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Probing shear-induced rearrangements in Fourier space. II. Differential dynamic microscopy
摘要： We discuss in two companion papers how Fourier-space measurements may be coupled to rheological tests in order to elucidate the relationship between mechanical properties and microscopic dynamics in soft matter. In this second companion paper, we focus on Differential Dynamic Microscopy (DDM) under shear. We highlight the analogies and the differences with dynamic light scattering coupled to rheology, providing a theoretical approach and practical guidelines to separate the contributions to DDM arising from the affine and the non-affine part of the microscopic displacement field. We show that in DDM under shear the coherence of the illuminating source plays a key role, determining the effective sample thickness that is probed. Our theoretical analysis is validated by experiments on 2D samples and 3D gels.
关键词： non-affine deformation,shear,soft matter,affine deformation,rheology,Differential Dynamic Microscopy
更新于2025-09-23 15:23:52
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Designing soft pyroelectric and electrocaloric materials using electrets
摘要： A temperature variation can electrically polarize a pyroelectric material. In its converse manifestation, the electrocaloric effect entails a change in temperature due to the application of an electric field. These phenomena have wide applications ranging from infrared detection sensors and solid-state refrigeration to energy harvesting. However, the pyroelectric–electrocaloric effect is typically observed in certain classes of hard, brittle crystalline materials that must satisfy a stringent set of lattice symmetry conditions. Some limited experiments have however demonstrated that embedding immobile charges and dipoles in soft foams (thus creating an electret state) may lead to a pyroelectric-like response as well as large deformations desired from soft matter. In this work, we develop a systematic theory for coupled electrical, thermal and mechanical responses of soft electrets. Using simple illustrative examples, we derive closed-form explicit expressions for the pyroelectric and electrocaloric coefficients of electrets. While pyroelectricity in electrets has been noted before, our derived expressions provide a clear quantitative basis to interpret (and eventually design) this effect as well as insights into how the geometrically nonlinear deformation and Maxwell stress give rise to its emergence. We present conditions to obtain a larger pyroelectric and electrocaloric response. In particular, the electrocaloric effect is predicted for the first time in such materials and we show that a proper design and a reasonable choice of materials can lead to a temperature reduction of as much as 1.5 K under the application of electrical fields of 10 MV cm?1.
关键词： material design,soft matter,theoretical framework,electrets,pyroelectricity,electrocaloric effect
更新于2025-09-23 15:23:52
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In-Line Holography in Transmission Electron Microscopy for the Atomic Resolution Imaging of Single Particle of Radiation-Sensitive Matter
摘要： In this paper, for the first time it is shown how in-line holography in Transmission Electron Microscopy (TEM) enables the study of radiation-sensitive nanoparticles of organic and inorganic materials providing high-contrast holograms of single nanoparticles, while illuminating specimens with a density of current as low as 1–2 e???2s?1. This provides a powerful method for true single-particle atomic resolution imaging and opens up new perspectives for the study of soft matter in biology and materials science. The approach is not limited to a particular class of TEM specimens, such as homogenous samples or samples specially designed for a particular TEM experiment, but has better application in the study of those specimens with differences in shape, chemical composition, crystallography, and orientation, which cannot be currently addressed at atomic resolution.
关键词： TEM,radiation damage,atomic resolution imaging,nanostructured drugs,organic materials,in-line holography,soft matter,single particle imaging
更新于2025-09-23 15:19:57
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X-ray fluorescence holography for soft matter
摘要： X-ray fluorescence holography (XFH) is a technique that can directly image the 3D arrangement of atoms around an element in a sample. The holograms contain both intensity and phase information, allowing atomic reconstruction without needing prior structural information or a tentative structural model. XFH has already been used to reveal the local structures of various inorganic samples, and recently, work has begun on XFH for soft matter. In this paper, we review the progress of XFH on soft materials. First, we review the fundamental principles of XFH. Second, we review inverse mode XFH on soft materials, and the results of the experiments on hemoglobin, myoglobin, and κ-(BEDT-TTF)2Cu[N(CN)2]Br crystals. In the last section, we report the progress of the development of normal mode holography for soft materials. The new apparatus and scanning method is described, and results of the initial tests on the protein Photosystem II are discussed.
关键词： normal mode holography,atomic reconstruction,X-ray fluorescence holography,inverse mode XFH,soft matter
更新于2025-09-16 10:30:52