arXiv subjects

Alexander N. Semenov

Publications and source records attributed to Alexander N. Semenov.

3 recordsLinked to original sources

arXiv2026

Space-resolved stress correlations and viscoelastic moduli for polydisperse systems: the faces of the stress noise

Several advances in the theory of space-resolved viscoelasticity of liquids and other amorphous systems are discussed in the present paper. In particular, considering long-time regimes of stress relaxation in liquids we obtain the generalized compressibility equation valid for systems with mass polydispersity, and derive a new relation allowing to calculate the wavevector-dependent equilibrium transverse modulus in terms of the generalized structure factors. Turning to the basic relations between the spatially-resolved relaxation moduli and the spatio-temporal correlation functions of the stress tensor, we provide their new derivation based on a conceptually simple argument that does not involve consideration of non-stationary processes. We also elucidate the relationship between the stress noise associated with the classical Newtonian dynamics and the reduced deviatoric stress coming from the Zwanzig-Mori projection operator formalism. The general relations between the stress noise and the tensor of relaxation moduli are discussed as well.

cond-mat.soft↗

arXiv2013

New conserved structural fields for supercooled liquids

By considering Voronoi tessellations of the configurations of a fluid, we propose two new conserved fields, which provide structural information not fully accounted for by the usual 2-point density field fluctuations (structure factor). One of these fields is scalar and associated to the Voronoi cell volumes, whereas the other one, termed the "geometrical polarisation", is vectorial, related to the very local anisotropy of the configurations. We study the static and dynamical properties of these fields in the supercooled regime of a model glass-forming liquid. We show in particular that the geometrical polarisation is both statically correlated to the force field and contrary to it develops a plateau regime when the temperature is lowered. We attribute this behaviour to the microsopic disorder of the underlying inherent structures (IS) which dictate the dynamics on time scales larger than the true microscopic time, in the strong supercooled regime. In this respect, this work raises the issue of to what extent the inter IS dynamics, intrinsically anisotropic and collective (cf. T.B. Schrøder et al. {\it J. of Chem. Phys.}, {\bf 112}, 9834 (2000)), could be related to their polarisation field.

cond-mat.stat-mech↗

arXiv2006

Microphase separation in thin block copolymer films: a weak segregation mean-field approach

In this paper we consider thin films of AB block copolymer melts confined between two parallel plates. The plates are identical and may have a preference for one of the monomer types over the other. The system is characterized by four parameters: the Flory-Huggins chi-parameter, the fraction f of A-monomers in the block copolymer molecules, the film thickness d, and a parameter h quantifying the preference of the plates for the monomers of type A. In certain regions of parameter space, the film will be microphase separated. Various structures have been observed experimentally, each of them characterized by a certain symmetry, orientation, and periodicity. We study the system theoretically using the weak segregation approximation to mean field theory. We restrict our analysis to the region of the parameter space where the film thickness d is close to a small multiple of the natural periodicity. We will present our results in the form of phase diagrams in which the absolute value of the deviation of the film thickness from a multiple of the bulk periodicity is placed along the horizontal axis, and the chi-parameter is placed along the vertical axis; both axes are rescaled with a factor which depends on the A-monomer fraction f. We present a series of such phase diagrams for increasing values of the surface affinity for the A-monomers. We find that if the film thickness is almost commensurate with the bulk periodicity, parallel orientations of the structures are favoured over perpendicular orientations. We also predict that on increasing the surface affinity, the region of stability of the bcc phase shrinks.

cond-mat.soft↗