Underexcitation prevents crystallization of granular assemblies subjected to high-frequency vibration.
Underexcitation prevents crystallization of granular assemblies subjected to high-frequency vibration.
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DOI：
10.1073/pnas.2306209120
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发表时间：
2023-07-18
影响因子：
11.1
通讯作者：
Deshpande, Vikram S.
中科院分区：
文献类型：
--
作者：
Al Mahri, Sara;Grega, Ivan;Shaikeea, Angkur J. D.;Wadley, Haydn N. G.;Deshpande, Vikram S.
单分散球体集合体的非布朗振动诱导结晶将堆积分数从致密随机值增加到接近理论最大值 0.74。提高结晶速率有助于加快各种粉末技术应用中的制造过程，但结晶水平会降低到最佳振动频率以上。在这里，我们表明，高频振动会减少由于过度激励而导致的结晶（类似于高温下形成无定形液体）的公认观点是错误的。事实上，与直觉相反的是，对于高频下激发不足的颗粒组件来说，情况恰恰相反。对欠激励机制的了解使我们能够设计出允许高频结晶的方案。通过施加振动使干颗粒组装体结晶是组装微/宏观晶体的可扩展途径。众所周知，存在一个最佳频率可以使结晶最大化，并且人们普遍认为该最佳频率的出现是因为高频振动会导致组件的过度激励。通过使用包括间断 X 射线计算机断层扫描和高速摄影与离散元件模拟相结合的测量结果，我们发现，与直觉相反的是，高频振动会使组件激发不足。高频振动产生的大加速度产生流化边界层，防止动量传递到大量颗粒组件中。这导致颗粒激发不足，从而抑制结晶所需的重排。对机制的清晰理解使得我们能够开发出一种抑制流化的简单概念，从而在高频振动下实现结晶。
The non-Brownian vibration-induced crystallization of an assembly of monodisperse spheres increases the packing fraction from the dense random value to nearly the theoretical maximum of 0.74. Increasing the rate of the crystallization helps speed up manufacturing processes in a wide range of powder technology applications, but the level of crystallization reduces above an optimal vibration frequency. Here, we show that the accepted view that high-frequency vibration reduces crystallization due to overexcitation, akin to formation of an amorphous liquid at high temperatures is erroneous. In fact, rather counterintuitively, the opposite is true with the granular assembly underexcited at high frequencies. An understanding of the mechanisms of underexcitation has enabled us to devise schemes to allow crystallization at high frequencies. Crystallization of dry particle assemblies via imposed vibrations is a scalable route to assemble micro/macro crystals. It is well understood that there exists an optimal frequency to maximize crystallization with broad acceptance that this optimal frequency emerges because high-frequency vibration results in overexcitation of the assembly. Using measurements that include interrupted X-ray computed tomography and high-speed photography combined with discrete-element simulations we show that, rather counterintuitively, high-frequency vibration underexcites the assembly. The large accelerations imposed by high-frequency vibrations create a fluidized boundary layer that prevents momentum transfer into the bulk of the granular assembly. This results in particle underexcitation which inhibits the rearrangements required for crystallization. This clear understanding of the mechanisms has allowed the development of a simple concept to inhibit fluidization which thereby allows crystallization under high-frequency vibrations.
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DOI：
10.1073/pnas.1916817117
发表时间：
2020-03-17
影响因子：
11.1
作者：
Portela, Carlos M.;Vidyasagar, A.;Kochmann, Dennis M.
通讯作者：
Kochmann, Dennis M.
影响因子：
3.5
作者：
An, Xizhong;Li, Changxing
通讯作者：
Li, Changxing
影响因子：
8.6
作者：
Carvente, O;Ruiz-Suárez, JC
通讯作者：
Ruiz-Suárez, JC
三维振动下均匀球体堆积的实验研究
影响因子：
5.2
作者：
Li, C. X.;An, X. Z.;Yu, A. B.
通讯作者：
Yu, A. B.
影响因子：
8.6
作者：
Morales-Barrera, D. A.;Rodriguez-Gattorno, G.;Carvente, O.
通讯作者：
Carvente, O.