Dispersion and Stabilizing Effects of n-Hexadecane on Tetralin and Benzene Metastable Droplets in Surfactant-Free Conditions

Abstract

The size distribution of metastable oil droplets in water was investigated by the dynamic light-scattering method for tetralin (1,2,3,4-tetrahydronaphthalene), benzene, n-hexadecane, and their mixtures under surfactant-free conditions. For pure tetralin, droplets appeared with multiple peak distributions, first at sizes around 5 × 102 to 2 × 103 nm, and shortly coalesced to grow discretely to 3 μm within 30 min. On the contrary, for pure n-hexadecane, droplets appeared with a single location at 40−120 nm and their sizes remained unchanged for several hours. The addition of a small amount of n-hexadecane, even at 1:1000 and 1:100 molar ratios, to tetralin significantly improved the dispersion and stability of tetralin droplets. Peculiarly, the interfacial tension of the mixed oils with water was raised with the n-hexadecane concentration. The dispersed solutions of benzene could be further stabilized (for as long as 1 month) with the addition of hexadecane. Expulsion of n-hexadecane onto the droplet surfaces and the related surface modification seem to be responsible for the stabilization effects.

Suspension Polymerization of Styrene Monomer without Emulsifier and Initiator.

“…We have prepared surfactant-free O/W emulsions by ultrasonic treatments (5)(6)(7)(8)(9)(10)(11). When a mixture of benzene and water was ultrasonically treated at 40 kHz to prepare a benzene/water emulsion, the dispersion stability of benzene droplets was good for about 3 hr in the absence of surfactant (5,6).…”

“…When a mixture of benzene and water was ultrasonically treated at 40 kHz to prepare a benzene/water emulsion, the dispersion stability of benzene droplets was good for about 3 hr in the absence of surfactant (5,6). The dispersion stability of oil droplets depends strongly on the properties of the oil phase and a similar ultrasonic treatment permited to prepare surfactant-free O/W emulsions that are stable over a year when hexadecane, glycerin trioleate, etc are used (8,9). Monodispersed spherical polystyrene particles with about 350nm in size have been prepared in the absence of surfactant through polymerization of styrene monomer in its metastable droplets formed by ultrasonic irradiation as the reaction field (12).…”

In Vitro Evaluation of Topical Microemulsion of Capsaicin Free of Surfactant

“…[12][13][14][15] This article was intended to investigate the potential of a new microemulsion formulation without surfactant for topical drug delivery of capsaicin. Surfactant-free microemulsions were prepared in other fields, [16][17][18] but were not used in topical pharmaceuticals. The novel microemulsion was based on benzyl alcohol and short-chain alcohol.…”

“…Such phenomenon was also discovered by previous studies. 16,27) In the systems with low oil fraction, there is a high ratio of propylene glycol, and this relatively high ratio of cosurfactant could distribute into the oil phase, which causes the oil droplet similar to amphiphilic particles. In a dynamic equilibrium course, these droplets are incorporated into the outer phase and also dispersed as inner phase.…”

“…Benzyl alcohol is a potential transdermal enhancer and has an amphiphilic molecular structure, 19) which is helpful for the formation of microemulsion, 16) and can be used as oil phase in microemulsions. 20,21) Furthermore, benzyl alcohol is a commonly used drug for local anesthesia and alleviating itching, thus, it may be helpful to reduce the side-effects of capsaicin.…”