Thermo-responsiveness and tunable optical properties of asymmetric polystyrene/PNIPAM-gold composite particles

Environmentally responsive polystyrene/poly (N-isopropylacrylamide)-gold composite particles are successfully synthesized via a Pickering emulsion polymerization method. It is found that the core-shell and asymmetric structured particles are simultaneously formed during the polymerization. Compared with the core-shell structured composite particles, the asymmetric particles have a higher thermo-responsiveness as a result of differences in morphology and formation mechanism. For asymmetric composite particles, an increase in N-isopropylacrylamide (NIPAAM) content leads to more significant size variation upon temperature changes. From rheology measurements, the viscosity of asymmetric particles suspension greatly decreases as temperature is increased above the lower critical solution temperature (LCST). The large size decrease in asymmetric composite particles gives rise to a significant scattering intensity increase, as a result of increased refractive index contrast between the PNIPAM content and surrounding water. The resulting size decrease also leads to tunable surface plasmon resonance properties.