Effect of ionic interaction on linear and nonlinear viscoelastic properties of ethylene based ionomer melts

The effect of ionic interaction on linear and nonlinear viscoelastic properties was investigated using poly(ethylene-co-methacrylic acid) (E/MAA) and its ionomers which were partially neutralized by zinc or sodium. Dynamic shear viscosity and step-shear stress relaxation studies were performed. Stress relaxation moduli G(t, y) of the E/MAA and its sodium or zinc ionomers were factorized into linear relaxation moduli G°(t) and damping functions h(y). The relaxation modulus at the smallest strain in each ionomer agreed with the linear relaxation modulus calculated from storage modulus G and loss modulus G. In the linear region, the ionic interaction shifted the relaxation time longer with keeping the same relaxation time distribution as E/MAA. In the nonlinear region, the ionic interaction had no influence on h(y) when the ion content was low. At higher ion content, however, the ion bonding enhanced the strain softening of h(y).     

Proliferation and Insulin Secretion Function of Mouse Insulinoma Cells Encapsulated in Alginate/Sol-Gel Synthesized Aminopropyl-Silicate/Alginate Microcapsule

Alginate/aminopropyl-silicate/alginate microcapsules, ca. 15 m in membrane thickness and ca. 500 m in diameter, were prepared via sol-gel process. The aminopropyl-silicate membrane was derived from two silicone alkoxide precursors, tetramethoxysilane and 3-aminopropyl-trimethoxysilane on Ca-alginate micro gel beads. Pancreatic -cell line (MIN6) cells were encapsulated in the microcapsule. The encapsulated MIN6 cells proliferated and formed spheroidal tissues in vitro. The diameter of the MIN6 spheroids increased to approximately 250 m with an increase in the incubation period until the day 35. Storeptozotocin-induced diabetic mice became normoglycemia after implantation of the MIN6-enclosing microcapsules. The normoglycemic state remained until the retrieval of the implanted microcapsules for 1 month. These results indicate that the potential use of the alginate/aminopropyl-silicate/alginate microcapsule as a vehicle for a genetically engineered cell-enclosing therapeutic material delivery system.     

Poly(ethylene oxide) thin films produced by electrospray deposition: morphology control and additive effects of alcohols on nanostructure

Nanostructured thin films were prepared by electrospray deposition (ESD) from poly(ethylene oxide) (PEO) aqueous solution. The surface morphologies of the deposited films were observed using scanning electron microscopy (SEM). The SEM images revealed the correlations between the morphologies and the ESD conditions. By changing the applied voltage and solution properties such as viscosity, surface tension, conductivity, and molecular weight, PEO thin films with diverse nanostructures--from nanospheres to nanofibers--were fabricated. It was also revealed that the addition of alcohols to polymer solution, which enables simultaneously changing the viscosity, the surface tension, and the conductivity, enhanced the formation of the fibrous structure. These results indicate that the ESD method is potentially a useful option for producing nanoengineered polymer surface.     

Simulations of polymer crystallization under high pressure

High pressure crystallization of polypropylene was studied by means of PVT measurements and computer simulations. The isothermal crystallization behaviour were described by using a model which takes into account the effect of pressure on the temperature dependence of nucleation rate and linear growth rate. The agreement between the simulation and the experiments was seen in the tendency that the crystallization was accelerated by the high pressure. The non-isothermal crystallization behavior was also simulated by applying a generalized Avrami equation. The simulation curves well reproduced the experimental values below relative crystallinity 0.5 and below 100 MPa.     

Thermal dehydrations

The behaviour of thermal dehydrations of isomorphous complexes of calcium copper acetate hexahydrate, CaCu(CH₃CO₂)₄·6H₂O and calcium cadmium acetate hexahydrate, CaCd(CH₃CO₂)₄· 6H₂O was studied by means of thermal analyses and X-ray structural analysis. The enthalpy changes for the dehydration of CaCu(CH₃CO₂)₄·6H₂O and CaCd(CH₃CO₂)₄·6H₂O were 315±9.7 and 295±8.0 kJ mol^–1, respectively. The DSC curves of the dehydrations indicated that the seemingly simple dehydrations are more complex than they appear at first sight. Apparent activation energies for the dehydrations of CaCu(CH₃CO₂)₄·6H₂O and CaCd(CH₃CO₂)₄·6H₂O were 85.7±7.4 and 87.9±12.5 kJ mol^–1, respectively.The authors wish to express their thanks to Associate Professor Yasuhiko Yukawa of the Niigata University for the analysis of the X-ray-intensity data.     

