Theoretical Study On Phase Behaviors And Rheological Properties Of Complex Block Copolymers

Simply structured and homogeneous macromolecular materials are falling short of the urgent demands of developing advanced materials with excellent properties,as the modern techniques are growing rapidly.Designing novel molecular structure or blending of the existing polymers have become the focus of obtaining advanced materials.It is possible to acquire new function materials,which has diversified sizes and shapes,by tuning molecular parameters such as molecular weight,molecular architecture,copolymer compostion and processing conditions such as temperature,external shear field,etc.The study on phase behaviors and rheological properties has close relationship with macromolecular materials' pattern formation and properties,which ultimately linked to the performance of these materials.Complex polymer systems not only provide people with novel materials capable of performing various purposes and possessing excellent properties,but also add extra parameters and conditions to confuse the material design.Therefore,theoretical study which is able to help people understand the governing factors of the behaviors of multicomponent polymer systems,assist in the designing of advanced materials.People are now paying more attention to the set up of appropriate theorectial methods to predict,design and control the process of obtaining ordered multiphase complex polymer systems.Till recently,there is still lack of a systematic description of the relation between complex polymer structure and property,composite modification,processing conditions.In this dissertation,we managed to give a primary answer to the previous questions by combining different theoretical methods,such as equilibrium thermodynamics and phase separation dynamics,etc.The link beween microscopic molecular structures and macroscopic properties and rheological behaviors enables us to study the phase behavior and mechanical properties of complex polymer systems.The results are presented in the following parts:complex block copolymers under external shear;phase separation dynamics and rheological properties of block copolymers;the effect of molecular structure and composition on Order-Disorder Transition temperation;prediction of miscibility and morphology of multicomponent polymer blends;self assembly of amphiphilic copolymers in dilute solutions.Chapter 1,gives the overview of the theoretical methods and research purposes.Chapter 2,external field effects and their resulting properties have long been studied in the frontier of condensed matter and macromolecular science.For instance, polymers can be oriented in the external flow field.We combine DSCFT scheme with variable cell shape method in the description of boundary conditions,and applied to the study of topological effect,such as differences between A/B blends and AB diblock,linear ABC and star ABC triblock copolymers,on the behavior of these copolymers under simple shear flow.After that,topologically different linear copolymers are treated under the oscillatory shear.The results are able to give the shearing conditions for the appearance of lamellae orientations such as Parallel, Perpendicular and Transverse.Chapter 3,one of the most important goals in the material research is to obtain macroscopic properties and rheological behaviors from known micro structures. There are few theoretical methods capable of predicting mechanical properties,yet the researches on the structure-property relation of block copolymers are still fancy. We obtain the stress-strain relations by introducing the deformation field into the DSCFT functions and sinle chain propagator q(r,s).Therefore,the topological information is naturally put into the calculation which enables the study of the relation between micro structures and rheological properties.At first,we give the stress distribution of triblock copolymers.Then,storage modulus G',which is sensitive to the possible structure change,is calculated by linear fit of stress-strain curves,and is used to compare the differences between AB diblock and A/B blend in the phase separation mechanism.Finally,the DSCFT scheme is applied to distinguishing of one step,two step separation mechanism in linear and star ABC triblock copolymers.Chapter 4,the study on ODT and OOT of block copolymers is able to help to the design of processing conditions in the industry.Variable cell shape DSCFT proposed in this dissertation not only take into account the relation between storage modulus G' and interaction parameters x~N,but topological and polydispersity effects on the ODT of block copolymers.Chapter 5,polymer blends,which exhibit outstanding microstructure and excellent properties,have become more and more important in the advanced material design.In this chapter,Flory-Huggins mean field theory and DSCFT scheme is used to investigate the component and topological structure effects on the miscibility and equilibrium morphologies of polymer blends.Miscibility of ternary blend systems such as PP/Elastomer/Plastic are predicted and verified by previous experimental results.Possible advices are given for the improvement of the miscibility.Then, DSCFT scheme is applied to the study of pattern formation of PP multiphase systems.We give detailed description of the particular morphologies and conditions for these morphologies to occur.The simulation results show that the composition of the copolymers have fundamental impact on the pattern formation of the blend system.Chapter 6,polymer and solvent mixtures can be regarded as another type of multicomponent blends,which had covered areas of paints,coatings,adhesives and biodegradable materials.In this chapter,SCFT is applied to study self-assembly of amphiphilic block copolymers in selective solvents.The polydispersity effect of "crew-cut" AB diblock copolymers and different architectures such as star,comb-coil on the self-assembled morphologies in solution has been investigated.The theoretical results provide useful guidance to the synthesis and preparation of various types of aggregates in dilute solutions.