Stimuli-responsive polymers result in on-demand regulation of properties and functioning of various nanoscale systems. In particular, they allow stimuli-responsive control of flow rates through membranes and nanofluidic devices with submicron channel sizes. They also allow regulation of drug release from nanoparticles and nanofibers in response to temperature or pH variation in the surrounding medium. In the present work two relevant mathematical models are introduced to address precipitation-driven deposition of surface layers of stimuli-responsive polymers and describe a possible effect of swelling-shrinkage transition of such polymers on drug release.

We compare dewetting characteristics of a thin nonwetting solid film in the absence of stress, for two models of a wetting potential: the exponential and the algebraic. The exponential model is a one-parameter (r) model, and the algebraic model is a two-parameter (r, m) model, where r is the ratio of the characteristic wetting length to the height of the unperturbed film, and m is the exponent of h (film height) in a smooth function that interpolates the system's surface energy above and below the film-substrate interface at z = 0. The exponential model gives monotonically decreasing (with h) wetting chemical potential, while this dependence is monotonic only for the m = 1 case of the algebraic model. Linear stability analysis of the planar equilibrium surface is performed. Simulations of the surface dynamics in the strongly nonlinear regime (large deviations from the planar equilibrium) and for large surface energy anisotropies demonstrate that for any m the film is less prone to dewetting when it is governed by the algebraic model. Quasiequilibrium states similar to the one found in the exponential model [M. Khenner, Phys. Rev. B, 77 (2008), 245445.] exist in the algebraic model as well, and the film morphologies are similar.

We consider the formation of solid drops (“islands”) occurring in the growth of strained solid films. Beginning from a detailed model for the growth of an alloy film that incorporates the coupling between composition, elastic stress and the morphology of the free boundary, we develop an asymptotic description of the shape and compositional nonuniformity of small alloy islands grown at small deposition rates. A key feature of the analysis is a “thin domain” scaling in the island which enables recasting the free boundary problem into a set of integrodifferential equations for the shape and composition profile. The integrodifferential system can be decomposed into two parts: one part gives a single integrodifferential equation for the shape analogous to that obtained for a single-component island determined by Shanahan and Spencer (2002), and the other part gives the composition profile in terms of the shape. Thus, the shape of an alloy island is identical to that of a single-component island with the same system parameters, but with a nonuniform composition that depends on the stress-composition coupling and alloy solution thermodynamics. Finally, we characterize the structure and magnitude of the compositional nonuniformity and also interpret our theoretical results in the context of SiGe alloy films.

Propagation of chemical waves at very low temperatures, observed experimentally [V.V. Barelko et al., Advances in Chem. Phys. 74 (1988), 339-384.] at velocities of order  10 cm/s, is due to a very non- standard physical mechanism. The energy liberated by the chemical reaction induces destruction of the material, thereby facilitating the reaction, a process very different from standard combustion. In this work we present recent experimental results and develop a new mathematical model which takes into account mechanical and chemical processes. We carry out numerical simulations and suggest a simplified model in order to obtain an explicit expression for the wave speed. This modelling allows us to give a possible explanation of the existence of two modes of propagation observed experimentally and of the dependence of the speed of propagation on the radiation dose.

The self-organization of porous nanostructures in anodic metal oxide is considered. A mathematical model which incorporates the chemical reactions at the metal-oxide and oxide-electrolyte interfaces and elastic stress caused by the electrostrictive effects is developed. It is shown through linear stability analysis, that a short-wave instability exists in certain parameter regimes which can lead to the formation of hexagonally ordered pores observed in anodized aluminum oxide.