Abstract
Highly charged (zeta potential ζ = +105 mV, acetate counterions) chitin nanoparticles (NCh) of three different average aspect ratios (∼5, 25, and >60) were obtained by low-energy deconstruction of partially deacetylated chitin. The nanoparticles were effective in reducing the interfacial tension and stabilized the oil/water interface via network formation (interfacial dilatational rheology data) becoming effective in stabilizing Pickering systems, depending on NCh size, composition, and formulation variables. The improved interfacial wettability and electrosteric repulsion facilitated control over the nanoparticle’s surface coverage on the oil droplets, their aspect ratio and stability against coalescence during long-term storage. Emulsion superstabilization (oil fractions below 0.5) occurred by the microstructuring and thickening effect of NCh that formed networks at concentrations as low as 0.0005 wt %. The ultrasound energy used during emulsion preparation simultaneously reduced the longer nanoparticles, producing very stable, fine oil droplets (diameter ∼1 μm). Our findings indicate that NCh surpasses any reported biobased nanoparticle, including nanocelluloses, for its ability to stabilize interfaces at ultralow concentrations and represent a step-forward in efforts to fully replace surfactants in multiphase systems.
Highlights
Oil-in-water emulsions are thermodynamic unstable systems but of great practical interest due to their applicability in foodstuff, cosmetics, and pharmaceutical industries.[1]
It is worth noting that the nonordered domains of chitin chains in NCh are likely to be preserved because no hydrolysis occurs
We note that chitin nanorods of smaller sizes were present in NCh-L suspension, indicating their high size polydispersity, as it is typical from random processes during microfluidization.[47]
Summary
Oil-in-water emulsions are thermodynamic unstable systems but of great practical interest due to their applicability in foodstuff, cosmetics, and pharmaceutical industries.[1] In practice, it is the kinetic stability that allows the design of emulsions to overcome their tendency to otherwise phaseseparate, ensuring long shelf life.[2] Early reports have demonstrated that stable emulsions can be obtained by amphiphilic surfactants and by solid particles of colloidal dimensions, the so-called Pickering systems.[3,4] A strong mechanical barrier at the oil−water interface can be readily generated, preventing droplet breakage, if solid particles are used under a balanced interfacial wettability.[5] Compared to conventional surfactants, Pickering emulsions offer superior stability at relative low particle loading due to their irreversible adsorption at interfaces.[6] This feature is highly desirable for environmental-friendly emulsion products because it can minimize the amount of stabilizer used.[7] Pickering systems are promising in designing and optimizing the formulation of safe and green emulsions
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