Atomic-scale-controlled liquid crystal glasses consisting of two-dimensional self-assembled quasi-ferroelectrics

The unique features of the phosphonium salts as functional materials were r eviewed. Emphasis was placed on the comparison between the phosphonium salt s and the commonly available quaternary ammonium salts with the same struct ure except for positively-charged heteroatoms. The antimicrobial activity o f onium salts with different long-chain segments was described, with specia l reference to structure-activity relationships. An unexpected relation bet ween the antibacterial activity and the aggregation behavior in aqueous sol ution (i.e. lyotropic liquid-crystalline property) was revealed through the systematic studies on antibacterial activity of the phosphonium salts as a novel class of cationic biocides. The phosphonium salts can act as thermot ropic liquid crystals in spite of the amphiphiles being without a rigid cor e. This work has shown for the first time that a multilayer self-assembly, which is formed by the phosphonium salts, acts as a polar thin film with di polar order. The existence of two-dimensional self-assembled atomic layers with spontaneous polarization was revealed through the evaluation of second -order nonlinear optical properties of solid-state layered thin films which are built by phosphonium liquid crystals. In an ionic layer within the mul tilamellar assembly, it was found that spontaneous polarization occurs para llel to the layer plane because of the, ferroelectric ordering of ion pairs as an electric dipole. In the theoretical calculations, the generation of in-plane polar structure was assumed to originate from the variety of bondi ng manners of phosphorus atom. Furthermore, polar order of the phosphonium thin films was enhanced by application of an external electric field. Such polarization treatment seems to lead to alignment of the spontaneous polari zation of the ionic layers resulting from the rearrangement of the ions. In addition, it was found that introduction of bivalent metal and trivalent r are-earth ions into the amphiphiles leads to enhancement of the thermal pro perties. The metal-containing complexes showed a stable liquid-crystalline phase, and exhibited a distinct polymorphism. in the smectic A phase and a unique structure in the self-organization.