title: Influence of interfacial rheological properties of mixed emulsifier films on the stability of water-in-oil-in-water emulsions.
abstract: The purpose of this study was to investigate the influence of mixtures of the emulsifiers Span 80, 83 and 85 and Tween 80 on multiple emulsion stability. An oscillatory ring-surface rheometer was used to measure interfacial elasticity at the oil-aqueous interface. Multiple emulsions were prepared via a two-step emulsification process and stability was evaluated by investigation of drug transport from freshly prepared and eight-day-old emulsions by use of a dialysis method. Photomicrography and droplet-size analysis of multiple emulsions were also conducted. Spans 80 and 83 were appreciably elastic (683.10+/-29.13 mNm(-1) and 1128.09+/-14.81 mNm(-1), respectively at 5% w/v) when present at the mineral oil-aqueous interface whereas Span 85 and Tween 80 were not (11.10+/-3.88 mNm(-1) (5% w/v) and 0 (0.1-5% w/v) respectively). The interfacial elasticities of Spans 80 and 83 decreased in the presence of Tween 80 in the aqueous phase; this was attributed to co-adsorption of Tween 80 at the interface or aqueous-phase solubilization of the Spans within mixed micelles, or both. Drug-transport studies indicated that drug release on storage was lower from water-in-oil-in-water (w/o/w) emulsions prepared with 5% w/v Span 80 or 83 and 0.1% w/v Tween 80 than from emulsions prepared with 5% w/v Spans 80 or 83 and 1% w/v Tween 80. Photomicrography and droplet-size analysis indicated the same trend-emulsions containing a higher percentage of Tween 80 were less stable. The relatively stable w/o/w emulsions (e.g. 5% w/v Spans 80 or 83 and 0.1% w/v Tween 80) contained a large number of multiple droplets for up to eight weeks of storage whereas the relatively unstable w/o/w emulsions (e.g., 5% w/v Span 85 and 0.1% w/v Tween 80 and 5% w/v Spans and 1% w/v Tween 80) contained mostly simple droplets after only one week of storage. The mean volume/weight droplet size decreased on storage with breakdown of these w/o/w emulsions to simple oil-in-water emulsions. There was a positive correlation between the interfacial elasticity and emulsion stability data. Mixed emulsifiers giving higher film strength, as quantified by interfacial elasticity measurements, resulted in more stable w/o/w emulsions.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, University of Connecticut, Storrs 06269, USA.
authors.forename: F O
authors.initials: FO
authors.lastname: Opawale
authors.forename: D J
authors.initials: DJ
authors.lastname: Burgess
mesh_terms: D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000737:chemistry; D004355:Drug Stability; D004655:Emulsions / Q000737:chemistry*; D006601:Hexoses / Q000737:chemistry; D008899:Mineral Oil / Q000737:chemistry*; D010784:Photomicrography; D011136:Polysorbates / Q000737:chemistry; D012212:Rheology; D012980:Sodium Salicylate / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D004655:Emulsions; D006601:Hexoses; D011136:Polysorbates; D013501:Surface-Active Agents; D014867:Water; C018665:sorbitan monooleate; D008899:Mineral Oil; C005693:sorbitan trioleate; D012980:Sodium Salicylate