Cluster formation by acoustic forces and active fluctuations in levitated granular matter
Cluster formation by acoustic forces and active fluctuations in levitated granular matter
复制标题
DOI：
10.1038/s41567-019-0440-9
复制
发表时间：
2019-05-01
期刊：
影响因子：
19.6
通讯作者：
Jaeger, Heinrich M.
中科院分区：
文献类型：
--
作者：
Lim, Melody X.;Souslov, Anton;Jaeger, Heinrich M.
机械搅拌的颗粒物质常作为探索与硬球系统相关的丰富物理现象的原型，通过振动或摇晃引入有效温度（1 - 6）。虽然排空相互作用会促使胶体发生团聚和组装（7 - 10），但宏观颗粒之间并不存在等效的短程吸引力。在此，我们克服了这一局限，利用声悬浮和捕获技术来研究颗粒团簇的形成（11 - 13）。散射的声波在小颗粒之间建立起短程吸引力（14），而对声阱进行失谐则会产生主动涨落（15）。为了阐明吸引力与涨落之间的相互作用，我们研究了由少量粒子组成的二维团簇基态之间的转变。我们通过实验和建模得出的主要结果表明，与热胶体不同，在非平衡颗粒系综中，主动涨落的强度不仅控制着组装速率，还控制着组装路径和基态统计特性。这些结果为非侵入式操控宏观粒子、调节它们的相互作用以及引导它们的组装开辟了新的可能性。
Mechanically agitated granular matter often serves as a prototype for exploring the rich physics associated with hard-sphere systems, with an effective temperature introduced by vibrating or shaking(1-6). While depletion interactions drive clustering and assembly in colloids(7-10), no equivalent shortrange attractions exist between macroscopic grains. Here we overcome this limitation and investigate granular cluster formation by using acoustic levitation and trapping(11-13). Scattered sound establishes short-range attractions between small particles(14), while detuning the acoustic trap generates active fluctuations(15). To illuminate the interplay between attractions and fluctuations, we investigate transitions among ground states of two-dimensional clusters composed of a few particles. Our main results, obtained using experiments and modelling, reveal that, in contrast to thermal colloids, in non-equilibrium granular ensembles the magnitude of active fluctuations controls not only the assembly rates but also their assembly pathways and ground-state statistics. These results open up new possibilities for non-invasively manipulating macroscopic particles, tuning their interactions and directing their assembly.