Critical Casimir effect

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In analogy to the quantum Casimir effect, in which two uncharged dielectric plates in a vacuum can attract or repel each other due to zero-point fluctuations of the quantized electromagnetic field, the critical Casimir effect describes the possibility of attractive or repulsive forces between two surfaces due to confined density or concentration fluctuations. This effect occurs when the lengthscale <math>\xi</math> of these fluctuations is on the order of the separation between the two surfaces; while this lengthscale is typically very small, it can often be relevant to colloidal systems -- for example, for colloidal particles suspended in a binary mixture near its critical point, at which <math>\xi</math> can be very large.