Fabrication Of A Series Of Primary Aggregation Morphologies Of Block Copolymers At The Liquid/Liquid Interface

Block copolymers have abundant self-assembly behaviors,which can form a variety of ordered structures with different morphologies,including spherical and cylindrical micelles,vesicles,hexagonal packed cylindrical structures,layered structures,inverse mesophase structures,nanodots,nanobelts,honeycomb structures,etc.Due to their unique physical and chemical properties,they have broad applications in the fields of drug transport and release,separation membranes,photonic crystals,template synthesis,and catalysis,etc.The self-assembly of block copolymers have attracted extensive attention.During the assembly process,the molecular structures of the block copolymers,microenvironmenst,assembly approaches and other factors will affect the self-assembly behavior and the final aggregated structures.The self-assembly behavior of block copolymers in solution,in films,and at the air/liquid interface has been extensively and deeply studied.However,there are few studies on the self-assembly behavior of block copolymers at the liquid/liquid interface,and systematic studies are even more rare.So,in order to systematically investigate the self-assembly behavior of block copolymers at the liquid/liquid interface,and to broaden the morphology and application of the self-assembled aggregated structures formed by block copolymers,our research group has carried out a large number of work in recent years.In this paper,on the basis of previous works in our laboratory,a series of polystyrene-block-poly(2-vinylpyridine)(PS-b-P2VP)/inorganic primary aggregated structures were obtained by using an improved liquid/liquid interface self-assembly approach.The influence of molecular structure of the block copolymers,the types of the inorganic components,the dripping way of the inorganic components to the water phase,the dripping rates,etc.on the self-assembly behavior of the block copolymers,and on morphology of the obtained aggregate structures have been investigated,and the formation mechanism of these nanostructures has been discussed based on the intermolecular interactions.Specifically,this paper has carried out the following two parts:1.Formation of a series of primary aggregated structures of PS-b-P2VP/chloroauric acidPS-b-P2VP was first dissolved in chloroform,and a flat liquid/liquid interface was constructed by covering pure water on the organic solution.Then chloroauric acid aqueous solution was added dropwise into the water phase.Thin films were rapidly formed at the liquid/liquid interface.The thin films were transferred to different substrates,the structure,morphology and composition of these thin films were meticulously characterized,and the formation mechanism was discussed in depth.It was found that nanodot/nanostrands dotted films,honeycomb-like films and foam-like films were sequentially formed at the liquid/liquid interface with increasing the amount of the chloroauric acid aqueous solution.It was demonstrated that the addition of chloroauric acid and the protonation of the P2VP block are the keys for the formation of the ordered films.In order to reduce the interfacial tension,PS-b-P2VP will adsorb at the interface as soon as the formation of the flat liquid/liquid interface.However,the adsorption layer is unstable.With the addition of chloroauric acid solution into the water phase,the P2VP block in PS-b-P2VP will be protonated by combining with H+ ions,which makes PS-b-P2VP stably adsorbed at the liquid/liquid interface and self-assemble into ordered nanostructures through combining with AuCl4-further.It was illuminated that the formation mechanism of nanodot/nanostrand dotted films is different from that of honeycomb and foam films.When less chloroauric acid solution was added into the water phase,AuCl4-combined with the protonated PS-b-P2VP in a controllable and slow way.Nucleation and growth occurred gradually,leading to the formation of the nanodots/nanobelts dotted films.The size of the nanodots and nanostrands can be regulated by changing the dripping methods and dripping rates of chloroauric acid aqueous solution,and by post-treatment with different pH hydrochloric acid solutions.When increasing the amount of the chloroauric acid solution,a water flow to the interface was formed due to the diffusion of chloroauric acid,which makes the interface spontaneously emulsification,resulting in the appearance of small water holes.The block copolymer molecules and chloroauric acid self-assemble around the water hole spontaneously,leading to the formation of the regular honeycomb-like films.The size of the honeycomb structure can be further regulated by changing the volume of chloroauric acid added.When the volume of chloroauric acid solution added into the water phase increased further,the complete interfacial spontaneous emulsification occurred,and small emulsion droplets formed.The block copolymer molecules and the inorganic components self-assemble around these droplets to form microcapsules.The formed microcapsules are squeezed and stacked on each other at the interface to form a foam-like film finally.2.Large-area nanodots arrays formed by PS-b-P2VP and heteropolyacids or metal ionsIn order to further understand the self-assembly behavior of PS-b-P2VP at the liquid/liquid interface,and understand the formation mechanism of nanodots arrays,heteropolyacids(phosphotungstic acid and phosphomolybdic acid)and transition metal ions were selected to induce the formation of nanodots dotted films.The results show that quasi-hexagonally stacked nanodots dotted films are formed at the liquid/liquid interface,regardless of adding heteropolyacids or transition metal ions to the water phase.This indicates that this is a general method to form nanodots dotted films at the liquid/liquid interface.In addition to protonation,the coordination interaction between metal ions and the P2VP blocks also enables the stable adsorption of PS-b-P2VP at the liquid/liquid interface and induces self-assembly.This further indicates that the stable adsorption of block copolymers at the interface and the interaction between inorganic components and block copolymers are the keys to the formation of nanodots dotted structures.