Multi-scale kinetics of a field-directed colloidal phase transition
Multi-scale kinetics of a field-directed colloidal phase transition
复制标题
场定向胶体相变的多尺度动力学
DOI：
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发表时间：
2012
影响因子：
11.1
通讯作者：
E. Furst
中科院分区：
文献类型：
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作者：
J. Swan;P. Vasquez;P. Whitson;E. M. Fincke;Koichi Wakata;S. Magnus;Frank de Winne;M. Barratt;J. Agui;R. Green;N. Hall;D. Bohman;C. Bunnell;A. Gast;E. Furst
当暴露在稳定、均匀的场中时，极化胶体有望形成晶体平衡相。然而，当胶体局部化时，这种场诱导的相变就会停止，悬浮液作为一种动力学捕获的渗透结构无限期地持续存在。我们通过在不同频率切换磁场强度来退火这种由磁流变流体形成的凝胶。这一过程允许被冻结的结构周期性地松弛到平衡状态——富含胶体的圆柱形柱。观察到两种不同的生长机制：一种是通过凝胶的扩散松弛使粒子域成熟，另一种是通过场驱动的相互作用使系统跨越结构崩溃和柱状域明显合并。作为磁场强度和开关频率的函数，有一个明显的边界来区分这两种状态。这些结果证明了胶体相变的动力学屏障是如何通过测量的、周期性的驱动力变化而被破坏的。这种定向组装可以利用胶体的分散体来制造独特的材料。
Polarizable colloids are expected to form crystalline equilibrium phases when exposed to a steady, uniform field. However, when colloids become localized this field-induced phase transition arrests and the suspension persists indefinitely as a kinetically trapped, percolated structure. We anneal such gels formed from magneto-rheological fluids by toggling the field strength at varied frequencies. This processing allows the arrested structure to relax periodically to equilibrium—colloid-rich, cylindrical columns. Two distinct growth regimes are observed: one in which particle domains ripen through diffusive relaxation of the gel, and the other where the system-spanning structure collapses and columnar domains coalesce apparently through field-driven interactions. There is a stark boundary as a function of magnetic field strength and toggle frequency distinguishing the two regimes. These results demonstrate how kinetic barriers to a colloidal phase transition are subverted through measured, periodic variation of driving forces. Such directed assembly may be harnessed to create unique materials from dispersions of colloids.