关键词: 纤维素纳米晶须, 复合材料, 电流变液, 二氧化钛, 稳定性

Abstract: [Objective]Electrorheological fluid (ERF), having flow properties that can be modified with electric field, is a suspension liquid composite with micron to nanometer particles dispersed in the oil phase. The ERF is thus expected to be used for semi-automated damping system, clutch brakes, and fluid valves. High dielectric Ti-O system is a common ERF material, but it has some problems such as easy sediment, unstable performance, etc. The cellulose nanowhisker (CNW) which can be disintegrated from forest residues, has the advantages of nanoscale morphology, high aspect ratio, large specific surface area, and high surface energy. The combination of CNW and Ti-O system can be expected to improve the performance and stability of ERF, in terms that the hydroxyl groups at the side chains of CNW can effectively adsorb polar molecules, leading to the chain polymerization easily in the electric field.[Method]In this paper, we prepared the CNWs through the hydrolysis with concentrated sulfuric acid, and the composites comprised TiO₂ and CNWs via a sol-gel method. The proportion of CNW in the composite was tailored to 10%, 20% and 30% by adjusting the addition ratio of raw materials. When the CNW-TiO₂ composites were added into dimethyl silicone, some properties including the effects of urea addition, electric field intensity, shear rate and temperature on the shear strength of ERF were analyzed. The anti-sedimentation and recycling uses of the ERF were also investigated. [Result]The results showed that the CNW surfaces were covered by amorphous TiO₂, exhibiting a 10-15 nm diameter fibrous structure. With the addition of CNW, the sedimentation rate of TiO₂ reduced from 46% to less than 20%. With the CNW content increased, lower sedimentation rate of the complex and a more stable performance at high temperature were observed. A certain amount of CNW addition can enhance the performance of ERF shear strength by 1-2 times. Repeatability tests displayed that the electrorheological properties of ERF remained stable, which could effectively avoid the electrical breakdown. [Conclusion]The results confirmed that the addition of CNW making the Ti-O system ERF reduce loss of polar molecules. A significant improvement on the electrorheological performance and service life was achieved.

Key words: cellulose nanowhisker, composite, electrorheological fluid, titania, stability