Mu Shik Jhon

Temperature-induced phase transition of poly(N,N-dimethylaminoethyl methacrylate-co-acrylamide)

Copolymers of N,N-dimethylaminoethyl methacrylate (DMAEMA) and acrylamide (AAm) were prepared to demonstrate a temperature-induced phase transition. Poly DMAEMA has a lower critical solution temperature (LCST) around 50°C in water. With copolymerization of DMAEMA with AAm, the LCST shifts to the lower temperature was observed, probably due to the formation of hydrogen bonds between amide and N,N-dimethylamino groups. FT-IR studies clearly show the formation of hydrogen bonds which protect N,N-dimethylamino groups from exposure to water and result in a hydrophobic contribution to the LCST.

Characterization of wettability gradient surfaces prepared by corona discharge treatment

Abstract A new method for preparing wettability gradients on polymer surfaces was developed. Wettability gradients were produced on low density polyethylene surfaces by treating the polymer sheets in air with corona from a knife-type electrode whose power gradually increases along the sample length. The wettability gradient surfaces prepared by the corona discharge treatment were characterized by the measurement of water contact angle, Fourier-transform infrared spectroscopy in the attenuated total reflectance mode, electron spectroscopy for chemical analysis, and scanning electron microscopy. The gradient surfaces prepared can be used to systematically investigate the interactions of biological species in terms of the surface hydrophilicity/hydrophobicity of polymeric materials.

The effect of ZnCl2 on the formation of polysulfone membrane

In the preparation of ultrafiltration membranes, the effect of the addition of ZnCl2 in a casting solution, polysulfone (PSf)/N-methylpyrrolidone (NMP) solution, was investigated on the membrane performance. PSf is an uncharged polymer, but PSf/NMP with ZnCl2 showed an electroviscous behavior. The addition of 3 wt% ZnCl2 to PSf induced a red shift of 3 cm−1 in the 1152.2 cm−1 peak which was assigned to a symmetric vibrational stretching because of ZnCl2 interacted with PSf chain. The addition of ZnCl2 increased the reduced viscosity and decreased the critical concentration, resulting from the association between extended chains. The PSf/NMP solution with ZnCl2 required less water for the precipitation point than saltless solution did. It was observed that the addition of ZnCl2 increased the rejection rate and lowered the molecular weight cut-off (MWCO) of PSf membrane.

A SEMI-INTERPENETRATING NETWORK SYSTEM FOR A POLYMER MEMBRANE

Abstract A semi-interpenetrating network has been prepared for a polymer membrane. The first network consists of sodium alginate which provides the crosslinked network. The other is polyacrylic acid or polyacrylamide which imparts its characteristic into the polymer network. Using atomic absorption spectroscopy, it was observed that the swelling of the polymer membrane could be regulated by the control of the concentration of calcium ion. Two types of solutes were used for membrane permeation. In the case of hydrocortisone, used as a hydrophilic solute, the permeation pattern was closely related to the swelling behavior of the polymer membrane. However, permeation of indomethacin, used as a hydrophobic solute, was influenced by the intermolecular interaction in the polymer membrane characterized by FTIR spectroscopy.

pH/Temperature dependent phase transition of an interpenetrating polymer network: Anomalous swelling behavior above lower critical solution temperature

Abstract Anomalous swelling behavior has been observed in interpenetrating polymer networks (IPNs) gel composed of poly (N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAA). Calorimetric endotherms, FT-IR (Fourier transform-infrared) spectra and compression modulus show that the molecular interaction such as hydrogen bond and hydrophobic interaction serve as a driving force which takes place with an anomalous swelling behavior.

