Mitsuru Nagasawa

Artificial membranes from multiblock copolymers. : I. Fabrication of a charge-mosaic membrane and preliminary tests of dialysis and piezodialysis

Abstract We succeeded in preparing a charge-mosaic membrane from pentablock copolymers of the BABCB type by selectively introducing anion- and cation-exchange groups into the separated microphases. The three-layer lamellar structure of the starting pentablock copolymer film was not disturbed by the modifications. The membrane obtained showed a piezodialytic effect for aqueous solutions of sodium chloride. It also showed a high permeability for sodium chloride only in aqueous solutions of sodium chloride mixed with non-electrolytes such as saccharose. Marked pH-dependent permeabilities were also observed for amino acids.

A New Charge-Mosaic Membrane from a Multiblock Copolymer

A charge-mosaic membrane was prepared from a pentablock copolymer of the BABCB type by selectively introducing anion and cation exchange groups into the microseparated phases. The three-layer lamellar structure of the starting pentablock copolymer film was not disturbed by the modifications. The membrane obtained was highly permeable only to sodium chloride in mixed aqueous solutions of sodium chloride and organic species of low molecular weight, such as sucrose. Marked pH-dependent permeabilities were also observed for amino acids.

Time Dependent Viscoelastic Properties of Concentrated Polymer Solutions

Measurements of stress growth and stress relaxation after onset and cessation of steady simple shear flow in concentrated polymer solutions were carried out with a Weissenberg rheogoniometer R‐17 having a gap servo system. By using monodisperse polymers and their blends, the effect of molecular weight distribution on those transient phenomena is discussed. The so‐called stress‐overshoot was observed in both experiments of shear and normal stress growths. Ratio of the time of the maximum normal stress difference and that of the maximum shear stress is close to 2 at the limit of low shear rate for both monodisperse and polydisperse polymers. In the range of finite shear rate, the ratio is remarkably dependent on shear rate for polydisperse samples, whereas it is almost independent of shear rate for monodisperse polymers. Shear rate dependence of the ratio of the apparent relaxation time of normal stress difference and that of shear stress in stress relaxation experiments is also found to be remarkably affec...

The Fractionation of Copolymers by Chemical Composition

Abstract Phase diagrams for the system of methyl ethyl ketone, cyclo-hexane, and styrene-acrylonitrile copolymer were determined. The phase diagrams indicate that the copolymer may be fractionated by chemical composition in this system. Discussions of the thermodynamics are also presented, to show that copolymers can effectively be fractionated into fractions of different compositions if a system can be found in which the difference between the Flory interaction parameters (x parameters) of two constituents of the copolymer with solvent is sufficiently large. Theoretically, the fractionation of copolymer must always occur to a certain extent, depending both on chemical composition and molecular weight. The composition fractionation results of styrene-acrylonitrile copolymers are given to confirm the discussions.

Thermoosmosis through charged membranes. theoretical analysis of concentration dependence

A theoretical equation for thermoosmosis through charged membranes in electrolyte solutions is derived from nonequilibrium thermodynamics. The theory shows that the volume flux through the membrane is proportional to the temperature difference across the membrane. The proportionality constant, i.e., the thermoosmotic coefficient is a function of electrolyte concentration. The electrolyte concentration dependence of the thermoosmotic coefficient calculated is compared with our previous experimental results. Agreement between theory and experiments is satisfactory.

Raman spectroscopic studies on the interaction between divalent counterion and polyion

The nature of the interaction between polyacrylate ion and several divalent cations, such as Cu2+, Mn2+, Zn2+, Ba2+ and Mg2+, was investigated using Raman spectroscopy. A specific Raman band characteristic of a carboxyl group is shifted upon addition of Cu2+, Zn2+ and Mn2+ to partially neutralized poly(acrylic acid). On the other hand, no frequency shift of the specific Raman band is observed on addition of Mg2+ and Ba2+, though the intensity of the specific Raman band decreases with concentration of MgCl2. It is concluded from these Raman data that the interaction between polyacrylate ion and Cu2+, Zn2+ or Mn2+ includes a specific interaction with bond formation, whereas in the case of Mg2+ and Ba2+, the electrostatic interaction is dominant.

Anomalous osmosis and salt concentration dependence of the reflection coefficient in charged membranes

Rates of permeation of water and electrolytes through an anion exchange membrane, prepared by the adsorption of a polycation on preformed collodion membrane, were measured. The experimental results are in agreement with a theory presented previously. An equation for the salt-concentration dependence of the reflection coefficient was derived and compared with both the theory of Kedem and Katchalsky and the experimental data. The agreement between the two theories and experiments is good. It is shown quantitatively that the total entropy production in negative osmosis is positive, because the absolute value of the entropy production due to solute is very much larger than that due to water.

Ion-Binding Phenomena of Polyelectrolytes

The alkali ion salts of carboxylic or sulplionic acid are in general completely dissociated in aqueous solutions if those salts are ordinary simple electrolytes. Even though those groups are fixed on a linear polymer skeleton such as polyacrylate or polystyrene sulphonate, it is reasonable to believe that those salts are completely dissociated in aqueous solutions. Nevertheless, it has often been pointed out that the physical properties of polyelectrolyte solutions can be well explained if we assume that the effective charge density is much lower than the analytical charge density. That is, the counter-ions appear to be bound on fixed charges to decrease the charge density. Such an idea of ion-binding (fixation, condensation etc.) has long been employed by various authors to explain the physical properties of linear polyelectrolyte solutions.

Raman spectroscopic studies on the interaction between counterion and polyion

The interaction between alkali metal ions and the polyacrylate ion was investigated by means of Raman spectroscopy. in comparison with the Raman spectra of propionate salts. The Raman bands due to the metal-oxygen bond were not apparent and no significant difference was observed among the Raman spectra of several univalent salts of polyacrylate. except in the case of the lithium salt. The apparent degree of dissociation of lithium polyacrylate, as determined from the relative intensity of a specific band characteristic of the carboxylate ion, was lower than those of the other alkali metal salts. It is concluded from the Raman data that the electrostatic interaction between counterions and a polyion is not specifically modified by forces of a nonionic nature. Moreover, it is pointed out that the local conformation of polyacrylate changes gradually with the degree of neutralization, but that the change is not like a conformational transition between globular and random coil forms.

Thermoosmosis through charged membranes

Thermoosmosis through oxidized collodion and collodion-sulfonated polystyrene interpolyrene interpolymer membranes has been observed in KCl solutions of various concentrations. The effective temperature difference acting for thermoosmosis was determined by measuring the thermal membrane potential appearing on both sides of membrane. It was found that the velocity of thermoosmosis is proportional to the effective temperature difference and the proprtionality constant (themoosmotic coefficient) is a function of electrolyte concentration. The dependence of the thermoosmotic coefficient of charged membranes on the electrolyte concentration is found to have a characteristic feature.