Network-forming materials are ubiquitous and appear in industrial products such as tires, food andcosmetics as well as composing the cytoskeleton within the cells of living organisms. They arelightweight and display properties such as optical transparency and reversible deformability up to largestrains. However, microscopic mechanisms protecting a network against macroscopic fracture and theprocesses that control crack growth are still poorly understood. A deeper understanding is needed tofully exploit the potential of polymer networks in advanced and novel material design. To this end, weadapt photon correlation imaging [1] (PCI) to reveal the microscopic rearrangements within poly(ethylacrylate) networks [2] during deformation by extension and fracture (see figure 1).PCI creates a time-resolved macroscopic map (field of view of several mm) of the microscopicmovements (on the order of 1µm) induced by the applied strain preceding fracture. We find that, in ournearly transparent samples, surface scattering dominates the PCI signal, obscuring bulk rearrangements.To address this issue, we first minimise surface scattering by immersing the sample in a pool filled withrefractive index matching glycerol, where the geometry of the pool walls is carefully designed to avoidreflections. Furthermore, the pool design allows PCI to be performed at both high (176o) and low (4o)angles simultaneously to measure rearrangements of the polymer network on length scales of 200 nmand 5 µm, respectively. Second, we introduce melamine formaldehyde nanoparticles to the polymernetworks to increase the scattering from the bulk. Preliminary measurements reveal non-affinecontributions even at low strain, well within the linear regime. We will continue by investigating therole that network architecture, such as interpenetrated multiple networks [3,4], has in the dynamicresponse of the network and the resultant resistance to fracture. References[1] A. Duri, D. A. Sessoms, V. Trappe, and L. Cipelletti Phys. Rev. Lett., 2009 102(8), 085702.[2] P. Millereau, E. Ducrot, J. M. Clough, M. E. Wiseman, H. R. Brown, R. P. Sijbesma, and C.Creton, PNAS, 2018 115(37), 9110–9115.[3] J. P. Gong, Y. Katsuyama, T. Kurokawa, and Y. Osada Adv. Mater., 2003 15, 1155.[4] E. Ducrot, Y. Chen, M. Bulters, R. P. Sijbesma, and C. Creton Science, 2014 344, 186.

We have used large-scale molecular dynamics simulations in order to investigate the surface properties of lithium, sodium, and potassium silicate glasses containing 25 mol% of alkali oxide. We have studied two types of surfaces, a melt-formed surface (MS) and a fracture surface (FS), and we have found that the influence of the alkali modifier on the surface properties depends strongly on the nature of the surface. The MS show a saturation of elemental concentration when the alkali is changed from Na to K, while the FS exhibit a monotonic increase of modifier concentration with increasing the alkali size. For the FS we find that larger alkali ions reduce the concentration of under-coordinated Si atoms at the surface and increases the fraction of two-membered rings.For both types of surfaces, the surface roughness of the surfaces are found to increase with alkali size, with the effect being more pronounced for the FS than for the MS. The height-height correlation function of the surfaces show a scaling behavior that is independent of the alkali species considered: The one for the MS is compatible with the prediction of thefrozen capillary wave theory while the ones for the FS shows a logarithmic growth, i.e., on the nanoscale these surfaces are not self-affine fractals. The influence of the modifier on the surface properties are rationalized in terms of the interplay between multiple factors involving the size of the ions, bond strength, and charge balance on the surface.

This Research Topic originates from the symposium Probing Out-of-Equilibrium Soft Matter that was held on October 22–23, 2021 at the University of Fribourg (Switzerland) to celebrate and honor the career of Véronique Trappe. The symposium assembled leading scientists in the rapidly growing field of non-equilibrium soft matter physics, a field to which V. Trappe has made key contributions that have changed the view of many [1–6]. While the equilibrium behaviour of soft matter is amply studied and understood, novel tools are needed to capture the complexity of out-of-equilibrium soft materials. A particular challenge is getting access to and understanding the fast processes occurring at the nano- and micro-scale of the elementary constituents, while simultaneously capturing the slower evolution of bulk properties in non-equilibrium conditions. To take on this task, new theoretical, numerical and experimental methodologies need to be developed that enable the investigation of the structure, dynamics, thermodynamics, and rheology of out-of-equilibrium soft matter. Adopting a comprehensive view that covers fundamental topics as well as research focusing on processes and issues faced in applications, this Research Topic aims to showcase some of the latest advancements and innovations in the field.