| Amphiphilic polymers can form various aggregate structures with different morphologies through self-assembly,such as micelles,vesicles and inverse phase structures in solutions,ordered columnar and lamellar structures in thin films,and dotted,ribbon-like and planar aggregate structures at the gas/liquid interface.These aggregate structures have unique properties and a wide range of applications in different fields.However,the adsorption and selfassembly of amphiphilic polymers at the liquid/liquid interface have been relatively less explored.The large and planar liquid/liquid interface is a special place for assembly and reaction.It has been widely used for the synthesis and assembly of low-dimensional,especially one-dimensional(1D)and two-dimensional(2D)functional nanostructures due to the interfacial confinement effect and the feature that reactants with different solubilities can be dispersed into two phases.Although the adsorption and self-assembly behaviors of some amphiphilic polymers,especially block copolymers,at the liquid/liquid interface have also been investigated,the studies are relatively less and not comprehensive enough,and further studies are still necessary.For this purpose,we have selected the two systems and obtained the following results.1.Temperature and molecular structure-dependent self-assembly of PS-b-PEO at the liquid/liquid interfacePolystyrene-block-polyethylene oxide(PS-b-PEO)was dissolved in chloroform at first,and then the solution was covered with pure water to form a flat liquid/liquid interface.Then,copper acetate aqueous solution was added dropwise to the pure water.After 24 h,films formed at the liquid/liquid interface.It was found that spontaneous interfacial emulsification occurred when Cu2+ aqueous solution was added to water at 28℃.The PS-b-PEOs with different PS:PEO ratios self-assembled into foam structures composed of hollow spheres,hierarchical structures composed of hollow spheres around hollow spheres,hollow spheres with layered walls,and Janus lamellar structures in sequence with increasing relative length of the PEO blocks.And Janus sheet structures with monolayers or stepped multilayers were formed through interfacial adsorption and assembly at lower temperatures,such as 18 and 8℃,respectively.In addition,the concentrations of PS-b-PEO and Cu2+ also affect the self-assembly behavior of the block copolymers and the aggregate morphologies.The formation mechanism of the aggregate structure under various conditions was analyzed from the viewpoint of the change of hydrophilicity of PEO blocks with temperature,the interaction between Cu2+ ions and the PEO blocks,the hydrophobic interaction between the PS blocks,and the influence of the relative length of the two blocks on the molecular packing.This study provides a reference for the assembly of multi-level nanostructures and the selection of emulsifiers.2.Assembly of P2VP and PS-b-P2VP composite helical nanowire arrays at the liquid/liquid interfaceTwo experimental methods were applied.The first one is directly covering method in which an aqueous solution of inorganic species covers a chloroform solution of the polymers to form a liquid/liquid interface;the second one is dropping method in which pure water covers a chloroform solution to form a liquid/liquid interface first,and then the aqueous solution containing inorganic species is added into the water phase dropwise.Helical nanowire arrays of atactic poly(2-vinylpyridine)(P2VP)or polystyrene-block-poly(2-vinylpyridine)(PS-bP2VP)with inorganic components such as HAuCl4 were successfully obtained by finely regulating the experimental conditions without the addition of chiral inducers.The formation of P2VP/HAuCl4 helices is the result of straightening of polymer chains by repulsive interactions between the protonated pyridine groups,hydrophobic interactions between polymer backbones,π-π interactions between pyridine groups,ordered stacking of the pyridine groups,and the interfacial confinement.The formation of helical wire arrays is induced by interfacial pressure that causes ordered orientation of the formed nanowires.The formation of the block copolymer helices is the result of the self-assembly of block copolymer molecules with chloroauric acid in the interfacial phase.They self-assemble into worm-like micelles with PS core and P2VP outer shell.The helical structure arises from the ordered stacking of the pyridine groups in the P2VP blocks.These results expand the scope of research on polymer self-assembly and the application of liquid/liquid interface fabrication techniques. |
