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  • 1
    Electronic Resource
    Electronic Resource
    Soft elasticity and mechanical damping in liquid crystalline elastomers (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6530-6535 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamic soft response of polydomain liquid crystalline elastomers to simple shear is reported. Significantly, these materials also show extremely large loss behavior with tan δ exceeding 1 or even 1.5 over very wide temperature ranges, with clear implications for damping applications. By comparing materials that exhibit different types of liquid crystalline phases, we identify the nematic state as a better damping phase than that in materials with smectic phases. Additionally, we provide experimental evidence for directions which should be explored for further improvements in the damping behavior of liquid crystalline elastomers. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1368177
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  • 2
    Electronic Resource
    Electronic Resource
    Pulsed gradient spin-echo nuclear magnetic resonance of confined Brownian particles (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 4619-4624 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present here a model calculation of the spin-echo gradient nuclear magnetic resonance signal of a Brownian particle diffusing in a confined environment, described by a harmonic potential well. The general expression reduces to characteristic scaling laws in limiting cases: long and short pulses, comparative to the spin-echo duration, and long, intermediate, and short durations of the spin phase reversal cycle, comparative to the internal system characteristic times scales. Spin-echo measurements in these limits enable one to detect independently the particle's mass, viscous drag, and the confining potential strength. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469510
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  • 3
    Electronic Resource
    Electronic Resource
    Dynamic mechanical response of polymer networks (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 5531-5538 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamic-mechanical response of flexible polymer networks is studied in the framework of the tube model, in the limit of small affine deformations, using the approach based on Rayleighian dissipation function. The dynamic complex modulus G*(ω) is calculated from the analysis of a network strand relaxation to the new equilibrium conformation around the distorted primitive path. Chain equilibration is achieved via a sliding motion of polymer segments along the tube, eliminating the inhomogeneity of the polymer density caused by the deformation. The characteristic relaxation time of this motion τe separates the low-frequency limit of the complex modulus from the high-frequency one, where the main role is played by chain entanglements, analogous to the rubber plateau in melts. The dependence of storage and loss moduli, G′(ω) and G″(ω), on crosslink and entanglement densities gives an interpolation between polymer melts and crosslinked networks. We discuss the experimental implications of the rather short relaxation time and the slow square-root variation of the moduli and the loss factor tan δ(ω) at higher frequencies. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290134
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  • 4
    Electronic Resource
    Electronic Resource
    Orientational Order in Strained Nematic Networks (1994)
    s.l. : American Chemical Society
    Macromolecules 27 (1994), S. 7067-7075 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00102a010
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  • 5
    Electronic Resource
    Electronic Resource
    Lamellar ordering in symmetric diblock copolymers (1993)
    s.l. : American Chemical Society
    Macromolecules 26 (1993), S. 3344-3350 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00065a017
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  • 6
    Electronic Resource
    Electronic Resource
    Finite extensibility effects in nematic elastomers (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 8743-8748 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a model calculation of the elasticity of a nematic elastomer of finite-length network strands under affine deformation. The result is derived in its full tensorial structure, and its predictions are examined. In particular, we look at the non-Gaussian corrections to the effects of soft elasticity and elastic anisotropy. We find that the soft modes can at most be hardened at O(N−2) when compared to the conventional rubber elastic energy, where N is the number of monomer units along a typical strand. The elastic moduli for extensions parallel and perpendicular to the nematic director are found to differ at O(N−1). © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476303
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  • 7
    Electronic Resource
    Electronic Resource
    Second-order flexoelectric effect in chiral nematic liquid crystals (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9199-9207 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A molecular–statistical model for the second-order flexoelectric effect in chiral nematics is developed, accounting for additional chiral terms in the pair intermolecular potential U(1,2). It is shown by symmetry analysis, that there are four independent chiral terms in the flexoelectric polarization, proportional to the square of director gradients, P∼λ∇n∇n. A molecular–statistical theory is developed for the second-order chiral flexoelectric constants λ. Their values, obtained in the mean-field approximation, depend on molecular dimensions, interaction parameters, and the degree of molecular chirality. Possible experimental situations are discussed where this effect can be observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464427
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  • 8
    Electronic Resource
    Electronic Resource
    Rotational viscosity coefficients of nematic and smecticC liquid crystals: Statistical theory (1990)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 12 (1990), S. 1223-1232 
    Details
    ISSN: 0392-6737
    Keywords: Liquid crystals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The rotational diffusion of a rodlike molecule in a nematic and smecticC liquid crystal is considered in the molecular-field approximation. The microscopic friction constant, which determines the molecular rotation drag, possesses an exponential temperature dependence with the activation energy determined by the isotropic part of the intermolecular interaction energy. The rotational viscous coefficients,γ 1 andγ ⊥ are obtained by averaging of the corresponding microscopic stress tensor with the nonequilibrium distribution function. The additional activation energy, proportional to the corresponding order parameter, appears in the expressions for the rotational viscosity coefficients both in nematics andC smectics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02450387
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  • 9
    Electronic Resource
    Electronic Resource
    Light-scattering study of random disorder in liquid crystalline elastomers (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 198 (1997), S. 3485-3498 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We report on the structural study of a non-uniform (polydomain) director texture in nematic and smectic liquid crystalline elastomers. Polarised light scattering is used to probe the equilibrium director correlations in the region of transition under stress between the opaque polydomain material and the transparent, macroscopically monodomain elastomer. A characteristic four-peak scattering image is obtained in this transient region. The lobes of intensity are oriented along and perpendicular to the axes of crossed polarisers, with anisotropy along the direction of principal extension. We propose a theoretical model, based on the competition between the random disordering field due to the network crosslinks and the external aligning field
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1997.021981113
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  • 10
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    Elasticity of rubber with smectic microstructure (2000)
    American Physical Society
    Details
    Publication Date: 2000-10-01
    Print ISSN: 1063-651X
    Electronic ISSN: 1095-3787
    Topics: Physics
    Published by American Physical Society
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