Orlando Rojas


Research Interests

Nanopolysaccharides (based on cellulose, chitin, starches and others)
Bacterial nanocelluloses
Cellulose derivatives
Lignins, colloidal lignins, nanolignins and their uses
Renewable biopolymers (hemicelluloses, proteins, chitin and chitosan, alginates and others)
Multiphase systems (emulsions, foams, dispersed systems), gels, aerogels
Films, filaments and hybrid materials
Bioactive systems
Fiber processing
Pulp and paper

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Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Surface interactions between chitin nanocrystals and an anionic surfactant : from fundamentals to applications (2023)

We elucidate the interactions between positively charged chitin nanocrystals (ChNC) and an anionic surfactant, sodium dodecyl sulfate (SDS), and report on their role in the stabilization of Pickering emulsions. ChNC/SDS interactions were systematically investigated by using electrophoretic mobility, surface tensiometry, and quartz crystal microgravimetry. The results indicate that SDS molecules undergo different regimes when adsorbing on the chitin nanoparticles. At low SDS concentration, a monolayer is assembled on the surface of ChNC, attributed to the hydrophobic effect and electrostatic interactions. We suggest that with the increased SDS concentration, adsorption in the form of bilayer or patchy bilayers occurs followed by the formation of adsorbed hemi-micelles and micelles. We further suggest that hydrophobic interactions play a critical role in defining the transitions presented by the adsorbed species and their conformations. At the highest SDS concentrations tested, we observe charge neutralization and flocculation, in the form of SDS/ChNC aggregates. Remarkably, at given concentrations, the adsorbed SDS introduces hydrophobicity to the chitin nanoparticles, which opens the opportunity to achieve tailorable conditions for Pickering stabilization. Hence, a facile method is proposed by in-situ surface modification, using the physical adsorption of SDS on ChNC, which extends the potential of renewable nanoparticles in the area of complex fluids, for instance, in the formulation of household and healthcare products.

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