Role of Absorbing Nanocrystal Cores in Soft Photonic Crystals: A Spectroscopy and SANS Study

Periodic superstructures of plasmonic nanoparticles have attracted significant interest because they can support coupled plasmonic modes, making them interesting for plasmonic lasing, metamaterials, and as light-management structures in thin-film optoelectronic devices. We have recently shown that noble metal hydrogel core–shell colloids allow for the fabrication of highly ordered 2-dimensional plasmonic lattices that show surface lattice resonances as the result of plasmonic/diffractive coupling (Volk, K.; Fitzgerald, J. P. S.; Ruckdeschel, P.; Retsch, M.; König, T. A. F.; Karg, M. Reversible Tuning of Visible Wavelength Surface Lattice Resonances in Self-Assembled Hybrid Monolayers. <i>Adv. Optical Mater</i>. <b>2017</b>, <i>5</i>, 1600971, DOI: 10.1002/adom.201600971). In the present work, we study the photonic properties and structure of 3-dimensional crystalline superstructures of gold hydrogel core–shell colloids and their pitted counterparts without gold cores. We use far-field extinction spectroscopy to investigate the optical response of these superstructures. Narrow Bragg peaks are measured, independently of the presence or absence of the gold cores. All crystals show a significant reduction in low-wavelength scattering. This leads to a significant enhancement of the plasmonic properties of the samples prepared from gold-nanoparticle-containing core–shell colloids. Plasmonic/diffractive coupling is not evident, which we mostly attribute to the relatively small size of the gold cores limiting the effective coupling strength. Small-angle neutron scattering is applied to study the crystal structure. Bragg peaks of several orders clearly assignable to an fcc arrangement of the particles are observed for all crystalline samples in a broad range of volume fractions. Our results indicate that the nanocrystal cores do not influence the overall crystallization behavior or the crystal structure. These are important prerequisites for future studies on photonic materials built from core–shell particles, in particular, the development of new photonic materials from plasmonic nanocrystals

Monitoring the Coordination Modulator Shell at MOF Nanocrystals

A small angle neutron scattering (SANS) study is presented, which investigates the impact of a modulator on nucleation and growth of MOF-5 nanoparticles. Two DMF solutions, one with the secondary building unit Zn₄O­(C₆H₅COO)₆ (SBU) and one with terephthalic acid (BDC) as a linker, were mixed, and 5 min after generation of the mixture, monodentate 4-<i>n</i>-decylbenzoic acid was added as a modulator agent. Time-resolved SANS during the initial stages of the particle formation process offered insight into morphological transformations during the first hours. Subsequently, it could be demonstrated that a shell is formed by the modulator wrapping around the growing MOF-5 particles while directing the formation of MOF-5 nanoparticles. This has been made possible by an identification of a mixture of deuterated and hydrogenated solvent (DMF), which matches the scattering contrast of MOF-5, thus giving access to the scattering signal of the modulator

Small-Angle Neutron Scattering Study of Structure and Interaction of Nanoparticle, Protein, and Surfactant Complexes

Small-angle neutron scattering (SANS) measurements have been carried out from the multicomponent system composed of Ludox HS40 silica nanoparticle, bovine serum albumin (BSA) protein, and sodium dodecyl sulfate (SDS) surfactant in an aqueous system under the solution condition that all the components are negatively charged. Although the components are similarly charged, strong structural evolutions among them have been observed. The complexes of different components in pairs (nanoparticle–protein, nanoparticle–surfactant, and protein–surfactant) have been examined to correlate the role of each component in the three-component nanoparticle–protein–surfactant system. The nanoparticle–protein system shows depletion interaction induced aggregation of nanoparticles in the presence of protein. Both nanoparticle and surfactant coexist individually in a nanoparticle–surfactant system. In the case of a protein–surfactant system, the cooperative binding of surfactant with protein leads to micelle-like clusters of surfactant formed along the unfolded protein chain. The structure of the three-component (nanoparticle–protein–surfactant) system is found to be governed by the synergetic effect of nanoparticle–protein and protein–surfactant interactions. The nanoparticle aggregates coexist with the structures of protein–surfactant complex in the three-component system. The nanoparticle aggregation as well as unfolding of protein is enhanced in this system as compared to the corresponding two-component systems

