Effect of moisture in κ-carrageenan films on their tensile and relaxation behavior studied by correlation between stress and birefringence

A picture on the molecular level describing the deformation and the following relaxation of κ-carrageenan chains has been proposed based on the three-domain structural model for κ-carrageenan films and on the idea of the modified stress-optical rule. The uniaxial tensile and the relaxation behavior for dry and moist κ-carrageenan films has been examined by using a homemade apparatus available for the simultaneous mechanical and birefringence measurements. It has been suggested that the continuous amorphous phase of κ-carrageenan in the dry film is deformed together with the local glass component, and only the glass component relaxes in the following process. On the other hand, concerning the moist film, the crosslinks of κ-carrageenan aggregates in addition to the continuous phase are movable with deformation, while the following relaxation is attributed only to the unbridged κ-carrageenan chains in the continuous phase

Effects of gelation concentration on cyclic deformation behavior of κ-carrageenan hydrogels

The aim of this study is to elucidate the relationship between the network structure of κ-carrageenan hydrogels and their mechanical properties. First κ-carrageenan hydrogels have been prepared at different gelation concentrations, and then the mechanical behavior during four cyclic deformations has been examined at the same κ-carrageenan concentration. Young's modulus is higher for the gel prepared at 5 gL⁻¹ (C05) compared to that for the gel prepared at 30 gL⁻¹ (C30). C30 shows almost linear relation between the stress and the strain like an ideal rubber, while a residual strain appears in each cyclic deformation for C05. The extent of the residual strain depends on the maximum strain and the deformation speed, indicating that C05 deforms plastically to some extent. The residual strain for C05 decreases gradually even after a cyclic deformation and disappears in the case of a small strain as if there were a memory of the structure. The effects of the gelation concentration on the mechanical properties have been explained based on the network structure specific to κ-carrageenan hydrogels. The higher modulus for C05 has been attributed to the higher helix content and the plastic deformation of C05 to the loosely-aggregated crosslinks

親水性高分子ゲルの臨界挙動と物理化学的性質

京都大学0048新制・論文博士博士(工学)乙第8979号論工博第3006号新制||工||1005(附属図書館)UT51-95-V466(主査)教授 升田 利史郎, 教授 尾崎 邦宏, 教授 堤 定美学位規則第4条第2項該当Doctor of EngineeringKyoto UniversityDFA

Rheological properties of concentrated solutions of galactomannans in an ionic liquid

The rheological behavior of galactomannans in concentrated solutions was examined by using dynamic viscoelasticity measurements. Concentrated solutions of three galactomannans, guar gum, tara gum, and locust bean gum were prepared with an ionic liquid 1-butyl-3-methylimidazolium chloride as the solvent. Each galactomannan solution showed angular frequency dependence curves of the storage modulus and the loss modulus which were characteristic of a solution of entangled polymer chains. The molecular weight between entanglements (Me) was obtained from the plateau modulus and the concentration dependence of Me showed Me in the molten state (Me, melt) to be 4.6 × 10[3], 3.2 × 10[3], and 2.7 × 10[3] for guar gum, tara gum, and locust bean gum, respectively. It was found that the material constant Me, melt depends on the mannose/galactose ratio of the galactomannans. The number of monosaccharide units between entanglements in the molten state for the galactomannans varied within the range found for other polysaccharides such as cellulose and agarose in ionic liquids, suggesting that all the galactomannans take a random-coil conformation in ionic liquid solutions

Effects of side groups on the entanglement network of cellulosic polysaccharides

The transient entanglement networks of cellulosic polysaccharides in concentrated solutions were characterized by the molecular weight between entanglements (M e) using dynamic viscoelasticity measurements. From the concentration dependence ofM e, M e for the cellulosic polysaccharides in the molten state (M e, melt) was estimated as the material constant reflecting the chain characteristics. The values of M e, meltwere compared among three cellulosic polysaccharides: cellulose, methylcellulose, and hydroxypropyl cellulose. Methylcellulose and hydroxypropyl cellulose were employed as cellulose derivatives having small and large side groups, respectively. It appeared that hydroxypropyl cellulose had significantly larger M e, melt compared with cellulose and methyl cellulose. However, the numbers of repeating glucose-ring units between entanglements were very close to each other among the three polysaccharides

Electrically driven director-rotation of swollen nematic elastomers as revealed by polarized Fourier transform infrared spectroscopy

We have investigated the director reorientation behavior of unconstrained nematic gels (nematic elastomer swollen by low molecular mass liquid crystals) under electric fields by means of polarized Fourier transform infrared (FTIR) spectroscopy. The polarized FTIR reveals that the director rotates about the (y) axis normal to the original director (x axis) and field directions (z axis), and the nematic order remains unchanged in the plane where the director stays confined during rotation. The rotation angle of director (θ) is estimated as a function of imposed voltage amplitude on the basis of the absorbances of the cyano group which is aligned along the long axis of the mesogen for light linearly polarized in the x and y directions. The director-rotation drives a two-dimensional macroscopic deformation which is characterized by a contraction along the x axis, an extension in the z direction, and nonappreciable length change along the y axis. The strain in the x direction is linearly proportional to sin2 θ in agreement with the expectation of soft or semisoft elasticity theory for thin nematic elastomer films where the shear contribution becomes negligibly small

Molecular weight between entanglements for κ- and ι-carrageenans in an ionic liquid.

The molecular weight between entanglements (Me) for κ- and ι-carrageenans, sulfated galactans, was examined in concentrated solutions using an ionic liquid 1-butyl-3-methylimidazolium acetate as a solvent. The dynamic viscoelasticity data for the solutions measured at different temperatures were overlapped according to the time-temperature superposition principle, and the obtained master curves exhibited the flow and rubbery plateau zones, being typical of concentrated polymer solutions having entanglement coupling. The values of Me for κ- and ι-carrageenans in the solutions were determined from the plateau moduli. Then the values of Me in the molten state (Me, melt) estimated as a material constant to be 6.6×10(3) and 7.2×10(3), respectively. The close values of Me, melt for κ- and ι-carrageenans indicate that 4-sulfate group of ι-carrageenan are not so influential for the entanglement network. Compared with agarose, a non-sulfate galactan, carrageenans have larger values of average spacing between entanglements

Application of a Clapeyron-Type Equation to the Volume Phase Transition of Polymer Gels

The applicability of the Clapeyron equation to the volume phase transition of cylindrical poly(N-isopropylacrylamide)-based gels under external force is reviewed. Firstly, the equilibrium conditions for the gels under tension are shown, and then we demonstrate that the Clapeyron equation can be applied to the volume phase transition of polymer gels to give the transition entropy or the transition enthalpy. The transition enthalpy at the volume phase transition obtained from the Clapeyron equation is compared with that from the calorimetry. A coefficient of performance, or work efficiency, for a gel actuator driven by the volume phase transition is also defined. How the work efficiency depends on applied force is shown based on a simple mechanical model. It is also shown that the force dependence of transition temperature is closely related to the efficiency curve. Experimental results are compared with the theoretical prediction