Abstract
Understanding the dynamic and reversible assembly of colloids and particles into complex constructs, inspired by natural phenomena, is of fundamental significance for the fabrication of multi-scale responsive and reconfigurable materials. In this work, we investigate the pH-triggered and reconfigurable assembly of structures composed of binary mixtures of oppositely charged polyacrylic acid (PAA)-modified non-Janus and poly(2-dimethylamino)ethyl methacrylate (PDMAEMA)/poly(N-isopropylacrylamide) (PNIPAM)-modified Janus particles driven by electrostatic interactions. Three different target structures are visible both in dispersions and in dry state: half-raspberry structures, colloidal clusters and colloidal chains depending on the mass, numerical and particle size ratio. All formed structures are well-defined and stable in a certain pH range. Half-raspberry-like structures are obtained at pH 6 and numerical ratios N (JP/PAA-HP) of 1 : 500 (for 200-PAA-HP), 1 : 44 (for 450-PAA-HP) and 1 : 15 (for 650-PAA-HP), respectively, due to electrostatic interactions between the central JP and the excessive PAA-HP. Colloidal chains and cluster-like structures are generated at numerical ratios N (JP/PAA-HP) of 4 : 5 (for 200-PAA-HP), 4 : 3 (for 450-PAA-HP), and 4 : 1 (for 650-PAA-HP). Moreover, the smaller the size of a "connecting" PAA colloid, the larger is the average length of a colloidal chain. Depending on the particle size ratio S (JP/PAA-HP), some of the observed structures can be disassembled on demand by changing the pH value either close to the IEP of the PDMAEMA (for half-raspberries) or PAA (for colloidal clusters and chains) and then reassembled into new stable structures many times. The obtained results open a pathway to pH-controlled reconfigurable assembly of a binary mixture composed of polymeric-modified non-Janus and Janus particles, which allow the reuse of particle building blocks.