Raghavan SR, Khan SA
Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina, 27695-7905
J Colloid Interface Sci. 1997 Jan 1;185(1):57-67. doi: 10.1006/jcis.1996.4581.
Suspensions of fumed silica in polypropylene glycol exhibit shear-thickening under steady shear and "strain-thickening" under oscillatory shear. Strain-thickening refers to a sharp increase in the complex viscosity eta* observed at critical combinations of strain-amplitude and frequency. Two regimes of strain-thickening behavior have been found: The first occurs at high critical strains and low frequencies, whereas the second occurs at high critical frequencies and a constant lower strain. Strain-thickening in the first regime can be explicitly correlated with steady shear-thickening, using a modified version of the Cox-Merz rule. Accordingly, strain-thickening data for the complex viscosity eta* as a function of the maximum dynamic shear-rate gamma0omega can be superposed against shear-thickening data for the steady viscosity as a function of the steady shear rate. Such a correlation between the two kinds of thickening phenomena has not been reported previously. The combination of shear- and strain-thickening behavior can be qualitatively explained using a clustering mechanism, which attributes the various phenomena to the formation of temporary, flow-induced clusters. The two regimes of strain-thickening are a result of differences in the relative ease of cluster formation.
气相二氧化硅在聚丙二醇中的悬浮液在稳态剪切下表现出剪切增稠，在振荡剪切下表现出“应变增稠”。应变增稠是指在应变幅度和频率的临界组合下观察到的复数粘度η急剧增加。已发现两种应变增稠行为模式：第一种发生在高临界应变和低频下，而第二种发生在高临界频率和恒定较低应变下。使用Cox-Merz规则的修正版本，可以将第一种模式下的应变增稠与稳态剪切增稠明确关联起来。因此，作为最大动态剪切速率γ0ω的函数的复数粘度η的应变增稠数据可以与作为稳态剪切速率的函数的稳态粘度的剪切增稠数据叠加。此前尚未报道过这两种增稠现象之间的这种关联。可以使用聚集机制定性地解释剪切增稠和应变增稠行为的组合，该机制将各种现象归因于临时的、流动诱导的聚集体的形成。两种应变增稠模式是聚集体形成相对难易程度差异的结果。
