Liquid/liquid Interface Mass Transfer-assisted Self-assembly In Solutions

In recent years,organized molecular assemblies(supramolecules)and nanoparticle assemblies(superstructures and superlattices,etc.)with various properties and functions have attracted widespread attention,and have been widely used in many fields,such as fabrication of advanced materials,drug delivery,catalysis,sensing and photovoltaic devices.In general,two strategies,i.e.self-assembly and template-directed assembly have been exploited to fabricate ordered molecular and nanoparticular assemblies,and self-assembly is more commonly used,in which weak interactions between molecules or between ligands of nanoparticles,such as electrostatic interactions,hydrogen bonds,coordination bonds,?-? interactions,and hydrophobic(solvophobic)effect are usually utilized.A variety of self-assembly methods have been developed,for example,mixing solvents in solutions,solvent evaporation in solutions and thin films(spin coating and casting films),adsorption and self-assembly at interfaces(air/liquid,liquid/liquid and liquid/solid interfaces).In our previous works,the liquid/liquid interface phase transfer-assisted self-assembly method has been developed and used to fabricate amphiphilic polymer molecules and metal ions in solutions into organized aggregates.In this method,a planar liquid/liquid interface between the bottom phase of a DMF/chloroform mixed solutionof polymer and the upper phase of an aqueous solution of metal salt was constructed.Due to Ouzo effect,phase transfer occurred across the interface and spontaneous emulsification process took place to form an O/W emulsion in the upper phase and a W/O emulsion in the lower phase.In this way,the components in the original two phases were in the same emulsion,combined with each other,and self-assembled into ordered aggregates.This method was extended in this work to fabricate organized aggregates of amphiphilic block copolymer/organic molecule,superstructures of metal nanoparticle/ligands,and lamellar nanosheets of amphiphilic molecules/metal ions.The main research results are as follows:1.Regulation of the aggregate morphologies of amphiphilic block copolymer with organic moleculesA DMF/CHCl3 mixed solution of polystyrene-b-polyacrylic acid(PS-b-PAA)was used as the bottom phase,and an aqueous solution of small organic molecules(such as diamines,dopamine and dye molecules)was used as the upper phase to form a liquid/liquid interface.Due to the phase transfer caused by the Ouzo effect,DMF droplets carried block copolymer molecules into the aqueous phase.The polymer molecules combined with small organic molecules by virtue of electrostatic interactions or hydrogen bonding,and assembled into aggregates with various morphologies,including long uniform nanowires,hollow spheres and foams,which corresponded to worm-like micelles,vesicles and aggregates of microcapsules,respectively.The influence of the molecular structure of organic molecules,especially the diamine molecules,on the formation of the aggregates was investigated and discussed,and the formation mechanism of these aggregates was analyzed.It is expected that this work can provide a reference for the construction of functional small molecule/block copolymer composite micro/nano structures.2.Assembly of noble metal nanoparticle superstructures and superlatticesA DMF/CHCl3 mixed solution of fatty amine was used as the bottom phase,and the freshly prepared gold or silver hydrosol was used as the upper phase to form a liquid/liquid interface.DMF brought the ligand molecules into the hydrosol through the phase transfer process across the interface.The ligands are then combined with the sol particles and assembled into various aggregated structures,including ellipsoidal and spherical superstructures composed of spherical nanoparticles,network structures composed of spherical nanoparticles and nanorods,and hierarchical structures composed of nanorods.The chain length of the fatty amines,the size of the colloidal particles,and even the type and concentration of the reducing agent during the preparation of the sol exerted great influences on the morphology and structure of the aggregates.The satellite-core network structure of Au nanoparticle/Ag nanoparticle was obtained by further assembly.These structures exhibited good heterogeneous catalytic performance and SERS property.This work provides a facile technique for the assembly of nanoparticle assemblies.3.Assembly of lamellar nanosheets of amphiphilic moleculesThe techniques of assembling amphiphilic molecules to lamellar structures include Langmuir monolayer technique and LB deposition,layer-by-layer deposition and self-assembly monolayer technique.In this part,the liquid/liquid interface phase transfer-assisted self-assembly method was further extended to fabricate lamellar structures of amphiphilic molecules.A mixed DMF/chloroform solution of amphiphilic molecules(such as 10,12-pentacosadiynoic acid,docosandioic acid,stearic acid,etc.)was used as the bottom phase,and an aqueous solution of metal ions(such as Zn2+ and Cu2+)was used as the upper phase to construct a liquid/liquid interface.By virtue of phase transfer across the interface,the amphiphilic molecules entered into the aqueous phase and combined with the metal ions to form a nanosheet with a lamellar structure through a self-assembly process.It was found that nanosheets are composed of an even number of monolayers,with two outer surfaces of the carboxyl/metal ion coordination layers.Hydrophobic effect and coordination effect are the driving forces for the nanosheet formation.At the same time,we also attempted to drop the DMF solution of the amphiphilic molecules directly on the surface of the aqueous solution,and found that nanosheets with a lamellar structure also appeared at the air/liquid interface.However,these nanosheets consisted of an odd number of monolayers.One outer surface is composed of a carboxyl/metal ion coordination layer;and another outer surface is composed of a lipid chain layer.suggesting that the nanosheet is a Janus one.The formation of such nanosheets is the result of the simultaneous spreading and diffusing of the DMF solution.This method is significantly different from the traditional Langmuir monolayer technique which requires that the spreading solution is immiscible with water.Therefore,it can be considered that this method is an extension of the traditional Langmuir monolayer technique.By further treatment,metal ions in the lamella can be transformed into metal sulfides,such as zinc sulfide nanosheets.This also provides a way to fabricate semiconductor nanostructures in a confined environment.