Birth and growth kinetics of brome mosaic virus microcrystals

Gold nanoparticle superlattice crystallization probed in situ

The nucleation and growth of three-dimensional superlattices of gold nanoparticles has been followed directly in situ by means of small angle x-ray scattering. These assemblies spontaneously form in a dilute solution providing the particles are large enough to generate a van der Waals driven attraction sufficient to counterbalance the thermal energy. The superlattices nucleate very soon after the birth of the individual particles and their growth kinetics is slower than predicted by a mechanism of simple diffusion of the nanoparticles towards the superlattices. The superlattices are first limited in size (170 nm in diameter) and have a globular shape with a low polydispersity. They present a fcc inner structure with nanoparticles being separated by a capping agent bilayer yielding a low gold internal volume fraction (phi SL = 0.33). In a second stage, these superlattices coalesce with time.

Probing fast kinetics in complex fluids by combined rapid mixing and small-angle X-ray scattering

Stopped-flow mixing coupled to small-angle X-ray scattering (SAXS) is an established technique for investigating structural kinetics in solution down to the millisecond range. More recently, the emphasis has shifted to the sub-millisecond range using continuous flow microfluidic mixing devices. The aim of this article is to review the present status and limitations when applying mixing techniques to a wide range of soft matter and biological systems. In the case of SAXS, special consideration of the mixing quality is necessary for a quantitative description of the scattered intensity. This is demonstrated through two representative examples involving protein refolding and micellar self-assembly.