arXiv subjects

V. S. Volkov

Publications and source records attributed to V. S. Volkov.

23 records · Page 2Linked to original sources

arXiv2003

Analysis of weak elasticity of nematic solids using a continuum approach

This paper formally analyses effects of nematic weak elasticity using the five parametric de Gennes (DG) potential. The analysis is trivialized in a specific (local) Cartesian coordinate system whose one axis is directed along the initial director. We demonstrate that depending on closeness of material parameters to the marginal stability conditions, DG potential describes the entire variety of soft, semi-soft and harder behaviours of weakly elastic nematic solids. We found that along with known shearing soft modes, additional soft stretching mode acting along the director may also exist. For stress tensor components, we proved a theorem of special rotational invariance that is closed to rotational invariance principle postulated by Olmsted. When the only shearing modes are soft, stress tensor is symmetric and DG potential scaled with isotropic shear modulus is reduced to a one-parametric, only strain dependent nematic potential. When additionally the stretching mode is also soft, this dimensionless, strain dependent nematic potential has no additional parameters and shows that the free energy is always less than that in isotropic phase.

cond-mat.soft↗

arXiv2003

On the weak nematic elasticity and soft deformation modes

The paper investigates the general case of incompressible non-classical elasticity with small deformations and rotations. It is shown that the internal spin rotations are important only when a specific Born term is presented in the free energy. The thermodynamic stability conditions and existence of soft deformational modes are analysed for free energy with three rotational degrees of freedom and scalar order parameter. It is shown that the soft deformation modes do not always exist. If the conditions for existence of soft modes are satisfied and the Born term is absent, the stress tensor is proved to be symmetric. It is shown that the infinitesimal Warner potential satisfies these conditions. When the stress symmetry could be assumed only approximately, a simplified, "reduced" relations are derived for the free energy and stress. The reduce formulation, which preserves the general stability conditions and the condition for existence of soft deformations, also allows easy calculations of stress-strain-rotation relations.

cond-mat.soft↗

arXiv2003

On the weak nematic elasticity

The paper considers the general case of incompressible non-classical elasticity with small deformations and rotations. The thermodynamic stability is analysed for free energy density with three rotational degrees of freedom. Although the theory generally predicts the stress to be non-symmetric, the stress tensor can still be considered as symmetrical in the absence of external fields and when the inertia effects of internal rotations and couple stresses are neglected. When the condition of stress tensor symmetry is applied, it results in simplified, "reduced" expressions for the free energy density and stress, which preserve the general stability conditions and allow easy calculations of stress-strain relations and rotations. Using this reduced formulation, a general condition of existence of soft deformations is analysed for the weak nematic elasticity. The reduction procedure is exemplified using the infinitesimal Warner potential derived from a molecular model.

cond-mat↗

arXiv2002

Internal Rotations and Stress Tensor Symmetry in Theories of Nematic Liquids and Solids

The paper analyses kinematics and dynamics of internal rotations with spin and their effects on the constitutive relations for uniaxial (nematic) liquids and for weakly elastic nematic solids. It is shown that neglecting the internal rotational inertia terms and effects of director gradient made the stress symmetric. This not only highly simplifies the theories but also allows calculating all the kinematic variables of internal rotations without any additional constants, other than those presented in the simplified theory with symmetric stress.

cond-mat.soft↗

arXiv2002

A theory of viscoelastic nematodynamics

A nonlinear viscoelastic theory of nematodynamic type is developed for nematic liquid crystalline (LC) semi-flexible polymers. A measure of transient elastic strain due to the change in length of macromolecular strands under stress, and the director of unit length are employed in the theory as hidden variables. In the marked contrast to the common theoretical approaches to low molecular nematics, the effect of directors space gradient is neglected in the present theory. Nevertheless, the theory allows describing nonlinear anisotropic viscoelasticity and evolution equation for the director in flows of LC polymers. When LC macromolecules are relatively rigid or when they are soft but the flow is slow, a weakly nonlinear viscoelastic anisotropic behavior is described by few temperature dependent parameters. In the infinitesimal case the evolution equation for director reminds the Ericksens equation, but with an additional relaxation term. The present theory can also be applied for analyzing flows of concentrated polymer suspensions and nano-composites filled with uniaxially symmetric particles.

cond-mat↗