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arXiv 0909.3050cond-mat.softcond-mat.dis-nn
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以反熔融为特征的分子液体中的剪切增稠

Shear thickening in molecular liquids characterized by inverse melting

R. Angelini, G. Salvi, G. Ruocco

摘要:

我们研究了由$α$ -环糊精、水和4-甲基吡啶组成的分子溶液在不同温度和浓度下的流变行为。该体系表现出明显的非牛顿行为,表现出典型的剪切增稠特征。具体地,在临界剪切速率$\dotγ_c$下观察到从牛顿流体到剪切增稠体系的转变。作为T的函数的该临界剪切速率的值遵循阿雷尼乌斯行为$\dotγ_c(T)=$ B exp $(E_a/K_BT)$,其中活化能$E_a$接近于$α$ -CD分子的O-H基团的氢键能的值。我们认为,粘度随剪切速率的增加(剪切增稠转变)是由于氢键聚集体的形成所施加的剪切场诱导。最后,我们推测非牛顿流变学和逆熔融行为之间可能的相互作用,提出一个单一的机制是在这两种现象的起源。

英文摘要:

We studied the rheological behavior of a molecular solution composed of $α$-cyclodextrin, water and 4-methylpyridine, a liquid known to undergo inverse melting, at different temperatures and concentrations. The system shows a marked non-Newtonian behavior, exhibiting the typical signature of shear thickening. Specifically, a transition is observed from a Newtonian to a shear thickening regime at a critical shear rate $\dotγ_c$. The value of this critical shear rate as a function of T follows an Arrhenius behavior $\dotγ_c(T)=$ B exp$(E_a/K_BT)$, with an activation energy $E_a$ close to the value of the hydrogen bond energy of the O-H group of the $α$-CD molecules. We argue that the increase of viscosity vs shear rate (shear thickening transition) is due to the formation of hydrogen bonded aggregates induced by the applied shear field. Finally, we speculate on the possible interplay between the non-Newtonian rheology and the inverse melting behavior, proposing a single mechanism to be at the origin of both phenomena.

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