聚合物-胶体混合物中再入凝固是由于竞争的熵和焓吸引力的结果。
Re-entrant solidification in polymer-colloid mixtures as a consequence of competing entropic and enthalpic attractions.
机构信息
Center for Soft Matter Research, Physics Department, New York University, 4 Washington Place, New York New York 10003, USA.
1] Center for Soft Matter Research, Physics Department, New York University, 4 Washington Place, New York New York 10003, USA [2] Chemistry Department, New York University, 100 Washington Square East, New York New York 10003, USA.
出版信息
Nat Mater. 2015 Jan;14(1):61-5. doi: 10.1038/nmat4109. Epub 2014 Oct 19.
In polymer-colloid mixtures, non-adsorbing polymers dispersed with much larger colloids provide a universal yet specific entropic attraction between the colloids. Such so-called depletion interaction arises from an osmotic-pressure imbalance caused by the polymers and is considered to be independent of temperature. Here we show that, for the most commonly used polymer-colloid depletion systems, the polymer undergoes a crossover from non-adsorbing to adsorbing and that, consequently, the effective colloidal interactions depend on temperature. We also find that a combination of the enthalpic (polymer bridging) and entropic (polymer exclusion) interactions, both attractive, leads to a re-entrant regime where the colloids are dispersed and form solids both on heating and on cooling. We provide a simple model to explain the observed transitions and to fill the theoretical gap at the polymer-adsorption crossover. Our findings open possibilities for colloidal self-assembly, the formation of colloidal crystals and glasses, and the behaviour of temperature-controlled viscoelastic materials.
在聚合物-胶体混合物中，与大得多的胶体分散的非吸附聚合物在胶体之间提供了一种普遍但特定的熵吸引力。这种所谓的耗尽相互作用源于聚合物引起的渗透压失衡，被认为与温度无关。在这里，我们表明，对于最常用的聚合物-胶体耗尽系统，聚合物经历从不吸附到吸附的转变，因此，有效的胶体相互作用取决于温度。我们还发现，焓（聚合物桥接）和熵（聚合物排斥）相互作用的组合都是吸引力的，导致再进入状态，其中胶体在加热和冷却时都会分散并形成固体。我们提供了一个简单的模型来解释观察到的转变，并填补聚合物吸附转变处的理论空白。我们的发现为胶体自组装、胶体晶体和玻璃的形成以及温度控制的粘弹性材料的行为开辟了可能性。
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