Kenji Urayama

In this perspective, we discuss select issues investigated in recent studies on liquid crystal elastomers (LCEs) and gels−soft solids having a mobile director. A considerable amount of knowledge accumulated during the past decade proves that LCEs are not simple extensions of liquid crystals (LCs) and elastomers. The strong coupling of orientational order of LCs and rubber elasticity of polymer networks leads to novel stimulus-response behavior that provides not only a wealth of academically inte

Swollen nematic elastomers unconstrained by electrodes exhibit macroscopic deformation as well as an almost full (90°) rotation of director in fast response to sufficiently high electric fields normal to the initial director. The deformation is strongly coupled to the director rotation: The deformation takes place dominantly in the plane where the director rotates whereas almost no dimensional variation occurs in the direction irrelevant to the director rotation. There exists a threshold for the

We demonstrate a silicone damping elastomer with a constant high damping performance (tan δ = E‘ ‘/E‘ ≈ 0.3 where E‘ and E‘ ‘ are the storage and loss Young's moduli, respectively) over a broad temperature range of 180 °C (−30 °C < T < 150 °C) utilizing a slow viscoelastic relaxation of an irregular network structure with many pendant chains. In addition to tan δ, E‘ is almost unaltered in the corresponding temperature range. These are in contrast to the markedly temperature-dependent damping an

We review our recent studies towards the molecular understanding of mechanical properties–structure relationships of elastomers using model polydimethylsiloxane (PDMS) networks with controlled topology. The model elastomers with controlled lengths of the network strands and known amounts of cross-links and dangling chains are obtained by end-linking the functionally terminated precursor PDMS with known molecular weights using multi-functional cross-linkers. Several modern entanglement theories o

Stretching driven polydomain−monodomain (PM) transitions have been investigated for the two types of polydomain nematic elastomers with different random alignments of the mesogens in the stage of cross-linking. One (I−PNE) is made by cross-linking in the high−temperature isotropic state and then cooling to the nematic state. The other (N−PNE) is directly obtained by cross-linking in the low-temperature polydomain nematic state. They are similar in the order of the induced monodomain as well as t

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPoisson's ratio of poly(vinyl alcohol) gelsKenji Urayama, Toshikazu Takigawa, and Toshiro MasudaCite this: Macromolecules 1993, 26, 12, 3092–3096Publication Date (Print):June 1, 1993Publication History Published online1 May 2002Published inissue 1 June 1993https://pubs.acs.org/doi/10.1021/ma00064a016https://doi.org/10.1021/ma00064a016research-articleACS PublicationsRequest reuse permissionsArticle Views968Altmetric-Citations92LEARN ABOUT THESE METRICSA

Polymer membranes comprising slide-ring gels with movable cross-links exhibit a nonlinear pressure-dependence in the fluidic flow rate. The proportional constant between the flow rate and pressure significantly changes at a critical pressure. The slide-ring gels are promising polymer membrane materials, which would allow for the on-off control of fluid permeability using an imposed pressure.

We present a biaxial tensile tester to characterize the nonlinear stress–strain behavior of extremely soft polymer gels with very low shear moduli, of the order of 102 Pa, under general (equal and unequal) biaxial strain. Stretching of gel sheet specimens in a solvent bath can avoid finite self-weight bending deformations that have precluded biaxial tensile experiments with such extremely soft gels. General biaxial strain covers a wide range of physically accessible deformations in contrast to t

Five molecular models of rubber elasticity which employ different treatments of entanglement effects (the Kloczkowski−Mark−Erman diffused-constraint model, the Edwards−Vilgis (E−V) slip−link model, the tube models of Gaylord−Douglas (G−D), Kaliske−Heinrich, Rubinstein−Panyukov versions) are assessed using biaxial deformation data for an entanglement-dominated network of end-linked poly(dimethylsiloxane) (PDMS) in which trapped entanglements are dominant in number relative to chemical cross-links

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTElectrooptical Effects with Anisotropic Deformation in Nematic GelsKenji Urayama, Seiji Honda, and Toshikazu TakigawaView Author Information Department of Material Chemistry, Kyoto University, Kyoto 615-8501, Japan Cite this: Macromolecules 2005, 38, 9, 3574–3576Publication Date (Web):March 29, 2005Publication History Received12 February 2005Revised17 March 2005Published online29 March 2005Published inissue 1

We have investigated the degree of equilibrium swelling and the elastic modulus of networks prepared by end-linking oligo(dimethylsiloxane)s (ODMS) in solution as a function of polymer concentration at crosslinking. The molecular weight of ODMS is so low that entanglement couplings are not formed in uncrosslinked state. It has been found from the preparation concentration dependence of elastic modulus in preparation state that trapped entanglements are formed by the introduction of crosslinks, a

We investigate the mesogen reorientation behavior of thin films of liquid crystal elastomers (LCEs) under uniaxial elongation (z-axis) normal to their initial homeotropic alignment (x-axis). The stress−strain relation is characterized by three regions: (I) a small-strain regime exhibiting a linear relationship, (II) a moderate-strain region with a quasi-plateau stress, and (III) a large-strain region where the stress again increases. The Poisson's ratio μyz is strain-dependent: μyz ≈ 0.17 in reg

Rubber elasticity is one of the most fascinating properties that stem from the nature of polymers. Crosslinked rubbers exhibit reversible high extensibility with a markedly low elastic modulus that originates from the entropic elasticity of the polymer chains—a property unparalleled in solid materials. Rubbery materials have been widely used in industrial products because of their unique properties. The research on rubber elasticity has a long history, and currently, it appears to have secured c

The electrically driven deformations of side chain nematic networks swollen by nematic solvents (nematic gels) have been investigated. The strains of freely suspended gels between electrodes were measured as a function of field strength (E) . The deformation of the gels composed of a network and solvent with identical signs of dielectric anisotropy (Delta epsilon) is dominated by the electrically induced alignment of the nematogens. As a result, the stretching direction is variable according to

Stretching experiments with various geometries are performed using a custom-built tensile tester to reveal the intriguing features of the mechanical softening phenomena of filled elastomers in loading-unloading cycles, commonly known as the Mullins effect. The dissipated energy (D), residual strain (ε^r), and dissipation factor (Δ; the ratio of D to input strain energy) in the loading-unloading cycles are evaluated as a function of the maximum stretch in cyclic loading (λ_m)