Zheng, LF (Zheng, Ling-fei)^{[ 1 ]} ; Wang, Z (Wang, Zheng)^{[ 1 ]} ; Yin, YH (Yin, Yu-hua)^{[ 1 ]} ; Jiang, R (Jiang, Run)^{[ 1 ]} ; Li, BH (Li, Bao-hui)^{[ 1 ]}

摘要

The self-assembly of symmetric ABA tri-block copolymers inside an oil-in-water emulsion droplet upon solvent evaporation is investigated by Monte Carlo simulations, and the simulation results are compared with those in AB di-block copolymer systems. A morphological phase diagram is constructed in the two-dimensional space composed of surfactant concentration (phi) and the volume fraction of B segments (f(B)). Non-porosity particles, closed-porosity particles, open-porosity particles, capsules, and micelles are observed. The study shows that when f(B) <= 1/2, the increase of phi leads to a morphological evolution from non-porosity particle to closedporosity particle and open-porosity particle, while for f(B) > 1/2, micelles are observed in a larger phi window. The fraction of bridge chains (v(B)) as a function of phi is always much lower than the corresponding bulk value. Moreover, the mean-square radius of gyration (< R-g(2)>) of the ABA tri-block copolymer chains is much smaller than that of the corresponding AB di-block copolymer chains with the same f(B) and phi values under the same condition. Due to the influence of chain conformation, no capsule appears in the ABA tri-block copolymer system when f(B) <= 1/2, which is different from the case of the corresponding AB di-block copolymer system. The specific surface area of particles with the same morphology falls into almost the same p regime, which indicates that the particle morphology largely determines its specific surface area. By calculating the formation energy of particles, it is confirmed that the surfactants in the system are the key to the formation of porous particles. All these are the same as what have been observed in AB di-block copolymer systems. In addition, the radial density distributions of water molecules in ABA tri-block system and the corresponding AB di-block system are not exactly the same, but the particle sizes are basically identical. The evolution processes including the typical non-porosity particles, closed-porosity particles, and open-porosity particles, as well as the bridging fraction during solvent evaporation are further discussed.