Monodomains mechanical properties

Mechanical Properties of Monodomains Liquid Single Crystal Elastomers... 

Martinoty P, Stein P, Finkehnarm H, Pleiner H, Brand HR (2004) Mechanical properties of monodomain side chain nematic elastomers. Eur Phys J E 14(4) 311-321. doi 10.1140/epje/ i2003-10154-y... 

Rogez D, Martinoty P (2011) Mechanical properties of monodomain nematic side-chain liquid-crystalline elastomers with homeotropic and in-plane orientation of the director. Eur Phys J E Soft matter 34(7) 69. doi 10.1140/epje/i2011-11069-8... 

Later on, semi-soft elasticity concept has been extended to the dynamical case. The theory, which is based on the separation of time scales between the director and the network, describes the mechanical properties of monodomain NEs in the linear response regime, when the sample is subjected to a sinusoidal shear of small amplitude (Terentjev and Warner 2001). When the shear is applied in a plane containing the director, the theory predicts the existence of a low frequency semi-soft elastic plateau, in addition to the usual rubbery plateau observed at higher frequencies. 

Lebar A, Kutnjak Z, Zumer S, Finkelmann H, Sanchez-Ferrer A, Zalar B (2005) Evidence of supercritical behavior in liquid single crystal elastomers Phys Rev Lett 94 197801 1-4 Martinoty P, Stein P, Finkelmann H, Pleiner H, Brand HR (2004a) Mechanical properties of monodomain side-chain nematic elastomers. Eur Phys J E Soft Matter 14 311-321 Martinoty P, Stein P, Finkelmann H, Pleiner H, Brand HR (2004b) Reply to the commentary by Teientjev EM, Warner M on Mechanical properties of monodomain side chain nematic elastomers . Eur Phys J E 14 329-332... 

Rogez D, Brommel E, Finkelmann H, Martinoty P (2011) Influence of swelling on the shear mechanical properties of monodomain side-chain liquid-crystal elastomers Gaussian versus non-Gaussian elasticity. Macromol Chem Phys 212 2667-2673... 

Theoretical investigations by Brand [ 135] and Brand and Pleiner [136] predicted that a monodomain liquid-crystalline elastomer exhibiting a cholesteric or a chiral smectic C phase should display piezoelectric properties due to a modification of the pitch of the helix under strain. So, a piezoelectric voltage should be observed across the sample when a mechanical field is applied parallel to the helicoidal axis. In this description, the crosslinking density is supposed to be weak enough to allow the motion of the director, and deformations of the sample (compression, elongation, etc.) are assumed to be much smaller than those that should lead to a suppression of the helix. The possibility of a piezoelectric effect do not only concern cholesteric and chiral smectic C phases, but was also theoretically outlined for more exotic chiral layered systems such as chiral smectic A mesophases [137]. 

To account for the mechanical reorientation properties of monodomains (LSCE), which differ depending on whether the crosslinking has been done in the nematic or the isotropic phase, the concept of frozen order has been suggested [22]. The essen-... 

More recently, it has been theoretically predicted by Brand [81] that elastomeric networks that have chiral nematic or smectic C mesophases should have piezoelectric properties. The non-centro-symmetric material responds to the deformation via a piezoelectric response. Following this prediction, both Finkelmann and Zental have reported the observation of piezoelectricity. In one case, a nematic network was converted to the cholesteric form with the addition of CB15, 2 -(2-methylbutyl)biphenyl-4-carbonitrile [82]. By producing a monodomain, it is possible to measure the electro-mechanical or piezoelectric response. Compression leads to a piezoelectric coefficient parallel to the helical axis. Elongation leads to the perpendicular piezoelectric response. As another example, a network with a chiral smectic C phase that possesses ferroelectric properties can also act as a piezoelectric element [83]. Larger values of this response might be observed if crosslinked in the Sc state. 

FIGURE 7.9 Photoresponsive properties of monodomain homogeneously aligned films of crosslinked PLCPs and their plausible mechanism of photoinduced bending and unbending behaviors. Reproduced with permission from Reference 28. Copyright 2003 John WUey Sons, Inc. 

LC elastomers based on the side-chain and main-chain LC polymers containing rather small concentrations of the chiral mesogens can form SmC mesophase-possessing domains with permanent electric dipole moment, which exhibit piezoelectric properties. The application of an uniaxial mechanical field (shear) produces a centrosymmetric morphology, where the piezoelectric effeas are observed. The piezoelectric coefficient reaches its maximum at a certain shear angle that corresponds to the completion of polydomain to monodomain transformation. The piezoelectric module of different types of such LC elastomers can be higher than those... 

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