Determination of the Parameters Controlling Swelling of Chemically Cross-Linked pH-Sensitive Poly(N-vinylimidazole) Hydrogels
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- 作者：M. Jesú ; s Molina ; M. Rosa Gó ; mez-Antó ; n ; Iné ; s F. Pié ; rola
- 刊名：Journal of Physical Chemistry B
- 出版年：2007
- 出版时间：October 25, 2007
- 年：2007
- 卷：111
- 期：42
- 页码：12066 - 12074
- 全文大小：326K
- 年卷期：v.111,no.42(October 25, 2007)
- ISSN：1520-5207
文摘
The number of variables controlling the behavior of ionic gels is large and very often some of them areunknown. The aim of this work is to interpret quantitatively the swelling behavior of pH sensitive gels, withthe minimum number of simplifying assumptions. With this purpose, the equilibrium degree of swelling (S)and protonation () of chemically cross-linked poly(N-vinylimidazole) (PVI) immersed in aqueous salt solutionswere measured as a function of the ionic strength (), in the whole range of pH. In acid solutions with pHin the range 0 to 4, imidazole moieties become protonated, and PVI behaves as a polyelectrolyte gel: Sdecreases upon increasing both for NaCl and for CaCl2, with HCl as protonating acid. In aqueous solutionswith larger pH, between 4 and 12, the hydrogel is practically neutral, and S increases as rises, showing asalting-in effect. From the quantitative analysis of these results, the following facts emerged. Protonationinduces chain stiffness (as measured by the non-Gaussian factor) and worsening of the solvent quality of theaqueous media (as measured by the polymer-solvent interaction parameter). For below 33%, swellingseems to be governed by the excess of mobile counterions inside the gel with respect to the bath, with aminor but still significantly negative contribution of the osmotic swelling pressure due to polymer-solventmixing. Above 33% protonation, it is necessary to consider Manning counterion condensation to get parameterswith physical meaning. The crossover between polyelectrolyte and salting-in effects corresponds to and values with the same ionic and mixing contributions to the osmotic swelling pressure. The formation of ionicnonpermanent cross-links, with H2SO4 as the protonating acid, was discarded.