Abstract
X-ray photon correlation spectroscopy (XPCS) has emerged as a unique technique allowing the measurement of dynamics of materials on mesoscopic lengthscales. One of the most common problems associated with the use of bright x-ray beams is beam-induced radiation damage, and this is likely to become an even more limiting factor at future synchrotron and free-electron laser sources. Flowing the sample during data acquisition is one of the simplest methods allowing the radiation damage to be limited. In addition to distributing the dose over many different scatterers, the method also enables new functionalities such as time-resolved studies. Here, we further develop a recently proposed experimental technique that combines XPCS and continuously flowing samples. More specifically, we use a model colloidal suspension to show how the macroscopic advective response to flow and the microscopic dissipative dynamics (diffusion) can be quantified from the x-ray data. Our results show very good quantitative agreement with a Poisseuille-flow hydrodynamical model combined with Brownian mechanics. The method has many potential applications, e.g. in the study of dynamics of glasses and gels under continuous shear/flow, protein aggregation processes and the interplay between dynamics and rheology in complex fluids.
Highlights
X-ray Photon Correlation Spectroscopy (XPCS) has emerged as a unique technique allowing the measurement of dynamics in materials on mesoscopic lengthscales
Applications in soft matter physics cover a broad range of topics which include, but are not limited to, nanostructured materials such as colloidal suspensions or polymers, dynamics at liquid surfaces, membranes and interfaces, and the glass or gel transition
Over the past several years, X-ray Photon Correlation Spectroscopy (XPCS) has become a well established experimental technique which allows the direct measurement of dynamics in materials
Summary
Over the past several years, X-ray Photon Correlation Spectroscopy (XPCS) has become a well established experimental technique which allows the direct measurement of dynamics in materials (see e.g. Refs [1, 2, 3, 4]). This will become an even more important issue at new (or upgraded) high brilliance third generation synchrotron sources, and at fourth-generation light sources - free electron lasers and energy-recovery linacs - with their unprecedented brilliance several orders of magnitude stronger than available today [6]. We use the XPCS data to quantitatively measure both the diffusive and the advective, flow-induced, motion of the particles. This is achieved by taking advantage of the anisotropy of the measured correlation functions. The method has the unique ability of being able to simultaneously study the interplay between the advective motion of the scatterers in response to applied shear and the dissipative microscopic dynamics due to thermal diffusion
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