  Aqueous mixtures of small molecules, such as lower n-alkanols for example,
are known to be micro-segregated, with domains in the nano-meter range. One
consequence of micro-segregated domains would be the existence of long range
domain-domain oscillatory correlations in the various atom- atom pair
correlation functions, and subsequent pre-peaks in the corresponding atom atom
structure factors, in the q-vector range corresponding to nano-sized domains.
However, no such pre-peak have ever been observed in the large corpus of
radiation scattering data published so far. Here, through large scale
simulations of aqueous-1propanol mixtures, I report that the domain pre-peak
contributions in the atom-atom structure factors exactly cancel each other in
the total scattering intensity, thus suppressing the pre-peak in agreement with
the experimental findings. This cancellation is explained by drawing an analogy
between the charge order found in ionic fluids and the segregated domain order.
This finding opens new interpretation of the well known scattering pre-peak
observed in micro-emulsions. In particular, it implies that scattering
experiment cannot detect homogeneous domain segregation, hence cannot lead to a
proper microscopic description of atom-atom correlations in domain ordered
mixtures.
