Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA.
J Chem Phys. 2018 Mar 28;148(12):124506. doi: 10.1063/1.5021347.
We measure the kinetics of crystal growth from a melt of triblock Janus colloids using non-equilibrium molecular dynamics simulations. We assess the impact of interaction anisotropy by systematically varying the size of the attractive patches from 40% to 100% coverage, finding substantially different growth behaviors in the two limits. With isotropic particles, the interface velocity is directly proportional to the subcooling, in agreement with previous studies. With highly anisotropic particles, the growth curves are well approximated by using a power law with exponent and prefactor that depend strongly on the particular surface geometry and patch fraction. This nonlinear growth appears correlated to the roughness of the solid-liquid interface, with the strongest growth inhibition occurring for the smoothest crystal faces. We conclude that crystal growth for patchy particles does not conform to the typical collision-limited mechanism, but is instead an activated process in which the rate-limiting step is the collective rotation of particles into the proper orientation. Finally, we show how differences in the growth kinetics could be leveraged to achieve kinetic control over polymorph growth, either enhancing or suppressing metastable phases near solid-solid coexistence lines.
我们使用非平衡分子动力学模拟来测量由三嵌段各向异性胶体熔体中晶体的生长动力学。我们通过系统地改变吸引斑的大小，从 40%到 100%的覆盖率，评估了相互作用各向异性的影响，发现这两种极限情况下有很大的不同的生长行为。对于各向同性颗粒，界面速度与过冷度成正比，这与以前的研究一致。对于高度各向异性的颗粒，生长曲线可以很好地用幂律来近似，其指数和前因子强烈依赖于特定的表面几何形状和斑分数。这种非线性生长似乎与固-液界面的粗糙度有关，最平滑的晶体表面生长抑制最强。我们得出结论，对于有斑点的颗粒，晶体生长不符合典型的碰撞限制机制，而是一种激活过程，其中速率限制步骤是颗粒集体旋转到适当的方向。最后，我们展示了如何利用生长动力学的差异来实现对多晶生长的动力学控制，无论是增强还是抑制近固-固共存线的亚稳相。
