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Review of scientific instruments 92(2), 023907 (2021). doi:10.1063/5.0035529, Dynamic Light Scattering (DLS) and Small-Angle Neutron Scattering (SANS) are two key tools to probe the dynamic and static structure factors, respectively, in soft matter. Usually, DLS and SANS measurements are performed separately, in different laboratories, on different samples, and at different times. However, this methodology has particular disadvantages for a large variety of soft materials, which exhibit a high sensitivity to small changes in fundamental parameters, such as waiting times, concentration, pH, and ionic strength. Here, we report on a new portable DLS-SANS apparatus that allows one to simultaneously measure both the microscopic dynamics (through DLS) and the static structure (through SANS) on the same sample. The apparatus has been constructed as a collaboration between two laboratories, each an expert in one of the scattering methods, and was commissioned on the LOQ and ZOOM SANS instruments at the ISIS Pulsed Neutron and Muon Source, U.K., Published by American Institute of Physics, [S.l.]

We present a short communication to discuss some of the results of two works by Fujitstuka et al. [M. Fujitsuka, H. Kasai, A. Masuhara, S. Okada, H. Oikawa, H. Nakanishi, A. Watanabe, O. Ito, Chem. Lett. (1997) 1211; M. Fujitsuka, H. Kasai, A. Masuhara, S. Okada, H. Oikawa, H. Nakanishi, O. Ito, K. Yase, J. Photochem. Photobiol. A 133 (2000) 45] in which the photochemical and photophysical properties of a dispersion of fullerene fine particles are discussed. One of the simplest way to growth organic fine particles is the reprecipitation method. In this way microcrystals of fullerene molecules can be obtained with a good control on dimension and size distribution of the final aggregates. The existence and the distribution of fullerene clusters in these liquid solutions is usually attained and characterized by dynamic light scattering technique. In this short communication we want to address a common mistake derived from the widely used reprecipitation method. We show that photoncorrelation measurements from [M. Fujitsuka, H. Kasai, A. Masuhara, S. Okada, H. Oikawa, H. Nakanishi, A. Watanabe, O. Ito, Chem. Lett. (1997) 1211; M. Fujitsuka, H. Kasai, A. Masuhara, S. Okada, H. Oikawa, H. Nakanishi, O. Ito, K. Yase, J. Photochem. Photobiol. A 133 (2000) 45] are faulty due to the presence of a microemulsion between the two solvents used. In ethanol/carbon disulfide mixtures, CS2 droplets dispersed in ethanol mimic in fact the existence of ≈ 300 nm clusters which, actually, do not exist.

The dynamic structure factor of glassy and liquid glycerol has been measured by inelastic X-ray scattering in the exchanged momentum ($Q$) region $Q$=2$\div$23 nm$^{-1}$ and in the temperature range 80$\div$570 K. Beside the propagating longitudinal excitations modes, at low temperature the spectra show a second non $Q$-dispersing peak at $\hbar \Omega_T$$\approx$8.5 meV. We assign this peak to the transverse dynamics that, in topologically disordered systems, acquires a longitudinal symmetry component. This assignment is substantiated by the observation that, in the liquid, this peak vanishes when the structural relaxation time $\tau_\alpha$ approaches $\Omega_T^{-1}$, a behavior consistent with the condition $\tau_\alpha \Omega_T^{-1}$$>>$1 required for the existence of a transverse-like dynamics in the liquid state., Comment: 13 pages, 5 PostScript figures

The relevance of anisotropic interactions in colloidal systems has recently emerged in the context of the rational design of new soft materials1. Patchy colloids of different shapes, patterns and functionalities2 are considered the new building blocks of a bottom-up approach toward the realization of selfassembled bulk materials with predefined properties3-7. The ability to tune the interaction anisotropy will make it possible to recreate molecular structures at the nano- and microscales (a case with tremendous technological applications), as well as to generate new unconventional phases, both ordered and disordered. Recent theoretical studies8 suggest that the phase diagram of patchy colloids can be significantly altered by limiting the particle coordination number (that is, valence). New concepts such as empty liquids8--liquid states with vanishing density--and equilibrium gels8-10-- arrested networks of bonded particles, which do not require an underlying phase separation to form11--have been formulated. Yet no experimental evidence of these predictions has been provided. Here we report the first observation of empty liquids and equilibrium gels in a complex colloidal clay, and support the experimental findings with numerical simulations.

An unexpected dichotomic long time aging behaviour is observed in a glassy colloidal clay suspension investigated by X-ray photon correlation spectroscopy and dynamic light scattering. In the long time aging regime the intensity autocorrelations are non-exponential, following the Kohlrausch–Williams–Watts functional form with an exponent bQ. We show that for spontaneously aged samples a stretched behaviour (bQ < 1) is always found. Surprisingly a compressed exponent (bQ > 1) appears only when the system is rejuvenated by application of a shear field. In both cases the relaxation times scale as Q 1. These observations shed light on the origin of compressed exponential behaviour and help in classifying previous results in the literature on anomalous dynamics.