Seeding effects in phase transitions quenched far from of equilibrium

相变中的种子效应在远离平衡时被淬灭

• 批准号: 237282255
• 负责人: Dr. Peter Keim
• 金额: --
• 依托单位: Arbeitsgruppe Theorie der weichen Materie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2014-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/237282255?language=en
• 关键词: Seeding; effects; phase; transitions; quenched

The investigation of phase transitions and the corresponding symmetry breaking mechanism is a fascinating research topic in physic since long. It has been an enormous achievement in statistical physics to classify quite different systems into universality classes depending on their symmetries and the symmetries of the respective order parameters. For Example, the melting scenarios in 3D and 2D systems are very unequal. A prerequisite for the successful statistical description was, that the systems are in thermodynamic equilibrium. One famos example for a system falling out of equilibrium is the glass transition yet another is crystallization with extremely large cooling rates where systems are far out of thermodynamic equilibrium. For 2D system we were able to show, that the mechanism of freezing in equilibrium and out of equilibrium are quite different. Here we would like quantify crystallization far from equilibrium on a microscopic level, while a nucleation seed is offered during a temperature quench.The system consists of super-paramagnetic colloidal particles confined at an absolutely flat liquid/air interface constituting a 2D monolayer. Since the dynamics of the particles is slow enough to be resolved by digital image processing the full phase-space information is available and can be compared to theoretical models. Using an outer magnetic field, the ratio between repulsive interaction of the particles and thermal energy can be varied, controlling the system temperature as function of time. This way the system can be cooled on time scales 10-4-times shorter compared to intrinsic time scales - a unique feasibility in our experiment.Since the out of equilibrium phase transition can not be described with classical nucleation theory as we showed previously we want to investigate the influence of fluctuations of the local order parameters. Therefore we want to impose a seed (small crystalline structures or walls) using holographic optical tweezers during the time of quench. The effect of such a crystalline seed during the quench (where we avoid to name it heterogeneous nucleation) will be studied thoroughly in this project by varying different parameters including the size of the seed and its geometry, quench rate and depth. We will finally compare the results with predictions of Brownian dynamic simulations, dynamic density functional theory, and phase field theory calculations to get deeper insight in this out of equilibrium process of self organization

相变及其相应的对称性破缺机制的研究长期以来一直是物理学界一个令人着迷的研究课题。根据系统的对称性和各自序参数的对称性，将完全不同的系统分类为普遍性类别，这是统计物理学中的一项巨大成就。例如，3D 和 2D 系统中的熔化场景非常不平等。成功统计描述的先决条件是系统处于热力学平衡。系统失去平衡的一个常见例子是玻璃化转变，另一个例子是具有极大冷却速率的结晶，其中系统远离热力学平衡。对于二维系统，我们能够证明，平衡状态和非平衡状态下的冻结机制是完全不同的。在这里，我们希望在微观水平上量化远离平衡的结晶，同时在温度淬火期间提供成核种子。该系统由超顺磁性胶体颗粒组成，这些颗粒被限制在构成二维单层的绝对平坦的液体/空气界面上。由于粒子的动力学足够慢，可以通过数字图像处理来解析，因此可以获得完整的相空间信息，并且可以与理论模型进行比较。使用外部磁场，可以改变颗粒的排斥相互作用和热能之间的比率，从而控制系统温度作为时间的函数。这样，系统可以在比本征时间尺度短 10-4 倍的时间尺度上冷却——这在我们的实验中具有独特的可行性。正如我们之前所表明的，由于失平衡相变不能用经典成核理论来描述，所以我们想要研究局部有序参数波动的影响。因此，我们希望在淬火期间使用全息光镊施加种子（小晶体结构或壁）。在本项目中，将通过改变不同的参数（包括晶种的尺寸及其几何形状、淬火速率和深度）来彻底研究这种晶种在淬火过程中的影响（我们避免将其命名为异质成核）。最后，我们将结果与布朗动力学模拟、动态密度泛函理论和相场理论计算的预测进行比较，以更深入地了解这种自组织的非平衡过程

项目成果

Specific heat in two-dimensional melting.

• DOI: 10.1103/physrevlett.113.127801
• 发表时间: 2013-12
• 期刊: Physical review letters
• 影响因子: 8.6
• 作者: S. Deutschländer;A. Puertas;G. Maret;P. Keim