Abstract
Stimuli-responsive surface-active microcrystalline cellulose (MCC) particles are obtained by interaction with conventional cationic surfactants such as cetyltrimethylammonium bromide (CTAB) in aqueous media, where MCC are in situ hydrophobized by adsorption of the cationic surfactant in water via electrostatic interaction and with the in situ hydrophobization removed by adding an equimolar amount of an anionic surfactant such as sodium dodecyl sulfate (SDS). The trigger is that the electrostatic interaction between the oppositely charged ionic surfactants is stronger than that between the cationic surfactant and the negative charges on particle surfaces, or the anionic surfactant prefers to form ion pairs with the cationic surfactants and thus making them desorbed from surface of MCC. Reversible O/W Pickering emulsions can then be obtained by using the MCC in combination with trace amount of a cationic surfactant and an anionic surfactant, and the anionic surfactant with a longer alkyl chain is more efficient for demulsification. With excellent biocompatibility, biodegradability, and renewability, as well as low toxicity, the biomass cellulose particles that can be made stimuli-responsive and able to reversibly self-assemble at fluid interface become ideal biocompatible particulate materials with extensive applications involving emulsions and foams.
Highlights
The emulsions stabilized by colloid particles are called Pickering emulsions
Demulsification/Restabilization Cycling of Emulsions Emulsions stabilized by 0.3 wt% microcrystalline cellulose (MCC) dispersed in 0.01 mM cationic surfactant were destroyed by adding 0.07 mL concentrated (1 mM) anionic surfactant solution followed by gentle agitation with a stick and leaving standing for 30 min
Dodecane-in-Water Pickering Emulsions Costabilized by Microcrystalline Cellulose and cetyltrimethylammonium bromide (CTAB)
Summary
The emulsions stabilized by colloid particles are called Pickering emulsions. They are very stable because there is a dense particle film at the oil–water interface, providing a strong barrier to prevent coalescence of the droplets (Aveyard et al, 2003; Binks and Horozov, 2006). We report that cellulose particles can be made surface-active by in situ hydrophobization in water via interaction with a cationic surfactant, and the surface activity of the particles can be switched off at room temperature to achieve reversible self-assemble at fluid interface. This is accomplished by adding an anionic surfactant of equimolar amount into the systems, forming ion pairs with the cationic surfactant and resulting in loss of surface activity of particles. The dispersion was left on stand for 24 h to reach equilibrium; the zeta potentials (ζ) of the particles were measured using a Zetasizer Nano (Malvern) instrument at room temperature
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