Gemini surfactants shape

A theoretical explanation of experimental results, obtained for modified (non rigid spacer) gemini surfactants, was presented by Andelman and Diamant.47 They noted that the aggregate morphology for dimeric surfactants is related mainly to the influence of the spacer on the specific area X. The geometrical parameter, that determines aggregate shape, is the packing parameter denoted by the formula 48,49... 

Micelle shape and effect on rheology of solutions of gemini surfactants... 

The micelles present in the aqueous solutions of some types of Gemini surfactants can form unusual shapes for instance ring-like or elongated with numerous branches. 

Additions of (3-cyclodextrin increased the CMC of bisquaternary ammonium surfactants [95]. Addition of (3-cyclodextrin to nonionic gemini surfactant [Q] where X = OH causes a gradual change in the size and form of the aggregates. Rod-shaped aggregates form upon increasing cyclodextrin content. More and more rods form whereas the micellar aggregates break up [96,97]. 

VI. PROPERTIES OF MICELLES OF GEMINI SURFACTANTS A. Micelle Size and Shape... 

Molecular dynamics simulations of gemini surfactants in aqueous solutions accounted for the change of micelle shape from spheroidal to elongated upon decreasing spacer carbon number [115]. They also predicted the formation of branched thread-like micelles. Oligomeric surfactants are capable of forming such structures because the different alkyl chains of such a surfactant can take different relative orientations in the micelles. 

Trimeric and oligomeric surfactants have also been prepared (Zana, 1995 Sumida, 1998 In, 2000 Onitsuka, 2001). Their CMC values are even smaller than those of the analogous geminis. As the number of hydrophobic groups per molecule increases for gemini quaternary C12 ammonium compounds with polymethylene -(CH2) j spacers, their surface layers become more dense, their micellar microviscosity increases, and their micellar shape changes from spherical to wormlike, to... 

Fig. 40a-g. Various types of oligomeric surfactants a bola dimer b gemini dimer c linear hexamer ( tail end type) d linear hexamer ( head type) e cyclic hexamer, f star-shaped hexamer ( tail end type) g star-shaped hexamer ( head type)... 

Fig. 41a-d. Examples of oligomeric surfactants a bola dimer [426-428] b gemini dimer [435, 445, 448] c cyclic hexamer of tail end type [419] d star-shaped trimer of tail end type [420]... 

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