Refractive Index Change Due to Volume-Phase Transition in Polyacrylamide Gel Nanospheres for Optoelectronics and Bio-photanics

Poly(N-isopropylacrylamide) (PNIPAM) hydrogel nanospheres response to global temperature stimuli across the low critical solution temperature is studied as the water content in the polymer network is modified. The refractive index of gel nanoparticles was measured as a function of temperature using spectroscopic ellipsometry. The volume of the nanospheres reduces by 40% resulting in a modification of light scattering properties of the medium. A change in temperature from 33 to 34 degrees C results in a volume contraction of nanospheres which is accompanied by 8-10% enhancement in the refractive index of the gel network. (c) 2009 The Japan Society of Applied Physics