Absolute small angle light scattering measurements from weakly scattering systems in a shear flow apparatus

We describe an optical detection layout that allows absolute small angle light scattering measurements on samples sheared in a concentric cylinders geometry. The two main features are the use of a focused incident beam and of a spatial filter that minimize the problem of stray light arising from digs and scratches in the optical path. The scattering intensity is imaged directly onto a cooled 12 bits charge-coupled device sensor. We are thus able to measure scattering intensities as low as about 4×10−4 cm−1 (about ten times the intensity scattered from a toluene standard) for scattering wave vector values between 5×10−5 and 3.5×10−4 Å−1. Some preliminary results of experiments on dilute surfactant solutions are given to demonstrate the performance of the instrument.