Volume Phase Transition Of Gels Research Articles

Salt effect on volume phase transition of a gel.

The salt effect on the phase transition of N-isopropylacrylamide (NIPA) gel was studied for alkali-metal chlorides (NaCl, KCl, and CsCl). Low-frequency Raman scattering experiment was conducted to know the dynamic state of water molecule under the presence of salt and its correlation to macroscopic phase behavior of the gel was investigated together with the thermodynamic activities of water molecule of aqueous alkali-metal chloride solutions. The series of swelling experiment reveal that the change in the gel volume phase transition strongly depends on the salt concentration and is related to the dehydration with respect to hydrophobic hydration. From the analysis of the reduced low-frequency Raman spectra in water and aqueous alkali-metal chlorides solutions by the use of the relaxation mode that takes into account the inertia and the non-white effects, the characteristic values of aqueous salt solutions (i.e., relaxation time and modulation speed) indicate that the addition of alkali-metal chloride to gel fluid affects the disruption of water molecules in the hydration shell around the NIPA gel and the formation of the hydrogen-bonded network structure of water around themselves, as a result of which the gel collapses. The chemical potential and the dynamic nature of water molecule at the transition points are well correlated: the chemical potentials at the transition points are almost constant whereas the structure of bulk water is changed by addition of alkali-metal chlorides or change in temperature. These results strongly suggest that the swelling ratio of N-isopropylacrylamide gel is a function of hydration degree, which is regulated by the chemical potential of water.

Intrinsic fluorescence investigation on the change in conformation of cross-linked gelatin gel during volume phase transition

Gelatin gel cross-linked with glutaraldehyde was prepared. Its volume is sensitive to the acetone–water composition. Near 50% acetone content, a discontinuous macroscopic volume phase transition (VPT) occurred. The gel was found to emit intrinsic blue fluorescence at 415nm, which is attributed to the formation of dimeric species of tyrosine (bityrosine) in the gelatin network. The ratio of intensity of bityrosine to that of tyrosine monomer, IB/IM, was used to examine the change in conformation of gelatin during volume phase transition (VPT). With the increasing acetone concentration, IB/IM continuously increased till VPT, and then dropped little, revealing a high yield of bityrosine species, which is considered to stem from the closer contact of inter-coil, inter-helix, intra-helix and coil-helix in the collapsed network. The continuous IB/IM change suggests the non-discontinuous volume phase transition of gel occurring in microscale.

1G1115 ゲルの相転移挙動からみるトレハロースの水和構造

1G1115 ゲルの相転移挙動からみるトレハロースの水和構造

Volume Phase Transitions of Gels in Liquid Crystal Solvents

A simple mean field theory is introduced to describe volume phase transitions of gels dissolved in a liquid crystal solvent. We predict that the gel shows the second-order volume phase transition at the nematic-isotropic transition temperature T°NI of the pure liquid crystals existing outside of the gel. Below T°NI , the gel is condensed due to the nematic ordering of the pure liquid crystals. We also find the first-order volume phase transition in the isotropic phase above T°NI .

Pattern formation of constrained acrylamide/sodium acrylate copolymer gels in acetone/water mixture

Pattern formation and evolution in constrained acrylamide/sodium acrylate (PAAM/SA) gels have been investigated in acetone/water mixture. The constraint is achieved by cross linking the gel slabs onto a rigid substrate. All samples are initially kept in water with the hexagonal pattern develop on the surface before being immersed in the acetone/water mixture. Depending on the solvent composition and ionic strength of the sample, different patterns, i.e., hexagonal, grains, and bubbles, have been observed. These patterns are formed at acetone concentration below, near, and above the concentration at which the gel volume phase transition occurs. The wavelengths of hexagonal and bubble patterns are found to be the same, while that of the grain pattern is four times smaller. It is suggested that the shrinking patterns are formed due to the dense gel surface produced during the shrinking process.

Phase transition in polymer gels due to local heating by illumination of light

Abstract The volume phase transition in gels induced by visible light and its related properties are presented, the mechanism of which is based on local heating of a polymer network by illumination of light. The gels consist of a covalently cross-linked copolymer network of thermosensitive N-isopropylacrylamide and a chromophore. Without light illumination, the gel volume changes sharply, but continuously at approximately 34°C when the temperature is varied. At a fixed temperature of an appropriate value, a discontinuous volume transition is observed when the light intensity is gradually changed. The phase transitions can be understood in terms of the temperature increment at the immediate vicinity of polymer chains due to the local heating via light absorption and subsequent thermal dissipation of light by the chromophore. The results can be qualitatively described by the Flory-Huggins mean-field equation of state of gels. In order to make clear the mechanism of the light-induced phase transition in the ...

Temperature hysteresis and morphology of volume phase transition of gels.

Temperature hysteresis is theoretically studied for the volume phase transition of chemically cross-linked gels. The condition of the appearance of a ``surface skin layer'' of new phase is formulated and calculated. The result predicts that the surface skin layer is destabilized near the critical point of the transition due to volume fluctuations. We discuss the relevance of this result to inaccessibility to the Ising critical point [L. Golubovi\ifmmode \acute{c}\else \'{c}\fi{} and T. C. Lubensky, Phys. Rev. Lett. 63, 1082 (1989)].

