engleski

AFM Imaging of Liquid Crystal Surface

Atomic force microscope (AFM) imaging is already proven [1] to be a powerful method for characterisation of the surface morphology and other surface properties [2]. AFM has been often used in surface and molecular science, and in electrochemistry and polymer science. Visualisation and definition of the surface morphology of a liquid crystalline phase is just one of such problems. In order to recognise the ordered surface structure of the liquid crystalline aggregate as a part of the inner aggregate structure in this study we use phase imaging of tapping mode AFM [3], a relatively new technique which allow the determination of surface stiffens and other material properties, to be plotted in the image. The aim of this investigation was to prove the AFM imaging as a method for characterisation of the surface morphology for the liquid crystalline phase. Previously [4], the lamellar/inverse hexagonal transition of 4-(1-butyloctyl) benzenesulphonate (4SDBS) in the electrolyte/water/octanol solvent was investigated. The textures of phases were determined by a light polarization microscope with a hot-stage. By heating the liquid crystalline sample above 55 °C the solution became isotropic; following cooling the homogeneous nucleation of an inverse hexagonal phase from the isotropic solution was observed. A three-dimensional dendrite-like growth of the liquid crystalline aggregate was interpreted using a fractal approach; it was treated using a two-dimensional cut represented by the microscopic image. The fractal dimensions for the diffusion limited aggregation resulting in growth of the star-like and the rod-like dendrites were found to be Dstar≈ 1.36-1.4 (time dependent) and Drod = 1.25 (time independent), respectively. In the present work the comparison between the macro-level polarisation microscope images of the hexagonal dendrites and the AFM micro-imaging of their surface morphology was done, and the aggregation of the clusters in term of self-similarity was interpreted. We succesfully visualise and recognise either a random or ordered surface film on the liquid crystalline substrate, clearly demonstrate that phase imaging is a valuable tool for such a complex visualisation process.

AFM imaging; Lamellar/Inverse Hexagonal transition; Nanostructures

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