The addition of water to native cellulose/1-ethyl-3methylimidazolium acetate solutions catalyzes the formation of gels, where polymer chain-chain intermolecular associations act as cross-links. However, the relationship between water content (Wc), polymer concentration (Cp), and gel strength is still missing. This study provides the fundamentals to design water-induced gels. First, the sol-gel transition occurs exclusively in entangled solutions, while in unentangled ones, intramolecular associations hamper interchain cross-linking, preventing the gel formation. In entangled systems, the addition of water has a dual impact: at low water concentrations, the gel modulus is water-independent and controlled by entanglements. As water increases, more cross-links per chain than entanglements emerge, causing the modulus of the gel to scale as Gp ∼ C p^2 Wc^3.0±0.2. Immersing the solutions in water yields hydrogels with noncrystalline, aggregate-rich structures. Such water-ionic liquid exchange is examined via Raman, FTIR, and WAXS. Our findings provide avenues for designing biogels with desired rheological properties.

Optical metasurfaces are two-dimensional assemblies of nanoscale optical resonators and could constitute the next-generation of ultra-thin optical components. The development of methods to manufacture those nanostructures on a large scale is still a challenge, while most performance demonstrations were obtained with lithographically fabricated metasurfaces, that are restricted to small scales. Self-assembly fabrication routes are scattering of the nanoresonators in a meta-fluid, and show that they present strong optical magnetic resonances and directional forward scattering patterns, with scattering efficiencies of up to 4. The metasurfaces consist in homogeneous films, of variable surface density, of colloidal clusters which have the same extinction properties on the surface and in the fluid. This experimental approach allows for the large scale production of metasurfaces.

Plastic pollution in the aquatic environment has been assessed for many years by ocean waste collection expeditions around the globe or by river sampling. While the total amount of plastic produced worldwide is well documented, the amount of plastic found in the ocean, the distribution of particles on its surface and its evolution over time are still the subject of much debate. In this article, we propose a general fragmentation model, postulating the existence of a critical size below which particle fragmentation becomes extremely unlikely. In the frame of this model, an abundance peak appears for sizes around 1mm, in agreement with real environmental data. Using, in addition, a realistic exponential waste feed to the ocean, we discuss the relative impact of fragmentation and feed rates, and the temporal evolution of microplastics (MP) distribution. New conclusions on the temporal trend of MP pollution are drawn.

Recent studies of self-assembly in binary systems of bio-surfactants, either of microbial origin or saponins extracted from plants, are reviewed. Saponins in water reported in the first section include aescin, glycyrrhizin, and quillaja saponins, while rhamnolipids are discussed in the second section on microbial surfactants. Studies of surface activities are a natural starting point of the characterization of surfactants, but here we focus mainly on physico-chemical and structural properties of self-assembled bulk structures in solution, often characterized by scattering techniques. When quantitative modelling is performed, self-assembly parameters like aggregation numbers, head group areas, and resulting shapes can be followed as a function of physical-chemical parameters like concentration, composition, temperature, or pH. Morphologies include micelles and their structural evolution with addition of other bio- or synthetic surfactants, co-surfactants, proteins or phospholipids.

The interplay of soft responsive particles, such as microgels, with nanoparticles (NPs) yields highly versatile complexes that show great potential for applications, ranging from plasmonic sensing to catalysis and drug delivery. However, the microgel–NP assembly process has not been investigated so far at the microscopic level, thus hindering the possibility of designing such hybrid systems a priori. In this work, we combine state-of-the-art numerical simulations with experiments to elucidate the fundamental mechanisms taking place when microgel–NP assembly is controlled by electrostatic interactions and the associated effects on the structure of the resulting complexes. We find a general behavior where, by increasing the number of interacting NPs, the microgel deswells up to a minimum size after which a plateau behavior occurs. This occurs either when NPs are mainly adsorbed to the microgel corona via the folding of the more external chains or when NPs penetrate inside the microgel, thereby inducing a collective reorganization of the polymer network. By varying microgel properties, such as fraction of cross-linkers or charge, as well as NP size and charge, we further show that the microgel deswelling curves can be rescaled onto a single master curve, for both experiments and simulations, demonstrating that the process is entirely controlled by the charge of the whole microgel–NP complex. Our results thus have a direct relevance in fundamental materials science and offer novel tools to tailor the nanofabrication of hybrid devices of technological interest.

Soft materials are usually defined as materials made of mesoscopic entities, often self-organized, sensitive to thermal fluctuations and to weak perturbations. Archetypal examples are colloids, polymers, amphiphiles, liquid crystals, foams. The importance of soft materials in everyday commodity products, as well as in technological applications, is enormous, and controlling or improving their properties is the focus of many efforts. From a fundamental perspective, the possibility of manipulating soft material properties, by tuning interactions between constituents and by applying external perturbations, gives rise to an almost unlimited variety in physical properties. Together with the relative ease to observe and characterize them, this renders soft matter systems powerful model systems to investigate statistical physics phenomena, many of them relevant as well to hard condensed matter systems. Understanding the emerging properties from mesoscale constituents still poses enormous challenges, which have stimulated a wealth of new experimental approaches, including the synthesis of new systems with, e.g., tailored self-assembling properties, or novel experimental techniques in imaging, scattering or rheology. Theoretical and numerical methods, and coarse-grained models, have become central to predict physical properties of soft materials, while computational approaches that also use machine learning tools are playing a progressively major role in many investigations. This roadmap paper intends to give a broad overview of recent and possible future activities in the field of soft materials, with experts covering various developments and challenges in material synthesis and characterization, instrumental, simulation and theoretical methods as well as general concepts.

Small-angle scattering is a commonly used tool to analyze the dispersion of nanoparticles in all kinds of matrices. Besides some obvious cases, the associated structure factor is often complex and cannot be reduced to a simple interparticle interaction, like excluded volume only. In recent experiments, we have encountered a surprising absence of structure factors (S(q) = 1) in scattering from rather concentrated polymer nanocomposites [A.-C. Genix et al, ACS Appl. Mater. Interfaces 11 (2019) 17863]. In this case, quite pure form factor scattering is observed. This somewhat “ideal” structure is further investigated here making use of reverse Monte Carlo simulations in order to shed light on the corresponding nanoparticle structure in space. By fixing the target “experimental” apparent structure factor to one over a given q-range in these simulations, we show that it is possible to find dispersions with this property. The influence of nanoparticle volume fraction and polydispersity has been investigated, and it was found that for high concentrations only a high polydispersity allows reaching a state of S = 1. The underlying structure in real space is discussed in terms of the pair-correlation function, which evidences the importance of attractive interactions between polydisperse nanoparticles. The calculation of partial structure factors shows that there is no specific ordering of large or small particles, but that the presence of attractive interactions together with polydispersity allows reaching an almost “structureless” state.