Phase mechanics of colloidal gels: osmotic pressure drives non-equilibrium phase separation
Phase mechanics of colloidal gels: osmotic pressure drives non-equilibrium phase separation
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DOI：
10.1039/d0sm02180f
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发表时间：
2021-04-14
期刊：
影响因子：
3.4
通讯作者：
Zia, Roseanna N.
中科院分区：
文献类型：
--
作者：
Johnson, Lilian C.;Zia, Roseanna N.
尽管具有数kT量级的颗粒间键的致密胶体凝胶通常被描述为是由相分离的停滞引起的，但由于其临时键的动力学，它们随着年龄的增长而继续变粗。这里k是玻尔兹曼常数T是绝对温度。凝胶老化的计算研究揭示了粒子尺度的动力学，让人想起冷凝，这表明非常缓慢，但正在进行的相分离。延迟屈服的后续研究揭示了与相分离的重新开始一致的结构变化。在本研究中，我们询问的想法，机械产量是连接到一个阶段逮捕释放。我们研究了适度集中到致密可逆胶体凝胶的老化和产量，并专注于相分离的两个宏观标志：伴随冷凝的表面积与体积比的增加和自由能的最小化。在老化或屈服过程中，外部施加的场、布朗运动和粒子间力之间的相互作用改变了整个凝胶中键长的分布，从而改变了宏观势能。微观势（粒子间力）的梯度给出了势能与应力的自然联系。我们发现，自由能随着年龄的增长而减少，但随着债券被玻璃般的挫折所拉伸，这一速度会减慢。外部扰动打破刚刚足够的债券释放负渗透压，我们显示驱动器的级联键松弛和势能的快速降低，符合更新相分离。总体而言，我们表明，可逆胶体凝胶的机械产率释放动力学逮捕，可以被视为非平衡相分离。
Although dense colloidal gels with interparticle bonds of order several kT are typically described as resulting from an arrest of phase separation, they continue to coarsen with age, owing to the dynamics of their temporary bonds. Here, k is Boltzmann's constant and T is the absolute temperature. Computational studies of gel aging reveal particle-scale dynamics reminiscent of condensation that suggests very slow but ongoing phase separation. Subsequent studies of delayed yield reveal structural changes consistent with re-initiation of phase separation. In the present study we interrogate the idea that mechanical yield is connected to a release from phase arrest. We study aging and yield of moderately concentrated to dense reversible colloidal gels and focus on two macroscopic hallmarks of phase separation: increases in surface-area to volume ratio that accompanies condensation, and minimization of free energy. The interplay between externally imposed fields, Brownian motion, and interparticle forces during aging or yield, changes the distribution of bond lengths throughout the gel, altering macroscopic potential energy. The gradient of the microscopic potential (the interparticle force) gives a natural connection of potential energy to stress. We find that the free energy decreases with age, but this slows down as bonds get held stretched by glassy frustration. External perturbations break just enough bonds to liberate negative osmotic pressure, which we show drives a cascade of bond relaxation and rapid reduction of the potential energy, consistent with renewed phase separation. Overall, we show that mechanical yield of reversible colloidal gels releases kinetic arrest and can be viewed as non-equilibrium phase separation.