Internal Coalescence as a Mechanism of Instability in Water-in-Oil-in-Water Double-Emulsion Globules

Abstract

Using capillary microscopy, internal coalescence between the internal aqueous compartments in a single water-in-oil-in-water (W1/O/W2) double-emulsion globule was investigated. Globules were prepared using either sodium dodecyl sulfate (SDS) (ionic) or Tween 80 (nonionic) as the water-soluble surfactants and Span 80 as the oil-soluble surfactant. Concentrations of both the hydrophobic and hydrophilic surfactants were varied until coalescence between the internal aqueous droplets was observed. Internal coalescence was observed when the concentration of SDS or Tween 80 in the internal aqueous phase was 1-3 CMC (critical micelle concentration) or 50-100 CMC, respectively, and occurred preferentially when the concentration in the internal phase was significantly greater than in the external phase. Internal coalescence always occurred in conjunction with coalescence between the internal W 1 and external W2 aqueous phases (external coalescence). When W1 and W2 were not too dissimilar in their overall surfactant concentrations, only external coalescence occurred. These phenomena were shown to also depend on the concentration of the Span 80 in the oil phase, the stabilizing ability of which was confirmed. Spontaneous emulsification was observed at low concentrations (<25 CMC Tween 80, <0.5 CMC SDS) of the hydrophilic surfactants in the internal aqueous phase. Deformation of W 1 occurred at high concentrations (>100 CMC Tween 80, >3 CMC SDS).

Polycaprolactone multicore-matrix particle for the simultaneous encapsulation of hydrophilic and hydrophobic compounds produced by membrane emulsification and solvent diffusion processes

“…The same trend was observed by Surh et al [37]. The increase of FG concentration did not increase the encapsulation efficiency of hydrophilic molecule or stability of inner water droplets but reduced the particle sphericity therefore in this study the concentration of FG in the inner aqueous phase was kept constant at 5%.The instability of a W 1 /O/W 2 emulsion can be affected also by the composition of the organic phase, which acts as a separating film modulating the internal coalescence and diffusion of water [38]. In Figure 3 …”

Controlled release from a nanocarrier entrapped within a microcarrier

“…To ensure the entrapment of nanohydrogels in the W 1 phase, we imposed conditions that eliminated coalescence of the internal aqueous droplets with the external aqueous phase (external coalescence) as well as spontaneous emulsification of the internal aqueous phase. We then focused on triggered dye release from the nanohydrogels via pH change of the W 1 phase, followed by transport of the dye through the oil and into the W 2 phase [17,19]. Fig.…”

“…n-Hexadecane was used instead of mineral oil and the concentrations of the nonionic surfactants Tween 80 and Span 80 corresponded to those previously reported to promote stability when using n-hexadecane as the oil phase [17]. NaCl was added to both aqueous phases in order to avoid spontaneous emulsification, known to occur when either or both aqueous phases consist of pure water or when there is a significant salt-concentration difference between the two aqueous phases [19].…”

“…To closely monitor the behavior of this double-carrier delivery system, the microcapillary technique previously developed [16] was used for producing individual W 1 /O/W 2 globules inside thinwalled glass capillaries and microscopically studying the ensuing phenomena with bright and fluorescent light. In the past, this technique has been successfully used to study mechanisms of instability [17,18] as well as transport in W 1 /O/W 2 double emulsions [19].…”

Oil-Frozen W1/O/W2 Double Emulsions for Dermal Biomacromolecular Delivery Containing Ethanol as Chemical Penetration Enhancer

“…Subsequent thawing triggers coalescence of the droplets of W 1 with W 2 phase, 39,40 termed external coalescence. [40][41][42][43] DEs have been regarded as suitable carriers for parenteral administration of vaccines, 44 and the shearing of emulsification procedures did not affect significantly the molecular weight 45 or the in vivo antigenicity of antigen. 46 In fact, upon intramuscular antigen administration, their use showed more effective immune responses when compared with other delivery vehicles such as polymeric nanoparticles.…”