Miglani Ankur, Basu Saptarshi
Department of Mechanical Engineering, Indian Institute of Science, Bangalore, Karnataka-560012, India.
Soft Matter. 2015 Mar 21;11(11):2268-78. doi: 10.1039/c4sm02553a.
Understanding the transients of buckling in drying colloidal suspensions is pivotal for producing new functional microstructures with tunable morphologies. Here, we report first observations and elucidate the buckling instability induced morphological transition (sphere to ring structure) in an acoustically levitated, heated nanosuspension droplet using dynamic energy balance. Droplet deformation featuring the formation of symmetric cavities is initiated by capillary pressure that is two to three orders of magnitude greater than the acoustic radiation pressure, thus indicating that the standing pressure field has no influence on the buckling front kinetics. With an increase in heat flux, the growth rate of surface cavities and their post-buckled volume increase while the buckling time period reduces, thereby altering the buckling pathway and resulting in distinct precipitate structures. However, irrespective of the heating rate, the volumetric droplet deformation exhibits a linear time dependence and the droplet vaporization is observed to deviate from the classical D(2)-law.
了解干燥胶体悬浮液中的屈曲瞬态对于制造具有可调形态的新型功能微结构至关重要。在此，我们首次报告了相关观察结果，并利用动态能量平衡阐明了在声悬浮加热的纳米悬浮液滴中屈曲不稳定性引发的形态转变（从球形到环形结构）。液滴变形以对称腔的形成为特征，这是由比声辐射压力大两到三个数量级的毛细管压力引发的，因此表明驻波压力场对屈曲前沿动力学没有影响。随着热通量的增加，表面腔的生长速率及其屈曲后的体积增加，而屈曲时间段缩短，从而改变了屈曲路径并导致形成不同的沉淀结构。然而，无论加热速率如何，液滴的体积变形都呈现出线性时间依赖性，并且观察到液滴蒸发偏离经典的D(2)定律。
