Conformations of poly(dihexylsilane) embedded in Langmuir-Blodgett multilayers of arachidic acid

Abstract

Poly(dihexylsilane) (PDHS) and arachidic acid (AA) were co-spread onto a cadmium-containing water subphase and transferred onto a solid substrate as multilayers by the Langmuir-Blodgett method. The structure of these films was evaluated by means of UV-visible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry, and film thickness measurements. The results indicated that the PDHS ultrathin film is incorporated into a well-structured AA multilayer matrix without appreciable destruction of the layer structure. The conformational behavior of PDHS embedded within this film was evaluated by UV-visible absorption spectroscopy. The phase transition temperature of the ordered (alltrans zigzag) to the disordered (helical gauche) state on the AA monolayer at the air-water interface is lowered and the conformational state is virtually maintained in the as-deposited multilayers during storage at room temperature at least for a month. PDHS in the AA multilayer on heating showed a substantially broadened transition around 40 8C, which clearly reflects a geometrical restriction effected by the AA multilayer matrix.

Monolayer Formation of Hydrophobic Polysilane on Water through Hybridization with Liquid Crystal Molecules

“…Earlier works have shown that successful LB deposition of other functional hydrophobic polymers, poly(alkylthiophenes) 13 and the vinyl copolymers with pendant chromophores, can be achieved when mixed with a long-chain fatty acid. We have also reported the formation of ultrathin PDHS film on an arachidic acid monolayer at the air/water interface and their LB deposition . Because of the poor miscibility of PDHS with arachidic acid, the contribution of PDHS to the lateral area in the monolayer was minor, showing a slight area increase at lower pressure regions in the π− A isotherms .…”

“…In this sense, the mixed films can be dubbed as “hybrid” films. In the case of mixing with a long-chain fatty acid, on the other hand, the mixed film gave only a slight expansion at low pressures in the π− A curve and did not show such systematic expansions with R . Cospread monolayers of polymer/fatty acid systems exhibit π− A isotherms characteristic of a phase separation of the two components. ,, …”

“…The homogeneity of the film surface was retained upon further compression in the second plateau region at 11−12 mN m -1 . Such a homogeneous BAM image has not been obtained for a PDHS/arachidic acid system 14a…”

“…We show in this paper that the spread monolayer of a fully hydrophobic polymer, poly(dihexylsilane) (PDHS), can be ideally spread on water with the assist of an expanding monolayer of a liquid crystal molecule, 4‘-pentyl-4-cyanobiphenyl (5CB); see Chart . Cospreading of hydrophobic polymers such as poly(alkylthiophene) and PDHS with a long-chain fatty acid have been undertaken; however, it is confirmed that the polymer chain in such composite films adopts a folded and aggregated state leading to microphase separated structures. To our knowledge, the present work describes for the first time the ideal monolayer formation of the fully hydrophobic polymer.…”

Abrupt Interfacial Transitions of Hydrophobic Polysilanes As Probed via Liquid Crystal-Assisted Stepwise Deposition

“…Fully hydrophobic soluble polymers such as polystyrene and polysilanes (Si-catenated polymers) having hydrocarbon substituents cannot be applied. Some attempts of LB deposition have been made for such polymers by mixing with monolayer-forming long chain carboxylic acid, , nevertheless the polymers are segregated within the LB films 11b and the monolayer spreading of such polymers has not been realized.…”