Solution And Surface Self-Assembly Of Amphiphilic Block Copolymers

The self-assembly of block copolymers is an important way to obtain novel nanomaterials,and it plays an important role in the fields biomedicine,electronic information,energy and catalysis.In recent decades,both theoretical and experimental researches of block copolymer self-asembly have achieved promising progress,especially in terms of micellar structures and phase structures in solution self-assembly and bulk self-assembly（mainly including the self-assembly method,path,mechanism and structures of block copolymers）.However,the complicated chemical synthesis and tedious assembly process greatly limit the development of matericals,and the rapid formation process is not conductive to our research on the self-assembly mechanism.It is still far away enough for us to understand the self-assembly of block copolymers in methods,paths,mechanisms,structures,etc.Further development and innovation still require our exploration and efforts to enable them to exert greater application.Thus,this paper mainly gave a systematic summary of the methods,pathways,morphologies and mechanism of the self-assembly of block copolymers.This paper was divided into seven chapters.The first chapter was a review about the research and development of block copolymer self-assembly,including the research work and achievements of self-assembly methods,formation mechanism and structural properties.The second chapter was the synthesis of block copolymers,using living anionic polymerization to synthesize polymers with lower polydispersity.The third to the sixth chaper were the self-assembly method design and structural characteristics of block copolymers,including micellar structures and complex structures in dilute solution,phase behavior in concentrated solution and micellar structures on a surface.The last chapter was the summaries and prospects.The contents and conclusions of this paper were shown as follow:1.Synthesis of block copolymersThe synthesis of amphiphilic block copolymers was described in detail by living anion polymerization.A series of block copolymers with different molecular weights,including PS-b-P2VP、PS-b-PMMA、PB-b-P2VP、PI-b-P2VP和PS-b-PB-b-P2VP,were synthesized in a glove box in an argon atmosphere at low temperature with tetrahydrofuran as the polymerization solvent system and sec-butyllithium as the initiator by changing the component of the added monomers and adjusting the amount of initiators and monomers.The chemical composition,degree of polymerization and polydispersity of polymers were confirmed.Moreover,the polydispersity index of diblock copolymers was less than 1.12.For PS-b-P2VP,the block ratio was between0.2 and 37（P2VP/PS）,and the degree of polymerization of PS is in the range of 80 to1130,and P2VP is in the range of 300 to 3300.2.Formation of low-curvature micellar structures of block copolymers by solution self-assemblyBlock copolymers can self-assemble into different micellar structures in selective solvents.For PS-b-P2VP,we obtained spherical micelles,worm-like micelles,lamelles,toroids and vesicles by tuning the block ratios,which indicated that the block ratios of core blocks and corona blocks had a strong influence on the formation of micellar morphologies.Moreover,we systematically investigated the self-assembly behaviors of PS-b-PB-b-P2VP triblock copolymers in acetone and cyclohexane mixed solvents.By chaning the volume ratio of acetone and cyclohexane,we successfully obtained disk arrays,disk clusters,single disk micelle and perforated disk-like micelles.However,if we replaced the mixted solvents to isopropanol and cyclohexane,spherical micelles were obtained across the full range of mixed isopropanol/cyclohexane solvents.The aboved results showed that the formation of disk-like micelles was mainly determined by the distinct selectivity of acetone and cyclohexane towards the PS,PB and P2VP blocks.Furthermore,θsolvents（acetone and cyclohexane）for the PS block and the cosolvency effect in mixted solvents were the key factors in the formation of low-curvature disk-like micelles.3.Crystallization and phase transition behavior of block copolymersWe studied the concentration and temperature dependence of the packing structures of spherical micelles of a PI-b-P2VP diblock copolymer in toluene using synchrotron radiation small angle X-ray scattering（SR-SAXS）and atomic force microscopy（AFM）techniques.Randomly packed spherical micelles were detected in dilute solution.While in concentrated solutions,the coherence effect between the spherical micelles increased,and face centered cubic（FCC）,body centered cubic（BCC）mixed crystal structures,and pure BCC crystal structures were observed with an increase in concentration.In-situ SAXS experiments on the FCC/BCC mixed crystal structures revealed a novel FCC/BCC→BCC→Disorder→BCC phase behavior during the thermal annealing process.The results demonstrated that the BCC phase was apparently more stable than the FCC phase in the current sphere-packing system,and FCC/BCC was a metastable state.4.Sequential self-assembly of block copolymer micelles on surfacesWe developed a solution-surface sequential self-assembly method for core-corona micelles,and obtained a series of complex nanostructures on a substrate.We found that PS₇₀₀-b-P2VP₉₆₀ spherical micelles with P2VP cores and PS corona formed in toluene were transformed into inverse spherical micelles when added into ethanol.While the spherical micelles that formed in toluene were transformed on a substrate sequentially into toroidal micelles by ethanol annealing,concentric toroidal micelles by cyclohexane annealing,and ring clusters upon annealing in ethanol solvent.This process was found in both diblock and triblock copolymer systems and appeared to be independent on the nature of the substrate and gravity.Thus,BCPs micelles with simple shapes could be further manipulated on a surface in a flexible fashion to constructed novel nanostructures.5.Co-assembly of block copolymer spherical micelles and inorganic nanoparticlesPS-b-P2VP spherical micelles and silica nanoparticles with uniform size were synthesized.Colloidal molecules of CO₂-type,SO₃-type and CH₄-type could be obtained by chaning the size of spherical micelles and silica nanoparticles.Moreover,colloidal superstructures,like one-dimentional nanochains,two-dimentional networks and three-dimentional stacking structures could be realized by tuning the number ratios of these two kinds of nanoparticles.The complex colloidal molecules and superstructures were self-assembled by the hydrogen bond interaction between P2VP coronas and the oxhydryl groups on the surface of silica nanoparticles.