Polymer ultrathin films with immobilized photosynthetic reaction center proteins

Properties of mixed monolayers of lipid-photosynthetic reaction center proteins (RC) were studied and the optimum conditions for stable films fabrication were determined. The following synthetic: N-acryloylphosphatidylethanolamine (ACPE), tetracosa-11, 13-diinoic acid (TDA), pentacosa-10, 12-diinoic acid (PDA), dioctadecyldienoylphosphatidylcholine (DODL) and natural lipids: L-α-phosphatidylethanolamine (PE), L-α-phosphatidylcholine (PC) were used. The rate of polymerization of the mixed ACPE-RC and TDA-RC monolayers is lower in comparison with corresponding values for pure lipid-like monomers on air/water interface. The optical and photoelectrical measurements provide evidence for an orientation of RCs on interface. Hydrophilic H-subunit in monomeric and polymeric ACPE-RCs, and monomeric DODL-RCs monolayers is preferentially oriented towards water as in the pure RC monolayers. Opposite orientation was found with TDA-RCs and PDA-RCs films. No preferential orientation for lipid-RCs from C. aurantiacus monolayers was found because of the RCs having low assymmetry of hydrophobic subunits (M and L).     

PM-IRRAS mapping of ultrathin molecular films with high spatial resolution

Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) is a very sensitive technique to characterize the degree of molecular ordering in thin films on metallic surfaces. This is the first report of the coupling of a PM-IRRAS microscope to a free electron laser (FEL), a light source of highest brilliance. Some FELs emit in the infrared region and permit the mapping of molecular properties at high lateral resolution. We studied the molecular orientation of octadecanephosphonic acid (OPA) attached to a gold surface with microstructured aluminum oxide islands on the gold. The spatial resolution achieved is 12 μm which corresponds to the diffraction limit of the infrared light used in this study. This is a substantial improvement compared to previous studies using a PM-IRRA accessory together with a commercial Fourier transform infrared spectrometer, where the lateral resolution is noise-limited rather than diffraction-limited. The spectral maps reveal that OPA is preferably attached to the aluminum oxide islands via the bidentate binding mode whereas the tridentate mode is dominating in case of OPA attached to the gold areas.     

Photopatterning of ultrathin electrochemiluminescent redox hydrogel films

Photoinitiated polymerisation is efficiently and rapidly carried out to immobilise ultrathin electrochemiluminescent redox hydrogel films. Microscale patterns are fabricated on an electrode surface by a simple photolithographic procedure and revealed by ECL imaging.     

Nanometer-scale decomposition of ultrathin multilayered polyelectrolyte films

We report that ultrathin multilayered films fabricated from plasmid DNA and synthetic polyamines undergo nanometer-scale transformations that resemble spinodal decomposition when incubated in aqueous media. The patterns and structures generated by this transformation are similar to those observed for the spinodal dewetting of thin films of conventional polymers. This behavior has not, however, been observed for this class of multilayered assemblies, for which long-range electrostatic interactions play significant roles in governing film structure and stability. We demonstrate that it is possible to promote this behavior, prevent it, or control it by varying polymer structure, film composition, or the conditions to which these materials are exposed. These results suggest the basis of methods that could prove useful for the generation of nanostructure on complex surfaces and contribute to methods for the localized delivery of DNA from surfaces.     

Entanglement of polymer chains in ultrathin films

This investigation aimed to clarify the issue of whether polymer chains are entangled in ultrathin films spin-coated onto substrates. This was done using a fluorescence probe method to observe the behavior of two types of poly(methyl methacrylate) (PMMA), one having a carbazolyl (Cz) moiety (PMMA-Cz) and the other having an anthryl (At) moiety (PMMA-At). In both cases, the moiety fraction was 1 unit for 400 units of polymer. We prepared ultrathin films (thickness: 4-88 nm) on quartz substrates from PMMA-Cz, PMMA-At, and a mixture of the two using a spin-coating method. When the PMMA films prepared from the mixture of the two PMMAs were excited at 292 nm, which is preferentially absorbed by Cz rather than At, the Cz fluorescence was found to be quenched dramatically while the At fluorescence increased significantly. This effect is due to the proximity of the Cz to the At, which permits the transfer of excitation energy between them. The average distance between Cz and At can be calculated using the F?rster mechanism. When the ultrathin film thickness was between 12 and 88 nm, the average distance was found to be 2 nm. This is much shorter than the radii of gyration of the polymers. From this it is clear that two polymer molecules in an ultrathin film do experience entanglement, as has been hypothesized. Thus, we conclude that the difference between certain properties of ultrathin films and the properties of the same materials in bulk are not induced by a decrease in the level of polymer chain entanglement.     

