Search

Abstract: Polymer/clay composite inks are exceptionally useful materials for fabrication processes based on 3D direct‐ink writing, however, there remains an insufficient understanding of how their physiochemical dynamics impact printability. Using a model system, N‐isopropylacrylamide/Laponite, the electrostatic interactions between Laponite platelets are modified to tune critical rheological properties in order to improve printability. Rheological measurements and X‐ray scattering experiments are carried out to monitor the nano/micro‐structural dynamics and complex physicochemical interactions of Laponite as it impacts complex modulus in the linear region, flow behavior, thixotropy, and yield stress of the composite ink. Modification of the electrostatic interactions between platelets reduces the yield stress of the material, while maintaining a complex microstructure that allows for sufficient recovery times upon removal of stress to form stable, and thus printable, filaments. A printing‐centric approach is established based on a fundamental understanding of electrostatic inter‐particle interactions, harnessing the innate microstructure of Laponite in 3D direct‐ink writing of composites. [ABSTRACT FROM AUTHOR]

The static structure and dynamic behavior of cadmium sulfide nanoparticles suspended in block copolymer matrix are investigated using transmission electron microscopy, small-angle X-ray scattering, and X-ray photon correlation spectroscopy. The transmission electron microscopy study shows that cadmium sulfide nanoparticles are preferentially segregated within the polyisoprene domain of a poly(styrene- block-isoprene) diblock copolymer. For the dynamics study, X-ray photon correlation spectroscopy captures the relaxation process of cadmium sulfide nanoparticles. The measured characteristic relaxation time reveals that the observed dynamics are hyperdiffusive. The characteristic velocity and corresponding activation energy, which are hallmarks of a hyperdiffusive system, are determined from the relationship between the characteristic relaxation time and the wavevector. [ABSTRACT FROM AUTHOR]

The technique of speckle visibility spectroscopy has been employed for the measurement of dynamics using coherent X-ray scattering. It is shown that the X-ray contrast within a single exposure can be related to the relaxation time of the intermediate scattering function, and this methodology is applied to the diffusion of 72 nm-radius latex spheres in glycerol. Data were collected with exposure times as short as 2 ms by employing a resonant shutter. The weak scattering present for short exposures necessitated an analysis formalism based on the spatial correlation function of individual photon charge droplets on an area detector, rather than the usual methods employed for intensity correlations. It is demonstrated that this method gives good agreement between theory and experiment and thus holds promise for extending area-detector-based coherent scattering methods to the study of faster dynamics than previously obtainable. [ABSTRACT FROM AUTHOR]

Using high-resolution x-ray scattering and x-ray photon correlation spectroscopy (XPCS), we have investigated the structure and dynamics of charge density wave (CDW) dynamics in pure and titanium-doped 1T-TaS2. Time-averaged scattering measurements of pure and doped samples reveal that 1T-TaS2 is a weakly pinned two-dimensional CDW system. Using XPCS, we find that after long anneals the CDW domain structure in the incommensurate phase is pinned and stable against spontaneous fluctuations thus rejecting phasons as spontaneous excitations in higher-dimensional CDW systems. By examining the dynamics of deeply quenched samples upon heating, we find that metastable CDW configurations collectively rearrange in a nonequilibrium manner. For nominally pure samples, we determine an energy barrier to relaxation of 4600 K that is considerably greater than that found for lower-dimensional CDWs. [ABSTRACT FROM AUTHOR]

As an increasingly important structural-characterization technique, grazing-incidence X-ray scattering (GIXS) has found wide applications for in situ and real-time studies of nanostructures and nanocomposites at surfaces and interfaces. A dedicated beamline has been designed, constructed and optimized at beamline 8-ID-E at the Advanced Photon Source for high-resolution and coherent GIXS experiments. The effectiveness and applicability of the beamline and the scattering techniques have been demonstrated by a host of experiments including reflectivity, grazing-incidence static and kinetic scattering, and coherent surface X-ray photon correlation spectroscopy. The applicable systems that can be studied at 8-ID-E include liquid surfaces and nanostructured thin films. [ABSTRACT FROM AUTHOR]

To determine the suitability of commonly used windows for small-angle X-ray scattering, a range of materials, including Kapton, (aluminized) Mylar, beryllium, high-purity aluminium foil, mica and silicon nitride have been studied. At small wavevector transfers, Q, in the range 2 × 10−3 to 0.2 nm−1, the scattering from Kapton, mica and beryllium is reasonably well described by power laws in Q with exponents of −3.25, −3.6 and −3.9, respectively. There are large variations in the scattering from mica, but a freshly cleaved natural mica window was by far the weakest scatterer. For applications where radiation in the infrared or visible range should be blocked, aluminized Mylar is the most suitable material. Both Mylar and Kapton can be used to make very simple demountable superfluid-tight windows using indium O-ring seals. [ABSTRACT FROM AUTHOR]

Recent measurements of the scattering function and of the dynamics of surface and interfacial fluctuations in thin supported molten films and bilayers using synchrotron X-ray diffuse scattering and photon correlation spectroscopy in reflection geometry are reported. The results for monolayer films thicker than four times of the radius of gyration of polystyrene show behavior of normal over-damped capillary waves expected for the surface fluctuations of a viscous liquid. However, thinner films show deviations indicating the need to account for viscoelasticity. The theory has been extended to the surface and interfacial modes in a bilayer film system. The results are discussed in terms of surface tension, viscosity and shear modulus. Also recent experiments to measure the isothermal compressibility of supported polystyrene films by studying `bulk' scattering from the interior of the films is discussed. [ABSTRACT FROM AUTHOR]

We have examined the formation and dissolution of gels composed of intermediate volume-fraction nanoparticles with temperature-dependent short-range attractions using small-angle x-ray scattering, x-ray photon correlation spectroscopy, and rheology to obtain nanoscale and macroscale sensitivity to structure and dynamics. Gel formation after temperature quenches to the vicinity of the rheologically determined gel temperature, Tgel, was characterized via the slowdown of dynamics and changes in microstructure observed in the intensity autocorrelation functions and structure factor, respectively, as a function of quench depth (ΔT=Tquench-Tgel), wave vector, and formation time tf. We find the wave-vector-dependent dynamics, microstructure, and rheology at a particular ΔT and tf map to those at other ΔTs and tfs via an effective scaling temperature, Ts. A single Ts applies to a broad range of ΔT and tf but does depend on the particle size. The rate of formation implied by the scaling is a far stronger function of ΔT than expected from the attraction strength between colloids. We interpret this strong temperature dependence in terms of cooperative bonding required to form stable gels via energetically favored, local structures. [ABSTRACT FROM AUTHOR]

We studied the dynamics of the Au (001) surface in 0.1 M HClO4 electrolyte solution using coherent surface x-ray scattering (CSXS). We find that edges of steps and islands on the Au (001) surface are highly dynamic in electrolyte and evolve continuously even at room temperature. The evolving speed increases nearly two orders of magnitude when the quasihexagonal reconstruction is lifted during slow potential sweep and is higher by more than four orders of magnitude than the speed measured previously in vacuum. In addition, we find that surface lattice dynamics appear when the reconstruction is lifted, and they are faster by two orders of magnitudes than the edge dynamics. Complementary scanning tunneling microscopy images are also presented for visual confirmation of the changes measured by the CSXS technique. [ABSTRACT FROM AUTHOR]