Tuning the aggregation of polyimide thin films by modification of their molecular interactions

Thin films of an organo-soluble polyimide based on 1,4-(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) and 2,2'-dimethyl-4,4'-methylene dianiline (DMMDA) have been studied. A prism coupler was used to measure the refractive indices. The average refractive indices of thin films prepared by annealing at different temperatures and times were chosen to characterize the condensation states of thin films. Thin films annealed at 200 degrees C show irreversible changes in physical properties, eg solubility. FTIR spectroscopy showed that the chain structures of the above thin films remained unchanged. It is proposed that specific molecular interactions induce the irreversible changes revealed by fluorescence spectroscopy. (C) 2000 Society of Chemical Industry.

Molecular orientation of copper phthalocyanine in thin films and their gas-sensing properties

Copper phthalocyanine derivative Langmuir-Blodgett (LB) films were prepared by vertical dipping and horizontal lifting methods. Molecular orientation of copper phthalocyanine derivative in thin films was studied by polarized UV-Vis spectra. The relationship between the molecular orientation of copper phthalocyanine in LB films and their gas-sensing properties was investigated.

Molecular orientation of copper phthalocyanine derivative ins copper phthalocyanine-Fe2O3 nanoparticles alternating LB films

Copper phthalocyanine-Fe2O3 nanoparticles alternating thin films were fabricated by Langmuir-Blodgett technique. Molecular orientation of [4-(4'-benzyloxy phenyl sulfonyl)phenoxy]-tris-4-(2,4-di-t-phenoxy) phthalocyanine copper (II) in its alternating LB films, deposited at different conditions,was studied by polarized UV-Vis spectra. The tilt extent of the copper phthalocyanine molecule omits LB films increases with the surface pressure of the subphase increasing on the same subphase, or with Fe2O3 concentration decreasing at the same pressure. The orientation of the copper phthalocyanine derivative is important for the gas-sensing properties. The bigger the tilt extent of the phthalocyanine molecule is, the greater the sensitivity of the film is.

Molecular and supramolecular deformations and disclinations in a liquid crystalline copolyether thin films under an electrostatic field

An alignment study of a liquid crystalline copolyether TPP-7/11(5/5) thin films has been carried out in a 10 kV . cm(-1) electrostatic field parallel to the thin film surface normal. This copolyether possesses a negative dielectric anisotropy. The chain molecules are homogeneously aligned in the electric field and they form two-dimensionally ordered lamellae in a tilted columnar phase when the samples were cooled to room temperature. It is observed that the chain molecules are splayed to form bent lamellae and the chain direction is perpendicular to the tangential direction of the lamellar surfaces. These lamellae thus become replicas of the chain orientation, Due to the flexoelectric effect and density fluctuation on the thin film free surface, disclinations having topological strength s = 1, c = pi /4 and defect walls form. These s = 1 disclinations possesses both left- and right-handednesses. Discussion of the defect formations have been attempted.

Water soluble polyaniline and its blend films prepared by aqueous solution casting

Polyaniline (PAn) was doped with phosphonic acid containing hydrophilic tails. The solubility of the doped PAn in water was controlled by changing the length of hydrophilic chain in the dopant. When poly(ethylene glycol) monomethyl ether (PEGME) with molecular weight M-w = 550 was used as the hydrophilic chain of the dopant, the doped PAn was entirely soluble in water. The film cast from aqueous solution showed good electrochemical redox reversibility, Aqueous solution blending of PAn with poly(ethylene glycol) (PEG, M-w = 20 000) and poly(N-vinyl pyrrolidone) (PVP, M-w = 360 000) was achieved. Percolation threshold of the composite film was lower than 3 wt.%. Electrical conductivity of the composite film was in the range of 10(-1)-10(-5) S cm(-1), depending on molecular weight of the acid and the content of PAn in the composite. (C) 1999 Elsevier Science Ltd. All rights reserved.

Study of molecular orientation in Langmuir-Blodgett films by FTIR

The structure information of orientation and packing of molecular chains can be obtained from infrared transmission and reflection-absorbance (RA) spectra. In the present paper, on the basis of Umemura et al., their FORTRAN program of minicomputer was developed and can be run on 486 personal computer. By comparison of infrared transmission and RA intensities, surface enhancement factors and molecular orientation angle were calculated using the above program, and the influence of complex refractive index, angle of incidence, and thickness of LB film were discussed. These results are consistent with that of Umemura et al.

Study of molecular order in organo-soluble polyimide thin films

The changes in refractive indices (n(TE) and n(TM)) in a direction normal to the plane of thin films of an organo-soluble polyimide based on 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride and 2,2'-dimethyl-4,4'-methylene dianiline were measured by a prism coupler. The results implied that the molecules near the substrate-polyimide interface were much ordered, while those near the polyimide-air interface were less ordered, judging from the variation in the level of negative birefringence with the depth of the films. The molecules are more condensed near the substrate surface, as seen by the average refractive index increasing from the polyimide-air interface to the substrate-polyimide interface, which implies that the condensed states of polyimide molecules change gradually in the depth direction. (C) 1997 Elsevier Science B.V.

Study on Ordered Assembly of SnO2 Nonoparticles-Arachidic Acid Composite LB Films

The hydrosol of SnO2 nanoparticles (NP) have been prepared by colloid chemistry method. The composite LB monolayer and multilayer of SnO2 NP-AA have been obtained by LB technique at the gas-liquid interface of the hydrosol subphase. The structures of the monolayer and multilayer were characterized by IR, UV-Vis, small angle X-ray diffraction spectroscopy and TEM technique, The results indicate that the coverage of SnO2 NP at the composite monolayer's surface is high and the sites of SnO2 NP are similar. The multilayer has good periodic structure.

EFFECT OF MOLECULAR-WEIGHT OF PMMA ON BETA PHASE CRYSTALLIZATION IN HIGHLY ORIENTED PVF2 FILMS

Polyvinylidene fluoride (PVF_2) exhibits at least four crystalline phases (α, β, γ, and δ). Among them, β phase is the most important one because it is directly related to the piezoand pyro-electric activities of PVF_2. In recent years, more attention has been paid to the β

Thin Ta films: growth, stability, and diffusion studied by molecular-dynamics simulations

We report results of classical molecular-dynamics simulations of bcc and beta-Ta thin films. Thermal PVD film growth, surface roughness, argon ion bombardment, phase stability and transformation, vacancy and adatom diffusion, and thermal relaxation kinetics are discussed. Distinct differences between the two structures are observed, including a complex vacancy diffusion mechanism in beta-Ta. Embedded atom method potentials, which were fitted to bcc properties, have been used to model the Ta-Ta interactions. In order to verify the application of these potentials to the more complex beta-Ta structure, we have also performed density functional theory calculations. Results and implications of these calculations are discussed.

Molecular layering and local order in thin films of 1-alkyl-3-methylimidazolium ionic liquids using X-ray reflectivity

X-ray reflectivity measurements in air of thin films of 1-alkyl-3-methylimidazolium salts in the liquid, liquid crystalline and solid states supported on Si( 111) are described. The films show Bragg features in both liquid crystalline and solid phases, but only after an initial annealing cycle. Kiessig fringes are observed only for the 1-octadecyl-3-methyl-imidazolium hexafluorophosphate films and, following analysis using Parratt32, a bi-layer model is proposed whereby the molecules are orientated with ionic groups at both salt-air and salt-silicon interfaces.