Mechanisms of chemical ageing reaction-diffusion coupling

6 Mechanisms of chemical ageing reaction-diffusion coupling 

In both oxidation and hydrolysis, the polymer matrix reacts with a small molecule coming from the environment (oxygen or water, for instance). In a thin elementary layer at a distance z from the sample surface, the reactant concentration balance can be ascribed as follows reactant concentration change = rate of reactant supply by diffusion - rate of reactant consumption by reaction. 

In the case of unidirectional diffusion, far from the sample edges, this balance equation can be written  

Resolution of Equation [12.33] requires the knowledge of two physical quantities the equilibrium concentration C of the reactant and its coefficient of diffusion D in the polymer matrix and one item of chemical data the concentration dependence of the reactant chemical consumption r(C). 

The main trends of structure-property relationships can be briefly summarized as follows  

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