title: Isotropic-nematic transition at the surface of a liquid crystal embedded in an aerosil network.
abstract: We reexamined the isotropic-nematic (Iso-N) phase transitions of 4-n-heptyl cyanobiphenyl (7CB) embedded in aerosils of silica nanoparticle dispersions using highly sensitive differential scanning calorimetry (HS-DSC), polarizing optical microscopy (POM), and retardation measurements. We found a simple and very profound relationship between the calorimetric and optical measurements; in addition to double DSC peaks, which have been observed previously, a two-step change of the retardation was clearly observed by varying temperature. From our analysis, there is no doubt that the Iso-N liquid-crystal phase transition certainly occurs in two steps, i.e., the bulk transition takes place at first and then the surface transition takes place upon cooling. We should note that the surface transition takes place below the bulk transition temperature, the opposite of what was recently observed in a polymer-dispersed liquid-crystal system.
authors.affiliation: Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Meguro, Tokyo, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Aya
authors.forename: Yuji
authors.initials: Y
authors.lastname: Sasaki
authors.forename: Fumito
authors.initials: F
authors.lastname: Araoka
authors.forename: Ken
authors.initials: K
authors.lastname: Ishikawa
authors.forename: Kenji
authors.initials: K
authors.lastname: Ema
authors.forename: Hideo
authors.initials: H
authors.lastname: Takezoe