Abstract
In preceding studies, we demonstrated that choline carboxylates ChCm with alkyl chain lengths of m = 12 - 18 are highly water-sol. (for m = 12, sol. up to 93 wt. % soap and 0 °C). In addn., choline soaps are featured by an extraordinary lyotropic phase behavior. With decreasing water concn., the following phases were found: micellar phase (L1), discontinuous cubic phase (I1' and I1''), ...
Abstract
In preceding studies, we demonstrated that choline carboxylates ChCm with alkyl chain lengths of m = 12 - 18 are highly water-sol. (for m = 12, sol. up to 93 wt. % soap and 0 °C). In addn., choline soaps are featured by an extraordinary lyotropic phase behavior. With decreasing water concn., the following phases were found: micellar phase (L1), discontinuous cubic phase (I1' and I1''), hexagonal phase (H1), bicontinuous cubic phase (V1), and lamellar phase (Lα). The present work is also focused on the lyotropic phase behavior of choline soaps but with shorter alkyl chains or different alkyl chain properties. We have investigated the aq. phase behavior of choline soaps with C8 and C10 chain-lengths (choline octanoate and choline decanoate) and with a C18 chain-length with a cis-double bond (choline oleate). We found that choline decanoate follows the lyotropic phase behavior of the longer-chain homologs mentioned above. Choline octanoate in water shows no discontinuous cubic phases, but an extended, isotropic micellar soln. phase. In addn., choline octanoate is at the limit between a surfactant and a hydrotrope. The double bond in choline oleate leads also to a better soly. in water and a decrease of the solubilization temp. It also influences the Gaussian curvature of the aggregates which results in a loss of discontinuous cubic phases in the binary phase diagram. The different lyotropic mesophases were identified by the penetration scan technique with polarizing light microscope and visual observations. To clarify the structural behavior small (SAXS) and wide (WAXS) angle X-ray scattering were performed. To further characterize the extended, isotropic micellar soln. phase in the binary phase diagram of choline octanoate viscosity and cond. measurements were also carried out. [on SciFinder(R)]
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