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arXiv 0908.1795cond-mat.softcond-mat.stat-mechquant-ph
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经典二元液体混合物中的临界Casimir效应

Critical Casimir effect in classical binary liquid mixtures

A. Gambassi, A. Maciolek, C. Hertlein, U. Nellen, L. Helden, C. Bechinger, S. Dietrich

摘要:

如果波动介质受到限制,其波动谱的随之而来的扰动会产生作用在其限制表面上的类卡西米尔有效力。在这种介质的连续相变附近,相应的序参量波动出现在所有长度尺度上,因此在临界点附近,这种效应具有普遍的特征,即,在很大程度上,它与实际系统的微观细节无关。因此,可以通过研究合适的代表性模型系统从理论上计算。我们报告的直接测量临界Casimir力的全内反射显微镜(TIRM),与飞秒牛顿分辨率。相应的电位被确定为在溶剂介质中的临界热噪声的作用下,由水和2,6-二甲基吡啶的二元液体混合物附近的较低的会溶点的作用下,浮在基板上的单个胶体颗粒。根据胶体和基底表面相对于二元液体混合物的两种组分的相对吸附偏好,我们观察到,在接近溶剂的临界点时,基于对作用在伊辛普适类内的薄膜几何中的临界Casimir力的认识,在边界相等或相反的情况下,条件下,我们提供了相应的理论预测的球平面壁的几何形状的实验。有效势的实验数据可以解释一致的这些预测和观察到一个显着的定量协议。

英文摘要:

If a fluctuating medium is confined, the ensuing perturbation of its fluctuation spectrum generates Casimir-like effective forces acting on its confining surfaces. Near a continuous phase transition of such a medium the corresponding order parameter fluctuations occur on all length scales and therefore close to the critical point this effect acquires a universal character, i.e., to a large extent it is independent of the microscopic details of the actual system. Accordingly it can be calculated theoretically by studying suitable representative model systems. We report on the direct measurement of critical Casimir forces by total internal reflection microscopy (TIRM), with femto-Newton resolution. The corresponding potentials are determined for individual colloidal particles floating above a substrate under the action of the critical thermal noise in the solvent medium, constituted by a binary liquid mixture of water and 2,6-lutidine near its lower consolute point. Depending on the relative adsorption preferences of the colloid and substrate surfaces with respect to the two components of the binary liquid mixture, we observe that, upon approaching the critical point of the solvent, attractive or repulsive forces emerge and supersede those prevailing away from it. Based on the knowledge of the critical Casimir forces acting in film geometries within the Ising universality class and with equal or opposing boundary conditions, we provide the corresponding theoretical predictions for the sphere-planar wall geometry of the experiment. The experimental data for the effective potential can be interpreted consistently in terms of these predictions and a remarkable quantitative agreement is observed.

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