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Hermosillo, Mexico

Fernandez-Quiroz D.,CIAD Guaymas | Gonzalez-Gomez A.,CSIC - Institute of Polymer Science and Technology | Gonzalez-Gomez A.,CIBER ISCIII | Lizardi-Mendoza J.,CIAD Hermosillo | And 6 more authors.
Colloid and Polymer Science

Conformational changes of the thermal transitions of chitosan-graft-poly(N-vinylcaprolactam) copolymers in aqueous solution were studied by varying of the length of the grafted poly(N-vinylcaprolactam) (PVCL) chains, as well as the ionic strength and the pH of the solution. The conformational properties of the copolymer were monitored by means of dynamic light scattering and ζ-potential measurements. A series of copolymers with defined molecular architecture were synthesized. Obtained results point out that hydrophobic hydration plays a crucial role on the solubility of this copolymer at neutral and slightly alkaline solutions. The evolution of the size of macromolecular aggregates indicates that, in the coil state, there is a monomodal distribution, passing through a bimodal distribution in the pre-transition region, just before the phase separation. The role of the charge of the copolymers on the cooperative transition is also analyzed. The phase transition of these amphiphilic copolymers shows a strong dependence on the ionic strength of the solution. © 2015, Springer-Verlag Berlin Heidelberg. Source

Rosas-Durazo A.,CIAD Guaymas | Lizardi J.,CIAD Hermosillo | Higuera-Ciapara I.,CICY | Arguelles-Monal W.,CIAD Guaymas | And 2 more authors.
Colloids and Surfaces B: Biointerfaces

The aim of this work was to develop and characterize a new type of nanocapsules. To this end, a nanoemulsion bearing an oily core (Miglyol 812) was obtained by spontaneous emulsification and stabilized by dodecyl-trimethylammonium chloride (DTAC), a commercial cationic surfactant; this nanoemulsion was coated with proportionally very small amounts of κ-carrageenan (at molar charge ratios of Z≤ 0.0045) that interact predominantly by an electrostatic mechanism with the positively charged sites at the polar heads of DTAC at the nanoemulsion's surface to harness nanocapsules of average size ∼250-330. nm and zeta potential (ζ) ranging from ∼+80 to +7. mV. The potential application of the new type of developed nanosystems as drug delivery vehicles has yet to be investigated and fully realized. © 2011 Elsevier B.V. Source

Fernandez-Quiroz D.,CIAD Guaymas | Gonzalez-Gomez A.,CSIC - Institute of Polymer Science and Technology | Gonzalez-Gomez A.,CIBER ISCIII | Lizardi-Mendoza J.,CIAD Hermosillo | And 7 more authors.
Carbohydrate Polymers

A series of thermoresponsive copolymers based on chitosan-g-poly(N-vinylcaprolactam) were synthesized by amidation reaction using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride as coupling reagent. The effect of molecular architecture on the thermoresponsive properties of the graft copolymers solutions was studied by varying the chain length of the grafted poly(N-vinylcaprolactam), PVCL, (in the range from 4 to 26 kDa) and the spacing between grafted chains onto the chitosan backbone. The most interesting characteristic of these copolymers is their solubility in water at temperatures below their lower critical solution temperature (LCST). These solutions presented a LCST between 36 and 44 °C, which decreases with the spacing and length of grafted PVCL chains onto the chitosan backbone, in contrast with the limited decrease of the LCST of PVCL above a critical M¯n value around 18 kDa. This behavior offers tangible possibilities for the preparation and application of sensitive bioactive formulations and "smart" drug delivery systems. © 2015 Elsevier Ltd. All rights reserved. Source

Rosas-Durazo A.,CIAD Guaymas | Hernandez J.,University of Veracruz | Lizardi J.,CIAD Hermosillo | Higuera-Ciapara I.,CICY | And 2 more authors.
Soft Matter

The gelation processes taking place in the non-stoichiometric complex between κ-carrageenan and dodecyltrimethylammonium chloride in KCl were studied. The mechanical properties of the hydrogels show a gradual reinforcement when the amount of surfactant in the complex increases, indicative of a more densely cross-linked polymer network. The thermal and viscoelastic behavior of complexes during cooling is similar to that of κ-carrageenan alone. Nevertheless, the melting of the gel splits into two endothermic processes. The emergence of a new transition during heating indicates that the overall polymer network is related to two types of networks: one formed by typical bonds between κ-carrageenan macromolecular chains and the other associated to hydrophobic blocks developing as a consequence of the cooperative nature of polyelectrolyte-surfactant interactions. In the hydrogel these two networks co-exist, probably semi-interpenetrated, somehow interconnected at the molecular level. © 2011 The Royal Society of Chemistry. Source

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