Tuneable Topography and Hydrophobicity Mode in Biomimetic Plant‐Based Wax Coatings

Across diverse natural surfaces, remarkable interfacial functionalities emerge from micro and nanoscale self-assemblies of wax components. The chemical composition of the epicuticular wax prescribes the intrinsic crystal morphology and resultant topography of the natural surfaces, dictating their interfacial wetting properties. The potential of regulating the topography of identical wax compositions through various crystallization routes is tested here. Crystallization through solvent evaporation produces diverse topographies with enhanced surface hydrophobicity compared to the slow cooling of the wax melt. Further, the microscale interfacial crystalline structure can be deliberately designed to operate in sticky or slippery hydrophobic regimes through control of the supersaturation level during the crystallization process. While the supersaturation level significantly impacts surface wettability by modulating the microscopic aggregation of rice bran wax crystals, the crystal structure at the molecular scale remains effectively unchanged. The relationships between the supersaturation level, surface topography and hydrophobicity modes, primarily derived for rice bran wax, are qualitatively validated for a wider range of plant-based waxes. Crystallization of inherently hydrophobic plant-based waxes from thermodynamically isotropic solutions offers an affordable single-step approach for the fabrication of biodegradable hydrophobic coatings, applicable to versatile materials and geometries

Depression recurrence is accompanied by longer periods in default mode and more frequent attentional and reward processing dynamic brain-states during resting-state activity

Recurrence in major depressive disorder (MDD) is common, but neurobiological models capturing vulnerability for recurrences are scarce. Disturbances in multiple resting-state networks have been linked to MDD, but most approaches focus on stable (vs. dynamic) network characteristics. We investigated how the brain's dynamical repertoire changes after patients transition from remission to recurrence of a new depressive episode. Sixty two drug-free, MDD-patients with ≥2 episodes underwent a baseline resting-state fMRI scan when in remission. Over 30-months follow-up, 11 patients with a recurrence and 17 matched-remitted MDD-patients without a recurrence underwent a second fMRI scan. Recurrent patterns of functional connectivity were characterized by applying Leading Eigenvector Dynamics Analysis (LEiDA). Differences between baseline and follow-up were identified for the 11 non-remitted patients, while data from the 17 matched-remitted patients was used as a validation dataset. After the transition into a depressive state, basal ganglia-anterior cingulate cortex (ACC) and visuo-attentional networks were detected significantly more often, whereas default mode network activity was found to have a longer duration. Additionally, the fMRI signal in the basal ganglia-ACC areas underlying the reward network, were significantly less synchronized with the rest of the brain after recurrence (compared to a state of remission). No significant changes were observed in the matched-remitted patients who were scanned twice while in remission. These findings characterize changes that may be associated with the transition from remission to recurrence and provide initial evidence of altered dynamical exploration of the brain's repertoire of functional networks when a recurrent depressive episode occurs.</p

Interfacial width and phase equilibrium in polymer-fullerene thin-films

Domain composition and interfacial structure are critical factors in organic photovoltaic performance. Here, we report neutron reflectivity, grazing-incidence X-ray diffraction and atomic force microscopy measurements of polymer/fullerene thin-films to test a hypothesis that these partially miscible blends rapidly develop composition profiles consisting of co-existing phases in liquid-liquid equilibrium. We study a range of polymer molecular weights between 2 and 300 kg mol−1, annealing temperatures between 120 and 170 oC, and timescales up to 10 min, yielding over 50 distinct measurement conditions. Model bilayers of fullerene-derivatives and polystyrene enable a rigorous examination of theoretical predictions of the effect of polymer mass and interaction parameter on the compositions, ϕ, and interfacial width, w, of the coexistent phases. We independently measure ϕ and w and find that both Flory-Huggins mean-field-theory and key aspects of self-consistent-field-theory are remarkably consistent with experiment. Our findings pave the way for predictive composition and interface design in organic photovoltaics based on simple experimental measurements and equilibrium thermodynamic theory

