Stabilization of Pickering foams by high-aspect-ratio nano-sheets

Guevara, Juan S.; Mejı́a, Andrés; Shuai, Min; Chang, Ya Wen; Mannan, M. Sam; Cheng, Zhengdong

doi:10.1039/c2sm27061g

Cited by 61 publications

(49 citation statements)

References 67 publications

(108 reference statements)

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“…[3][4][5][6][7] The ability of particles to stabilize interfaces, either oil-water or air-water, has been known already for more than a century, and particle-stabilized interfaces were first reported by Ramsden in 1903. These aerated systems, especially aqueous foams, are usually stabilized by low molecular weight (LMW) surfactants or proteins, but they often suffer from low stability due to many destabilization mechanisms that take place.…”

Section: Introductionmentioning

confidence: 99%

Aqueous foams stabilized by chitin nanocrystals

et al. 2015

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The aim of the present study was to explore the potential use of chitin nanocrystals, as colloidal rod-like particles, to stabilize aqueous foams. Chitin nanocrystals (ChN) were prepared by acid hydrolysis of crude chitin and foams were generated mainly by sonicating the respective dispersions. The foamability of the chitin nanocrystals was evaluated and the resulting foams were assessed for their stability, in terms of foam volume reduction and serum release patterns, during storage. Additionally, the samples were studied with light scattering and optical microscopy in order to explore the bubble size distribution and morphology of the foam. Nanocrystal concentration and charge density was varied to alter the packing of the crystals at the interface. At low concentrations of ChNs, foams were stable against coalescence and disproportionation for a period of three hours, whereas at higher concentrations, the foams were stable for several days. The enhanced stability of foams prepared with ChNs, compared to surfactant-stabilized foams, can be mainly attributed to the irreversible adsorption of the ChNs at the air-water interface, thereby providing Pickering stabilization. Both foam volume and stability of the foam were increased with an increase in ChNs concentration, and at pH values around the chitin's pKa (pH 7.0). Under these conditions, the ChNs show minimal electrostatic repulsion and therefore a higher packing of the nanocrystals is promoted. Moreover, decreased electrostatic repulsion enhances network formation between the ChNs in the aqueous films, thereby providing additional stability by gel formation. Overall, ChNs were proven to be effective in stabilizing foams, and may be useful in the design of Pickering-stabilized food grade foams.

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Section: Introductionmentioning

confidence: 99%

Aqueous foams stabilized by chitin nanocrystals

et al. 2015

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“…Still, these heat-induced protein particles are not known to produce the same Pickering effect as that of 10 hard colloidal particles. The foam half-life time (t 0.5 ) is only of the order of a few hours for protein particles as compared to many days or months for hard particles [7,8]. There appear to be many factors that govern the foaming properties of protein particles, such as size, mesoscale structure [9,10], and foaming method.…”

Section: Introductionmentioning

confidence: 99%

“…Hence, typically, either higher concentrations of particles (> 1% w/v) are required, or presence of a low molar mass surfactant with large particles is needed [6, 11,12,13,14]. A major 30 bottle-neck in these studies is a lack of data on meso-scale structural details, such as shape [7], particle (aggregate) density [15,16], softness [15], and charge [17]. In the case of heat-induced protein particles, when foams have been produced by whipping, the foam-stability was higher than foams made by sparging [4].…”

Section: Introductionmentioning

confidence: 99%

Enzymatic cross-linking of α-lactalbumin to produce nanoparticles with increased foam stability

et al. 2015

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Hard colloidal nanoparticles (e.g. partly hydrophobised silica), are known to make foams with very high foam-stability. Nanoparticles can also be produced from proteins by enzymatic cross-linking. Such protein based particles are more suitable for food applications, but it is not known if they provide Pickering foam stabilisation to the same extent as hard colloidal particles. α-Lactalbumin (α-LA) was cross-linked with either microbial transglutaminase (mTG) or horseradish peroxidase (HRP) to produce α-LA/mTG and α-LA/HRP nanoparticles. With both enzymes a range of nanoparticles were produced with hydrodynamic radii ranging from 20-100 nm. The adsorption of nanoparticles to the air-water interface was probed by increase in surface pressure (Π) with time. In the beginning of the Π versus time curves, there was a lag time of 10-200 s, for nanoparticles with Rh of 30-100 nm, respectively. A faster increase of Π with time was observed by increasing the ionic strength (I = 0-125 mM). The foam-ability of the nanoparticles was also found to increase with increasing ionic strength. At a fixed I, the foam-ability of the nanoparticles decreased with increasing size while their foam-stability increased. Foams produced by low-shear whipping were found to be 2 to 6 times more stable for nanoparticles than for monomeric α-LA (Rh≈ 2 nm). At an ionic strength of 125 mM ionic strength and protein concentration ≥ 10 g L(-1), the foam-stability of α-LA/mTG nanoparticles (Rh = 100 nm, ρapp = 21.6 kg m(-3)) was 2-4 times higher than α-LA/HRP nanoparticles (Rh = 90 nm, ρapp = 10.6 kg m(-3)). This indicated that foam-stablity of nanoparticles is determined not only by size but also by differences in mesoscale structure. So, indeed enzymatic cross-linking of proteins to make nanoparticles is moving a step towards particle like behavior e.g. slower adsorption and higher foam stability. However, the cross-link density should be further increased to obtain hard particle-like rigidity and foam-stability.

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“…Rod-like, sheet-like, and other asymmetric particles are fi nding use as foams and emulsion superstabilizers, [ 22 ] permeable capsules, [ 23 ] electro-optical media, and viscosity modifi ers. [ 24 ] The shear precipitation process takes place during direct injection of polymer solutions in the bulk of a viscous medium under shear. The polymer solvent is miscible with the shearing medium.…”

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confidence: 99%