Stamping patterns of insulated gold nanowires with self-organized ultrathin polymer films

A thermal contact transfer technique is presented for the fabrication of nanoscaled to microscaled patterns of polymer-insulated metal structures on ceramic surfaces using metal-coated, thermoplastic stamps. The thermally activated formation of polymer-metal-polymer (PMP) heterostructures occurs spontaneously when a metal-coated thermoplastic stamp is compressed against a ceramic substrate and subsequently heated. The presented technique exploits the dynamics of ultrathin polymer films localized at interfaces and interfacial forces to prompt local reorganization of polymer stamp materials during processing. Intercalation of polymer stamp materials into the metal-substrate interface yields a cohesive polymer layer that binds the metal layer to the substrate. Disproportionate adhesion between the bulk polymer and the polymer layer at the stamp-metal interface leaves a capping layer upon separation of the stamp from the substrate. Here we demonstrate this technique with single use, bilevel polymer stamps which afford transfer of two distinct general products. The transfer of insulated submicrometer wide wires from the raised stamp features affords patterns of trilayered PMP structures with uniform wire dimensions. Concomitant transfer from the recessed stamp features allows fabrication of multilayered PMP architectures with sub-100 nm spacing from microstructured polymer stamps. Thus, patterns with two different insulated nanowire widths are readily fabricated in a single stamping process. A variety of ceramic substrates, thermoplastic materials, and metals can be used; e.g., inexpensive gold-coated CD or DVD media can be used as stamps, where the combination of materials dictates the relative interfacial forces and the processing parameters.     

Fabrication of ultrathin films with large third-order nonlinear optical properties.

An ultrathin composite film containing anionic Ag-His complexes (His: L-Histidine) and oppositely charged BH-PPV was fabricated by means of the electrostatic layer-by-layer self-assembly technique. UV/Vis spectra showed a continuous deposition process of Ag-His complexes and BH-PPV. The film structure was characterized by using small-angle X-ray diffraction, AFM, and SEM. The nonlinear optical properties of the ultrathin film were studied by using the Z-scan technique with a laser duration of 8 ns at a wavelength of 532 nm. The film sample exhibited a strong nonlinear saturated absorption, with an alpha2 value of -3.9 x 10(-5) mW(-1) and a self-defocusing effect with an n2 value of -4.78 x 10 (-12) m2W(-1).     

Synthesis of ultrathin polymer films by self assembly

Recent progresses in the self assembly of ultrathin polymer films are described. Bilayer membranes of polymeric hydrogen-bond networks are formed in water. Two-dimensional networks of organic and inorganic polymers are formed in cast films of synthetic bilayer membranes to give stable multilayer films upon removal of the matrices. The monolayer at the air-water interface constitutes suitable templates for 2D polymer networks, and it may be either removed or part of the 2D film. Successive adsorption of polycations and polyanions under carefully controlled conditions produces layered polyion complexes in the stepwise manner. Various polymer chains are epitaxially adsorbed onto graphite. All these results indicate that molecularly defined 2D polymer structures are readily available.     

Dynamics of ultrathin films in the glassy state

We report hole growth experiments in free-standing polystyrene (PS) films at temperatures up to 10 degrees C below the bulk glass transition. The data show an unexpected result: the growth rate of nucleated holes increases with increasing molecular weight, up to a limiting value beyond which the rate is approximately constant. Film thicknesses of 45, 80, and 100 nm were studied, using PS molecular weights ranging from 65K to 11.4 Mg/mol. Hole diameters grew linearly with time, and no growing rims were observed to form around the developing holes. Possible explanations in terms of elasticity, yield, and influence of sample preparation and confinement effects are discussed.     

Structure of ultrathin polyethylene layers in multilayer films

The crystalline structures of “microlayer” and “nanolayer” polyethylene have been examined in coextruded films comprised of alternating layers of high-density polyethylene and polystyrene. Transmission electron microscopy (TEM), small-angle x-ray scattering (SAXS), and wide-angle x-ray scattering (WAXS) reveal that microlayer polyethylene, where the layer thickness is on the order of several microns, crystallizes with the normal unoriented lamellar morphology. In nanolayer films, where the film thickness of tens of nanometers is on the size scale of molecular dimensions, lamellae are oriented with the long axes perpendicular to the extrusion direction in a row-nucleated morphology similar to structures described in the literature. The lamellae are partially twisted about the long axes. The preferred twist angles of ±40° orient the lamellar surfaces normal to the layer surface. The row-nucleated morphology imparts highly anisotropic mechanical properties to the nanolayer polyethylene.     

Polymer crystallization of ultrathin films on solid substrates

Recently, polymer crystallization in ultrathin films (thickness less than 100 nm) on solid substrates has attracted increased attention. As it can be considered to be a quasi-two-dimensional (2D) system with one-dimensional (1D) confinement along the substrate normal, ultrathin polymer film offers unique possibilities for testing the theories of crystallization and for studying the effects of confinement and interface which may invoke new mechanisms other than those applied in bulk crystallization of polymers. In this article, we will summarize the important results of ultrathin film crystallization of polymers obtained in the past decades. The morphologies, the crystallization kinetics, and the transformation between monolayer crystals with various metastabilities are reviewed in depth, with an attempt at discussing the ultrathin polymer film crystallization in the general framework of thermodynamics and kinetics of crystallization.     