Organic/inorganic hybrid nano-microstructured coatings on insulated substrates by electrospray deposition

Organic/inorganic hybrid nano-microstructured coatings on insulated polymer films were prepared by electrospray deposition (ESD) from an acrylic resin/silica sol blend solution. The surface morphologies of the coated films were observed using scanning electron microscopy (SEM). The SEM images showed that a nano-microscaled fibrous structure was formed on the film. The fiber diameter decreased from 4.4 microm to 600 nm with the increase in the silica sol content. Energy-dispersive X-ray analysis also revealed that silica atoms were homogeneously distributed in the fibrous structure on the polymer film. These results indicated that the ESD method is potentially a useful option for producing nano-microstructured coatings on not only conductive, but also insulating surfaces.     

Membrane potential of a bipolar membrane: the effect of concentration perturbation of the intermediate phase around a certain value

A new model of a sandwich-type bipolar membrane potential was constructed by assuming the potential behavior of a bipolar membrane as a combination of each layer potential between two different states, i.e. the different concentrations of the bulk solution. Hence, we introduced the coion exclusion parameter that is derived from the Donnan equilibrium as a combinatorial function, which combined all the potential equations involved in our system. We assumed that the existence of the intermediate phase due to its volume would allow the Donnan equilibrium to play an important role, i.e. the vanishing of the coion exclusion effect of the membrane layer facing the bulk solution phase in high concentration. Sandwich-type bipolar membranes, which consist of a cation- (K-501) and an anion-exchange layer (A-501) were used in this study. A series of concentration perturbations of the intermediate phase was performed to examine the membrane potential behavior of the bipolar membrane experimentally. The experimental results showed a good agreement with the theoretical results, which led to the conclusion that explained the contribution of the intermediate phase to the membrane potential behavior through its volume and electrochemical properties.     

Chronopotentiometry study of a cation-exchange membrane in the presence of cationic surfactant in membrane surface vicinity

In this study, the effect of cationic surfactant (benzalkonium chloride) on the transport of KCl through a sulfonated styrene-divinyl benzene cation-exchange membrane was investigated. The presence of benzalkonium chloride as the cationic surfactant, which interacts with the sulfonic groups on membrane surface, has to disturb the transport of K⁺ ions and directly gives responses in its chronopotentiogram. The electrodialysis of the cationic surfactant solution showed an irreversible monotonous increase of the total system potential due to the fouling phenomena. However, a small amount of cationic surfactant in the membrane surface vicinity was observed to give a fluctuating chronopotentiogram at the high current density. This fluctuation is started by a steep increase and followed by the decrease of potential, which finally relaxed to reach a steady state. This potential fluctuation is proposed to be the response of a structural transformation of surfactant micelles on the membrane surface under perturbation of the externally applied electric field, which is discussed and examined qualitatively in this report.     

Fine structure of PVDF nanofiber fabricated by electrospray deposition

The fine structure of poly(vinylidene fluoride) (PVDF) nanofiber prepared by electrospray deposition (ESD) has been investigated by wide angle X‐ray diffraction (WAXD) and infrared spectroscopy (IR). The β‐phase crystal was dominant in the crystalline region. The degree of crystallinity of 0.54 for the nanofiber, determined by Ruland's method, was almost identical to that for a melt pressed sheet of PVDF. The disorder parameter k was 4, which is significantly smaller than the value of 6 for the melt pressed sheet of PVDF. Molecular orientation along the fiber axis was observed by the polarized infrared spectra of the uniaxially aligned nanofiber. These results suggest that the PVDF nanofiber possesses a fiber structure which is by no means inferior to that of practical fibers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 558–563, 2008     

Preparation of ion-exchange fiber fabrics by electrospray deposition

Ion-exchange fiber (IEF) fabrics were prepared by electrospray deposition (ESD) and post-deposition chemical modification of their surfaces. Nonwoven fibrous fabrics were obtained from the solutions of synthetic polymers-polystyrene (PS) and poly(4-vinylpyridine) (P4VP)-of various concentrations. The diameter of the fiber in the fabrics ranged from 600 nm to 1.70 microm. Cation- and anion-exchange fiber (CEF and AEF) fabrics were obtained from the sulfonation of PS fabrics and the quaternization of P4VP fabrics, respectively. These fabrics were thoroughly characterized by a series of techniques, such as scanning electron microscopy (SEM), permporometry, nitrogen adsorption measurements, and potentiometric titrations. The SEM images showed that the fabrics had a porous structure after their chemical modification. The mean pore size, porosity, and specific surface area of the flow-through pores were 1.67-3.53 microm, about 80%, and 13 m(2)/g, respectively. The ion-exchange capacity was in the range from 0.78 to 1.34 mmol/g. The AEF fabric, on the other hand, showed a high specific surface area, i.e., the Brunauer-Emmett-Teller (BET) surface area of 600 m(2)/g, due to the formation of much smaller pores on the surface of the fiber structure in the fabric. The secondary chemical modification of the nano-microfiber fabrics by ESD provides novel functional materials with a large adsorption capacity and a high catalytic activity.