Research And Application Of Pickering Emulsion Based On Cellulose Nanocrystals

Pickering Emulsion is a new type of emulsion using solid particles as the surfactant to stabilize the oil-water interface.In recent years,it has received extensive attention from researchers and has been closely linked with people's daily lives due to its excellent stability,low toxicity,low foaming,and stimuli-responsive potential.The internal properties and stability of the emulsion system are affected by many factors,such as oil-water ratio,size and nature of the stable particles,salt concentration of the system,pH and etc.This inquiry has important implications for the use of Pickering emulsions in daily life.Previous researchers have systematically studied Pickering emulsions,but most of them use spherical nanoparticles.Studies have shown that the larger the aspect ratio of the particles,the more stable the emulsion formed,and the current exploration for the application of rod-like nanoparticles in emulsions is not enough.In recent years,rod-like nanoparticle cellulose nanocrystalline(CNC)has attracted extensive attention in the field of nanomaterials and nanotechnology.With the development of society,the problem of environmental pollution has become more and more intensified,and people's demand for renewable and sustainable materials is increasing.CNC is derived from extremely abundant organic cellulose in the natural world.It has many excellent characteristics,such as high aspect ratio,low density,high mechanical strength,and etc..It also has the advantages of renewable,degradable,and non-toxic.It is widely used in industry and daily life.Researchers have tried to use CNC as solid emulsifier to stabilize the oil-water interface and have develpoed Pickering emulsions with a high-stability structure,excavating its prospects for the application of emulsions.However,systematic research on the effect of preparation conditions on the state of emulsion is still lacking,such as pH,salt concentration,etc.,and these factors will play a key role in the production and application of emulsions.Therefore,CNC was selected as solid emulsifier in this paper,particle concentration,oil-water ratio,salt concentration,pH and other factors were changed,internal morphology evolution(droplet size,aggregation)of Pickering emulsion was examined.The effects were further characterized by rheology.At the same time,two incompatible polymer solutions were used as oil and water phase,and a polymer composite with excellent mechanical properties was prepared.The specific content and main results are as follows:(1)The preparation parameters of the emulsion was changed to explore the basic principles of emulsion.Common liquid paraffin is used as the oil phase,and the water phase is ordinary deionized water.The effects of the particle concentration,oil-water ratio,salt concentration,pH and the stirring rate and time during emulsion preparation were investigated.The change of the emulsion droplet size and adhesion between the droplets was measured by microscope and Laser Particle Sizer.The study found that:With the increased of the oil,emulsion droplets gradually became larger,and the size appeared monodisperse.Increasing CNC concentration,pH and NaCl concentration will make the size of droplets in the Pickering emulsion decrease until the critical value is reached.Emulsion stability has also improved;However,too much NaCl or emulsion system is over-acid or over-alkali is not conducive to the preparation and stability of the emulsion.(2)Internal structure of emulsion under different factors was further explored by rheological measurements.It was found that rheological properties of the emulsion will be the combined influence of droplets and particles.Changes in system can lead to agglomerations between particles-particles and droplets-droplets in the system,both of which will increase the viscosity and modulus of the system.A network structure will formed between the droplets because of the weak flocculation,which is beneficial to the stability of the emulsion.However,particles will united with each other to form an big floc when the flocculation inside the system is too strong,which is not conducive to the stability of emulsion.The rheological approach can be more intuitive to monitor the change of the internal network structure in the system.(3)PVA-water solution was used as water phase,and PCL-dichloromethane solution was used as oil phase,a composite material was prepared by Pickering emulsion template.The interfacial adhesion between the two phases was investigated by morphology observation,mechanical properties testing and etc.The results show that as the concentration of the polymer liquid increased,the interfacial tension of the two phases decreased.Two high-concentration liquid phase can be mixed together under high shear without CNC,and no demulsification occurs within a certain period of time.However,the interfacial of composite materials without CNC is loose,CNC can increase the interface between the two phases and improve the mechanical properties of the material.