Study On Dielectric Relaxation Behavior Of Nanoparticle-Based Pickering Emulsions And Its Stabilizer Suspensions

Pickering emulsion is a kind of emulsion with solid particles as stabilizer.It has the advantages of excellent stability,biocompatibility,low toxicity and simple recovery.Therefore,it is widely used in food industry,biomedicine,interface catalysis and other fields.In this work,hydrophilic fumed nano-silica and cellulose nanocrystals(CNC)were selected as emulsion stabilizers to prepare O/W Pickering emulsions.The dielectric relaxation behavior of the emulsion system was measured by dielectric relaxation spectroscopy.In order to accurately explore the dielectric relaxation behavior of the emulsion system,the fumed silica/water and CNC/water suspensions dielectric measurements were carried out at the same time.On the basis of understanding the dielectric relaxation behavior of the suspension,the dielectric relaxation behavior of the emulsion system is explored.The specific results obtained are as follows:(1)Two dielectric relaxation behaviors were observed in the fumed silica/water suspension,and it was found that with the increase of the particle concentration,the existing form of the particles in the suspension gradually changed from a single aggregate to a cluster structure,and the transition concentration was 0.6%.The droplet size of fumed silica-based Pickering emulsion decreases with the increase of solid particle concentration,and the stability gradually increases.Three dielectric relaxation behaviors were observed around the frequency of 3.0×10~3 Hz,1.5×10~4 Hz and 2.0×10~5 Hz in the emulsion system,it is inferred that the three relaxations from low frequency to high frequency in the emulsion system are respectively derived from the oil phase/silica layer interfacial polarization of interfaces,counter ion polarization and interfacial polarization of silica layer/aqueous phase interface.Through the analysis of the characteristic parameters of the low-frequency relaxation characteristic of the emulsion,it is obtained that the relaxation strength and the variation trend of the emulsion droplet size with the solid particle concentration are basically the same,and the particle aggregates are closely arranged at the oil phase interface.(2)Three dielectric relaxation behaviors were observed in the CNC/water suspension,and it was found that the rod-shaped CNC particles tended to align perpendicular to the direction of the electric field on the length scale under the action of an applied electric field.The particle size of CNC-based Pickering emulsion decreases with the increase of solid particle concentration,and the stability gradually increases.Three dielectric relaxation behaviors were observed around 6.0×10~4 Hz,6.8×10~5 Hz and 4.0×10~6 Hz in the CNC-based Pickering emulsion,the three relaxation behaviors presented on the dielectric relaxation spectrum from low frequency to high frequency are sequentially derived from the counter ion polarization mechanism of ions migrating along the surface on the diameter scale of the CNC particles,and the interfacial polarization mechanism at the oil phase/CNC particle interface and Maxwell-Wagner interface polarization mechanism of the CNC/water interface.Through the analysis of the characteristic parameters of intermediate frequency relaxation and the emulsion droplet size of the emulsion,it is found that the structure of CNC particles and silica particles at the oil phase interface is different.The former forms a network structure at the oil phase interface,while the latter has spherical aggregates closely arranged at the oil phase interface,the ability of CNC particles to stabilize the emulsion is superior to that of fumed silica particles.For the first time,dielectric spectroscopy has been applied to Pickering emulsions to investigate their properties.The adsorption structure of fumed silica and CNC particles at the oil-phase interface was obtained by analyzing the dielectric relaxation behavior of the emulsion system obtained by dielectric spectroscopy.This study demonstrates that dielectric spectroscopy can provide valuable information about Pickering emulsion systems,and lays a theoretical and experimental foundation for in-depth research of the mechanism of storage and release of active substances in Pickering emulsions using this method.