Percorrer por autor "Hilliou, Loic"
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- From the seaweeds' carrageenan composition to the hybrid carrageenans' hydrogel elasticity: identification of a relationship based on the content in iota-carrageenanPublication . Hilliou, Loic; Moraes, Izabel Cristina Freitas; Marques de Almeida, PedroThe carrageenan composition of 12 commercial seaweeds used in the production of hybrid carrageenans (HC) is estimated from the analysis of solid-state NMR spectra and is systematically compared with the chemical structure of HC extracted in hot water. 1H NMR showed that the isolated HC contain from 5 to 80 mol% kappacarrageenan, from 90 to 10 mol% iota-carrageenan, while from 8 to 23 mol% biological precursors are present in the copolymer's chain. A good correlation is found between the iota-carrageenan content in the seaweeds and in the extracted HC. The shear elastic modulus of 1 wt% HC gels in the presence of 0.1 M KCl is significantly weaker and gels form at lower temperatures when the iota-content in the seaweed is larger than the kappa-content. However, these weaker gels show strain hardening. A cut-off of 30 mol.% of iota-carrageenan in the polysaccharide is identified that separates strain softening stiffer gels from strain hardening softer gels. Overall, the set of data suggests that the carrageenan gel elasticity is ruled by the self-assembly of iota-carrageenan moieties in the HC, and HC gel elasticity can be directly linked to the iota-carrageenan composition of seaweeds.
- Rheo-optical characterization of liquid crystalline acetoxypropylcellulose melt undergoing large shear flow and relaxation after flow cessationPublication . Teixeira, Paulo F.; Fernandes, Susete N.; Canejo, João; Godinho, Maria Helena; Covas, José A.; R. Leal, Catarina; Hilliou, LoicThe rheological and structural characteristics of acetoxypropylcellulose (APC) nematic melt are studied at shear rates ranging from 10 s(-1) to 1000 s(-1) which are relevant to extrusion based processes. APC shows a monotonic shear thinning behavior over the range of shear rates tested. The negative extrudate-swell shows a minimum when a critical shear rate (gamma) over dot(c) is reached. For shear rates smaller than (gamma) over dot(c), the flow-induced texture consists of two set of bands aligned parallel and normal to the flow direction. At shear rates larger than (gamma) over dot(c), the flow induced texture is reminiscent of a 2 fluids structure. Close to the shearing walls, domains elongated along the flow direction and stacked along the vorticity are imaged with POM, whereas SALS patterns indicate that the bulk of the sheared APC is made of elliptical domains oriented along the vorticity. No full nematic alignment is achieved at the largest shear rate tested. Below (gamma) over dot(c), the stress relaxation is described by a stretched exponential. Above (gamma) over dot(c), the stress relaxation is described by a fast and a slow process. The latter coincides with the growth of normal bands thicknesses, as the APC texture after flow cessation consists of two types of bands with parallel and normal orientations relative to the flow direction. Both bands thicknesses do not depend on the applied shear rate, in contrast to their orientation. (C) 2015 Elsevier Ltd. All rights reserved.