Quasielastic light scattering study of chemically crosslinked gelatin solutions and gels |
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Authors: | J Sharma H B Bohidar |
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Institution: | (1) School of Physical Sciences Jawaharlal Nehru University New Delhi 110 067, India e-mail: bohidar@jnuniv.ernet.in, IN |
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Abstract: | Quasielastic light scattering measurements are reported for experiments performed on mixtures of gelatin and glutaraldehyde
(GA) in the aqueous phase, where the gelatin concentration was fixed at 5 (w/v) and the GA concentration was varied from 1×10−5 to 1×10−3 (w/v). The dynamic structure factor, S(q,t), was deduced from the measured intensity autocorrelation function, g
2(τ), with appropriate allowance for heterodyning detection in the gel phase. The S(q,t) data could be fitted to S(q,t)=Aexp(−D
f
q
2
t)+Bexp(−t/τc)β, both in the sol (50 and 60 ∘C) and gel states (25 and 40 ∘C). The fast-mode diffusion coefficient, D
f showed almost negligible dependence on the concentration of the crosslinker GA; however, the resultant mesh size, ξ, of the
crosslinked network exhibited strong temperature dependence, ξ∼(0.5−χ)1/5exp(−A/RT) implying shrinkage of the network as the gel phase was approached. The slow-mode relaxation was characterized by the stretched
exponential factor exp(−t/τc)β. β was found to be independent of GA concentration but strongly dependent on the temperature as β=β0+β1
T+β2
T
2. The slow-mode relaxation time, τc, exhibited a maximum GA concentration dependence in the gel phase and at a given temperature we found τc(c)=τ0+τ1
c+τ2
c
2. Our results agree with the predictions of the Zimm model in the gel case but differ significantly for the sol state.
Received: 25 May 1999 /Accepted in revised form: 27 July 1999 |
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Keywords: | Quasielastic light scattering studies Gelatin gels Chemical crosslinking Fast and slow modes |
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