Charge-Induced Self-Assembly of 2-Dimensional Thermosensitive Microgel Particle Patterns

The self-assembly of charged microgel particles into two-dimensional arrays on various substrates have been investigated by depositing the diluted microgel dispersion on the substrate and drying at room temperature. Core-shell type thermosensitive microgel particles consist of poly(styrene) (PS) core, whereas the shell consists of poly(N-isopropylacrylamide) (PNIPA) network cross-linked by N,N'-methylenebisacrylamide (BIS). It is found that the electrostatic interactions between microgel particles and charged substrate surface play an important role for the formation of ordered 2-D pattern. When microgel particles are deposited onto the substrate with opposite surface charges, microgels will form ordered 2-D arrays with constant distance between particles. When substrate with same surface charge as microgel particles was used, the electrostatic repulsion between microgel particles and substrate will destroy the ordered structure. Moreover, after embedding Au nanoparticles into the thermosensitive microgel particles, the microgel-Au composite particles can also assemble into 2-D arrays on the substrate.