Optical properties and photonic devices of doped carbon nanotubes

Chemical doping of carbon nanotubes provides a variety of opportunities for tailoring the physical properties of carbon nanotubes. In this review, we discussed the optical properties of doped carbon nanotubes and the related applications as nanoscale photonic devices. The fundamental optical properties of carbon nanotubes with various chemical doping have been summarized. Novel optoelectronic and photonic devices based on doped carbon nanotubes, such as optical nonlinear materials, optical limiting devices, photovoltaic devices, etc., have been discussed.     

The structure of ultrathin Langmuir-Blodgett films of cadmium behenate

Grazing incidence x-ray-diffraction investigations of the structures of Langmuir-Blodgett films of cadmium behenate with 1, 2, 3, 5, and 21 monolayers are reported. The single monolayer film, deposited on a hydrophilic substrate, showed a hexagonal structure, whereas the bilayer film, deposited on a hydrophobic substrate, had a rectangular structure with herringbone orientation of the acyl chains. With multilayer films formed on a hydrophilic substrate, it was possible to detect that the hexagonal structure of the first layer was retained when additional layers were deposited and that the additional layers had the same rectangular structure as the bilayer.     

Photoinduced liquid crystal alignment by layer-by-layer ultrathin films with dual photoreaction moieties

A novel layer-by-layer (LBL) film containing dual photoreaction groups, cinnamoyl and azobenzene, was prepared from poly(diallyldimethylammonium chloride) (PDDA) and a photosensitive polyanion, PCAzo, in aqueous solution via electrostatic attraction. The film was able to induce uniform alignment of liquid crystals (LCs) with good stability and 2.3° pretilt angle by oblique irradiation with linearly polarised ultraviolet light (LPUVL). UV absorption and FTIR spectroscopic results indicate that the photoreactions of the two photoreactive groups jointly participate in generating the anisotropy of the film. The dichroic ratio of the film was found to depend on the number of adsorbed layers. The thicker film has the larger dichroic ratio after the LPUVL irradiation. The reorientation behaviour of the LC molecules was found to be associated with the LBL film thickness. Experiment results revealed that the photo-crosslinking of the cinnamoyl groups was responsible for the stability of the anisotropic orientation, and the isomerisation of the azobenzene chromophores led primarily to the appropriate pretilt angle.     

Surface-induced phase transitions in ultrathin films of block copolymers

We study theoretically the lamellar-disorder-lamellar phase transitions of AB diblock and tetrablock copolymers confined in symmetric slitlike pores where the planar surface discriminatingly adsorbs A segments but repels B segments, mimicking the hydrophobic/hydrophilic effects that have been recently utilized for the fabrication of environmentally responsive "smart" materials. The effects of film thickness, polymer volume fraction, and backbone structure on the surface morphology have been investigated using a polymer density-functional theory. The surface-induced phase transition is manifested itself in a discontinuous switch of microdomains or a jump in the surface density dictated by the competition of surface adsorption and self-aggregation of the block copolymers. The surface-induced first-order phase transition is starkly different from the thickness-induced symmetric-asymmetric or horizontal-vertical transitions in thin films of copolymer melts reported earlier.     

Surface patterning via evaporation of ultrathin films containing nanoparticles

The dewetting dynamics of ultrathin films containing potentially surface-active nanoparticles is considered in the presence of evaporation. Evolution equations for the film height and particle surface and bulk concentration are derived using a lubrication model coupled by a constitutive relation for the dependence of the viscosity on local particle concentration. A linear stability analysis and numerical simulations are used to determine how particle mass distribution depends on the various physical parameters such as equilibrium film separation distance, initial packing concentration, rate of evaporation, and particle surface activity. Our results show that when starting from an initially uniform distribution the particles become aligned into distinct "bands" in rectilinear geometry, or "rings" in cylindrical geometry. The functional dependence of the pattern spacing on relevant system parameters is studied and detailed herein.     

Preparation of ultrathin polypyrrole films using an adhesion promoter

Adhesive ultrathin polypyrrole films were deposited on Si/SiO₂ substrates modified with the new adhesion promoter 11-(Pyrrol-1-yl Undecyl) TrichloroSilane (PUTS). The oxidation potential of PUTS in solution was determined electrochemically by cyclic voltammetry. Self-assembled monolayers of PUTS were investigated by cyclic voltammetry, contact angle measurements, ellipsometry, and X-ray photoelectron spectroscopy. Several oxidants for the deposition of pyrrole on adhesion promoter modified substrates were tested and a strong dependence on the obtained film morphology was found. It was possible to deposit chemically ultrathin polypyrrole films on insulating substrates.     

Structural phase transition in ultrathin films of disk-shaped molecules

We have used grazing-incidence X-ray diffraction and atomic force microscopy to study Langmuir-Blodgett films of 2-(3-hydroxypropyl)oxy-3,6,7,10,11-pentapentyloxytriphenylene, a disk-shaped molecule which also forms a bulk liquid crystalline columnar phase. Upon heating, we observe a phase transition from a low symmetry ordered crystalline structure to a high temperature liquid crystal. The transition is reversible, with considerable hysteresis.