Span/Tween mixtures solubilization

Matsumoto and Sherman [190] have obtained an equation which describes the behaviour of benzene/water microemulsions stabilized by Tween 20/Span 20 mixtures with particle diameters in the range 54 to 125 nm. The volume (s) of benzene solubilized in micelles of excess emulsifier is considered and the equation takes the form. 

Spans and Tweens have been used to overcome similar problems in the formulation of medicines for internal use. The solubilization of resinous components of tinctures such as benzoin and myrrh in aqueous vehicles and the incorporation of water-soluble ingredients into oily vehicles has been discussed by Stoklosa and Ohmart [230]. Gerding and Sperandio [229] give examples of mixtures of tinctures and fluid extracts which, on addition of polysorbate 20, will not precipitate on dilution. Cetomacrogol 1000 added in small amounts to opiate linctus of squill, syrup of ginger, compound mixtures of camphor, and of lobelia and stramonium has a similar clearing action [207]. 

Figure 6.31 Shifting of optimum water solubilization by addition of lauryl alcohol. (Emulsions contain 30 % oil phase, 65 % deionized water, and 5 % surfactant mixtures. Surfactant mixtures consist of hydrophilic Tween 20 and lipophilic Span 20 at ratios and corresponding HLB values indicated by abscissa. Dotted lines represent data for pure mineral oil systems. Solid lines represent data for oil mixture consisting of 8 parts mineral oil and 2 parts lauryl alcohol). From Lin et al [236].

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