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Thickening & Thixotropic Properties of Fumed Silica
We may get confused and do not know how to choose when we pick coatings for home decoration. Then the sales may recommend a brand which is easy to paint and makes wall looked flat, bright and scratch-resistant. Why coatings has such magic performance? That’s partly due to the thickening and thixotropic properties of fumed silica,which is added into coatings.
Thickening means the increase in viscosity;Thixotropy is closely related with shear thinning.Shear thinning means that the viscosity of a liquid changes in relation to shear stress - it is dependent on the force acting on the coating film. At high levels of shear stress, lower viscosity is observed. This viscosity increases when the shear stress is reduced. The effect of a liquid increasing in viscosity as the duration of shear exposure increase, while the shear intensity remains constant, is referred to as thixotropy.
When thickening and thixotropic agent is added into your product, thickening and thixotropy property is gained.Fumed silica is one of the most common used agents for this purpose.Except from the good behavior in thickening and thixotropy property, fumed silica has other special properties. That’s the reason why fumed silica is the preferred choice for a lot of applications,including coatings application.
The thickening and thixotropy property of fumed silica is mainly related to its unique structure. Fumed silica is white fluffy powder, looks like smoke.
But in microscopic state, fumed silica is three-dimensional chain-like structure(dendritic structure). There are plenty of si-oh on the surface of fumed silica. SI-OH forms hydrogen bonds and links silica together as silica network; meanwhile, si-oh also forms hydrogen bonds with matrix like polar liquid or polymer materials. The two hydrogen bonds forms interpenetrating network structure, thus results in good thickening performance.
The force of hydrogen bonds and the physical adsorption force are relatively weak, when shear thinning is applied, this network is easy to break,viscosity decreases; when shear thinning is removed, network is restored,viscosity increases, thixotropic property shows.
Fumed silica performs good thickening and thixotropic properties, and has function of anti-settling, anti-sagging and reinforcing in these applications.
In powders like drinking powders, protein powders and seasoning powders, fumed silica is used for thickening function and good taste, what’s more, fumed silica can improve their anti-caking properties, which have a positive effect on the storage of the end product.
In cosmetic products like facial cream, good thixotropic property and UV-reflection are observed if fumed silica is added; and also anti-settling function in nail polish.
Through high-speed stirring, fumed silica is dispersed in electrolyte liquid, due to its excellent thickening and thixotropic properties, electrolyte liquid is in low viscosity and good free-flow state at initial stage, so it’s easy for model pouring; after model pouring and standing stage, electrolyte liquid turn into electrolyte gel, which avoids battery leakage and improves battery service life. Fumed silica has become an indispensable additives in gel batteries already.
As described above, fumed silica is becoming a popular chemical additives in daily life and production activities now.