Browsing by Author "Sencadas, V"

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    Millisecond structural dynamics during the piezoelectric cycle of silk fibroin by synchrotron Xray scattering & comparison with DFT calculation
    (2021-08-14) Garvey, CJ; Mudie, ST; Music, D; Olsson, PAT; Sencadas, V
    While simple associations exist between piezoelectric properties and processing history, there is considerable scope for design of materials based on a more detailed molecular understanding of the re-arrangements that underpin the piezoelectric phenomenon in silk fibroin.[1] Crystallinity, and the two-phase model of semi-crystalline model of polymers, are often used to understand the properties of protein based materials where there is considerable thermodynamic drive to short range ordering of polymer chains, folding, which is not present in melt processed thermoplastics. Our investigations aim to probe the relationship between structure and dynamics in silk fibroin based materials and correlate these with the piezo-electric signal. Recently, we have used a triggered and summative data acquisition scheme to synchronise X-ray scattering data collection with a piezoelectric cycle of a compressed electro-spun fibroin mat.[2] This mode enabled a steady perturbed state to be sampled. The summation of the scattering patten from this state across multiple cycles provides superior statistics than could be achieved by sampling a single cycle. The setup is shown in Figure 1A. At rest this poorly ordered system exhibits a limited number of very broad peaks but quite a high degree of chain folding.[3] With compression there is marked increase in the scattered intensity, both in the small (SAXS) and the wide (WAXS) angle regimes, as well as a shift and reduction in broadness of the WAXS peaks (Figure 1B). We interpret the increase in the SAXS signal as an increase in scattering from grain boundaries and the WAXS as the formation of new crystalline domains. However, the limited number of very broad diffraction peaks make these data unsuitable for structural determination. In order to provide an alternative, but complementary, perspective on the structural dynamics and the nature of the potential surface along which the polymer folds, during the piezo cycle we have turned to a computation approach. Density functional theory (DFT) calculations were performed within the framework of the projector augmented wave potentials parametrised by Perdew et al., [3] and the Tkatchenko-Scheffler correction [4] with a self-consistent screening to account for the weak correlations. Full structural optimisation of orthorhombic C20O8N8H32 was performed. The calculated lattice parameters (a = 9.409 Å, b = 6.984 Å, c = 9.221 Å) and the corresponding diffraction pattern (black vertical lines) are compared with the experimental data in Figure 1C. © The Authors
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    Thermoresponsive hybrid colloidal capsules as an inorganic additive for fire-resistant silicone-based coatings
    (American Chemical Society, 2022-09-07) Pham, ST; Tieu, AK; Sencadas, V; Joseph, P; Arun, M; Cortie, DL
    Improving the fire-resistant efficiency of silicone-based polymeric coatings is important in the building industry and electrical utilities. In this study, the water-containing hybrid calcium carbonate (CaCO3)-silica (SiO2) colloidal capsule has been developed and optimized as an inorganic flame-retardant additive. This capsule exhibits excellent thermal stability up to 1000 °C with a remaining intact hollow spherical structure. When used as an inorganic filler at 15 wt %, it not only reduces the potential fire hazards by over 44% (i.e., the sumHRC reduced from 112.00 J/g K to 62.00 J/g K) but also improves the heat-barrier efficiency by over 30% (i.e., the temperature at the steady state reduced from 350 to 360 °C to below 250 °C) of the silicone-based polymeric coatings. In addition, the capsule-polymer composite coating exhibits excellent ductility which can withstand heat-induced mechanical stresses and prevent crack propagation under radiative heating conditions. The fire-resistant mechanism of the colloidal capsule is related strongly to the encapsulated water core and the reactions between SiO2 and CaCO3 at elevated temperatures. They not only contribute to a cooling effect on the flammable pyrolysis gases but also induce the insulative effect to the resulted char during combustion. The significant advances in this study will have a high impact in customizing the functional inorganic additives for a better design of the flame-retardant composite coating. © 2022 The Authors. CC-BY 4.0