  Microfluidic mixing is an important means for in-situ sample preparation and
handling while Small Angle X-Ray Scattering (SAXS) is a proven tool for
characterising (macro-)molecular structures. In combination those two
techniques enable investigations of fast reactions with high time resolution
(<1 ms). The goal of combining a micro mixer with SAXS, however, puts
constraints on the materials and production methods used in the device
fabrication. The measurement channel of the mixer needs good x-ray transparency
and a low scattering background. While both depend on the material used, the
requirement for low scattering especially limits the techniques suitable for
producing the mixer, as the fabrication process can induce molecular
orientations and stresses that can adversely influence the scattering signal.
Not only is it important to find a production method that results in a device
with low background scattering, but it also has to be versatile enough to
produce appropriate mixer designs. Here we discuss two methods - laser ablation
of polycarbonate and injection moulding of Topas - which were found suitable
for our needs, provided care is taken in aligning the mixing/reaction channel,
where the actual measurements will be carried out. We find injection moulding
to be the better of the two methods.