Temperature-sensitive swelling behavior of polymer gel composed of poly (N,N-dimethylaminoethyl methacrylate) and its copolymers

Polymer gels composed of N,N-dimethylaminoethyl methacrylate (DMAEMA) and acrylamide (AAm) (or ethyl acrylamide (EAAm)) were prepared to observe temperature-sensitive swelling behavior. The temperature dependence of equilibrium swelling of poly (DMAEMA-co-AAm) gel was in accordance with the change of the lower critical solution temperature (LCST) of poly (DMAEMA-co-AAm) aqueous solution as a function of chemical composition. However, poly (DMAEMA-co-EAAm) gel did not show the similar trend to poly (DMAEMA-co-AAm) gel. In the case of poly (DMAEMA-co-AAm), the hydrogen bond, which played an important role in controlling the LCST, was maintained with the formation of the gel network. However, the hydrogen bond in poly (DMAEMA-co-EAAm) was disrupted significantly with the formation of the gel network. This led to the difference in swelling behavior of polymer gels in response to temperature.

The effect of an external electric field on the structure of liquid water using molecular dynamics simulations

Abstract Using molecular dynamics simulations with the rigid TIP4P water model, we have analyzed the structural change of liquid water induced by an external electric field. The temperature was controlled with a Nose–Hoover thermostat. In this paper, we report the acquisition of liquid water with the enhanced structural regularity by applying an electric field. From the simulations under various strengths of the electric field, we can see that the threshold for the significant structural change is thought to be between 0.2 and 0.15 V/A. When the number of six-membered rings is increased by the external electric field, so that water is forced to have structural regularity, we calculate the diffusion coefficients and discover that water we make in the simulations is not solid but still liquid under the electric field.

Fluid–fluid phase separations in nonadditive hard sphere mixtures

We investigated the phase stability of a system of nonadditive hard sphere (NAHS) mixtures with equal diameters, d, between like species and an unequal collision diameter, d(1+α), between unlike species. It is based on an analytic equation of state (EOS) which refines an earlier expression [J. Chem. Phys. 100, 9064 (1994)] within the mixed fluid phase range. The new EOS gives a reliable representation of Monte Carlo EOS data over a wide range of density, composition, and nonadditivity parameters (α). Comparisons with available computer simulations show that the new EOS predicts satisfactory phase boundaries and the critical density line. It is superior to results derived from integral equations (the Percus–Yevick, the Martynov–Sarkisov, and the modified Martynov–Sarkisov) and analytic theories (the MIX1 model, the van der Waals one‐fluid model, and the scaled particle theory). The present study shows that, unless α exceeds 0.026, the fluid phase will remain fully miscible up to the freezing point of pure ...

Nature of water in synthetic hydrogels: III. Dilatometry, specific conductivity, and dielectric relaxation of poly(2,3-dihydroxypropyl methacrylate)

Abstract The hypothesis that three classes of water exist in hydrogels, namely, X water (bulk water-like), Z water (bound water-like) and Y water (intermediate water), has been verified, and the dynamic aspects of those waters have been studied in poly(2,3-dihydroxypropyl methacrylate) (PDHPMA) hydrogels. Bulk gel conductivity data for PDHPMA gel was obtained. The activation energy for specific conduction was obtained from the specific conductivity curve at various temperatures. A plot of the activation energy vs volume percent of water in the gels clearly indicated three different zones, showing three classes of water in the gels. These results were confirmed by thermal expansion measurements. The high-water-content gels (60%) showed an extremely sharp volume change at 0°C, indicating the presence of normal bulk water. Lower-water-content gels (20%) showed no anomalous change in thermal expansion, indicating that the water is bound. The medium-water-content gels exhibited intermediate behavior. A semiquantitative analysis of the three classes of water is presented. The third method used was dielectric relaxation. At low frequencies the dielectric constant of PDHPMA gels is much higher than that of water. The dielectric constant decreases continuously as the frequency increases, tending to level off at about 10 8 Hz. The higher the concentration of polymer in the gel, the lower the dielectric constant. Results are most reasonably explained by assuming the more structured phase of water for the low dielectric constant.

DESCRIPTION OF THE POTENTIAL ENERGY SURFACE OF THE WATER DIMER WITH AN ARTIFICIAL NEURAL NETWORK

Abstract A potential energy function for the water dimer has been developed with an artificial neural network (back propagation of error algorithm). The potential energy surface was obtained with 6s3p3d/3s3p MP2 ab initio MO calculations. The trained neural network reproduced the potential energy surface of the water dimer very well, not only in the low-energy region but also in the high-energy region.