Effects of molecular weight, solvent and substrate on the dewetting morphology of polystyrene films

Surface morphology of polystyrene (PS) films on different substrates by spin-coating before and after annealing was observed using atomic force microscopy (AFM). The effects of polymer molecular weight, substrates, solvents, and annealing conditions on the morphology of the films were investigated. Before annealing, the grain height decreases, and simultaneously the grain diameter increases with molecular weight (M-w) within the measured molecular weight. After annealing. the situation is opposite, i.e., the grain height increases while the grain diameter decreases with M-w. Furthermore, after annealing the smaller surface roughness (Ra) was obtained. It was also found that film surface roughness (Ra) depends on the vapor pressure and dipole moment of different used solvents as well as the substrates. The experimental results show that when the used solvents have similar dipole moment but different vapor pressure, the Ra of PS film decreased with the decreasing vapor pressure of solvents whether on silicon or on mica. And when the used solvents have close vapor pressure but different dipole moment, the Ra decreased with the increasing of solvent dipole moments on both substrates.

Thickness-dependent molecular chain and lamellar crystal orientation in ultrathin poly(di-n-hexylsilane) films

The molecular chain and lamellar crystal orientation in ultrathin films (thickness < 100 nm) of poly(di-n-hexylsilane) (PDHS) on silicon wafer substrates have been investigated by using transmission electronic microscopy, wide-angle X-ray diffraction, atomic force microscopy, and UV absorption spectroscopy. PDHS showed a film thickness-dependent molecular chain and lamellar crystal orientation. Lamellar crystals grew preferentially in flat-on orientation in the monolayer ultrathin films of PDHS, i.e., the silicon backbones were oriented along the surface-normal direction. By contrast, the orientation of lamellar crystals was preferentially edge-on in ultrathin films thicker than ca. 13 nm, i.e., the silicon backbones were oriented parallel to the substrate surface. We interpret the different orientations of molecular chain and lamellar crystal as due to the reduction of the entropy of the polymer chain near the substrate surface and the particularity of the crystallographic (001) plane of flat-on lamellae, respectively. A remarkable influence of the orientations of the silicon backbone on the UV absorption of these PDHS ultrathin films was observed due to the one-dimensional nature of sigma-electrons delocalized along the silicon backbone.

Molecular weight effects on the phase morphology of PS/P4VP blend films on homogeneous SAM and heterogeneous SAM/Au substrates

The effects of the molecular weight of polystyrene (PS) component on the phase separation of PS/poly(4-vinylpyridine) (PS/P4VP) blend films on homogeneous alkanethiol self-assembled monolayer (SAM) and heterogeneous SAM/Au substrates have been investigated by means of atomic force microscopy (AFM). For the PS (22.4k)/P4VP (60k) system, owing to the molecular weight of PS component is relatively small, the well-aligned PS and P4VP stripes with good thermal stability are directed by the patterned SAM/Au surfaces. With the increase of the molecular weight of PS component (for the PS (582k)/P4VP (60k) system), the diffusion of P4VP is hindered by the high viscosity of PS during the fast spin-coating process. The phase separation behavior of PS/P4VP on the SAM/Au patterned substrates is similar to that on the homoueneous SAM and cannot be easily directed by the patterned SAM surfaces even though the characteristic length of the lateral domain morphology is commensurate with the stripe width.

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.

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.

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.