Abstract
Experiments on swelling and solute transport in polymeric systems clearly indicate that the classical parabolic models fail to predict typical non-Fickian features of sorption kinetics. The formulation of moving-boundary transport models for solvent penetration and drug release in swelling polymeric systems is addressed hereby employing the theory of Poisson–Kac stochastic processes possessing finite propagation velocity. The hyperbolic continuous equations deriving from Poisson–Kac processes are extended to include the description of the temporal evolution of both the Glass–Gel and the Gel–Solvent interfaces. The influence of polymer relaxation time on sorption curves and drug release kinetics is addressed in detail.
Highlights
Many fluids and polymeric liquids, suspensions, and gels possess viscoelastic properties, which, in the simplest case, can be characterized through a single relaxation time [1], leading to constitutive equations with memory for the stress tensor as a function of the deformation tensor
We investigate the influence of the polymer relaxation time on the release kinetics of a drug initially loaded in the thin dry film
This section investigates the influence of the polymer relaxation time on the release kinetic of a drug initially loaded in the thin dry film
Summary
Many fluids and polymeric liquids, suspensions, and gels possess viscoelastic properties, which, in the simplest case, can be characterized through a single relaxation time [1], leading to constitutive equations with memory for the stress tensor as a function of the deformation tensor. Gels 2021, 7, 32 adopted and extended to describe and investigate the effect of polymer relaxation time on solvent penetration in glassy polymers To this end, an extra convective term is included in the classical partial wave transport equations to account for the contribution of the swelling point-wise velocity. The original PK model has been generalized to define a broader class of processes possessing Markovian transitions, where the characteristic velocity and the transition rate are continuous functions of the overall density [13] This extension permits the investigation of the effect of both a polymer relaxation time and a solvent diffusivity that are exponential functions of the local solvent concentration, as established by simplified versions of the free volume theory [25,26,27]. Release kinetics are strongly influenced by the polymer relaxation time and, unexpectedly, are not necessarily slowed down for intermediate values of the Deborah number
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