reported that the mixed suspensions of synthetic clay particles laponite and PEO showed the shake-gel phenomenon. Their results confirmed that the suspensions can become shake-gels at appropriate silica and PEO concentrations. They observed the states, gelled or not, of silica-PEO suspensions under several silica and PEO concentrations. conducted experiments on shake-gels made up of suspensions with silica particles and poly(ethylene oxide) (PEO) and reported that the mixed suspensions can become shake-gels. Because of this interesting characteristic, several previous studies were conducted to reveal the mechanism of shake-gel formation. The shake-gel can even show the phenomenon of relaxation that is, shake-gels in a gel state can turn back to a sol state after being left standing. Along with the increase in viscosity, some of the suspensions show gel-like behaviors with shaking and shear flow. One phenomenon occurring due to an increase in viscosity with shear rate is called shear-thickening. Many colloidal suspensions, with or without polymers, change their viscosity with a change in shear rate. This result supports the hypothesis that the bridging effect is the main cause of shake-gel formation, which can help us to understand the conditions necessary for shake-gel preparation. Our results elucidated that the radius of gyration of the PEO should be 2.5 times larger than the distance between the silica surfaces in order to promote the formation of a shake-gel. Thus, we conducted a series of experiments to examine the effects of the radius of gyration of the PEO and the distance between the silica particles by controlling the PEO molecular weight and the silica concentration. However, we noted that the influence of PEO size compared to the separation distance between silica particles regarding shake-gel formation has not been systematically investigated, while the PEO size should be larger than the particle–particle separation distance for polymer bridging in order to form gels. Previous works discussed the conditions necessary to form a shake-gel and suggested that the bridging effect of the polymer is one of the important mechanisms for shake-gel formation. Under specific conditions, the silica-PEO suspension can create a phenomenon called a shake-gel. To control the rheological property of suspensions, poly(ethylene oxide) (PEO) polymers are often used. Colloidal silica suspensions are widely used in many fields, including environmental restoration, oil drilling, and food and medical industries.
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