**1. Introduction**

Microfluidics is a multidisciplinary field dealing with the manipulation and behaviour of liquids and gases in dimensions below 1000 micron. The origin of microfluidics can be traced back to the 1970s, when miniaturisation became more and more developed. Applications in various fields, such as analytics, biology, chemistry, medicine and technology, became much more apparent with the development of *rapid prototyping.* Rapid prototyping describes a combination of photolithography, soft lithography and commercial printing, which makes the fast and efficient fabrication of custom designed microfluidic devices possible. Microfluidic devices for analysing aqueous samples were first introduced by Manz [1, 2], Harrison [3], Ramsey [4] and Mathies [5].

The most important benefit of microfluidic devices is their ability to perform quantitative and qualitative analysis with high sensitivity and resolution, while being a low cost method for fast, highly efficient analysis [6]. These factors make it especially useful for time resolved measurements, and coupling to small angle X-ray scattering (SAXS) measurements for the analysis of the average particle size and shape, and the evolution thereof under various *in situ* conditions. These approaches, in particular the coupling of microfluidics to SAXS, finds application in various areas, including biological materials, polymers, colloids, chemistry,

nanocomposites, metals, minerals, food, pharmaceuticals and quality control [7]. Here we aim to detail background information important for the design of microfluidic devices for time resolved measurements, and the applications of these devices in time-resolved SAXS nanoparticle and self-assembly experiments.
