Ideal spread monolayer and multilayer formation of fully hydrophobic polythiophenes via liquid crystal hybridization on water

The spread monolayer formation of hydrophobic poly(3-alkylthiophene)s (P3ATs), regioregular poly(3-hexylthiophene) ( HT-P3HT), regioregular poly(3-dodecylthiophene) ( HT-P3DT), and regioirregular poly(3-hexylthiophene) ( RI-P3HT), were attained on the water surface via cospreading with a liquid-crystal molecule, 4'-pentyl-4-cyanobiphenyl (5CB). The spread monolayers were characterized by pi- A isotherms, Brewster angle microscopy (BAM), and atomic force microscopy (AFM). The molecular area for the cospread mixtures of P3ATs and 5CB expanded more than that of pure P3ATs as shown from the pi-A isotherms. BAM revealed that the mixed film forms the monomolecularly uniform and flat films on water. AFM elucidated that the spread monolayer of the hydrophobic P3ATs formed on the top of the 5CB monolayer on water with thicknesses of ca. 1.6 and ca. 2.6 nm for the two P3HTs and HT-P3DT, respectively. The P3AT/5CB hybrid monolayers could be fully transferred onto a solid substrate, and pure P3AT monolayers were obtained after volatilization of 5CB by gentle heating. The multilayer formation of pure P3AT monolayers was prepared by layer-by-layer deposition involving repeating horizontal deposition and successive volatilization of 5CB. Grazing angle incidence X-ray diffraction measurements showed that the lamella plane of the P3ATs is perfectly oriented parallel to the substrate plane in the resulting thin films. This shows a marked contrast with those obtained by spin casting using the identical polymer, where both in-plane and out-of-plane lamellae are involved. These thin films with perfectly controlled lamella orientation should be of great significance as the model system for evaluating the charge mobility for organic polymer electric devices.     

Is the alignment of nematics on a polymer slab always along the rubbing direction? A molecular dynamics study

ABSTRACT

We have studied the alignment and molecular organisation within a thin film of the popular nematic 5CB sandwiched between two flat polymer slabs, examining the effect of polymer chemical nature and morphology with atomistic molecular dynamics simulations. We have chosen two common polymers: polystyrene (PS) and polymethylmethacrylate (PMMA), either with their chains in random coil conformation (disordered) or with chains unidirectionally stretched (ordered). We found that, independently on the arrangement of the chains, both surfaces align planarly the liquid crystal, in accord with experimental observation. Moreover, while 5CB molecules align along the chains stretching direction of the PMMA ordered surface, on the combed PS surface they arrange on average perpendicularly to the stretching direction. This behaviour is attributed to the chemically specific interactions between the respective aromatic moieties of PS and 5CB.     

Reorganization of hydrogen-bonded block copolymer complexes

Poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) copolymers and poly(acrylic acid) (PAA) have been mixed in organic solvents. Complexation via hydrogen bonding occurs between the P4VP and PAA blocks. Those insoluble complexes aggregate to form the core of micelles surrounded by a corona of PS chains. Reorganization of these structures occurs upon addition of acidic or basic water, which results in the breaking of the hydrogen bonds between the P4VP and PAA blocks. After transfer of the initial complexes in acidic water, micelles consisting of a PS core and a protonated P4VP corona are observed. In basic water, well-defined nanoparticles formed by the PS-b-P4VP copolymers are obtained. It is demonstrated that these nanoparticles are stabilized by the negatively charged PAA chains. Finally, thermally induced disintegration of the micelles is investigated in organic solvents.     

Conformational change in an isolated single synthetic polymer chain on a mica surface observed by atomic force microscopy

