SiO2纳米颗粒与聚氧乙烯对Pickering乳液的协同稳定作用简

研究了聚氧乙烯(PEO)与SiO2纳米颗粒对水/二甲苯体系Pickering乳液的协同稳定作用. 实验发现,PEO的存在减小了乳液液滴的平均直径,抑制了乳液的相反转,有效阻止了乳液的熟化,使乳液具有更好的稳定性. 进一步对纳米颗粒膜的流变性质进行研究,结果表明,PEO高分子促进了纳米颗粒形成更大尺寸的聚集结构,提高了其在界面上的吸附性,增强了颗粒膜的力学性能,在较小颗粒用量条件下使得Gibbs稳定性判据得到满足.

Stability Mechanisms of Pickering Emulsion Co-stabilized by Silica Nanoparticles and PEO

The Pickering emulsions with 65% water and 35% xylene system stabilized by silica nanoparticles or by both the particles and polyethylene oxide(PEO) additives were prepared. The emulsification was performed using a rotor-stator homogenizer under varied rotation speeds from 5000 r/min to 24000 r/min. The emulsion droplets were observed using an optical microscope, consequently, the droplet diameters vs. rotation speed and aging time were obtained. For most cases, W/O type emulsion was obtained. It is found that the mean diameter of water droplets decreases with increasing shear rate or shear duration. With the presence of PEO, the diameters of the droplets are significantly reduced and the phase inversion from W/O to W/O/W is prevented, which occurs in the system without PEO when prolong the shear duration. In addition, the coalescence of droplets is completely inhibited. To elucidate the ultrastability of the Pickering emulsion resulted from co-stabilization by silica nanoparticles and PEO, we study the rheological properties of the particle layers at the gas-liquid interface using the Langmuir trough equipped with a Wilhelmy plate. The silica nanoparticles were spreaded on the surface of either water or PEO water solution, consequently and the effect of PEO additives on particle layer properties was investigated. The results confirm that PEO additives can favor the trapping of particles at the water/xylene interface, due to the formation of larger size aggregates with the presence of PEO. Therefore, the particle layer has a higher compression modulus. The stronger mechanical property of the particle layer protects the water/xylene interface from rupture when exerted turbulent shearing, hence preventing the occurrence of phase inversion from W/O emulsion to the W/O/W one. Owing to the satisfaction of the Gibbs stability criterion, the coalescence of droplets is almost completely inhibited. The results demonstrate that the rheological properties of the liquid/liquid interface play an important role in the stability of Pickering emulsion.