Behavioral Research Of The Nanoparticle Self-assembly At Oil/water Interface

The self-assembly of nanoparticles and polymers at the liquid/liquid interface can not only realize the preparation of functional polymer nanocomposites,but also realize the structure of liquid,showing a broad application prospect in all liquid printing,catalysis,energy storage,biomedicine and other fields.It is of great theoretical significance to deeply study the evolution of microstructure and properties of assemblies in the process of assembly for further understanding the structure performance relationship and guiding the design of advanced self-assembly system.In this paper,cellulose nanocrystals(CNCs),silicon dioxide nanoparticles(SiO2)and iron oxide nanoparticles(Fe3O4)were self-assembled with polymer surfactants at the liquid/liquid interface,respectively.The microstructure and performance evolution of the three self-assembled systems were studied in situ by adjusting the pH value of the solution,the concentration of particles and surfactants,and the molecular weight of the polymer.The formation conditions and mechanism of structured droplets were elucidated.The main achievements are as follows:Firstly,we probed the microscopic assembly structure of cellular nanocrystals surfactants(CNCSs)at the interface by means of in-situ AFM.The characterization results prove that the surface coverage is much higher and the assembly structure is more stable at lower pH due to strong electrostatic attractive interaction between the negatively charged particles and positively charged surfactants.The force-distance curves also indicate that the particles formed at lower pH are stably anchored at the interface.Upon the inplane compressive force during the evaporation of the oil droplet,the nanoparticle-surfactants formed at higher pH will be rearranged until perpendicular to the interface.Subsequently,we investigated the interparticle interaction varying with the size of the particles and molecular weight of the surfactants by analyzing the reduction rate of the interfacial tension.The stronger the interaction attractive force,the faster the rearrangement rate.The experimental results show that larger nanoparticles and high polymer molecular weights are beneficial to enhance the capillary attraction between the nanoparticle active agents and accelerate their rearrangement speed at the interface,and the in-situ AFM and TEM data also show that particles will form denser structure at the interface.By mixing large particles and small particles together,we can successfully obtain structure droplets.Finally,we combined the microscopic characterization,experimental and simulation results to study the paramagnetic to ferromagnetic transition mechanism of functionalized ferromagnetic liquid droplets.By studying the motion process of ferromagnetic droplets formed at different conditions under rotating and gradient magnetic fields,and characterizing the microscopic assembly structure with AFM and TEM,we revealed that the magnetic particles form the short-range order structure at the jamming interface.The higher pH would weaken the remanence of the ferromagnetic liquid droplet by decreasing the interfacial activity of the surfactants and increasing the electrostatic repulsion among the magnetic particles at the interface.By comparing the relationship between the droplet equilibrium angular velocity and the droplet size of the experimental and simulated data,it is found that the dispersed particles can also attribute to the total magnetic field intensity of the droplet.