Dissipative Particle Dynamics Simulations Of Self-assembled From Amphiphilic Random Copolymers

Compared to block copolymers, amphiphilic random copolymers are much easy tosynthesis, so they have potential applicable prospects. Computer simulations can effectivelycompensate for technical defects on the polymer microstructure and properties byexperimental study. It not only can predict aggregation morphology of amphiphiliccopolymer on molecular structure, but also predict macro-and mesoscopic properties ofpolymer materials. Molecular simulations have become a new direction of research in thefield of polymer science. In this paper, microphase separation behaviors of self-assembly ofamphiphilic random copolymers in solution were investigated via the dissipative particledynamics （DPD） simulations. The paper divides three parts.1. Surface hydrophilicity of spherical micelle formed from self-assembly of amphiphilicrandom copolymers in solution was investigated via DPD simulations. The coarse grainedmodels with different ratio（r） of number of hydrophilic particles to hydrophobic particleswere built. The surface hydrophilicity of micelles increases with the increase of the contentof hydrophilic unit. In addition, with repulsion parameters between hydrophobic and solventparticle (a_BS) increasing, the surface hydrophilicity of spherical micelles also increases. Withrepulsion parameters (a_AS) between hydrophilic and solvent particle increasing, the surfacehydrophilicity of spherical micelles increases. With simulation time increasing, the surfacehydrophilicity of spherical micelles increases. With the volume fraction of copolymerincreasing, the diameter of spherical micelle increases and gradually transformed into the rodand perforated layered, layered micelles.2. Study on vesicle formation self-assembly from amphiphilic random copolymers insolution was investigated via DPD simulations. The content of hydrophilic particles, theselectivity of the solvent was mainly investigated vesicle formation. Simulation shows thatrandom copolymers can self-assemble into vesicles at r=1，a_AS=25; r=1.5or2，a_AS=20; r=3，a_AS=15when a_BS=75. The inner hole of vesicle become smaller with a_BSincreasing andtransform into solid spherical micelle at a_BS=130when a_AS=20and r=1.5. Mutualtransformation between spherical micelles and vesicles was occurred by changing a_AS. Themechanism of vesicle formation from amphiphilic random copolymer was investigated indetail. When a_AS=20, a_BS=75and r=1.5, flat-like micelle bends and changes its shape tobowl-like micelle. With more solvent particles encapsulated by this bowl-shaped micelle, aspherical vesicle is formed. When a_AS=25, a_BS=75and r=1, random copolymer self-assembleinto spherical micelle with hydrophilic kernel firstly. With solvent diffused into the sphericalmicelles, spherical vesicles were formed.3. Self-assembly of amphiphilic ternary random copolymers in solution was investigatedvia DPD simulations under a_AS=30and aCS=80. With the repulsion parameters a_BSincreasing,the surface hydrophilicity of spherical micelles decreases. In addition, ternary randomcopolymer P（St-co-AA-co-DM） was synthesized and self-assembled in solution.Experimental results show that the particle size of the micelles has responsiveness with pH.