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Abstract:
Carbon-13 NMR measurements are reported for the hexagonal (hex) and lamellar (lam) mesophases formed by water and dipotassium hexadecanedioate (isotopically enriched in the carboxyl group). The average anisotropic 13C chemical shift tensor in both mesophases has uniaxial symmetry and is almost independent of temperature with average values (relative to TMS) of (σ∥)hex = 171·3 ppm, (σ1)hex = 192·4 ppm, <σ∥>lam = 200·2 ppm, <σ⊥>lam = 177·1 ppm and σiso = 184·8 ppm. These results together with earlier quadrupole interaction data of the α-methylene deuterons, and a simple model for the structure of the −CαH2COOK moiety are used to estimate the effective order parameters, n, of the disoap head groups along the direction normal to the water interfaces. The results are nhex ≈ 0·44 and n lam ≈ 0·27.
