A theory of case II diffusion

Thomas, Noreen L.; Windle, A. H.

doi:10.1016/0032-3861(82)90093-3

Cited by 610 publications

(458 citation statements)

References 18 publications

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“…Monomer diffusion becomes non-Fickian and must be described by case-II diffusion. 29 When the polymer is rubbery, the swelling occurs almost instantaneously. When, on the other hand, the polymer is glassy, the monomer first moves, creating a higher density, and swelling goes slowly.…”

Section: Discussionmentioning

confidence: 99%

Reaction–diffusion model for the preparation of polymer gratings by patterned ultraviolet illumination

Leewis

Jong

IJzendoorn

et al. 2004

Journal of Applied Physics

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A model is developed to describe the migration mechanism of monomers during the lithographic preparation of polymer gratings by ultraviolet polymerization. The model is based on the FloryHuggins theory: a thermodynamic theory that deals with monomer/polymer solutions. During the photoinduced polymerization process, monomer migration is assumed to be driven by a gradient in the chemical potential rather than the concentration. If the chemical potential is used as the driving force, monomer migration is not only driven by a difference in concentration, or volume fraction, but also by other entropic effects such as monomer size and the degree of crosslinking of the polymer network, which is related to the ability of a polymer to swell. Interaction of the monomers with each other or the polymer is an additional energetic term in the chemical potential. The theoretical background of the model is explained and results of simulations are compared with those of nuclear microprobe measurements. A nuclear microprobe is used to determine the spatial monomer distribution in the polymer gratings. It is shown that two-way diffusion is expected if the monomers are both difunctional and have the same size. In some cases, if one monomer is considerably smaller than the other, it can eventually have a higher concentration in the illuminated regions, even when it has a lower reactivity. The model is used to simulate the grating formation process. This results in a calculated distribution of the monomer volume fractions as a function of position in polymer gratings. An excellent agreement with the nuclear microprobe measurements is obtained.

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Section: Discussionmentioning

confidence: 99%

Reaction–diffusion model for the preparation of polymer gratings by patterned ultraviolet illumination

Leewis

Jong

IJzendoorn

et al. 2004

Journal of Applied Physics

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“…Several models have been proposed which aim to couple the diffusion of absorbed solvent throughout the film with the elastic [40,41,42] or viscoelastic [43,44,45,46] response of the polymer network. Simplifications of these models that neglect the detailed mechanics of the polymer matrix have been proposed in the context of drug delivery [47,48,49].…”

Section: Introductionmentioning

confidence: 99%

A minimal model for solvent evaporation and absorption in thin films

Hennessy

Ferretti

Cabral

et al. 2017

Journal of Colloid and Interface Science

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We present a minimal model of solvent evaporation and absorption in thin films consisting of a volatile solvent and nonvolatile solutes. An asymptotic analysis yields expressions that facilitate the extraction of physically significant model parameters from experimental data, namely the mass transfer coefficient and composition-dependent diffusivity. The model can be used to predict the dynamics of drying and film formation, as well as sorption/desorption, over a wide range of experimental conditions. A state diagram is used to understand the experimental conditions that lead to the formation of a solute-rich layer, or "skin", at the evaporating surface during drying. In the case of solvent absorption, the model captures the existence of a saturation front that propagates from the film surface towards the substrate. The theoretical results are found to be in excellent agreement with data produced from dynamic vapour sorption experiments of ternary mixtures comprising an aluminum salt, glycerol, and water. Moreover, the model should be generally applicable to a variety of practical contexts, from paints and coatings, to personal care, packaging, and electronics.

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“…This elongation is then counter balanced by an elastic-restrictive force to oppose the swelling. Eventually a state of equilibrium is reached when both forces are balanced, these process can significantly alter the kinetics of drug diffusion through the polymer network and are highly influenced by time-scale associated structural changes in the polymer [69][70][71][72] . The move towards anomalous transport over 8 weeks may suggest a polymer network timeassociated affect 73,74 , which becomes more apparent over the longer stability study.…”

Section: Stability Assessmentmentioning

confidence: 99%

Development and Evaluation of a Novel Intranasal Spray for the Delivery of Amantadine

Lungare

Bowen

Badhan

2016

Journal of Pharmaceutical Sciences

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The aim of this study was to develop and characterise an intranasal delivery system for amantadine (AMT). Optimal formulations (F) consisted of a thermosensitive polymer Pluronic ® 127 (P127) and either carboxy methyl cellulose (CMC) or chitosan (CS) which demonstrated gel-transition at nasal cavity temperatures (34 °C ± 1 °C). Rheologically, the loss tangent (Tan δ) confirmed a three-stage gelation phenomena at 34 °C ± 1 °C and nonNewtonian behaviour. Storage of FCMC and FCS at 4 °C for 8 weeks resulted in repeatable release profiles at 34 °C when sampled, with a Fickian mechanism earlier on but moving towards anomalous transport by week 8. Polymers (P127, CMC and CS) demonstrated no significant cellular toxicity to human nasal epithelial cells up to 4 mg/mL and up to 1 mM for AMT (IC50: 4.5 mM ± 0.05 mM). FCMC and FCS demonstrated slower release across an in-vitro human nasal airway model (43-44 % vs 79 % ± 4.58 % for AMT). Using a human nasal cast model, deposition into the olfactory regions (potential nose-to-brain) was demonstrated upon nozzle insertion (5 mm) whereas tilting of the head forward (15°) resulted in greater deposition in the bulk of the nasal cavity. KEYWORDSParkinson's disease; rheology; nasal; RPMI 2650; nose to brain; thermoresponsive; 3 INTRODUCTION Parkinson's disease (PD) is an ageing associated progressive neurological disorder and affects 1.5 % of the population over 65-years of age 1 , with age-adjusted prevalence rates thought to be around 150 per 100,000 with a suggested mean onset in the 70's 1 . Ageing is the largest single risk factor for the development of PD and the pathogenesis of PD is composed of a range of events leading towards neuronal apoptosis, primarily of degradation of dopamine neurones in the sustantia nigra. The mainstay of clinical drug therapy focuses on increases the levels of dopamine (DA) in the brain, with oral dosing of levodopa being the most commonly used to pharmacological intervention treatment to reverse the symptoms of PD. It is also common to use adjunct therapies in conjunction with levodopa, such as the weak NMDA-type receptor antagonist amantadine, which can aid in blocking dopamine reuptake.

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A theory of case II diffusion

Cited by 610 publications

References 18 publications

Reaction–diffusion model for the preparation of polymer gratings by patterned ultraviolet illumination

Reaction–diffusion model for the preparation of polymer gratings by patterned ultraviolet illumination

A minimal model for solvent evaporation and absorption in thin films

Development and Evaluation of a Novel Intranasal Spray for the Delivery of Amantadine

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