The random coil conformation of an isolated conventional synthetic polymer chain was clearly imaged by atomic force microscopy (AFM). The sample used was a poly(styrene)-block-poly(methyl methacrylate) diblock copolymer. A very dilute solution of the copolymer with benzene was spread on a water surface. The structure thus formed on water was subsequently transferred and deposited onto mica at various surface pressures and observed under AFM. The AFM images obtained with films deposited at a low surface pressure (<0.1 mN/m) showed a single polystyrene (PS) block chain aggregated into a single PS particle with a single poly(methyl methacrylate) (PMMA) block chain emanating from the particle. Immediately after the deposition, the single PMMA block chain aggregated to form a condensed monolayer around the polystyrene particles. However, after exposing the deposited film to highly humid air for 1 day, the PMMA chains spread out so that the single PMMA block chain could be identified as a random coil on the substrate. The thin water layer formed on the mica substrate in humid air may enable the PMMA block chain to be mobilized on the substrate, leading to the conformational rearrangement from the condensed monolayer conformation to an expanded and elongated coil. The elongation of the PMMA chain was highly sensitive to the humidity; the maximum elongation was obtained at 79% relative humidity. The elongation was a slow process and took about 20 h.     

Fabrication of Au/Titania Composite Nanodot Arrays from Au‐Loaded Block Copolymer Micellar Films

Summary: A simple route to an ordered array of metal/semiconductor oxide composite nanodots is presented. Micellar monolayer films of polystyrene‐block‐poly(2‐vinyl pyridine) (PS‐b‐P2VP) loaded with HAuCl₄ in the P2VP nanodomains are used as templates. TiO₂ is generated selectively within the polar P2VP domains of PS‐b‐P2VP/HAuCl₄ films by chemical vapor deposition of TiCl₄. Subsequent removal of the organic matrix by oxygen plasma or UV light leads to an array of Au/TiO₂ composite nanoparticles on the substrate surface.

Schematic illustration of the process to fabricate an array of Au/titania composite nanodots.     

Surface Morphology Evolution of a Thin Polymeric Supramolecular Film by Tuning Interactions

Summary: A polymeric supramolecule consisting of symmetric polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP), dodecylbenzenesulfonic acid (DBSA), and 3‐pentadecylphenol (PDP) was formed by proton transfer and hydrogen bonding. The surface morphology of a thin film of the polymeric supramolecule has been investigated. The spherical PS microdomains embedded in a P4VP(DBSA)_1.0(PDP)_1.0 matrix are observed for the as‐cast film because the weight fraction, f_comb, of the P4VP(DBSA)_1.0(PDP)_1.0 blocks is much higher than that of PS as a result of the non‐covalent interactions of P4VP and DBSA and DBSA and PDP. Upon annealing the PS‐b‐P4VP(1:1)(DBSA)_1.0(PDP)_1.0 film at high temperatures, the hydrogen bonding between the DBSA and PDP diminishes, which leads to a change of overall morphology from an ordered sphere to a pitted structure.

AFM topographic image of a PS‐b‐P4VP(1:1)(DBSA)_1.0(PDP)_1.0 thin film.     

Controlled rearrangement of adsorbed undecanol films on mica surfaces induced by an atomic force microscopy tip

An undecanol film adsorbed on a mica surface was found to rearrange and spread in a position-controlled way induced by a tapping mode atomic force microscopy (AFM) probe. AFM images of varying scanning times showed that before forming an ordered monolayer the undecanol molecules were adsorbed on the mica surface in the disordered and disorganized status. With the proceeding of scanning, these undecanol molecules gradually formed an ordered and flat film. Such behavior was caused by the formation of a stable film and had never been reported for other alcohols.     

Study of the surface and interfacial tensions in systems containing a low molar mass liquid crystal

The surface tension of a low molar mass liquid crystal (LMMLC), 4-cyano-4'-n-heptyloxybiphenyl (70CB), was measured as a function of temperature using the pendant drop method, forming drops of different volumes ranging from 5 to 11 mm³. Contact angles formed by drops of 70CB in the nematic and isotropic phases on plates of polystyrene (PS) and of a liquid crystal polymer (LCP), VECTRA A910, were also measured. Only large drops could be used for surface tension analysis. It was shown that in the nematic phase the surface tension of 70CB decreases with increasing temperature, and that in the isotropic phase the surface tension increases with increasing temperature. Using the values of contact angle and of surface tension of 7OCB it was possible to evaluate the interfacial energy between 7OCB and PS and between 7OCB and VECTRA. The interfacial energy between 7OCB and PS, and between 7OCB and VECTRA, decreased with increasing temperature for ranges of temperatures corresponding to both phases of 70CB.     

