Aggregate Behavior Of Amphiphilic Block Copolymer Solutions With Rigid Blocks

In recent 20 years,block copolymers with rigid blocks have attracted much attention due to their unique and abundant phase behavior.Compared with melt systems,rod/coil block copolymer solutions have some problems to be solved due to the complexity of research.In order to clarify the effect of the rod/coil block interface properties and solvent on self-assembly of block copolymer,the aggregation behavior of amphiphilic block copolymer solutions with rigid block was simulated by lattice self-consistent field model in this thesis.And the formation mechanism of micelles with rod cores was analyzed from the point of view of equilibrium dynamics.The main research contents are as follows:The aggregation behavior of rod/coil amphiphilic block copolymer solution was studied.Firstly,the micellar growth process of AB diblock copolymer solution was studied.According to the number of peak on heat capacity curve and micellar structure,it is found that the structure rearrangement behavior occurs during the system aggregation process.When the rod block length is short,star,rod and lamellar micelles appear at the low concentrations,as well as the diffusion of micelles and the mutual transformation between rod and lamellar micelles,accompanied by the dissolution behavior of micelles.At the medium concentrations,with quasi cubic micellar structure as the main structure,micellar rearrangement and growth with rod block micellar core were achieved by fragmentation/fusion of rod,lamellar and cubic micelles.Morphology transformation,fragmentation/fusion and dissolution of micelles of different morphology were observed in low and medium concentrations,and the systems showed strong structural rearrangement behavior.At relativel high and high concentrations,only the cubic micelles were observed,and the fusion and fragmentation behaviors only occurred between the cubic micelles.It was demonstrated that the increase in concentration leads to the weaknes of structure rearrangement.It was also found that the effect of increasing rod block length on rearrangement behavior is similar to that of increasing concentration.Secondly,self-assembly of rod/coil/rod ABA triblock copolymer solution was studied.Compared with diblock copolymers,the effects of concentration and rod block length on the aggregation of rod/coil/rod ABA triblock copolymer are more complex.When the rod block length was short,the micellar aggregation,diffusion and re-aggregation occurred at the low concentrations,accompanied by micellar fragmentation and fusion,but no micellar dissolution occurred.At the intermediate concentrations,micellar diffusion behavior weakened and cubic micellar aggregation and fusion appeared,accompanied by micellar dissolution.The multiple-step fusion behavior consisted of the linear,nonlinear fusion and branched micellar aggregates fusions occurred at the higher concentrations.At high concentrations,the emergences of the linear,nonlinear fusion become easy,but the fusion between the nonlinear micellar aggregates becomes more complex.The increase of rod block length promotes intermicellar fragmentation/fusion behavior,and weakens the rearrangement behavior of most concentration systems.Only the rearrangement behavior of the relatively high concentrations enhance.Finally,the effect of solvent size(addition of coil homopolymer)on the phase behavior of coil/rod/coil BAB triblock copolymer was studied.The results show that the coil/rod/coil block copolymer system is closely related to the concentration and rod block length due to the change of solvent size.At low concentrations,when the rod blocks are short,the increase in solvent size weakens the rearrangement behavior,but the fragmentation/fusion behavior of the system strengthen.The rearrangement behavior enhances with the increase in rod block length.The diffusion and its inverse processs related to the change of lamellae orientation appeared in the medium length and long rod block systems,respectively.At medium concentrations,when the rod block length is short,the number of rearrangement decreases obviously.With the increase in rod block length,the increase of solvent size promotes the fusion of micelles and thus shows more rearrangement behavior.At a relatively high concentrations,the effect of solvent size strengthen the rearrangement behavior with the increase in block length.The lamellar and inverse lamellar trends of micelles appear in the long rod block system.At the high concentrations,the effect in increasing solvent size decreased with increasing length of rod block.In the short rod block system,rearrangement behavior enhances.The system occurs ordered/unordered transition that would occur with a larger rod block length.In the long rod block system,the cooperative growth mechanism of is inhibited.The results show that the increase in solvent size limits the ability to regulate the configuration entropy of coil block to some extent,especially at low concentrations of short rod block and high concentrations of long rod block.In contrast,in the systems with high concentration of short rod block length and low concentration of long rod block length,the limitation of solvent size makes rich structure behavior under the influence of interfacial energy.