Activated swelling process

The final form of the Morton equation for the activated swelling process may be written by expressing the equilibrium swelling radius of the seed particles in terms of initial radius by using Eq. (10). 

The role of a swelling agent in the activated swelling method may be explained by considering the theoretical basis of the process. The swelling of pure polymer particles with the monomer can be described by the Morton equation ... 

A conceptualization of the swelling processes at the front is shown in Fig. 15. Protons, attached either to water or to buffer, must climb a free energy hill in order to reach an amine at the front This hill is due either to the hydrophobicity of the groups surrounding the amine, or to the low dielectric constant of the dry polymer. After ionization is accomplished, the (protonated) amine will hydrate and move away from the dry polymer, into a more energetically favorable, wet environment. These two steps can be viewed as a kind of activated process, the transition state being the initially ionized, dry amine. 

Equation 5.4 is the basis of a more detailed and fundamental study of the swelling process achieved through the study of resin-water vapour sorption isotherms obtained isopiestically i.e. at equal total pressures and equal resin water content). The isopiestic vapour pressure technique takes account of variable activity of the water in the resin (and therefore IT) by allowing the resin to come to equilibrium with water vapour at different partial vapour pressures P. It is assumed that two resins of the same structural type, but with different degrees of crosslinking, have the same water activity at the same equivalent water content. At equilibrium between resin and vapour phases the water activity in resins (1) and (2) are given by ... 

The composition of the structural material and the choice of the fabrication process are important in the preparation of controlled-release systems. Over the past decades, great advances have been made in the engineering of multicomponent, polymer-based, structural materials. These materials were designed to release active substances by different mechanisms (ref. 1) including diffusion, chemical control (polymer degradation) and solvent activation (swelling or osmotic pressure). In some cases, combinations of such mechanisms have been used. Experimental methods and theoretical analysis of mass transport phenomena in these materials have been developed (refs. 2,3). 

Abstract Shales present particular problems to drilling activities. Swelling, shrinkage and strength degradation may occur from pressure, chemical and thermal diffusion processes, leading to hole control problems that may lead to excessive times, hole loss, even blowouts. The article will describe qualitatively the major physical processes, field conditions, and explain how various mud systems address these issues. 

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