Self-assembly of plasmonic nanoparticles typically involves attractive interactions or out-of-equilibrium processes, impeding the dynamic structural tunability required for applications. Anisotropic nanoparticles, however, spontaneously assemble at equilibrium into responsive liquid-crystalline phases, driven primarily by repulsive interactions. Here, assemblies of plasmonic silver nanorods combining long-range order with fluidity over macroscopic scales, and organized in isotropic, nematic and smectic phases, were designed by balancing electrostatic and depletion interactions. These assemblies respond to multiple external stimuli, including electric and magnetic fields, temperature, and light, enabling both quick alignment and reversible phase transitions. Control over interparticle spacing and orientational order allows for collective plasmonic coupling and tunable polarization-dependent optical properties, establishing a simple and scalable route to reconfigurable plasmonic materials with dynamic optical functionalities.

Evaporation-induced self-assembly transforms dilute nanoparticle suspensions into ordered plasmonic superlattices, yet the microscopic mechanisms remain unclear for anisotropic particles in water. Here, we study the drying kinetics of silver nanorod (AgNR) dispersions in cetyltrimethylammonium chloride (CTAC) using time-resolved levitated small-angle X-ray scattering (SAXS), complemented by microbeam SAXS and focused ion beam-scanning electron microscopy on dried samples. The key parameter governing superlattice formation is the initial surfactant concentration, outweighing nanoparticle concentration and shape effects. AgNR ordering is synchronized with surfactant organization: CTAC micelles induce depletion attractions that drive nucleation and growth, followed by structural arrest upon CTAC gelation. These findings are directly relevant for improving the design of plasmonic metamaterial and nanoparticle (NP) self-assemblies in a broad sense. Moreover, the dual role played by CTAC micelles (promotion of NPs ordering followed by structural arrest) likely represents a mechanism applicable to other systems where depletants undergo gelation during drying.

This study describes a reproducible process for forming highly mesoporous, mechanically robust, and handleable aerogels based on entangled poly(3-hexylthiophene) (P3HT) and syndiotactic polystyrene (sPS) nanofibers for thermoelectric applications. The highly porous structure results in low thermal conductivity, allowing the temperature difference (between the hot and the cold side) to be maintained across the aerogel sample. Porosity also enables dopants to diffuse efficiently within the sample. When using 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4TCNQ), the highest dopant uptake leads to a maximum apparent electrical conductivity of 2 x 10-2 S cm-1 and a Seebeck coefficient (58 mu V K-1) close to the values obtained in thin films. The Seebeck coefficient is not affected by the high porosity of the material. To improve the doping level of the P3HT:sPS aerogels, FeCl3 or a mixture of F4TCNQ:FeCl3 is also used as a dopant. This enhances the power factor (0.2 mu W m-1 K-2) without significantly increasing the thermal conductivity (30-40 mW m-1 K-1). Finally, the use of the doped aerogel as a vertical thermoelectric generator with one leg is demonstrated by generating a few tens of nW at a thermal difference of 11 K. This result highlights the potential for integrating these polymer aerogels into wearable thermoelectric generators for powering microelectronics.

The chimie-douce route has emerged as an efficient strategy for synthesizing inorganic and organic-inorganic hybrid materials under mild conditions, enabling controls over material size, structure, and functionality. While sol-gel chemistry has been extensively studies to form silicate phases in-depth studies on tungsten oxide gel growth remain scarce. Here, we take advantage of recent advances in the development of in situ techniques and methodologies, particularly in the field of the liquid-phase transmission electron microscopy (LP-TEM), to shed light on the formation of these transition metal oxide-based materials. The starting tungstic acid solution consists of the polyanion decatungstate [W10O32 4-], which is the most stable polyanionic tungstate species at acidic pH, as confirmed by 183W liquid nuclear magnetic resonance (NMR) spectroscopy and synchrotron small-angle X-ray scattering (SAXS). SAXS and LP-TEM revealed the presence of several types of intermediate structures, in particular specific nanometric clusters rich in tungsten, referred to as tungsten-rich aggregates [Wrich-agg], which play a key role in the nucleation and growth of the gel. The observed first-order kinetics, measured by dynamic light scattering (DLS) and 17O NMR, is attributed to the consumption of [Wrich-agg] into intermediate bigger cluster aggregates [WOA] with sizes between 20 and 30 nm. Upon prolonged aging (typically after 24 h), SAXS and ex situ TEM measurements showed the formation of a dense tungsten oxide gel network with a fractal dimension of D f approximate to 2, characteristic of reaction-limited cluster-cluster aggregation (RLCCA). From a methodological perspective, this correlative approach, combining several multiscale techniques, including microscopy, scattering, diffraction, and spectroscopy, offers insights into the growth mechanism of materials obtained via a "chimie-douce" process.