Small angle neutron scattering study on poly(N-isopropyl acrylamide) gels near their volume-phase transition temperature

The small angle neutron scattering experiments were conducted on N-isopropyl acrylamide (NIPA) gels in D2O and on the corresponding NIPA solutions. The NIPA gels underwent a sharp, but a continuous volume phase transition at 34.6 °C from a swollen state to a shrunken state with increasing temperature. In the case of the gels, an excess scattering due to the presence of crosslinks was observed at low q region (q≤0.02 Å−1), where q is the magnitude of the scattering vector. The scattered intensity function for the gel was well described with a combination of Gauss and Lorentz-type functions, i.e., I(q)=IG(0)exp[−Ξ2q2]+[IL(0)/(1+ξ2q2)] as proposed by Geissler et al. IG(0) and IL(0) are the intensities at q=0 for the contributions of Gaussian and Lorentzian functions, respectively. The Gaussian part results from solidlike inhomogeneity, having a characteristic size of Ξ, which is due to the introduction of crosslinks into the system. The Lorentzian part is originated from the liquid nature of the local concentration fluctuations of the gel characterized with a thermal blob of dimension ξ. Ξ decreases systematically with polymer volume fraction, φ, indicating the nature of Ξ being the solidlike inhomogeneity. On the other hand, the intensity function for solutions was well fitted with the so-called Ornstein–Zernike (OZ) equation (a Lorentzian function), i.e., I(q)=[IL(0)/(1+ξ2q2)]. It was found that both ξ and IL(0) diverged at the spinodal temperature, Ts. The critical exponents, ν and γ, for the temperature dependence of ξ and IL(0), were estimated to be ∼0.60 and 1.2 for the gel, respectively, which were larger than the values for the solution of the same polymers (ν=0.45 and γ=0.8). These critical exponents for the gels support that the volume-phase transition of gels is classified to the three dimensional Ising model reported by Li and Tanaka. The concentration dependence of ξ and IL(0) was also well described with a power law relationship, i.e., ξ∼φνφ and IL(0)∼φγ;φ. The values of νφ and γφ at 23 °C are −3/4 and ∼−1/4, respectively, for the NIPA solutions, which are in good agreement with the theoretical prediction for polymer solutions in a good solvent. In the case of the NIPA gels, however, both νφ and γφ are ∼−1. These exponents were interpreted by taking account of the effects of crosslinking on the Flory’s interaction parameter.

Volume phase transitions of gels in hydrocarbons

A gel was designed that undergoes thevolume phase transition in organic solvents by ionizing the gel. The gel consists of a network of donor polymers (a styrene-4-vinylpyridine copolymer) that is swollen inin an organic solvent with acceptor molecules dissolved in it. The electron transfer ionizes the polymer network; the gel undergoes a discontinuous volume change in response to the changes in temperature, solvent composition or acceptor concentration

Chemical condition responsible for thermoswelling or thermoshrinking type of volume phase transition in gels: effect of relative amounts of hydrophobic to hydrophilic groups in the side chain

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTChemical condition responsible for thermoswelling or thermoshrinking type of volume phase transition in gels: effect of relative amounts of hydrophobic to hydrophilic groups in the side chainSeiji KatayamaCite this: J. Phys. Chem. 1992, 96, 13, 5209–5210Publication Date (Print):June 1, 1992Publication History Published online1 May 2002Published inissue 1 June 1992https://doi.org/10.1021/j100192a004RIGHTS & PERMISSIONSArticle Views63Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (242 KB) Get e-Alerts

A new model for the thermally induced volume phase transition of gels

A theoretical model that considers hydrophobic interaction is proposed for the thermally induced discontinuous shrinkage of hydrogels. In this model, the free energy of a hydrogel is divided into four parts: the elastic free energy of networks formulated according to the theory which takes the limit of elongation into account, the free energy arising from osmotic pressure of dissociated counterions in the gel, the free energy of interactions except for the hydrophobic interaction represented by a virial-type volume interaction equation, and the free energy of the hydrophobic interaction. By the former three terms, the thermally induced swelling of gels and the effects of aspect ratio of segment are expressed. The incorporation of the fourth hydrophobic interaction term makes it possible to explain the thermally induced shrinkage of gels, and suggests the possibility of an explanation of ‘‘convexo’’-type volume phase transition by means of the hydrophobic interaction.

Volume Phase Transition of Gels under Uniaxial Tension

We present the first experimental evidence of the effect of uniaxial tension on a volume phase transition (or gel-gel transition) of polymer gels. With an increase in the magnitude of tension, the first-order transition temperature T 0 of poly-N-isopropylacrylamide/water gel increases and the size discontinuity at the transition becomes larger. These results are consistent with a phenomenological theory of volume phase transition of gels under anisotropic stress. The magnitude of the shift of T 0 with tension can be correctly predicted using empirical parameters determined in previous studies.

Volume-Phase Transition in Constrained Gels

We consider a volume phase transition of gels which are allowed to swell or shirnk in only one or two directions. In gels, elastic anisotropy can strongly affect critical properties, two-phase coexistence, domain structures, etc. We predict stronly anisotropic scattering amplitudes.

Critical kinetics of volume phase transition of gels.

The volume phase transition of submillimeter spherical isopropylacrylamide gels shows critical kinetic behavior near the critical point; the transition takes an infinite time, and the thermal expansion becomes infinitely large. At the critical point the gels also undergo internal critical density fluctuations as revealed by photon-correlation spectroscopy. The observation of critical kinetics along with critical dynamics clarifies the physical principle of the kinetics of gel volume change.