Bruno Faria

A comparison between the gel properties of blends of kappa- and iota-carrageenans (K+Is) and hybrid carrageenans (KIs) with equivalent chemical compositions is here presented. The objective is to assess under which conditions hybrid carrageenans are valuable alternative to blends of kappa- and iota-carrageenans for gelling applications and to contribute to the identification of phase-separated structures or co-aggregated helices. Phase states constructed in sodium chloride and in potassium chloride confirm that KIs build gels under a much narrower range of ionic strength and polysaccharide concentration. Hybrid carrageenans displayed salt specificity, forming gels in KCl but not in NaCl, highlighting their limited gelling potential in Na⁺ environments. A two-step gelation mechanism was found in both systems at lower ionic strengths and when iota carrageenan is the major component. The shear elastic moduli of KI gels are overall smaller than those of blends, but the opposite is observed at lower ionic strengths in KCl and in systems richer in iota-carrageenans. The nonlinear elastic properties of gels do not relate to the use of blends or hybrid carrageenans for their formulation. Instead, larger contents in iota-carrageenans lead to gels able to sustain larger strains before yielding to a fluid state. However, these gels are more prone to strain softening, whereas strain hardening is measured in gels containing more kappa-carrageenan, irrespective of their blend or hybrid structure.

A set of carrageenans produced in the potassium form and with chemical structures varying from pure iota-carrageenans to nearly pure kappa-carrageenans is submitted to ultrasonication to reduce their molecular masses Mw while maintaining a constant chemical structure and a polydispersity index around 2. The kinetics of ultrasound-induced chain scission are found to be slower for polysaccharides richer in kappa-carrageenan disaccharide units. From the elasticity of samples directly gelled in a rheometer at 1 w/v% in 0.1 M potassium chloride, a critical molecular mass Mc is identified as the mass below which no gel can be formed. Mc is found to be smaller for kappa- and kappa-2-carrageenans of the order of 0.13–0.21 MDa. The presence of more sulphated disaccharide units significantly increases Mc up to 0.28 MDa for iota-carrageenan and 0.57 MDa for a highly sulphated hybrid carrageenan. For the set of Mw and carrageenans tested, no plateau in the Mw dependence of the gels’ elasticities is found.

Graphene has been extensively studied as nanofiller to produce ultra‐strong and ductile metal nanocomposites but challenges such as poor adhesion at the metal–carbon interface have yet to be met. Carbon honeycombs (CHCs) are highly porous 3D graphene networks that possess a very large surface area‐to‐volume ratio, an outstanding physical absorption capacity and notable mechanical properties. Herein, these recently synthetized 3D CHCs are introduced in copper as nanofillers, and the mechanical properties of the nanocomposites, such as elastic modulus, tensile strength, failure strain, compressive strength, and critical strain, are obtained using molecular dynamics simulations. Three CHC lattice types are studied, and the metal–carbon interface is accurately modeled by using melting and recrystallization of the copper matrix around the nanofiller. Gains between 28% and 50% are obtained for the Young's modulus, while the tensile strength improved between 43% and 49%. Pullout tests reveal that the copper nanopillars that form by the filling of the honeycomb cells of CHC by copper atoms considerably increase the pullout force and are responsible for improvements in adhesion and in loading stress transfer.

Phenocrysts in volcanic rocks are recorders of magmatic processes that have occurred at depth before and during a volcanic eruption. Our petrological investigations of stratigraphically controlled tephrite and phonotephrite samples from the latest eruption of Fogo (Cape Verde Islands) aimed to reconstructing magma storage and transport. The dates of sample emplacement have been determined using satellite instrument - derived high resolution thermal infrared maps. All samples are strongly phyric and commonly contain complexly zoned clinopyroxene crystals and cumulate fragments. Clinopyroxenes from all samples exhibit 10-50 µm wide rim zones, inferred to have grown in a few days to weeks during the ongoing eruption as a consequence of H2O loss from the melt. Clinopyroxene-melt thermobarometry using tephrite groundmass compositions suggests that the rims formed at upper mantle pressures of around 600 MPa (21 km depth). This level is interpreted to reflect temporary reduction in magma ascent velocity by near-isobaric movement through a complex storage system. Previously, the tephrite magma had accumulated at a deeper level, possibly between 700 and 900 MPa as indicated by clinopyroxene cores (Mata et al., 2017). The cause for H2O loss initiating rim growth could be degassing after rise of the magma from the deeper level, or CO2 flushing by a carbonic fluid phase released at depth. Corresponding data from phonotephrites indicate last equilibration at around 440 MPa (16 km); the phonotephrite magma is inferred to be a residuum from an earlier magmatic event that was entrained by advancing tephrite. Microthermometry of CO2-dominated fluid inclusions in tephrite clinopyroxenes results in pressures of around 330 MPa (12 km), indicating another short pause in magma ascent in the lowermost crust. Rim zonations of olivine phenocrysts indicate that after leaving this final stalling zone, the magma ascended to the surface in less than half a day. In strong contrast to these petrological equilibration depths, seismic events precursory to the eruption were located at <5 km below sea level, with only two exceptions at 17 and 21 km depth consistent with our barometry. Our results enhance the understanding of this potentially dangerous volcano, which helps to interpret future pre-eruptive unrest.