Thermodynamics of highly interacting blend PCHMA/dPS by TOF-SANS

We investigate the thermodynamics of a highly interacting blend of poly(cyclohexyl methacrylate)/deuterated poly(styrene) (PCHMA/dPS) with small-angle neutron scattering (SANS). This system is experimentally challenging due to the proximity of the blend phase boundary (>200 °C) and degradation temperatures. To achieve the large wavenumber q-range and flux required for kinetic experiments, we employ a SANS diffractometer in time-of-flight (TOF) mode at a reactor source and ancillary microscopy, calorimetry, and thermal gravimetric analysis. Isothermal SANS data are well described by random-phase approximation (RPA), yielding the second derivative of the free energy of mixing (G″), the effective interaction (χ̅) parameter, and extrapolated spinodal temperatures. Instead of the Cahn–Hilliard–Cook (CHC) framework, temperature (T)-jump experiments within the one-phase region are found to be well described by the RPA at all temperatures away from the glass transition temperature, providing effectively near-equilibrium results. We employ CHC theory to estimate the blend mobility and G″(T) conditions where such an approximation holds. TOF-SANS is then used to precisely resolve G″(T) and χ̅(T) during T-jumps in intervals of a few seconds and overall timescales of a few minutes. PCHMA/dPS emerges as a highly interacting partially miscible blend, with a steep dependence of G″(T) [mol/cm3] = −0.00228 + 1.1821/T [K], which we benchmark against previously reported highly interacting lower critical solution temperature (LCST) polymer blends

A general mechanism for controlling thin film structures in all-conjugated block copolymer : fullerene blends

Block copolymers have the potential to self-assemble into thermodynamically stable nanostructures that are desirable for plastic electronic materials with prolonged lifetimes. Fulfillment of this potential requires the simultaneous optimisation of the spatial organisation and phase behaviour of heterogeneous thin films at the nanoscale. We demonstrate the controlled assembly of an all-conjugated diblock copolymer blended with fullerene. The crystallinity, nanophase separated morphology, and microscopic features are characterised for blends of poly(3-hexylthiophene-block-3-(2-ethylhexyl) thiophene) (P3HT-b-P3EHT) and phenyl-C61-butyric acid methyl ester (PCBM), with PCBM fractions varying from 0–65 wt%. We find that PCBM induces the P3HT block to crystallise, causing nanophase separation of the block copolymer. Resulting nanostructures range from ordered (lamellae) to disordered, depending on the amount of PCBM. We identify the key design parameters and propose a general mechanism for controlling thin film structure and crystallinity during the processing of semicrystalline block copolymers

Moisture uptake characteristics of a pultruded fibre reinforced polymer flat sheet subjected to hot/wet aging

This paper studies the moisture uptake characteristics of a pultruded E-glass fibre reinforced (isophthalic polyester) polymer after long-term exposure to hot/wet conditions. Both fully exposed samples of varying aspect ratios and selectively exposed samples were immersed in distilled water at 25 °C, 40 °C, 60 °C and 80 °C for a period of 224 days. For the fully exposed condition, bulk and directional diffusion coefficient values were determined. A three-dimensional approach using Fickian theory was applied to approximate the principal direction diffusions at 60 °C by using mass changes from samples having different aspect ratios. This revealed that the diffusion coefficient in the longitudinal (pultrusion) direction to be an order of magnitude higher than in the transverse and through-thickness principal directions. Diffusion coefficients in the three principal directions have also been determined for the selectively exposed condition at 60 °C through the application of one-dimensional Fickian theory. It was found that the size and shape of the samples influences moisture uptake characteristics, and thereby the values determined for bulk and directional diffusion coefficients. Furthermore, the influence of exposure temperature on moisture uptake and mass loss with time was examined. Investigation of the water medium by means of electrical measurements suggested that decomposition of the polymeric composite initiates very early, even after the very first day of immersion. Comparison between the infrared signatures from the pultruded material and the water's residual substances revealed significant decomposition, and this behaviour is verified by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopic (EDS) analysis as well as the recorded mass loss after 224 days of aging