Hybrid Carrageenans Versus Kappa–Iota-Carrageenan Blends: A Comparative Study of Hydrogel Elastic Properties Maria Alice Freitas Monteiro, Bruno Faria, Izabel Cristina Freitas Moraes, Loic Hilliou Gels, 2025 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.
Role of the Molecular Mass on the Elastic Properties of Hybrid Carrageenan Hydrogels Gabriela Gonçalves, Bruno Faria, Izabel Cristina Freitas Moraes, Loic Hilliou Gels, 2025 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.
Structure–Elasticity Relationships in Hybrid-Carrageenan Hydrogels Studied by Image Dynamic Light Scattering, Ultra-Small-Angle Light Scattering and Dynamic Rheometry Amine Ben Yahia, Adel Aschi, Bruno Faria, Loic Hilliou Materials, 2024 Hybrid-carrageenan hydrogels are characterized using novel techniques based on high-resolution speckle imaging, namely image dynamic light scattering (IDLS) and ultra-small-angle light scattering (USALS). These techniques, used to probe the microscopic structure of the system in sol–gel phase separation and at different concentrations in the gel phase, give access to a better understanding of the network’s topology on the basis of fractals in the dense phase. Observations of the architecture and the spatial and the size distributions of gel phase and fractal dimension were performed by USALS. The pair-distance distribution function, P(r), extracted from USALS patterns, is a new methodology of calculus for determining the network’s internal size with precision. All structural features are systematically compared with a linear and non-linear rheological characterization of the gels and structure–elasticity relationships are identified in the framework of fractal colloid gels in the diffusion limit.
Tensile and Compressive Behavior of CHC-Reinforced Copper using Molecular Dynamics Bruno Faria, Nuno Silvestre, José N. Canongia Lopes Advanced Engineering Materials, 2023 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.
