Use organosilicon surfactants
Due to the fundamental differences between the properties of hydrocarbon polymers and silicone polymers, traditional surfactants cannot effectively stabilize silicone oil emulsions. Therefore silicone surfactant based on silicone oil soluble main chain and hydrophilic modified group can replace hydrocarbon polymer to prepare silicone oil emulsion. These surfactants are obtained by grafting different hydrophilic groups onto organosilicone polymers. These surfactants were prepared from two types of silicones, linear copolymers and cyclic polymers. The surfactant can be well adsorbed on the surface of the silicone oil droplets because the main chain of the silicone oil has a high affinity with the silicone oil. Hydrophilic surfactants can extend into the aqueous phase to form interfacial films. These two interactions are beneficial to the stability of silicone oil emulsion.
The formation of the surfactant interface film between the two liquid phases contributes to the formation of a uniform emulsion with a diameter of 1.0 μm. The interfacial membrane inhibits the agglomeration between the droplets, thus improving the stability of the emulsion.
The concentration of surfactant has a significant effect on droplet size and size distribution. At low surfactant concentration, surfactant molecules are not enough to reduce the interfacial tension, forming large size, wide size distribution of emulsion, due to the increase of surfactant concentration leads to a significant decrease in interfacial tension, so that large droplets are more likely to break into small droplets. In addition, reducing the droplet size of the emulsion is very useful to improve the homogeneity and stability of the emulsion.
Add stabilizer
At a certain concentration, hydroxypropyl methyl cellulose (HPMC) stabilizer was added to obtain a relatively uniform emulsion. At a certain concentration, the droplet size of silicone oil increased with the increase of the molecular weight of HPMC (Fig. 5), which indicated that the viscosity of the aqueous phase decreased with the decrease of the molecular weight of HPMC, leading to the dispersion of the system easily. Increased stability of the emulsion.
Use of electrolytic silica suspensions
Silicone oil emulsion can effectively stabilize the use of electrolysis suspended silica particles. Electrolytic silica particles are strongly adsorbed on the surface of silicon oil droplets due to electrostatic action. With the increase of ionic strength of silica suspension, the interaction between the emulsion droplets and the electrolytic silica particles is enhanced, which prevents the release of water in the emulsion, and plays an important role in improving the stability of the emulsion.
Use of polar silicone oil
Polar silicone oil is a polydimethylsiloxane (PDMS) oligomer synthesized by the reaction of a circular chain of PDMS and a short linear substance with a high density polar hydroxyl group (OH). Due to hydrogen bonding, the linearly OH chain surfactant prefered to adsorb on the oil/water interface, thus increasing the Gibbs free energy of the droplet, reducing the interfacial tension, and inhibiting the droplet coalestion.