Synthesis of a thermosensitive surface by construction of a thin layer of poly (N-isopropylacrylamide) on maleimide-immobilized polypropylene

Thermosensitive surfaces were developed by the grafting of a thin layer of PNIPAAm through an UV-induced photopolymerization reaction of vinyl monomers with a free radical-activated polypropylene (PP) surface. PNIPAAm layer covering the PP surface corrected, to some extension, both depressions and fissures of the previously modified PP surfaces. The layered surfaces have morphological characteristic different from those of the non-layered surfaces, and their thickness was dependent on irradiation time. Water contact angles of the layered surfaces revealed a transition at approximately 33.5-36.5 °C as a result of a response to the variation of temperature. There was an increase in the values of the contact angles with an increase in temperature from 26 °C to 44 °C, revealing the nature both hydrophilic and hydrophobic of the surfaces due to a conformational rearrangement of PNIPAAm exposing its isopropyl groups to the liquid drop. This work offers a chemically stable thermosensitive surface (because it is covalently structured) with great potential for use as sensors and actuators.