Synchrotron‐based small‐ and wide‐angle X‐ray scattering is used to elucidate the structure of low‐dimensional lepidocrocite–titanate‐based nanofilaments. In the colloidal state, they consist of quantum‐confined 1D NFs, loosely associated into nanoribbons, one lepidocrocite sheet thick (about 4 Å), 30–40 Å wide (5–8 NFs), and more than 300 Å long. In the dry state, they reach a final state of extended sheets, stacked three to about twenty high, whose crystallinity increases with stack height, in parallel with a decrease in photocatalytic activity. These findings suggest a kinetic pathway for the self‐assembly of initially 1D titanate nanoribbons into 2D and ultimately 3D structures, providing context for a recent body of work on these low‐dimensional materials.

In this study, we expand the processing space of new, quantum-confined one-dimensional lepidocrocite (1DL) titania-based nanofilaments (NFs). Our previous work to date entailed reacting Ti-precursors (e.g., TiB2, TiOSO4, TiN, TiC, etc.) with the quaternary ammonium compound (quat) tetramethylammonium hydroxide (TMAH) for tens of hours under ambient pressures at temperatures ranging from 50 degrees C to 80 degrees C. Herein, we expand the list of quats that result in 1DL NFs to tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH), and choline hydroxide (ChoH). We also show that tetrabutylphosphonium hydroxide (TBPH) can be used to the same end result. These quats and TBPH are less toxic than TMAH, especially Cho+, which is fully biocompatible. And, while all the quats and TBPH result in the same 1D product, their de-flocculation in various organic solvents is different. Reacting with less polar quats (e.g., TBA) and washing with less polar solvents (e.g., dichloromethane) favors the formation of porous mesostructured particles. 2D structures are favored if the opposite is chosen. Said otherwise, by the judicious choice of a quat (e.g., TPAH) and solvent (e.g., tert-butanol) combination, we produced stable 1DL colloidal suspensions in dimethyl sulfoxide, methanol, ethanol, acetonitrile, isopropyl alcohol, butanol, and acetone. This enhanced colloidal stability is critical in applications in coatings, inks, and catalytic systems where non-aqueous stable dispersions are paramount. The high band-gap energies, Eg, measured (3.8-3.9 eV) confirm quantum confinement. The Eg are also quite insensitive to d spacings between the 2D sheets. These 1DLs exhibit significant adsorption and dye (rhodamine 6G) degradation capabilities. For example, TEA-1DL colloidal suspensions adsorb 64% of the dye in the dark in about 5 min and decolorize 99% of the remaining dye within 30 min under the irradiance of one sun.

We study experimentally and theoretically liquid crystal structure of smectic oily streaks, focusing on planar wall defects hosted within smectic flattened hemicylinders (SFHs). The wall configuration is singular both in orientational and translational order and we refer to it as the Total Wall Defect (TWD). Here "singular" refers to nematic director field and smectic phase field. In theoretical analysis of the TWD we use a mesoscopic Landau-de Gennes-Ginsburg approach in terms of the nematic tensor order parameter and smectic A (SmA) complex order parameter field. The smectic layer structure is experimentally determined using polarizing optical microscopy and X-ray diffraction measurements at Synchrotron facilities. We demonstrate theoretically and numerically that the experimentally observed abrupt change of the SmA layering in the centre of the wall defect is realized via nematic order reconstruction mechanism. Our experiments reveal that smectic layer spacing above and below the wall are almost similar. The theoretical analysis suggests that lateral SFH boundary conditions determine the vertical position of TWD.

Smectic liquid crystals can be viewed as model systems for lamellar structures for which there has been extensive theoretical development. We demonstrate that a nonlinear energy description is required with respect to the usual Landau-de Gennes elasticity in order to explain the observed layer spacing of highly curved smectic layers. Using x-ray diffraction we have quantitatively determined the dilation of bent layers distorted by antagonistic anchoring (as high as 1.8% of dilation for the most bent smectic layers) and accurately described it by the minimal nonlinear expression for energy. We observe a 1° tilt of planar layers that are connected to the curved layers. This value is consistent with simple energetic calculations, demonstrating how the bending energy impacts the overall structure of a thin distorted smectic film. Finally, we show that combined x-ray measurements and theoretical modeling allow for the quantitative determination of the number of curved smectic layers and of the resulting thickness of the dilated region with unprecedented precision.

