Pickering Emulsions Stabilized by a Lipophilic Surfactant and Hydrophilic Platelike Particles

Abstract

Liquid paraffin-water emulsions were prepared by homogenizing oil phases containing sorbitan oleate (Span 80) and aqueous phases containing layered double hydroxide (LDH) particles or Laponite particles. While water-in-oil (w/o) emulsions are obtained by combining LDH with Span 80, the emulsions stabilized by Laponite-Span 80 are always o/w types regardless of the Span 80 concentration. Laser-induced fluorescent confocal micrographs indicate that particles are absorbed on the emulsion surfaces, suggesting all the emulsions are stabilized by the particles. The difference of the particle-stabilized emulsion type may be explained by comparing particle contact angles and the oil-water interfacial tensions, indicating that more Span 80 molecules are adsorbed on the LDH particles than on Laponite. Apparently, the LDH particles are rendered more hydrophobic by Span 80, resulting in the formation of w/o emulsions. The long-term stability of the emulsions was also compared. Emulsions stabilized by Span 80 alone completely separate into two bulk phases of oil and water after 3 months. However, emulsion stability is greatly enhanced with the addition of LDH or Laponite particles. This synergism was accounted for by an increase of the dilational viscoelasticity modulus of the oil-water interface after particles were added to the aqueous phase. This increase indicates that the gel-like particle layer stays at the oil-water interface and resists emulsion coalescence. Scanning electron microscope (SEM) images display the presence of a firm layer surrounding the emulsion droplets and a three-dimensional particle network which extends into the bulk phase aiding emulsion stability.

Chains, Sheets, and Droplets: Assemblies of Hydrophobic Gold Nanocrystals with Saturated Phosphatidylcholine Lipid and Squalene

“…42, 43,44 Dodecanethiol-coated gold nanocrystals disperse in pure squalene, but squalene-nanocrystal mixtures did not emulsify in water without lipid. The positioning of the hydrophobic Au nanocrystals at the squalene-lipid interface increases the separation between the water and squalene phases, and also reduces the contact between lipid molecules and squalene, which do not mix according to recent studies.…”

Novel Nanostructured Solid Materials for Modulating Oral Drug Delivery from Solid-State Lipid-Based Drug Delivery Systems

“…Ultimately, these materials are more useful for encapsulation and delivery of anionic drug molecules, opposite to that demonstrated for montmorillonite. Likewise to montmorillonite, LDH particles are also capable of stabilizing Pickering emulsions and, thus, may also be used to solidify LBDDS in a similar manner to SLH microparticles (95)(96)(97). Of interest, Rahman et al utilized LDHs as a platform for adsorbing lipase enzymes from Candida rugosa to act as a biocatalyst for synthesizing esters (98,99).…”

Carminic Acid Linked to Silica Nanoparticles as Pigment/Antioxidant Bifunctional Excipient for Pharmaceutical Emulsions

“…Several materials have been used to prepare Pickering emulsions [21][22][23][24][25]; among them, silica is the most popular, because its surface is easily modified, either by chemical reaction or by physical adsorption of various compounds such as salts, low molecular weight surfactants, polymers and pigments and natural polyphenols, among others [25][26][27][28][29][30][31][32]. In particular, different types of silica materials (MCM-41, SBA-16, etc.)…”