Forces in the isotropic phase of a confined nematic liquid crystal 5CB - art. no. 051711

Using a temperature controlled atomic force microscope, we have measured th e temperature dependence of the force between a flat silanated glass surfac e and a silanated glass microsphere. immersed in the isotropic phase of the nematic liquid crystal 5CB (4'-n-pentyl 4-cyanobiphenyl). At separations o f several nanometers, we observed a weak, short range attractive force of t he order of 100 pN, which was increased by decreasing the temperature. The temperature dependence of the amplitude and the range of this attractive fo rce can be described by a combination of van der Waals and a mean-field pre nematic force due to the surface-induced nematic order. This is supported b y ellipsometric study and allows for the determination of the surface coupl ing energy of 5CB on a silanated glass surface.