Anisometric plasmonic nanoparticles find applications in various fields, from photocatalysis to biosensing. However, exposure to heat or to specific chemical environments can induce their reshaping, leading to loss of function. Understanding this process is therefore relevant both for the fundamental understanding of such nano-objects and for their practical applications. We followed in real time the spontaneous reshaping of gold nanotetrapods in solution via optical absorbance spectroscopy, revealing a two-step kinetics (fast tip flattening into {110} facets, followed by slow arm shortening) with characteristic times a factor of 6 apart but sharing an activation energy around 1 eV. Synchrotron-based X-ray scattering confirms this time evolution, which is much faster in solution than in the dry state, highlighting the importance of the aqueous medium and supporting a dissolution-redeposition mechanism or facilitated surface diffusion. High-temperature transmission electron microscopy of the dry particles validates the solution kinetics.

Plasmonic particles can be welded together, but controlling the metallurgy of the hotspots is a challenge in colloidal chemistry. In this paper, we demonstrate an original method that connects gold particles to their neighbors by another metal of choice. To achieve this goal, we first assemble gold bipyramids in a tip-to-tip configuration, yielding short chains of variable length. The good colloidal stability and surface accessibility make the nanochains suitable seeds to grow metallic junctions in a second step. We follow the oligomer formation and the deposition of the second metal (i.e. silver or palladium) via UV/Vis spectroscopy and we map the plasmonic properties of the nanostructures at nanometer scale using electron energy loss spectroscopy. The formation of silver bridges leads to a huge redshift of the longitudinal plasmon modes into the mid-infrared region, while the addition of palladium results in a redshift accompanied by significant plasmon damping.

Artificial molecular motors have the potential to generate mechanical work on their environment by producing autonomous unidirectional motions when supplied with a source of energy. However, the harnessing of this mechanical work to subsequently activate various endoenergetic processes that can be useful in materials science remains elusive. Here, it is shown that by integrating a light-driven rotary motor through hydrogen bonds in a β-amyloid-like structure forming supramolecular hydrogels, the mechanical work generated during the constant rotation of the molecular machine under UV irradiation is sufficient to disrupt the β-amyloid fibers and to trigger a gel-to-sol transition at macroscopic scale. This melting of the gel under UV irradiation occurs 25 °C below the temperature needed to melt it by solely using thermal activation. In the dark, a reversible sol-gel transition is observed as the system fully recovers its original microstructure, thus illustrating the possible access to new kinds of motorized materials that can be controlled by advanced out-of-equilibrium thermodynamics.

Multicomponent self-assembly has been explored to create novel metamaterials from nanoparticles of different sizes and compositions, but the assembly of nanoparticles with complementary shapes remains rare. Recent binary assemblies were mediated by DNA base pairing or induced by solvent evaporation. Here, we introduce depletion-induced self-assembly (DISA) as a novel approach to constructing tunable binary lattices. In situ structural analysis in the real and reciprocal spaces demonstrates DISA of a binary mixture of octahedra and tetrahedra into extended supercrystals with Fm3m symmetry. The interparticle distance, adjustable by depletant concentration, offers a versatile method for assembling nanoparticles into ordered structures while they remain dispersed in a liquid phase. We show that DISA can control the packing fraction of such binary supercrystals between phi = 0.37 and phi = 0.66, much lower than dense packing in the dry state. These findings highlight DISA's potential for creating complex and highly ordered metamaterials with tailored properties.

Mechanically active [c2]daisy chain rotaxanes were functionalized with mesogens to display liquid-crystalline properties. It was shown that the mechanical actuation of such bistable rotaxanes (between their contracted and extended states) modifies the transition temperature between their isotropic and smectic phases. In addition, small angle X-ray scattering (SAXS) experiments revealed a modification of the smectic phase corresponding to the modification of the interlayer distance as controlled by the mechanical bond. The work described by N. Giuseppone and co-workers in their Research Article opens new opportunities to implement [c2]daisy chain rotaxanes in responsive materials.

A bistable [ c 2]daisy chain rotaxane bearing two mesogenic units was synthesized, and its liquid crystal phase diagram was characterized. As a remarkable result, this study demonstrates that, depending on the contracted or extended state of its mechanical bond, the system can convert between an isotropic and a smectic A mesophase at constant temperature.

