Investigation of drying of poly(N-isoproplacrylamide-co-acrylamide) by fluorescence technique

Abstract

The steady-state fluorescence technique was performed on drying of various molar percentages of poly(N-isopropylacrylamide-co- acrylamide) [poly(NIPA-co-AAc)] to elucidate the mechanism of temperature-induced phase separation and the effect of monomer content. Poly(NIPA-co-AAc) copolymers were prepared by free radical cross-linking copolymerization. The fluorescence intensity, I, of pyranine, introduced as a probe, increased as drying time was increased for all samples. The behavior of I was modeled by using the Stern–Volmer equation combined with the moving boundary diffusion model. The desorption coefficient, D, increased as NIPA content was increased at a given temperature. Gravimetric and volumetric experiments also supported the results of the fluorescence technique. The energy, Δ E, values were measured for the drying processes for each molar percentage of NIPA monomer content by using fluorescence, gravimetric, and volumetric methods, respectively. It is understood that Δ E values decrease by increasing NIPA content, until 50% NIPA, and then increase after 50% NIPA, indicating that the phase separation has occurred at 50% NIPA. © 2012 Wiley Periodicals, Inc. 00:1–10, 2012; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.21269