![]() XPCS is a powerful technique for characterizing the spontaneous dynamics of soft materials. These limitations were eventually addressed by the development of X-ray Photon Correlation Spectroscopy (XPCS). In addition, PCS cannot measure diffusivity of systems where the particles are not freely diffusive and the dynamics cannot be described by Einstein-Stokes equation (e.g., colloidal gels). However, PCS is not suitable for materials that are opaque. In PCS, an optical laser is transmitted through the nanoparticle suspension and the variation of the nanoparticle position is evaluated via the temporal decorrelation of the intensity of the scattered light. ![]() This is the fundamental quantity reported by photon correlation spectroscopy (PCS, also known as Dynamic Light Scattering). Such information may also be unnecessary as the macroscopic properties of the soft material is usually determined by the statistics of the dynamics, i.e., how fast the system evolves at a particular length scale. The dynamics of the nanoparticles (i.e., Brownian motion) occur at the nanometer range and microsecond timescale, which makes it impossible to track the exact location of every particle in the vial at every moment. Consider a vial of silica nanoparticles suspended in water, which is a relatively simple soft material. The characterization of spontaneous dynamics in soft materials is a challenging task. Understanding the spontaneous dynamics of the spatial structures formed by competing phases under various conditions is therefore essential for the tailored design of soft materials. Ketchup is designed this way so that it flows more easily when it is squeezed out of a bottle, and sits still when it is on top of a plate. For example, some liquid becomes more fluidic temporarily after a shear is applied (a.k.a. The dynamic competition between the structures of phases in a soft material can have a significant impact on not only its properties, but also the tunability and reversibility of these properties. Most soft materials are complex fluids, which means that they contain a macroscopically uniform mixture of two or more phases. Some examples of soft materials include cream, toothpaste, and blood. Soft materials are ubiquitous in our daily lives, from the food we eat to the products we use to the materials that make up our bodies. The inset on the top right shows the suspended pendant drop captured by the inline optical system. (c) The robotic pendant drop setup in the adjacent chemical laboratory of the Beamline 8-ID-I, where the electronic pipette is shown picking up a fresh pipette tip for liquid handling. Sample preparation station with PCR plates and pipette tips. Reflective mirror with 1 mm diameter x-ray passthrough 6. The red lines and arrows indicate the incoming and scattered x-ray beams. (b) 'Digital Twin' of the robotic pendant drop setup in Nvidia Isaac simulation, where the electronic pipette is docked on the mounting plate for x-ray measurements. The red laser is used for coarse aligning of the x-ray beam in the vertical direction. ![]() The inset on the left shows the comparison of the XPCS results from the pendant drop and the reference setups, and the inset on the right shows a zoom-in optical image of the drop hanging from the pipette tip during the measurement. (a) SA-XPCS measurement on the pendant drop setup at Beamline 8-ID-I, Advanced Photon Source.
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