Study of the surface and interfacial tensions in systems containing a low molar mass liquid crystal

The surface tension of a low molar mass liquid crystal (LMMLC), 4-cyano-4'-n-heptyloxybiphenyl (70CB), was measured as a function of temperature using the pendant drop method, forming drops of different volumes ranging from 5 to 11 mm³. Contact angles formed by drops of 70CB in the nematic and isotropic phases on plates of polystyrene (PS) and of a liquid crystal polymer (LCP), VECTRA A910, were also measured. Only large drops could be used for surface tension analysis. It was shown that in the nematic phase the surface tension of 70CB decreases with increasing temperature, and that in the isotropic phase the surface tension increases with increasing temperature. Using the values of contact angle and of surface tension of 7OCB it was possible to evaluate the interfacial energy between 7OCB and PS and between 7OCB and VECTRA. The interfacial energy between 7OCB and PS, and between 7OCB and VECTRA, decreased with increasing temperature for ranges of temperatures corresponding to both phases of 70CB.     

Transformation from ordered islands to holes in phase-separating P2VP/PS blend films by adding Triton X-100

Our previous investigation showed that the ordered hexagonal island pattern in the phase-separating polymeric blend films of polystyrene and poly(2-vinylpyridine) (PS/P2VP) formed due to the convection effect by proper control of PS molecular weight, solvent evaporation rate, and the weight ratio of PS to P2VP. In this paper, we further illustrate that, by adding a proper amount of the surfactant Triton X-100 to the PS/P2VP toluene solution, the ordered hexagonal island pattern can be transformed to the ordered honeycomb pattern. The effects of the amount of Triton X-100 on the surface morphology evolution and the pattern transformation are discussed in terms of the collapse of Triton X-100, phase separation between Triton X-100/P2VP and PS, the interfacial interaction between Triton X-100/P2VP and the mica substrate, and the Bénard-Marangoni convection.     

Strands, networks, and continents from polystyrene dewetting at the air-water interface: implications for amphiphilic block copolymer self-assembly

We demonstrate that nanoscale aggregates similar to those formed via amphiphilic block copolymer self-assembly at the air-water interface, including strands, networks, and continents, can be generated by the simple spreading of PS homopolymer solutions on water. Two different PS homopolymers of different molecular weight (PS-405k, M(n) = 405?000 g mol(-1) and PS-33k, M(n) = 33?000 g mol(-1)) are spread at the air-water interface at various spreading concentrations ranging from 0.25 to 3.0 mg/mL. Aggregate formation is driven by PS dewetting from water as the spreading solvent evaporates. We propose that a high spreading concentration or a high molecular weight lead to chain entanglements that restrict macromolecular mobility in the solution, enabling the kinetic trapping of nanostructures associated with early and intermediate stages of PS dewetting. Comparison of PS-405k with a mainly hydrophobic PS-b-PEO block copolymer of similar molecular weight (PSEO-392k, M(n) = 392?000 g mol(-1), 2.0 wt % PEO) allows the effect of a relatively short surface active block on aggregate formation to be investigated. We show that whereas the PEO block is not a required component for the formation of strands and other nonglobular aggregates, it does increase the number of these aggregates at a given spreading concentration and decreases the minimum spreading concentration at which these aggregates are observed, along with decreasing the dimensions and polydispersity of specific surface features. The results provide supporting evidence for the role of PS dewetting in the generation of multiple PS-b-PEO aggregate morphologies at the air-water interface, as originally described in earlier paper from our group.     

Self-assembly of amphiphilic hexapyridinium cations at the air/water interface and on HOPG surfaces.

Mono- and multilayers of a novel amphiphilic hexapyridinium cation with six eicosyl chains (3) are spread at the air/water interface as well as on highly ordered pyrolytic graphite (HOPG). On water, the monolayer of 3 is investigated by recording surface pressure/area and surface potential/area isotherms, and by Brewster angle microscopy (BAM). Self-organized tubular micelles with an internal edge-on orientation of molecules form at the air/water interface at low surface pressure whereas multilayers are present at high surface pressure, after a phase transition. Packing motifs suggesting a tubular arrangement of the constituting molecules were gleaned from atomic force microscopy (AFM) investigations of Langmuir-Blodgett (LB) monolayers being transferred on HOPG at different surface pressures. These LB film structures are compared to the self-assembled monolayer (SAM) of 3 formed via adsorption from a supersaturated solution, which is studied by scanning tunnelling microscopy (STM). On HOPG the SAM of 3 consists of nanorods with a highly ordered edge-on packing of the aromatic rings and an arrangement of alkyl chains which resembles the packing of molecules at the air/water interface at low surface pressure. Additional details of the molecular packing were gleaned from single-crystal X-ray structure analysis of the hexapyridinium model compound 2b, which possesses methyl instead of eicosyl residues.     

