Study the influence of residual water during the preparation processes on the shear thickening behavior of silica/PEG200 suspensions

Silica/PEG200 shear thickening fluids (STFs) are widely used smart fluids. There is often residual water during the STF preparation process because of the strong water adsorbability due to the abundant hydroxyl group on the silica surface. Residual water usually influences the shear-thickening behavior of STFs. How much influence the residual water has during the preparation processes on the properties of STFs is still a problem. In this paper, six preparation processes were designed, and the influence of residual water content on the shear thickening behavior due to different preparation processes is analyzed. Firstly, three drying processes were used to prepare STFs, i.e., three kinds of silica powder, which were obtained from spray, freeze, or oven drying of the silica dispersion, were dispersed in PEG200 to obtain STFs. Secondly, three wet processes were used to prepare STFs, i.e., three kinds of silica slurry, which were obtained by centrifuging and washing through water, ethanol, or tetrahydrofuran of the silica dispersion, were directly dispersed into PEG200 and dried to obtain STFs. All the silica dispersion used in these six preparation processes was prepared using the Stöber method. The properties, microstructure, and residual water content of the STFs prepared by the six preparation processes were explored. The results showed that the preparation processes have a big influence on the properties of related STFs. The silica’s residual water content derived from different preparation processes is the critical factor that affects STFs’ shear thickening performance. The drying process using silica powder from spray drying of the silica dispersion resulted in the lowest water content and led to the best shear-thickening performance of the corresponding STFs. Meanwhile, the wet process using a slurry obtained by centrifuging and washing through tetrahydrofuran of the silica dispersion could also prepare STFs with good shear thickening behavior.