Water sorption studies in a RGP contact lens polymer paraperm by positron lifetime technique

Thimmegowda, M. C. and Sathyanarayana, P. M. and Shariff, Gani and Ashalatha, M. B. and Ramani, R. and Ranganathaiah, C. (2002) Water sorption studies in a RGP contact lens polymer paraperm by positron lifetime technique. Physica Status Solidi a Applied Research, 193 (2). pp. 257-270. ISSN 0031-8965

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Official URL: https://doi.org/10.1002/1521-396X(200209)193:2<257...

Abstract

The kinetics of moisture uptake in a rigid gas permeable contact lens material Paraperm has been investigated. The free volume changes accompanied by the sorption of water have been monitored using Positron Lifetime Spectroscopy (PLS) technique. The positron results indicate the swelling in the initial stages of sorption which seems to be balanced by the rearrangement of chains in the presence of water molecules and filling of vacant free volume sites with water at the later stages of sorption. The sorption curve suggests that diffusion process in this polymer follows dual‐mode sorption model. Using this model we have been able to separate the Fickian controlled diffusion and relaxation controlled diffusion. Further, the positron results combined with sorption results indicate that Fujita's free volume theory seems to be not valid for the diffusion process in the present sample under study. The variation of permeability as a function of free volume suggests the amount of water in a contact lens is a measure of its permeability.

Item Type: Article
Subjects: D Physical Science > Physics
Divisions: Department of > Physics
Depositing User: manjula User
Date Deposited: 20 Sep 2019 10:29
Last Modified: 20 Sep 2019 10:29
URI: http://eprints.uni-mysore.ac.in/id/eprint/8321

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