Molecular organization in two-dimensional films of liquid I. Langmuir films of binary mixtures of liquid crystals with a crystalline mixtures terminal cyano group

The Langmuir films of two liquid crystal materials, 4-octyl-4'-cyanobiphenyl (8CB) and 4-pentyl-4"-cyano-p-terphenyl (5CT), and of their mixtures have been studied by recording surface pressure-area isotherms and Brewster angle microscopy (BAM) images. The pure liquid crystals revealed very different characters of the surface pressure-area isotherms indicating different organization of the molecules and different molecular interactions in the monolayer at the water-air interface. The surface pressure-area isotherms of Langmuir films formed from 8CB/5CT mixtures give evidence for phase separation of the components over the whole range of molar fractions. Similar conclusions have been drawn on the basis of BAM image analysis.     

Temperature-triggered micellization of block copolymers on an ionic liquid surface

In situ neutron reflectivity was used to study thermally induced structural changes of the lamellae-forming polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer thin films floating on the surface of an ionic liquid (IL). The IL, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, is a nonsolvent for PS and a temperature-tunable solvent for P2VP, and, as such, micellization can be induced at the air-IL interface by changing the temperature. Transmission electron microscopy and scanning force microscopy were used to investigate the resultant morphologies of the micellar films. It was found that highly ordered nanostructures consisting of spherical micelles with a PS core surrounded by a P2VP corona were produced. In addition, bilayer films of PS homopolymer on top of a PS-b-P2VP layer also underwent micellization with increasing temperature but the micellization was strongly dependent on the thickness of the PS and PS-b-P2VP layers.     

Time-resolved IR studies of monolayer self-assembly on a gold substrate using planar array infrared (PA-IR) spectroscopy

Time-resolved and spatially resolved infrared spectra (line images) of self-assembled monolayers of octadecylthiol (ODT) on gold substrates were investigated by planar array infrared (PA-IR) spectroscopy, with a grazing incidence reflection attachment. It was observed that PA-IR spectra with a good signal-to-noise ratio that is comparable to those obtained from Fourier transform infrared spectroscopy could be acquired with a significantly shorter collection time. Focusing on the peak intensities and peak positions of the CH2 asymmetric stretch (approximately 2918 cm(-1)) and the CH3 symmetric stretch (approximately 2960 cm(-1)), respectively, the molecular orientation and organization of the monolayers were determined. The ODT formed a uniform monolayer on the surface of the gold whether it was deposited within 1-2 s or over a 40 h period. Disordered monolayers formed instantly, and with an increase in dipping time, the monolayer became more ordered, becoming highly ordered after dipping times of many ( > 24) hours.     

Self‐organization and luminescent properties of nanostructured europium (III)–block copolymer complex thin films

We introduce a simple method to create nanosized, ordered, and highly luminescent thin film of Eu (III)–block copolymer complex. Micelles of polystyrene–block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) in P4VP‐selective solvents (ethanol/N,N‐dimethylformamide (DMF) mixture) serve as nanoreactors for the synthesis of Eu(III)–block copolymer complex with the presence of 1,10‐phenanthroline (Phen) as cooperative ligand. The resulted quaternary complexes were characterized by FT‐IR spectra, ¹⁵N NMR spectra, and elemental analysis, indicative of a composition of Eu(III)–(PS‐b‐P4VP)–Phen–5DMF. Atomic force microscopy and transmission electron microscopy investigations reveal that the Eu(III)–(PS‐b‐P4VP)–Phen–5DMF complex can self‐organize into hexagonally ordered thin films when dip‐coated from the solution onto silicon or silica glass substrates. Such ordered thin films can emit red fluorescence of Eu³⁺ with strong intensity and long lifetime. This method can be easily extended to prepare other ordered luminescent rare earth–polymer complexes thin films. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2181–2189, 2005     

