Fumiyoshi Ikkai

pH and salt concentration dependence of the microstructure of poly(N‐isopropylacrylamide‐co‐acrylic acid) gels

The structure of environment‐sensitive gels consisting of poly(N‐isopropylacrylamide‐co‐acrylic acid) (NIPA/AAc) hydrogels was investigated by small‐angle neutron scattering (SANS). Effects of the variation of ionic circumstance were observed both on the volume phase transition and on the structure factors: (1) The volume phase transition temperature, Tc, increases with increasing pH from 4 to 9 and then decreases with further increasing pH. (2) the volume gap between the shrunken and swollen gels at Tc is highest around pH 7 to 9. (3) Though the structure factor, I(q), has a maximum above the Tc of the corresponding NIPA homopolymer gels, the peak intensity decreases with increasing pH, where q is the magnitude of the scattering vector. When NaCl is added, a similar scattering maximum appears for T≳Tc. However, strong ionic screening leads to a lower swelling power and a decrease in Tc, resulting in precipitation at a lower temperature than for the gel at a moderate pH. The roles of pH and salt are discu...

Effect of degree of cross-linking on spatial inhomogeneity in charged gels. I. Theoretical predictions and light scattering study

Analysis of the Rabin–Panyukov theory of scattering from polyelectrolyte gels shows that the theory predicts an anomalous cross-link density (CD) dependence of amplitude of spatial inhomogeneity in charged polymer networks. By increasing the interaction parameter or by decreasing the degree of ionization, one can pass from a regime in which the calculated structure factor is a monotonically increasing function of CD, to one in which an inflection in the CD dependence is predicted. These theoretical predictions were experimentally verified by light scattering experiments on a series of weakly charged polymer gels of N-isopropylacrylamide-acrylic acid copolymer. The ensemble average scattered intensity, a measure of the spatial inhomogeneity, increased with CD for χ χc, where χ and χc are the interaction parameter and the critical value of χ, respectively.

Microstructure and swelling behavior of ion-exchange resin

The microstructure and swelling kinetics of ion-exchange resins having sulfonic acid groups were investigated by small-angle neutron scattering (SANS) and swelling experiments as functions of the crosslinking density (CD), pH, and the salt concentration (Csalt). The swelling kinetics was analyzed on the basis of the Tanaka-Fillmore swelling equation for the cooperative diffusion of polymer gels. The swelling behavior was very sensitive to CD, but not to pH and Csalt. The SANS intensity functions, I(q), were independent of CD and well described with a power law function, I(q) ∼ q−D, where q and D are the magnitude of the scattering vector and the mass-fractal dimension, respectively. D was estimated to be ∼2, indicating that the resin consisted of a rather coarsely interconnected domains irrespective of CD at swelling equilibrium. It was found that CD is the most important parameter determining the swelling power of ion-exchange resin. However, no remarkable variations were found in the microstructure in the order of tens to hundreds of angstrom.

Complexation of poly(vinyl alcohol)–congo red aqueous solutions. 3. Dynamic light scattering study

Mesoscopic structures of poly(vinyl alcohol)(SINGLEBOND)Congo red (PVA(SINGLEBOND) CR) complexes in aqueous solutions were investigated in terms of dynamic light scattering (DLS) technique. The intensity-intensity time correlation function, g(2)(t), was analyzed with an equation including a single and a stretched exponential function. Two diffusion coefficients, Df (fast) and Ds (slow) were evaluated. Df was converted to the apparent correlation length, ξapp, via the mode-mode coupling hypothesis. The estimated ξapp was insensitive to the sol(SINGLEBOND)to(SINGLEBOND)gel transition but decreased with CR concentration. This change may be related to the electrostatic screening effect. On the other hand, Ds oscillates with increasing CR concentration at a specific PVA concentration range. This explains well the reentrant sol(SINGLEBOND)gel(SINGLEBOND)sol(SINGLEBOND)gel transition behavior observed in the PVA(SINGLEBOND)CR systems. Ds seems to represent the mobility of the PVA(SINGLEBOND)CR complexes, which annihilates at the gel point.

SAXS and dynamic viscoelastic studies on segmented polyurethaneurea solutions

Abstract The microstructure and dynamic mechanical properties of segmented polyurethaneurea (SPUU) in concentrated dimethyl acetamide (DMAc) solutions have been investigated by means of small-angle X-ray scattering (SAXS) and viscoelastic measurements, respectively. Kratky plots of SAXS intensity functions indicated the following: (1) Formation of hard segment domains introduced mainly by hydrogen bondings is promoted with increasing ratio of isocyanate to hydroxyl groups ([NCO]/[OH]) and polymer concentration, Cp. (2) The degree of completion of the hard segment domains increases with temperature up to 55°C and then gradually decreases by further increase of temperature. An analogy was found between [NCO]/[OH] dependence of the dynamic storage G′(ω) and loss shear moduli G″(ω) for SPUU in DMAc and time dependence of those for a chemically gelling system. G′(ω) and G″(ω) indicated that the properties of SPUU solutions change from sol-like to gel-like with increasing [NCO]/[OH]. By varying [NCO]/[OH], a relationship of G′(ω) ≈ G″(ω) ≈ ωk was observed around [NCO]/[OH] = 1.6. The exponent k is evaluated to be 0.67, which was similar to the literature value obtained at the gelation point. This corresponds to the ‘gelation threshold’ of the chemical gelation process.

Structural Colored Balloons Consisting of Polystyrene Microcapsules in Water

Structural colored balloons (SCBs) consisting of polystyrene microcapsules in water were prepared and characterized. SCBs were produced by the solvent evaporation method of W/O/W-type double emulsion. Because the surface thickness of SCB was controlled to be comparable to a visible-light wavelength, SCB developed various structural colors from violet to red depending on the surface thickness. SCB characterization revealed that (1) the surface thickness was independent of SCB size, (2) the developing color distribution was random, and (3) the surface thickness was strongly related to the developing color. The relationship between surface thickness, developed color, and capsule size can be predicted by an optical theory. Scanning electron microscopy (SEM) images proved the validity of the theoretical calculation.

Viscosity behaviour of weakly charged polymer-ion complexes comprising poly(vinyl alcohol) and Congo red

The reduced viscosity, η R , of poly(vinyl alcohol)-Congo red (PVA-CR) complexes in aqueous solution has some unique features, such as (1) an appearance of a maximum at a given PVA concentration ( C PVA ) and (2) a time evolution of η R , but only in the regime where the maximum appears. These characteristic features of the viscosity behaviour are simulated by using the theory of Rice and Kirkwood which takes into account the electrostatic interaction in the reduced viscosity.

Multiple-phase behavior and its microscopic implication for 4-acrylamidosalicylic acid gel

Poly(4-acrylamidosalicylic acid) gels exhibited multiple-phase behavior depending on their histories in the parameter space of pH and temperature. Four different phases, denoted as phase091 (as-prepared), phase244 (swollen at high pH), phase064 (heat-treated), and phase233 (swollen at high pH after heat treatment) were clearly resolved, where the three digits denote their linear swelling ratios in percentage with respect to their sizes at preparation. Each phase was stable and did not change its swelling ratio with pH or temperature as long as the values of pH or temperature were within limited ranges. Transitions among different phases were discrete with hysteresis loops. The structure factors corresponding to these four phases were obtained by small-angle neutron scattering, which indicated the presence of characteristic structures depending on pH and temperature, particularly in the shrunken state (i.e., phase064).