Coherent neutron scattering from the ionic mixture of ethylammonium nitrate and deuterated n-octanol in the critical region

Neutron scattering measurements were performed on the ionic mixture of ethy lammonium nitrate and deuterated iz-octanol in order to get information abo ut its microscopic structure in the vicinity of the critical point. Scatter ing spectra were recorded for momentum transfers q, ranging from 0.06 to 0. 46 A(-1). A sample at the critical salt mole fraction X-c = 0.760, was stud ied in its homogeneous phase at various temperatures between (T-c + 0.93)de grees C and (T-c + 24.12)degrees C, where T-c is the critical temperature. This corresponds to reduced temperatures tau = (T - T-c)/T-c, in the range 3.1 x 10(-3) less than or equal to tau less than or equal to 8.0 x 10(-2). The spectra of the coherent intensity scattered From the critical mixture a re described well by the Fisher-Langer approximation in a wide range of q x i values, xi being the critical correlation length. However, at least one a dditional shorter characteristic length is needed for a proper description of the spectra over the whole range of q.