The Coarse-grained Simulation Study On Dissipative Self-assembly Of Block Copolymer In Non-equilibrium States

Self-assembly of block copolymers provides the opportunity for creating various sophisticated functional materials because of the microphase separation transition during the assembled process.In nature,the execution of biological functions such as numerous cellular processes and most biological forms of adaptive or intelligent behavior is based on dissipative self-assembly.Therefore,inspired by the living systems in nature,dissipative self-assembly is adopted to design materials as sophisticated as biological ones.As a mode of organization depending on the amount of energy delivered to the system,dissipative self-assembly is a process in which the structure shapes when the system is forcefully driven away from the equilibrium state,leading to unique structures which are thermodynamic metastable states.In polymer systems,most studies use the fuel-driven dissipative self-assembly strategy to achieve the energy supply.However,the structure obtained is single,and the behavior in the dynamic process is not easy to control.Therefore,in this thesis,we propose two design strategies applied in polymer systems,those are reversible chemical reaction regulated dissipative self-assembly driven by the entropy change and external fields controlled dissipative self-assembly driven by the enthalpy change.Moreover,the theoretical framework is constructed to understand the universal behavior in dissipative self-assembly.We then construct a block copolymer model to confirm the conclusions from the theory.The main contents of this thesis include three parts:1.Reversible chemical reaction regulated dissipative self-assembly driven by the entropy change.For polymer chains,huge microstates lead to considerable conformational entropy.Therefore,it is of great significance to understand and design the dissipative self-assembly of polymer systems driven by entropy change.In this work,we propose the strategy of reversible chemical reaction controlled dissipative self-assembly of amphiphilic block copolymers.Through tuning the reaction direction periodically,we can obtain the exotic self-assembled vesicle with surface pores which is otherwise the thermodynamically metastable state.The type of chemical reaction and the reaction period are the two vital factors that determine the dissipative structures.The unique self-assembly structure appears only at a short reaction period in a suitable reversible reaction.During the dynamic process,the composition of the building block becomes the time-varying parameter.Therefore,we define the component ratio P and demonstrate that P less than 0.4 in the dissipative assembly process is the prerequisite to obtain perforated vesicles.Due to the competition of reaction and diffusion in the dissipative assembly,the local component of building blocks keeps changing,leading to the local surface tension bias from 0,resulting in the formation of the perforated vesicle.In order to identify the assembled structure in a dynamic process,we build up the relationship between the diffusion effect parameter P_diff,reaction probability P_r,and assembled structures.The dynamic self-assembly controlled by reversible chemical reaction holds great promise as a rational strategy to realize exotic functional materials that are not easily obtained in equilibrium.2.External fields controlled dissipative self-assembly driven by the enthalpy change.For dissipative self-assembly,trigging the periodic alternation of an external field is often considered to supply a continuous influx of chemical energy to systems.Several researches have shown that by coupling the external fields to colloidal systems,novel structures unavailable in equilibrium state can be obtained.Therefore,in this work,we seek to propose a design strategy of the stimuli-responsive triblock copolymer material by periodical energy input driven dissipative self-assembly.Utilizing the continuous alternation of enthalpy as the imposed energy flow by periodically regulating the interaction between blocks in the polymer chains,the mechanical nanogel is obtained which is distinct from two energy-favorable equilibrium states,incompact sphere micelles or the defective lamellae.Once the periodical process ceases,the nanogel disintegrates and reverts to the micelles or the lamellae according to the state at termination.Thus,the controlled“three-in-one”incompact-solid material is realizable.This material with distinct,interchangeable states may find potential uses in transient support of clinical treatment and adhesive applications.Furthermore,the dependency on the frequency of energy input is demonstrated in this work.The structural and kinetic analysis are made to understand the unique behavior under'high frequency'energy supply according to the time-averaged theory of non-equilibrium proposed by Tagliazucchi.We also clarify the definition of‘high frequency'in polymer systems for experiments.Besides,the power of energy supply which is reflected on the amplitude of interaction oscillation influences the relaxation time on kinetic,however not influence the dissipative structures.Notably,our design strategy of material can be realized in a wide range of concentrations from 20%-40%,making the experiment easy to complete.3.The theoretical framework of dissipative self-assembly and the verification by polymer system.In this work,we develop a theoretical framework based on the equations of motion and Floquet theory to reveal the dynamic behavior changing with frequency in the periodic external field driven self-assembly.We then construct a block copolymer model that can self-assemble in dilute solution to confirm the conclusions from the theory.The theoretical results show the coordinate-dependent external field is beneficial to obtain various dissipative structures.Comparing with a square wave,the cosine wave leads system reach the dissipative structure determined by the effective potential at a lower frequency.We then demonstrate how the system responds to oscillations with different finite frequencies.As the frequency?increases,the evolution of the system approaches to the regime in which the dissipative self-assembly structure is controlled by effective potential with?1/?,also does the amplitude of the structural oscillation.Besides,in a high-frequency regime,the dissipative steady state of the system is governed by the time-independent Liouvillean and tends to a state described by an effective mean potential at the scale of 1/?².Therefore,when driven by a periodic force,the system first relaxes to oscillating around the state controlled by the mean potential,and then the tiny oscillation disappears gradually.Our theoretical framework provides guidance for understanding dynamic behavior in a periodically driven process and promotes designing and constructing dissipative self-assembly systems.