Formation Mechanisms of Porous Particles from Self-Assembly of Amphiphilic Diblock Copolymers inside an Oil-in-Water Emulsion Droplet upon Solvent Evaporation

Zheng, LF (Zheng, Lingfei)^[ 1 ] ; Wang, Z (Wang, Zheng)^[ 1 ] ; Yin, YH (Yin, Yuhua)^[ 1 ] ; Jiang, R (Jiang, Run)^[ 1 ] ; Li, BH (Li, Baohui)^[ 1,2 ]

LANGMUIR, 2019, 35(17): 5902-5910

DOI: 10.1021/acs.langmuir.9b00613

Abstract

The formation mechanisms of porous particles from self-assembly of amphiphilic diblock copolymers inside an oil-in-water emulsion droplet upon evaporation of the organic solvent are investigated based on Monte Carlo simulations for the first time. A morphological diagram of particles is constructed as a function of the surfactant concentration (phi) and the copolymer composition characterized by the volume fraction of the hydrophilic B block (f(B)). Particles with various morphologies are predicted. Morphological sequences from non-porosity to closed-porosity to capsules and finally to open-porosity particles are usually observed with increasing phi when f(B) < ="1/2," with the only exception that capsules do not occur when f(b)="1/6." furthermore, the critical phi value for a given morphological transition usually decreases with increasing f(b). micelles are always observed at higher phi regions when f(b)> 1/2. It is found that the specific surface area falls on almost the same regime for particles with the same kind of morphology, indicating that the morphology of a particle largely determines its specific surface area. The chain stretching varies with the particle morphology. It is the presence of the surfactant that makes the formation of porous particles possible, while when phi > 0, multiple morphological transitions can be induced by changing f(B). In the process of organic solvent removal, the value of f(B) may affect the shape of pores inside the droplet and hence leads to the f(B) dependence of the morphological sequences. When the solvent evaporation is not too fast, the resulting morphological sequence does not depend on the evaporation rate. Our results are compared with related experiments.