The sequence of lyotropic liquid-crystalline phases occurring in a range of cationic surfactants with water has been determined using the 'penetration' optical microscopy technique. Of the order of 50 different surfactants were examined. The variation of the polar group structure includes the series -NHl, -NMel, NEtl, NPrl and N B u~. In addition, the effect of altering counter-ion and alkyl-chain length are also examined. Other surfactants studied include 2-hydroxyethyl alkylammonium salts, nitroxide ring substituents, alkyl pyridinium salts and alkyl indole surfactants where the indole substituent is part of the hydrophobic chain.The mesophase sequences are similar to the patterns of behaviour already known for non-ionic and anionic surfactants, with hexagonal (H,), bicontinuous cubic (V,) and lamellar (La) being the most frequently observed phases (in addition to micellar solution). For long-chain surfactants, intermediate (Int) rather than V, phases are shown to form at temperatures just above the Krafft boundary. Qualitatively, much of the phase behaviour can be analysed in terms of alkyl chain packing constraints and intermicellar forces. For bulky alkyl headgroups mesophase formation is suppressed, but the hydroxyethyl substituent causes surprisingly little change from a trimethylammonium headgroup. The behaviour of the indole surfactants suggests that the indole group resides mainly in the micelle interior.The mesophase behaviour of monoalkyl anionic and non-ionic surfactants in water has been fairly thoroughly documented. 1-3 Cationic surfactants have received far less attention. Only a few descriptions of their phase behaviour have been reported, and these are limited to alkylammonium and alkylmethylammonium ~a l t s .~-'~ In this study we have undertaken a survey of the liquid crystals formed by a range of cationic surfactants having a variety of headgroup stuctures. The phase types have been monitored using the optical-microscope penetration technique. This enables a qualitative picture of the mesophase sequences as a function of surfactant concentration to be obtained rapidly. From this initial survey, several compounds with novel features in their phase properties have been selected for detailed study. These studies will be the subject of further papers. Surfactant-Water-Mesophase FormationThe principal phases formed in monoalkyl surfactant-water mixtures are lamellar (La), hexagonal ( H I ) and cubic ( I , , V,) liquid crystals,'73 in addition to the micellar solution (L,). Reversed phases (cubic V,, I, and hexagonal, H,) can occur, but these are more common with dialkyl surfactants or with ionic-non-ionic mixtures. The cubic phases consist either of ordered globular micelles (I,) or have a bicontinuous structure (V,). 'Intermediate' phases (Int) can also occur. These are birefringent and form at compositions between hexagonal and lamellar phases instead of the V, phase. The factors responsible for their occurrence are not understood, nor are their structures fully elucidated. To date, intermediat...

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Lead(I1) carboxylates with even chain lengths from octanoate to octadecanoate have been investigated by differential scanning calorimetry, polarizing optical microscopy, X-ray diffraction, and dilatometry, together with Raman, infrared, and *07Pb N.M.R. spectroscopy. The reassignment of the high temperature mesophase as smectic A (L,) for the octanoate to dodecanoate is confirmed. This phase is most stable for the decanoate. The intermediate temperature mesophase is a highly ordered three dimensional lamellar structure based on ionic layers. The alkyl chains in this phase are partially disordered (melted) through the introduction of gauche conformations and show decreased lateral interactions; however, they remain largely in an extended conformation due to the constraints imposed by the ionic network. Melting of the alkyl chains occurs therefore in more than one step. Re-cooling to the crystalline phase appears to result in a different polymorphic crystalline form (albeit still lamellar) from the original.

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