Ring assembly of silica nanospheres mediated by amphiphilic block copolymers with oxyethylene moieties

Silica nanospheres (SNSs) of ca. 15 nm in diameter assemble into nanoring structures with the aid of amphiphilic block copolymers containing the oxyethylene side chains poly[(2-ethoxyethyl vinyl ether)-block-(2-methoxyethyl vinyl ether)] [poly(EOVE-b-MOVE)]. Cryo-transmission electron microscope observation confirms that the ring assembly of SNSs occurs in the liquid phase. The SNSs favorably assemble into ring-like nanostructures in the presence of 1-2 wt% EOVE₁₀₀-b-MOVE₃₁₀ at pH ∼7.8 and 45 °C. Irregular aggregates of SNSs form at 60 °C, most likely because of the hydrophobic collapse of the thermoresponsive block copolymer. A series of poly(EOVE-b-MOVE) with varying block lengths successfully induce the ring assembly of SNSs, whereas a random copolymer fails, indicating that the polymer's molecular structure critically affects the assembly mode of SNSs. Interestingly, SNSs of a larger size (ca. 30 nm) assemble one-dimensionally into chain-like nanostructures in the presence of EOVE₁₀₀-b-MOVE₃₁₀.