Polyoxometalate Induced Self-assembly Of Block Copolymer

Block copolymers(BCPs)self-assemble into versatile nanoscale morphologies,which is ideal templates to assemble nano-additives to fabricate nanoscale structure controllable hybrid materials with great application potential of catalysis,photics,electronic,magnetism and biology.Moreover,introducted nano-additives could controllable tune the structures and properties of BCP composites by inducing its morphological transition.The electrostatic cohesion between ionic compounds as nano-additives and BCPs leads to new nanostructure features that are unobtainable in uncharged systems can be realized.The related works mostly focus on the block copolymer systems doped by lithium ions instead of the multivalent ions that are preferable to achieving a strong electrostatic cohesion.Polyoxometalates(POMs)comprise a large class of molecular well-defined metal-oxide clusters,which have been widely used as typical inorganic macroions due to their abundant negative charges from 2 to more than 40 and nanoscale size from 0.5 to 6 nm.The sizes of POMs are smaller than the radius of gyration of common polymers,which may offer a small entropic penalty and facilitate POMs to enter a specific BCP domains as ultrasmall nano-additives.Among various BCP morphologies,the bicontinuous phase is particular appealing,which is comprised of two separated and interweaved domains extending throughout the material,which are highly desirable for a wide range of applications from nanoporous materials,solid polymer electrolytes to photovoltaic films in solar cells.However,the bicontinuous phase occupies a narrow window?3%in the phase diagram of block copolymers,which greatly limits its fabrication.Therefore,how to easily obtain a bicontinuous structure or broaden the range of bicontinuous phase is challenging in BCP self-assembly.The network structure of POM/BCP assembly in solution is similar to bitontinuous structure.Moreover,the high interfacial energy that arise from bicontinuous structure could be offset by high enthpy interaction.Hence,in this dissertation,we used POMs as nano-additives to tune the self-assembly of BCPs through non-covalent interaction.Core fusion of spherical micelles is observed and the facile method to fabricate bicontinuous structure is developed with tunable thermal and viscoelastic properties and proton conductivity.First,we developed a new method to fabricate micelles in solution through the hydrogen interaction between BCPs and pre-modified POMs.In this method,we endow a representative POM,(NH4)42[Mo132O372(CH3COO)30(H2O)72](M0132)with abundant carboxyphenyl groups on the periphery by electrostatic modification.Then modified M0132(C-Mo)could co-assemble with poly(styrene-block-4-vinylpyridine)(PS-b-P4VP)to form hybrid micelles through hydrogen bonding.IR and 1H NMR spectra indicate the existence of hydrogen bonding.Meanwhile,the DLS,AFM and TEM results reveal a high stable spherical micells with PS core and C-Mo/P4VP corona.Interestingly,the fusion of micellar cores are observed,which is ascribed to the inability to prevent the inter-micelle hydrogen bonding interaction at low PS density.The core fusion micelles can be readily adjusted by varying the length of PS blocks.Moreover,electrostatic modification of POMs is generally suitable for the whole anionic POM system and the modified groups can be extended to those that can provide other noncovalent interactions with BCP blocks,which is promising to create a large class of POM/BCP nanocomposites with tunable structures.Second,we present a facile and efficient approach to tune the BCP morphologies through electrostatic inducement,where commercial inorganic H4SiW12O40(SiW)macroions are used as electrostatic additives to protonate the pyridine groups of PS-b-P4VP.The XPS spectra confirm the existence of electrostatic interaction in SiW/PS-b-P4VP films.Meanwhile,the SAXS and TEM results reveal the bicontinuous structure of transparent and free-standing SiW/PS-b-P4VP films are tansformed from hexangonally packed cylindrical structure with SiW loading.Moreover,the charge number of POM and the regularity of cylindrical BCP structures show no effects on the morphological transition.Furthermore,the incorporated SiW clusters can not only act as electrostatic crosslinkers to reduce the free volume and tune the Tg of P4VP,but also can increase the storage moduli of nanocomposite as reinforcing nano-additives.These results provide new insights into understanding the self-assemble behavior of complex polymer systems upon loading nanoscale macroions.In addition,the easy fabrication of bicontinuous BCP structures may broaden the potential applications of BCP-based nanocomposites,especially in transporting membranes and solid electrolyte materials.Third,based on previous facile and efficient approach to tune the BCP morphologies through electrostatic inducement,we further explore electrostatic tuning on BCPs with lamellar structure.Similarly,inorganic SiW macroions are used as electrostatic additives to protonate the pyridine groups of poly(styrene-block-2-vinylpyridine)(PS-b-P2VP)to fabricate transparent and free-standing SiW/PS-b-P2VP films.The XPS spectra confirm the existence of electrostatic interaction in SiW/PS-b-P2VP films.Meanwhile,the SAXS and TEM results reveal the bicontinuous structure of SiW/PS-b-P2VP films are tansformed from regular lamellar structure with SiW loading.Moreover,the charge number of POM and the d-spacing of regular lamellar BCP structures show no effects on the morphological transition.Besides that,disordered bicontinuous structures are presumed to be derived from the core fusion of SiW/PS-b-P2VP micelles during the casting procedure to fabricate SiW/PS-b-P2VP bulk films,which is observed from its solution TEM photographs.The core fusion results from the inter-micelle electrostatic interaction,which is similar to the core fusion scheme of C-Mo/PS-b-P4VP.The introduced SiW,as high proton conductor,facilitates the proton conductivity of SiW/PS-b-P2VP bulk films and the proton conductivitie reaches to 0.1 mS/cm at room temperature.Moreover,the SiW/PS-b-P2VP bulk films maintain mechanical stiffness during proton conductive test and the storage moduli and loss moduli reach to 10 MPa and 1 MPa,respectively.These results not only provide new understanding on nanoscale self-assemble behaviour of ionic/polymer system,but also offer potential idea to fabricate functional polymer materials.In conclusion,in this thesis we use POM to tune the self-assembly of BCP in solution and bulk through the non-covalent interaction between POMs and BCPs.In solution,the uniform and stable spherical micelles are fabricated and the core fusion of solution micelles are observed.Moreover,the modified groups can be extended to other POMs that can provide other noncovalent interactions with BCP blocks.In bulk,POMs tuning the morphological transition of BCPs from cylindrical and lamellar structure to bicontinuous structures through electrostatic interaction.This methold presented here is not only facile and effective,but also expand the window of bicontinuous phase more then theoretical value.What's more,the micellar core fusion scheme provides a basis for the formation of bicontinuous structures.Meanwhile,the effects on thermal and viscoelastic properties due to POMs loading and proton conductivity and mechanical stiffness of POM/BCP bulk film are exploried.The study about POM tuning self-assembly of BCPs provide new understanding on self-assemble behaviour of hybrid polymer system,and offer potential idea to fabricate functional hybrid polymer materials.