Thermal analysis of PNIPAAm-PAAm mixtures via photopyroelectric technique

Evingur G. A. , Menon P., Rajesh R., Kuriakose M., Glorieux C.

15th International Conference on Photoacoustic and Photothermal Phenomena, Leuven, Belçika, 19 - 23 Temmuz 2009, cilt.214 identifier identifier


Crosslinked poly (N-isopropylacrylamide) (PNIPAAm) is a temperature-sensitive hydrogel with approximately 32 degrees C lower critical solution temperature (LCST) in pure water. The PNIPAAm chains hydrate to form extended structures in water when the latter is below LCST. However, when heated to above LCST, they become compacted by dehydration. In this work, we have used the PNTPAAm-polyacrylamide (PAAm) mixtures with varying molar percentages of PNTYAAm and PAAm that were prepared by free radical crosslinking copolymerization. N'-N'methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) were used as crosslinker and an initiator, respectively. A photopyroelectric technique was applied to test the universality of the sol- gel transition as a function of polymer concentration ratios and to determine thermal effusivity of PNIPAAm- PAAm mixtures. The effects of varying PAAm concentrations on the LCST were studied by determining the temperature dependence of the thermal effusivity, with emphasis is on the influence on the properties and formation on the LCST of PNIPAAm- PAAm mixtures of the acrylamide concentration.