Light scattering and small angle neutron scattering experiments with an aggregating binary liquid mixture of critical composition

Results of light scattering and small angle neutron scattering experiments with a 2‐butoxyethanol (2‐C 4 E 1 )/D 2 O mixture of critical composition (stoichiometric mole fraction of 2‐C 4 E 1 x   c 0= 0.0598; critical temperature T c (visual) = 42.714 °C) are reported. They are carried out with the aim to find out whether the temperature dependence of the correlation length ξ characterizing the extension of concentration fluctuations near T c is different from that characterizing the size of aggregates of the 2‐C 4 E 1 molecules which appear to exist at temperatures away from T c . The experiments show that the temperature dependence of ξ near T c is the same as that away from T c within the uncertainty of the measurements. – As a by‐product of this study, neutron scattering data were collected corresponding to a wide range of values of the scaling variable x (3 < x < 2100; x = q ξ q is the absolute value of the scattering vector). They are analysed in terms of the limiting form of the universal correlation scaling function g ξ( x ) = C 1 x −(2‐η) to determine the value of the universal critical exponent η. A value of η = 0.039 ± 0.004 is found. It is considered consistent with the theoretically expected values.