Accurate knowledge of polymer brush grafting density will enable direct correlation of tethered chain dynamics and conformational transitions to physicochemical properties and kinetics of polymer thin films. Current methods to estimate grafting density rely on the hypothesis that molecular weight of a planar surface-initiated polymer brush is comparable to molecular weight of a concurrent solution polymerization. Recent Monte Carlo simulations indicate that this assumption may be inaccurate due to differing polymerization rates at the surface and in solution, especially when the density of surface-bound initiator is high.To address this issue, grafting density was determined by utilizing the stimuli-responsive behavior of dense and highly extended brushes resulting from surface-initiated controlled polymerizations. Brushes swollen with solvents of varying quality change brush height (h0, h) and film density; however the distance between tethered chains (D) remains constant. In situ x-ray reflectivity measurements were conducted to measure brush swelling upon exposure to solvent vapors and grafting density was determined using modified mean-field theory of one-dimensional swelling. Good solvents demonstrate homogeneous swelling, while heterogeneous density profiles were observed with poor solvents.

Quantitative determination of grafting density in polymer brushes

247th National Meeting (2014)

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