Hai-Ming Wu

Structure and conductivity anisotropy of a new porphyrin Langmuir-Blodgett film

Abstract The orientation, lattice structure, and conductivity of the Langmuir-Blodgett film of a new porphyrin β-[(hexadecylcarboxy)-methoxy]-meso-tetraphenylporphyrincopper(II) are investigated. Three conclusions are obtained: a) The porphyrin ring plane is almost perpendicular to the air-water interface in a cofacial stacking manner: b) The molecular arrangement in the monolayer is ordered and anisotropic with a rectangular 2-dimensional lattice structure; c) The structural anisotropy leads to an anisotropy of conductivity. The two principal in-plane conductivity values ( δ rt ) are 2.5 × 10 −7 S cm −1 and 1.7 × 10 −9 S cm −1 without doping and reach 3.9 × 10 −5 S cm −1 and 1.3 × 10 −8 S cm −1 after iodine doping, respectively.

Morphologies of phase-separated monolayers investigated by atomic force microscopy

Abstract The miscibility behavior and surface morphology of a mixed monolayer, stearic acid (SA) with 5,10,15-triphenyl-20-(4-DL-phenylalanylamindo)phenyl porphyrin (TPPP), were studied by analyzing the surface pressure vs. molecular area isotherms and atomic force microscopy (AFM) images of the transferred monolayer films. The mixed monolayer is a two-phase system with a liquid-condensed phase consisting of SA and a liquid-expanded phase consisting of TPPP with a trace of SA. The different domain structures of SA sensitive to surface pressure, compression rate, annealing, etc. were also studied with AFM in detail.

Liquid-crystal alignment of helical polymer chains

Abstract Polymethylmethacrylate (PMMA) langmuir-Blodgett (LB) films can homogeneously align the nematic liquid crystal. Atomic force microscopy of PMMA LB films, reveals a helical chain structure, based on which the alignment mechanism is discussed. However, no capability of alignment could be observed on rubbed PMMA films, which is probably due to the easy fracture of PMMA chains under rubbing.

Alignment of Liquid Crystals on the Polymer Films Made by Pulsed Laser Ablation

Abstract We present the results of observation and study of alignment of liquid crystals on glass substrates deposited with polymers by pulsed laser ablation. Polarizing microscopy is used to observe the alignment of 5CB (nematic) and Nobambc (smectic). Depolarising Raman spectroscopy is used to obtain the order parameter S(= (1/2) ) of the aligned liquid crystal. S for 5CB is obtained 0.90, therefore, the effect of alignment is significant. Atomic force microscopy (AFM) is used to observe the surface morphology of the polymer films, which are found to be quite flat. Pictures of the depositing process and the aligning process show that dipolar interaction and van der Waals force are responsible for the alignment. This provides a new method to study the mechanisms of the interaction between the molecules of liquid crystals with the solid substrates. The technique is also of interest in the applications to Liquid Crystal Displays.

Polymorphism of domains in phase-separated Langmuir-Blodgett films

Abstract Mixed monolayer films composed of 5,10,15-triphenyl-20-(4-dl-α-phenylalanylamindo)phenyl porphyrin and arachidic acid are investigated by atomic force microscopy. The mixture phase separates, yielding two-dimensional domains. Some early stage of domain growth and the polymorphism of the domains were observed.

Liquid crystal alignment controlled by LB films

Abstract Copper phthalocyanine doped polymethacrylate Langmuir-Blodgett films were transferred to align a nematic liquid crystal 5CB. It is found that the pre-tilt angle of the liquid crystal can be controlled with the variation of the doped copper phthalocyanine molecular ratio and is correlated with the dichroic ratio of the aligning layer. The polarity of the aligning layer is regarded as the most likely underlying factor that causes the different LC alignment configurations.

Conductive porphyrin films prepared by the self-assembly method

Abstract This paper describes the preparation, characterization and conductivity of the self-assembly films of two newly synthesized bridged-porphyrins [FeTPPCN]n and [CoTPPpz]n. The bridged-porphyrins are bonded covalently to the gold surface or the foundational film surface on the gold substrate. The films are characterized by Auger electron spectroscopy and X-ray photoelectron spectroscopy. Raman studies reveal that the long axis of the CN-porphyrin is perpendicular to the surface and that of pyrazine-porphyrin tilts on the surface. The conductivity in the film normal direction is 9.1 × 10−4 S cm−1 and 3.8 × 10−4 S cm−1 respectively for [FeTPPCN]n and [CoTPPpz]n after doping with iodine.

Preparation and characterization of anisotropic chain structures in polyimide films

Polyimide (PI) films were prepared by the pulsed laser ablation, the rubbing of PI‐coated substrates, the transfer of PI monolayers by vertical dipping method and the horizontal deposition of flowing water supported PI monolayers, and investigated by atomic force microscopy. A macroscopic anisotropy was measured in all these films. However, we found PI chain molecules were not uniformly oriented on a microscopic scale in the films prepared by the pulsed laser ablation and rubbing methods while a relatively perfect local and global orientation of PI chains existed in PI monolayer films.

Atomic force microscopy studies of domain structures in phase-separated monolayers

Abstract Domain structures were studied with atomic force microscopy (AFM) in binary phase-separated monolayer films composed of 5, 10, 15-triphenyl-20-(4-dl-α-phenylalanylamindo) phenyl porphyrin (TPPP) and one of a series of fatty acids which are arachidic acid (AA), palmitic acid (PA), and lauric acid (LA). The liquid-condensed (LC) domain structures of AA and PA were observed in their corresponding mixed monolayers. However, instead of the fatty acid domain, a liquid-expanded (LE) domain structure of TPPP appears in the mixed monolayer of LA/TPPP.

Liquid Crystal Alignment on Polymer Films

The rubbed polyimide (PI) and PI LB films were fabricated and treated to align the nematic liquid crystal (LC) 5CB. The rubbed polyimide (PI) films aligned LC cell shows a higher LC pretilt angle t...