Colorado School of Mines, Department of Chemical and Biological Engineering, Golden, CO 80401, USA.
J Colloid Interface Sci. 2013 Apr 15;396:83-9. doi: 10.1016/j.jcis.2013.01.024.
Suspensions of corn starch and water are the most common example of a shear thickening system. Investigations into the non-Newtonian flow behavior of corn starch slurries have ranged from simplistic elementary school demonstrations to in-depth rheological examinations that use corn starch to further elucidate the mechanisms that drive shear thickening. Here, we determine how much corn starch is required for the average person to ‘‘walk on water’’ (or in this case, run across a pool filled with corn starch and water). Steady shear rate rheological measurements were employed to monitor the thickening of corn starch slurries at concentrations ranging from 0 to 55 wt.% (0-44 vol.%). The steady state shear rate ramp experiments revealed a transition from continuous to discontinuous thickening behavior that exists at 52.5 wt.%. The rheological data was then compared to macro-scopic (~5 gallon) pool experiments, in which thickening behavior was tested by dropping a 2.1 kg rock onto the suspension surface. Impact-induced thickening in the ‘‘rock drop’’ study was not observed until the corn starch concentration reached at least 50 wt.%. At 52.5 wt.%, the corn starch slurry displayed true solid-like behavior and the falling rock ‘‘bounced’’ as it impacted the surface. The corn starch pool studies were fortified by steady state stress ramps which were extrapolated out to a critical stress value of 67,000 Pa (i.e., the force generated by an 80 kg adult while running). Only the suspensions containing at least 52.5 wt.% (42 vol.%) thickened to high enough viscosities (50-250 Pa s) that could reasonably be believed to support the impact of a man’s foot while running. Therefore, we conclude that at least 52.5 wt.% corn starch is required to induce strong enough thickening behavior to safely allow the average person to ‘‘walk on water’’.
玉米淀粉和水的悬浮液是最常见的剪切增稠系统的例子。对玉米淀粉浆料的非牛顿流动行为的研究范围从简单的小学演示到深入的流变学研究，这些研究使用玉米淀粉来进一步阐明驱动剪切增稠的机制。在这里，我们确定了普通人需要多少玉米淀粉才能“水上行走”（或者在这种情况下，在一个装满玉米淀粉和水的水池上奔跑）。采用稳态剪切速率流变测量来监测浓度范围为 0 至 55wt.%（0-44 体积%）的玉米淀粉浆料的增稠情况。稳态剪切速率斜坡实验揭示了在 52.5wt.%存在从连续增稠到不连续增稠行为的转变。然后将流变数据与宏观（~5 加仑）水池实验进行比较，在该实验中，通过将 2.1kg 的岩石滴落到悬浮液表面来测试增稠行为。在玉米淀粉浓度至少达到 50wt.%之前，在“岩石掉落”研究中没有观察到冲击诱导的增稠。在 52.5wt.%时，玉米淀粉浆料表现出真正的固态行为，下落的岩石在撞击表面时“反弹”。稳态应力斜坡实验加强了玉米淀粉水池实验，这些斜坡实验被外推到一个临界应力值 67000Pa（即，一个 80kg 成年人跑步时产生的力）。只有含有至少 52.5wt.%（42 体积%）的悬浮液才能增稠到足够高的粘度（50-250Pa s），这可以合理地认为可以支撑人在跑步时的脚部冲击。因此，我们得出结论，至少需要 52.5wt.%的玉米淀粉才能诱导足够强的增稠行为，以确保普通人能够“水上行走”。