Throughout history scientists have looked to Nature for inspiration and attempted to replicate intricate complex structures formed by self-assembly. In the context of synthetic supercrystals, achieving such complexity remains a challenge due to the highly symmetric nature of most nanoparticles (NPs). Previous works have shown intricate coupling between the self-assembly of NPs and confinement in templates, such as emulsion droplets (spherical confinement) or tubes (cylindrical confinement). This study focuses on the interplay between anisotropic NP shape and tunable "prismatic confinement" leading to the self-assembly of supercrystals in cavities featuring polygonal cross sections. A multiscale characterization strategy is employed to investigate the orientation and structure of the supercrystals locally and at the ensemble level. Our findings highlight the role of the mold interface in guiding the growth of distinct crystal domains: each side of the mold directs the formation of a monodomain that extends until it encounters another, leading to the creation of grain boundaries. Computer simulations in smaller prismatic cavities were conducted to predict the effect of an increased confinement. Comparison between prismatic and cylindrical confinements shows that flat interfaces are key to orienting the growth of supercrystals. This work shows a method of inducing orientation in plasmonic supercrystals and controlling their textural defects, thus offering insight into the design of functional metasurfaces and hierarchically structured devices.

Packing solid shapes into regular lattices can yield very complex assemblies, not all of which achieve the highest packing fraction. In two dimensions, the regular pentagon is paradigmatic, being the simplest shape that does not pave the plane completely. In this work, we demonstrate the packing of plasmonic nanoprisms with pentagonal cross section, which form extended supercrystals. We do encounter the long-predicted ice-ray and Dürer packings (with packing fractions of 0.921 and 0.854, respectively) but also a variety of novel polymorphs that can be obtained from these two configurations by a continuous sliding transformation and exhibit an intermediate packing fraction. Beyond the fundamental interest of this result, fine control over the density and symmetry of such plasmonic assemblies opens the perspective of tuning their optical properties, with potential applications in metamaterial fabrication, catalysis, or molecular detection.

I present a simple derivation of the de Gennes narrowing phenomenon.

Well-controlled gelation of fibrillar PEDOT:PSS and growth of ice crystals yield robust anisotropic macroporous materials with a tuned pore size. The honey-comb like structure is at the origin of the low thermal conductivity.

Accurate shape description is a challenge in materials science. Small-angle X-ray scattering (SAXS) can provide the shape, size and polydispersity of nanoparticles by form factor modelling. However, simple geometric models such as the ellipsoid may not be enough to describe objects with complex shapes. This work shows that the form factor of gold nanobipyramids is accurately described by a truncated bicone model, which is validated by comparison with transmission electron microscopy (TEM) data for nine different synthesis batches; the average shape parameters (width, height and truncation) and the sample polydispersity are obtained. In contrast, the ellipsoid model yields worse fits of the SAXS data and exhibits systematic discrepancies with the TEM results.

Lead halide perovskites (LHPs) have emerged as promising candidates for a broad range of optoelectronic devices because of their unique physical properties. Methylammonium lead iodide (MAPI) perovskite has been the most commonly studied LHP due to its very promising optoelectronic properties. One of the main explored pathways for obtaining MAPI perovskites is the synthesis by ligand-assisted reprecipitation (LARP); however, this method is not totally understood from a phenomenological point of view. In this study, we took advantage of the development of a series of advanced in situ techniques to bring new insights into the pathway of this process that leads to MAPI perovskites from a precursor solution. First, we monitored the nucleation and growth processes of a solvated intermediate phase obtained via LARP by correlating local information obtained by a direct visualization of the reaction medium using liquid-phase transmission electron microscopy (TEM) and more global information brought by synchrotron-based X-ray scattering measurements. This combined analysis, in real time and under representative conditions of the synthesis method, allowed us to decipher the structural evolution of the emerging phases, from amorphous and roughly spherical objects in the early stages of the process toward elongated ribbon-like morphology particles after a few seconds, through a crystallization process. Second, we followed in situ the transition of the as-obtained solvated intermediate phase toward the final phase of MAPI perovskite during a thermal treatment at 80(degrees)C, using in this case a combination of gas-phase TEM, in image and diffraction modes, and temperature-resolved X-ray diffraction. We provided direct and unprecedented evidence of the fragmentation of the crystals, simultaneously to the occurrence of the structural transformation between the intermediate and final phases. Our approach, which involved also challenging development of new correlative methods, demonstrates the high interest of such an in situ correlative study for a better understanding of the synthesis and properties of new emerging materials including LHPs.