Phase Behavior Of Block Copolymer Blends

In recent decades,the micellar behavior of block copolymer selective solutions has been paid much attention by scholars,especially the kinetic process,because of its dual value of basic research and application.Since non-equilibrium dynamics does not give a real picture of dynamics,especially for the behavior in equilibrium state.Therefore,it is necessary to effectively detect and quantify the dynamic process of aggregation behavior in the equilibrium state of the system,that is,the equilibrium state dynamic behavior.However,there is still a lack of understanding about the dynamic properties of equilibrium state.Therefore,the lattice self-consistent field method is used to study the equilibrium aggregation behavior in amphiphilic block copolymer solutions and homopolymer/block copolymer blend system.The main research contents of this paper are as follows:1.The equilibrium aggregation behavior of amphiphilic AB diblock and BAB triblock copolymer solutions was studied.Firstly,by calculating the phase diagram and heat capacity of the system,it is found that with the increase in the polymer concentration,the temperature required by the emergence of the micellar structure increases.The non-direct backfolding polymer chain increases the volume repulsion effect,which provides a more favorable condition for the emergence of micellar structure,but also restricts the increase of micellar aggregation degree to a certain extent;Secondly,the effect of hydrophobic block length on equilibrium aggregation behavior of BAB triblock copolymer solution system was studied.When the length of hydrophobic block is small,the formation process of micelles has obvious and overall adjustment behavior in the large concentration range.In the low concentration system,the micelle aggregation is regulated by increasing the volume of micellar core in the system.The increase of the concentration provided an opportunity to adjust the average aggregation degree for the system.At higher concentrations,the micelle formation underwent a relatively smooth aggregation process through the cooperative change of the aggregation degree and the volume of micellar core in the system.In essence,the increase of concentration makes the fragmentation/fusion mechanism affect over a wide range of the temperature.In the case of large hydrophobic blocks,only aggregation fusion was observed at lower concentrations.As the concentration increases,the fragmentation/fusion mechanism dominates the micellar formation.Therefore,the length of hydrophobic blocks is an important factor affecting the dynamic behavior of micelles,which is consistent with the relevant experimental results.2.The effect of homopolymer length on the micellar behavior of amphiphilic block copolymers was studied.Compared with the block copolymer solutions,an adjustable parameter,the chain length of the homopolymer(solvent size),is added to the blend system.The results show that the influence of solvent size on micelle aggregation is related to the archetecture of chain and system concentration of block copolymer.In homopolymer/diblock copolymer blend systems,increasing solvent size increased transition width at low concentrations,and promoted micelle fusion to form larger micelle structures at medium concentrations,while the effect of solvent size gradually decreased at high concentrations.In addition,the size of the solvent at low concentration delayed the micelle aggregation,which was beneficial to the improvement of the micelle aggregation state,but limited the increase of the volume of the micellar core;In homopolymer/triblock copolymer blend system,an increase in solvent size reduces the number of specific heat peaks in heat capacity curve,similar to the effect of concentration or hydrophobic block length in the triblock copolymer solutions.Compared with the effect of hydrophobic block length,the effect of solvent size is relatively small.The nature of the aggregation equilibrium behavior influenced by solvent size is related to the fragmentation/fusion mechanism.The results show that the fragmentation/fusion mechanism is the main mechanism for the dynamic behavior of micelles in the amphiphilic block copolymers,which is consistent with the results obtained by molecular dynamics simulation method.