Paladugu Sathyanarayana, Callegari Agnese, Tuna Yazgan, Barth Lukas, Dietrich Siegfried, Gambassi Andrea, Volpe Giovanni
Soft Matter Lab, Department of Physics, Bilkent University, Ankara 06800, Turkey.
UNAM-National Nanotechnology Research Center, Bilkent University, Ankara 06800, Turkey.
Nat Commun. 2016 Apr 21;7:11403. doi: 10.1038/ncomms11403.
In soft condensed matter physics, effective interactions often emerge due to the spatial confinement of fluctuating fields. For instance, microscopic particles dissolved in a binary liquid mixture are subject to critical Casimir forces whenever their surfaces confine the thermal fluctuations of the order parameter of the solvent close to its critical demixing point. These forces are theoretically predicted to be nonadditive on the scale set by the bulk correlation length of the fluctuations. Here we provide direct experimental evidence of this fact by reporting the measurement of the associated many-body forces. We consider three colloidal particles in optical traps and observe that the critical Casimir force exerted on one of them by the other two differs from the sum of the forces they exert separately. This three-body effect depends sensitively on the distance from the critical point and on the chemical functionalisation of the colloid surfaces.
在软凝聚态物理中，有效相互作用常常因波动场的空间限制而出现。例如，溶解在二元液体混合物中的微观粒子，每当其表面将溶剂序参量的热涨落限制在接近其临界 demixing 点时，就会受到临界卡西米尔力的作用。从理论上预测，这些力在由涨落的体相关长度所设定的尺度上是非加和的。在此，我们通过报告对相关多体力的测量，提供了这一事实的直接实验证据。我们考虑处于光学陷阱中的三个胶体粒子，并观察到另外两个粒子对其中一个粒子施加的临界卡西米尔力不同于它们分别施加的力之和。这种三体效应敏感地依赖于与临界点的距离以及胶体表面的化学官能化。
