We report on tuning swelling of pH-sensitive poly(methacrylic acid) (PMAA) ultrathin hydrogels by controlling their internal structure. These hydrogels were produced by chemical cross-linking of PMAA layers in hydrogen-bonded layer-by-layer templates. The internal architecture of those hydrogels was strongly correlated with the internal structure of the as-deposited hydrogen-bonded films, which in turn depends on deposition conditions. A high stratification degree with preserved layering was found for hydrogels obtained from spin-assisted templates. In contrast, with conventional dipping, the hydrogels were highly intermixed with a significant decay in layering. The pH-triggered hydrogel swelling was strongly influenced by the network architecture.Highly swollen (up to 18 times the original dry thickness at pH=7.5) hydrogels, are obtained from well-stratified 'spin-assisted' templates; while a three-fold lower swelling observed for intermixed 'dipped' precursors. In addition, the well-structured hydrogels exhibited a ten-fold increase in thickness when pH was changed from 5 to 7.5 unlike the two-fold swelling observed in less organized hydrogels.  These hydrogels represent a unique example of an ultrathin but highly-swollen film capable of a 94% water uptake at pH=7.5. We believe that regulatingswelling behavior of stimuli-responsive hydrogelsat the nanoscale is crucial for advanced drug delivery and sensing applications.

Regulating architecture of nanothin hydrogels: Effect of layering on pH-triggered swelling

247th National Meeting (2014)

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