Impact of Additive Hydrophilicity on Mixed Dye-Nonionic Surfactant Micelles: Micelle Morphology and Dye Localization

The nonionic surfactant pentaethylene glycol-monododecylether C12E5 forms micelles in aqueous solutions with a lower critical solution temperature. This characteristic solution behavior of C12E5 is independent of the pH. Such micelles are used to solubilize a large variety of active guest molecules like for instance dyestuffs. An example is an acidic azo dye termed Blue used as a hair colorant. Depending on the pH, Blue gradually changes its hydrophilicity from the protonated BlueH at pH = 2 to the bivalent anion Blue2– at pH = 13 while keeping the shape and size of Blue essentially unchanged. These features of C12E5 and Blue offer the unique chance to investigate the sole impact of a tunable hydrophilicity of a guest molecule on the solution behavior of mixed micelles of the guest and C12E5. Accordingly, the present work establishes a phase diagram of Blue-C12E5 micelles and analyzes their morphology including the spatial distribution of Blue in the micelles as a function of the hydrophilicity of Blue. Small angle neutron scattering reveals the size and shape of the micelles, and detailed contrast matching of the C12E5 supported by 1H NMR with NOESY provided insight into the localization of Blue within the micelles as its hydrophilicity changes

Probing the Microstructure of Nonionic Microemulsions with Ethyl Oleate by Viscosity, ROESY, DLS, SANS, and Cyclic Voltammetry

Microemulsions are important formulations in cosmetics and pharmaceutics and one peculiarity lies in the so-called “phase inversion” that takes place at a given water-to-oil concentration ratio and where the average curvature of the surfactant film is zero. In that context, we investigated the structural transitions occurring in Brij 96-based microemulsions with the cosmetic oil ethyl oleate and studied the influence of the short chain alcohol butanol on their structure and properties as a function of water addition. The characterization has been carried out by means of transport properties, spectroscopy, DLS, SANS, and electrochemical methods. The results confirm that the nonionic Brij 96 in combination with butanol as cosurfactant forms a U-type microemulsion that upon addition of water undergoes a continuous transition from swollen reverse micelles to oil-in-water (O/W) microemulsion via a bicontinuous region. After determining the structural transition through viscosity and surface tension, the 2D-ROESY studies give an insight into the microstructure, i.e., the oil component ethyl oleate mainly is located at the hydrophobic tails of surfactant while butanol molecules reside preferentially in the interface. SANS experiments show a continuous increase of the size of the structural units with increasing water content. The DLS results are more complex and show the presence of two relaxation modes in these microemulsions for low water content and a single diffusive mode only for the O/W microemulsion droplets. The fast relaxation reflects the size of the structural units while the slower one is attributed to the formation of a network of percolated microemulsion aggregates. Electrochemical studies using ferrocene have been carried out and successfully elucidated the structural transformations with the help of diffusion coefficients. An unusual behavior of ferrocene has been observed in the present microheterogeneous medium, giving a deeper insight into ferrocene electrochemistry. NMR-ROESY experiments give information regarding the internal organization of the microemulsion droplets. In general, one finds a continuous structural transition from a W/O over a bicontinuous to an O/W microemulsion, however with a peculiar network formation over an extended concentration range, which is attributed to the somewhat amphiphilic oil ethyl oleate. The detailed knowledge of the structural behavior of this type of system might be important for their future applications

Conformation and Interactions of Polystyrene and Fullerenes in Dilute to Semidilute Solutions

We report the polymer conformation and fullerene aggregation in a ternary system containing polystyrene, C₆₀, and toluene measured by small angle neutron, static, and dynamic light scattering. We investigate polymer concentrations across the dilute and semidilute regime for five polymer molecular weights (<i>M</i>_w = 20 kg/mol to 1 Mg/mol), and fullerene concentrations below and above its miscibility threshold in toluene. We find that the polymer radius of gyration (<i>R</i>_g^poly), hydrodynamic radius (<i>R</i>_h), and the mixture correlation length (ξ) remain unchanged upon addition of C₆₀. The miscibility of C₆₀ in toluene, however, decreases upon addition of polystyrene forming aggregates with a time-dependent radius on the order of 100 nm, and this effect is amplified with increasing polymer <i>M</i>_w. Our findings are relevant to the solution processing of organic photovoltaics, which generally require the effective solubilization of fullerene derivatives and polymer pairs in this concentration range

