Thin films composed of softly condensed matter such as biomembranes, soap bubbles and polymer films have been studied for long years from the points of view of both basic science and application. A common feature of these films is the coexistence of the robustness and the flexibility, which plays an essential role in their functions and sometimes enables them to cause surprisingly large transformations. We are interested in the coupling between the deformation and the intrinsic properties of the soft films, especially in smectic LC films with hemi-spherical shape. Under appropriate external fields, smectic bubbles dramatically deform in response to them, from which we can extract such physical properties as surface tension, gas permeability, electric conductivity, capacitance etc.
Based on this idea, we studied the smectic bubbles deformation under chemical and electric forces, and quantitatively determined the gaseous permeability, surface tension and electric conductivity of 8CB films with a simple analysis. The result showed that 8CB films should have the selective permeability of conventional gas and that they sometimes exhibit periodic oscillation under DC electric field, in which we can directly observe the ionic motion in the 8CB films in real-time. Our experiment and analysis are both simple, but the result gives us a lot of information about the physical properties of the smectic LCs.
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