Control of light transmission in polymer gels by stimuli-responsive guest microparticles

We developed a soft, optical material of polymer gels with the capability of controlling the visible light transmission in response to temperature change. The polymer gel is a weakly cross-linked thermostable network of poly(acrylamide), which is slightly impregnated with thermoresponsive gel microparticles of poly(N-isopropylacrylamide). It was found that the light transmission can be reversibly controlled only by adjusting the temperature; the transmitted light intensity rapidly and continuously decreases with increasing temperature. The system can, therefore, behave as an optical "shutter". The phenomena were attributed to the local structural change induced by the volume phase transition of guest microparticles. The light transmission properties depend on the interpenetrating stare of guest microparticles immobilized in host networks. which are permanently introduced during gelation. The relaxation time depends on both the final and the initial temperatures. Static and kinetic properties are discussed phenomenologically on the basis of the volume phase transition of guest microparticles under mechanical constraint.