Dissipative Particle Dynamics Simulation On The Self-assembly Behavior Of POSS-based Block Copolymers

Block copolymers can self-assemble into various kinds of ordered micro phase separation structures in selective solvents.These highly ordered polymer materials exhibit new optical,electrical and mechanical properties,and show great promise in the fields of medicine,life sciences,nanodevices and optoelectronic materials.Polyhedral oligomeric silsesquioxanes(POSS),as an organic-inorganic hybrid molecule,posses a unique inorganic nanocage structure that can be incorporated into polymers to produce hybrid materials with excellent properties,which have aroused the widespread concern of researchers.Dissipative particle dynamics(DPD)simulation can provide valuable information on larger time and space scales,showing a strong advantage in studying the self-assembly of block copolymers.The main contents of this paper are as follows:(1)The self-assembly process of POSS-based block copolymers(PMMA-b-PMAPOSS and PMMA-b-PFMA-b-PMAPOSS)in THF was studied by DPD simulation.It was found that the entire dynamic process could be divided into four stages: firstly,the polymer chains were randomly dispersed in the solution;then curled chains formed small aggregates;and then small aggregates collided and merged into large ones;finally,the formation and stabilization of the micelle.The effects of the block sequence,length,polymer content and composition of the mixed solvents were discussed.For PMMA-b-PMAPOSS,only spherical,flat disk and lamellar micelles appeared with varying the block length and polymer content.For PMMA-b-PFMA-b-PMAPOSS,spherical micelles with "core-shell-corona" and "core-mixed shell" structures could be formed by regulating the block sequence.Changing the block length would form "Janus" particle.And with the increase of the polymer content,the morphologies of the micelles occurred a series of changes: spherical,flying saucer shape and Y-type to multi-compartment and snowman-like to flat disk and lamellar.In addition,the micelle size increased with trichlorotrifluoroethane(F113)content in the mixed solvents of tetrahydrofuran(THF)and F113.In comparison,the influence factors increased due to the increase of the block type for the triblock copolymer,thus the self-assembled morphologies were more abundant.(2)The self-assembly behavior of POSS-based hybrid amphiphilic triblock copolymer(PFMA-b-PAA-b-PMAPOSS)in selective solvents was studied by DPD simulation.The copolymers with different block sequence self-assembled in THF forming the "Janus" particle,"core-shell-corona" and "core-mixed shell" structures.Adjusting the block length would promote the transformation of micelle morphologies between sphere and "Janus" particles.As the concentration of the solution increased,there were "peanut-like","Y-shaped" and "worm-like" micelles piled up from the basic unit of spherical structure.Further increasing the concentration of the solution resulted in the flattening of the micelle forming the lamellar by hexagonal stacking.Adjusting the ratio of THF and F113 would form the strawberry-like,rod-like micelles and “Janus” particles,and the micelle size first increased,then decreased with the increase of the F113 content.