Critical domain fluctuations

The first step beyond mean field and Gaussian approximations is to expand the partition function in powers of the interae-tion (i.e. terms of order higher than 2 in q) and integrate over Gaussian fluctuations. It is a standard result that such perturbation expansion presents infrared divergences (i.e. for wavenumber fe->0) in three dimensions [8]. It can be used, however, to estimate the critical domain be-... 

When a phase transition occurs from a pure single state and in the absence of wettable surfaces the embryogenesis of the new phase is referred to as homogeneous nucleation. What is commonly referred to as classical nucleation theory is based on the following physical picture. Density fluctuations in the pre-transitional state result in local domains with characteristics of the new phases. If these fluctuations produce an embryo which exceeds a critical size then this embryo will not be dissipated but will grow to macroscopic size in an open system. The concept is applied to very diverse phenomena ... 

Veatch, S.L., Soubias, O., Keller, S.L., Gawrisch, K. Critical fluctuations in domain-forming lipid mixtures. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 17650-5. 

Very recently Tokita and Tanaka have performed a macroscopic measurement of the friction coefficient and have found its dramatic decrease with slight opacity near the critical point [86]. We conjecture that such a large anomaly was caused by stationary domain structures with large spatial scales and not by the thermal fluctuations decaying diffusively. 

As it is known [5], the intensity of the scattered light gives us an information about the system s disorder, e.g., presence therein of pores, impurities etc. Since macroscopically liquid is homogeneous, critical opalescence arises due to local microscopic inhomogeneities - an appearance of small domains with different local densities. In other words, liquid is ordered inside these domains but still disorded on the whole since domains are randomly distributed in size and space, they appear and disappear by chance. Fluctuations of the order parameter have large amplitude and involve a wide spectrum of the wavelengths (which results in the milk colour of the scattered light). 

Andrews SR, Cowley RA (1986) X-ray scattering from critical fluctuations and domain walls in KDP and DKDP. J Phys C 19 615-635... 

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