Mapping the anisotropy of lyotropic liquid crystal dispersions

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This work arose out of rather unusual circumstances. After more than three decades carrying out research into the formulation of cleaning products, I joined the University of Liverpool as an Honorary Senior Fellow where I met Peter Weightman, a Mott Medal prize winner of the Institute of Physics. The reflectance anisotropy spectrometer that Peter had constructed for surface research was an answer looking for problems. From my industrial experience with Unilever Research, I saw an application to quantify lyotropic liquid crystals in dispersions. The development of the understanding lyotropic liquid crystals has had a colourful history, especially in soap making. Procter and Gamble author F. B. Rosevear (1967) refers to the qualitative descriptions used by soap makers of “neat” and “middle” mesomorphic phases. Rosevear identified polarising microscopy as a technique for differentiating the different phases by the strange and beautiful textures observed. Quantitative instrumental methods have been vital to develop our understanding of liquid crystals, including: rheometry, x-ray scattering, nuclear magnetic resonance spectroscopy and especially electron microscopy coupled with fast freezing techniques. Electron microscopy has revealed the sub-microscopic world of lyotropic liquid crystal dispersions that play an important role in cleaning formulations. The relatively new technique of reflectance anisotropy spectroscopy addresses the problem of quantifying lyotropic liquid crystal dispersions. We have clearly shown that we can determine the boundary between isotropic and liquid crystal dispersions and the dependence of the anisotropy on temperature and concentration.

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