Abstract. We consider a stress-assist chemical reaction front propagation implying the reaction like silicon oxidation. We assume that the chemical reaction is localized at the reaction front that divides two solid constituents. The reaction is sustained and controlled by the diffusion of the gas constituent through the oxide. We determine a transformation strain tensor produced by the chemical reaction in dependence on the reaction parameters. Then we derive an expression of the entropy production due to the reaction front propagation and, as a result, obtain the formula of the chemical affinity tensor. The normal component of the chemical affinity tensor acts as a configurational force that drives the propagating reaction front. Then we introduce the notion of the equilibrium gas constituent concentration as the concentration at which the chemical affinity is zero. We formulate a kinetic relationship for the reaction front velocity in terms of current gas concentration at the reaction front and the equilibrium concentration that depends on stresses at the front. We obtain analytical solutions of simplest axially symmetric problems of mechanochemistry considering chemical reactions around a hole as a simplest stress concentrator and the oxidation of a cylinder. We demonstrate the reaction locking effects due to internal stresses and examine how stress state affects the reaction front kinetics. IntroductionThe influence of mechanical loading on chemical reaction kinetics remains to be of significant interest for both fundamental and applied engineering science. Chemo-mechanical problems have received a new attention in recent years due to miniaturization of structure elements. For example, fracture processes in micron-scale parts of MEMS made of polycrystalline silicon thin films involve sequential oxidation of polysilicon and environmentally-assisted crack growth inside an oxide layer. In turn, the kinetics of the oxide growth is determined by mechanical stresses produced by the crack. The catastrophic failure happens when the crack reaches the reaction front. Thus, major events which determine the life time of MEMS are related with coupling between stresses and chemical reactions (see details in [1,2]). Reactions similar to the silicon oxidation also take place in the process of metal hydride formation used in hydrogen storage applications (see e.g. [3]). Many models of silicon oxidation arise to pioneering papers by Deal and Grove [4], see for example a recent paper [3]. However neither external loading nor internal stresses were taken into account in these works. One of the first attempts to obtain an expression of the chemical potential in a multicomponent solid under stress was made by Larche and Cahn [5][6][7][8]. They considered diffusing solids and showed that the chemical potential depends on the trace of the stress tensor. This result was further developed in

The success of medical therapy depends on the correct amount and the appropriate delivery of the required drugs for treatment. By using biodegradable polymers a drug delivery over a time span of weeks or even months is made possible. This opens up a variety of strategies for better medication. The drug is embedded in a biodegradable polymer (the “carrier”) and injected in a particular position of the human body. As a consequence of the interplay between the diffusion process and the degrading polymer the drug is released in a controlled manner. In this work we study the controlled release of medication experimentally by measuring the delivered amount of drug within a cylindrical shell over a long time interval into the body fluid. Moreover, a simple continuum model of the Fickean type is initially proposed and solved in closed-form. It is used for simulating some of the observed release processes for this type of carrier and takes the geometry of the drug container explicitly into account. By comparing the measurement data and the model predictions diffusion coefficients are obtained. It turns out that within this simple model the coefficients change over time. This contradicts the idea that diffusion coefficients are constants independent of the considered geometry. The model is therefore extended by taking an additional absorption term into account leading to a concentration dependent diffusion coefficient. This could now be used for further predictions of drug release in carriers of different shape. For a better understanding of the complex diffusion and degradation phenomena the underlying physics is discussed in detail and even more sophisticated models involving different degradation and mass transport phenomena are proposed for future work and study.

Within the spatial description, it is customary to refer thermodynamic state quantities to an elementary volume fixed in space containing an ensemble of particles. During its evolution, the elementary volume is occupied by different particles, each having its own mass, tensor of inertia, angular and linear velocities. The aim of the present paper is to answer the question of how to determine the inertial and kinematic characteristics of the elementary volume. In order to model structural transformations due to the consolidation or defragmentation of particles or anisotropic changes, one should consider the fact that the tensor of inertia of the elementary volume may change. This means that an additional constitutive equation must be formulated. The paper suggests kinetic equations for the tensor of inertia of the elementary volume. It also discusses the specificity of the inelastic polar continuum description within the framework of the spatial description.