Self-assembly Behavior Of Nanomaterials With Different Dimensions At The Water-oil Interface

The liquid-liquid interface provides a broad platform for nanomaterials with various sizes and shapes to prepare the nanocomposites.The polymer is dissolved in the oil phase,the nanomaterials are dispersed in the aqueous phase,such as the polymer and the nanomaterials exist electrostatic,hydrogen bonds and other interactions,through interface assembly,can be prepared with electrical,optical,magnetic and other properties nanocomposites.The size effect of nanomaterials is one of the key factors that affect the microstructure and performance of the prepared nanocomposite.In this thesis,heterogeneous nanomaterials(such as zero-dimensional carbon quantum dots(CQDs),one-dimensional cellulose nanocrystals(CNCs),two-dimensional graphene oxide sheets(GOs))assembled with polymers,studied the self-assembly behavior of nanomaterials with different dimensions at the water-oil interface.The main progress and results are as follows:1.The discovery of assembly of zero-dimensional carboxylated carbon quantum dots(c-CQDs)and polystyrene-b-poly(2-vinylpyridine)(PS-b-P2VP)block copolymer at the water-toluene interface:The pH of the aqueous phase and the molecular weight of PS-b-P2VP have an important effect on the interfacial tension and assembled microstructure.With the pH decreasing,the protonation degree of the P2VP block increases,more P2VP blocks are immersed in water,and the interaction degree between the P2VP block and c-CQD increases.The extension of the PVP block into the aqueous phase increases the packing density of the PS block at the interface,which reflects in the modulus of the assemblies at the interface where marked increasing.Similarly,under the same situation,an increase in the molecular weight of the polymer also leads to an increase in the rheological modulus.By observing the micro structure of the assemblies transferred to the solid substrate,it is found that the assembly of CQDs and PS-b-P2VP at interface can form a microspherical structure at lower pH.As the pH increases,the tendency of orientation of the assembled spherical structure appears.This work demonstrates that nanoparticles can be used to manipulate the block copolymer interface potential to assemble the specific structure.2.The research on the interface assembly of one-dimensional rod-shaped cellulose nanocrystals(CNC)and functionalized polysilsesquioxane(POSS-NH₂)through Langmuir-Blodgett(LB)technology found that:CNC and POSS-NH₂ are randomly adsorbed at the interface in the long axis direction through electrostatic interaction,and a single-layer CNC-POSS-NH₂ assembly membrane is formed.Adjusting the moving speed of the Langmuir trough barriers can adjust the microstructure of the interface assembly membrane.The smaller the extrusion speed,the more stable the extrusion force of the nanoparticles at the interface,and the higher orientation of the assembled structure.The higher the extrusion speed,the rearrangement of nanoparticles is limited,forming a random arrangement of assembled structures.The evolution of the assembly structure is also reflected in the change of the ?-A isothermal curve.When the nanoparticles start to rearrange at the interface,the ?-A isothermal curve has an inflection point,and then the?-A isothermal curve continues to increase linearly with the nanoparticle rearrangement.3.The study on the self-assembly of two-dimensional graphene oxide(GO)and amino-terminated polystyrene(PS-NH₂)at the water/toluene interface found that:using GOs diffused in water phase assembled with PS-NH₂ dissolved in toluene phase can form GO-surfactants(GOSs)to decrease the interfacial tension.It was found that the smaller the GO size,the lower the interfacial tension,and the faster interfacial tension decreasing rate.The difference of the interfacial tension decreased rate is related to the diffusion rate of the GO to the interface,the degree of functionalization relative to GOs specific surface area,and the in-plane motion of GOs to accommodate more GOs effectively cover the interface.The pH of aqueous phase affects the assembly strength and stability of GOs at the interface by affecting the degree of dissociation of functional groups.When the assembly strength of GO and PS-NH₂ at the interface increasing at the lower pH,the interface can be completely covered by GOS,which can form the jamming phenomenon.And through rheological tests,it is found that the solid-like film formed by small-size GOs at the interface has a higher elastic modulus,which can better stabilize the non-equilibrium droplet,and maintain the non-spherical droplet structure for a long time.4.Using CQDs/CNCs mixed nanoparticles surfactants to stabilize Pickering emulsion and prepare functional porous materials.The stability,droplet size and size distribution of Pickering emulsions,as well as the pore diameter of porous materials prepared by freeze-drying all depend to the pH of the aqueous phase,molecular weight and concentration of polymers,and the ratio of CQDs to CNCs.The pore size has the consistent law as the droplet size of the emulsion.The smaller the pH,the smaller the molecular weight of the polymer,the smaller the emulsion droplet size and the pore diameter of the porous material,and the more uniform the size distribution.And the better the structural stability of the prepared porous material,the greater the electron mobility.This work demonstrates the application potential of nanoparticle interface self-assembly materials.