Thermoresponsive Hydrogels Based on Telechelic Polyelectrolytes: From Dynamic to “Frozen” Networks

A novel thermoresponsive gelator of (B-<i>co</i>-C)-<i>b</i>-A-<i>b</i>-(B-<i>co</i>-C) topology, comprising a poly­(2-(dimethyl­amino)­ethyl methacrylate) (PDMAEMA) weak polyelectrolyte as central block, end-capped by thermosensitive poly­(triethylene glycol methyl ether methacrylate/<i>n</i>-butyl methacrylate) [P­(TEGMA-<i>co</i>-<i>n</i>BuMA)] random copolymers, was designed and explored in aqueous media. The main target of this design was to control the dynamics of the stickers by temperature as to create an injectable hydrogel that behaves as a weak gel at low temperature and as a strong gel at physiological temperature. Indeed, at low temperatures, the system behaves like a viscoelastic complex fluid (dynamic network), while at higher temperatures, an elastic hydrogel is formed (“frozen” network). The viscosity increases exponentially upon heating, about 5 orders of magnitude from 5 to 45 °C, which is attributed to the exponential increase of the lifetime of the self-assembled stickers. The integration of thermo- and shear responsive properties in the gelator endows the gel with injectability. Moreover, the gel can be rapidly recovered upon cessation of the applied stress at 37 °C, simulating conditions similar to those of injection through a 28-gauge syringe needle. All these hydrogel properties render it a good candidate for potential applications in cell transplantation through injection strategies

Structure and Morphology of Charged Graphene Platelets in Solution by Small-Angle Neutron Scattering

Solutions of negatively charged graphene (graphenide) platelets were produced by intercalation of nanographite with liquid potassium–ammonia followed by dissolution in tetrahydrofuran. The structure and morphology of these solutions were then investigated by small-angle neutron scattering. We found that >95 vol % of the solute is present as single-layer graphene sheets. These charged sheets are flat over a length scale of >150 Å in solution and are strongly solvated by a shell of solvent molecules. Atomic force microscopy on drop-coated thin films corroborated the presence of monolayer graphene sheets. Our dissolution method thus offers a significant increase in the monodispersity achievable in graphene solutions

Pressure-Responsive, Surfactant-Free CO₂‑Based Nanostructured Fluids

Microemulsions are extensively used in advanced material and chemical processing. However, considerable amounts of surfactant are needed for their formulation, which is a drawback due to both economic and ecological reasons. Here, we describe the nanostructuration of recently discovered surfactant-free, carbon dioxide (CO₂)-based microemulsion-like systems in a water/organic-solvent/CO₂ pressurized ternary mixture. “Water-rich” nanodomains embedded into a “water-depleted” matrix have been observed and characterized by the combination of Raman spectroscopy, molecular dynamics simulations, and small-angle neutron scattering. These single-phase fluids show a reversible, pressure-responsive nanostructuration; the “water-rich” nanodomains at a given pressure can be instantaneously degraded/expanded by increasing/decreasing the pressure, resulting in a reversible, rapid, and homogeneous mixing/demixing of their content. This pressure-triggered responsiveness, together with other inherent features of these fluids, such as the absence of any contaminant in the ternary mixture (<i>e</i>.<i>g</i>., surfactant), their spontaneous formation, and their solvation capability (enabling the dissolution of both hydrophobic and hydrophilic molecules), make them appealing complex fluid systems to be used in molecular material processing and in chemical engineering

Amphiphilic Polymer Conetworks Based on End-Linked “Core-First” Star Block Copolymers: Structure Formation with Long-Range Order

Amphiphilic polymer conetworks are cross-linked polymers that swell both in water and in organic solvents and can phase separate on the nanoscale in the bulk or in selective solvents. To date, however, this phase separation has only been reported with short-range order, characterized by disordered morphologies. We now report the first example of amphiphilic polymer conetworks, based on end-linked “core-first” star block copolymers, that form a lamellar phase with long-range order. These mesoscopically ordered systems can be produced in a simple fashion and exhibit significantly improved mechanical properties