. This indicated that our membrane is useful for separating esters of polyunsaturated fatty acids based on the difference in the double-bond numbers. The effects of the water content in the ethanol solution used as diluent and the feed phase DHA-Et concentration on m...