Molecular organization in two-dimensional films of liquid I. Langmuir films of binary mixtures of liquid crystals with a crystalline mixtures terminal cyano group

The Langmuir films of two liquid crystal materials, 4-octyl-4'-cyanobiphenyl (8CB) and 4-pentyl-4"-cyano-p-terphenyl (5CT), and of their mixtures have been studied by recording surface pressure-area isotherms and Brewster angle microscopy (BAM) images. The pure liquid crystals revealed very different characters of the surface pressure-area isotherms indicating different organization of the molecules and different molecular interactions in the monolayer at the water-air interface. The surface pressure-area isotherms of Langmuir films formed from 8CB/5CT mixtures give evidence for phase separation of the components over the whole range of molar fractions. Similar conclusions have been drawn on the basis of BAM image analysis.     

Hydrogen bond mediated supramolecular micellization of diblock copolymer mixture in common solvents

We report a new approach toward preparing self-assembled hydrogen-bonded complexes having vesicle and patched spherical structures from two species of block copolymers in nonselective solvents. Two diblock copolymers, poly(styrene-b-vinyl phenol) (PS-b-PVPh) and poly(methyl methacrylate-b-4-vinylpyridine) (PMMA-b-P4VP), were synthesized through anionic polymerization. The assembly of vesicles from the intermolecular complex formed after mixing PS-b-PVPH with PMMA-b-P4VP in THF was driven by strong hydrogen bonding between the complementary binding sites on the PVPH and P4VP blocks. In contrast, well-defined patched spherical micelles formed after blending PS-b-PVPh with PMMA-b-P4VP in DMF: the weaker hydrogen bonds formed between the PVPh and P4VP blocks in DMF, relative to those in THF, resulted in the formation of spherical micelles having compartmentalized coronas consisting of PS and PMMA blocks.     

Fabrication of hybrid nanostructured arrays using a PDMS/PDMS replication process

In the study, a novel and low cost nanofabrication process is proposed for producing hybrid polydimethylsiloxane (PDMS) nanostructured arrays. The proposed process involves monolayer self-assembly of polystyrene (PS) spheres, PDMS nanoreplication, thin film coating, and PDMS to PDMS (PDMS/PDMS) replication. A self-assembled monolayer of PS spheres is used as the first template. Second, a PDMS template is achieved by replica moulding. Third, the PDMS template is coated with a platinum or gold layer. Finally, a PDMS nanostructured array is developed by casting PDMS slurry on top of the coated PDMS. The cured PDMS is peeled off and used as a replica surface. In this study, the influences of the coating on the PDMS topography, contact angle of the PDMS slurry and the peeling off ability are discussed in detail. From experimental evaluation, a thickness of at least 20 nm gold layer or 40 nm platinum layer on the surface of the PDMS template improves the contact angle and eases peeling off. The coated PDMS surface is successfully used as a template to achieve the replica with a uniform array via PDMS/PDMS replication process. Both the PDMS template and the replica are free of defects and also undistorted after demoulding with a highly ordered hexagonal arrangement. In addition, the geometry of the nanostructured PDMS can be controlled by changing the thickness of the deposited layer. The simplicity and the controllability of the process show great promise as a robust nanoreplication method for functional applications.     

Micellar structures of poly(styrene-b-4-vinylpyridine)s in THF/toluene mixtures and their functionalization with gold

The effects of the block copolymer composition and the solvent selectivity on the micellar morphologies of poly(styrene- b-4-vinylpyridine)s (PS- b-P4VPs) and their functionalizations with gold were studied in 10 mg/mL solutions using small-angle X-ray scattering and transmission electron microscopy (TEM). The solvent selectivity for the PS block was controlled by toluene/tetrahydrofuran (THF) mixtures in which toluene and THF are selective for PS and nonselective, respectively. The micellar structure was strongly dependent on phi (wt % toluene in toluene/THF mixture) and the composition of the block copolymers. PS(12K)- b-P4VP(11.8K) (symmetric) showed spherical micelles in the entire range of phi except phi = 0 (THF, nonselective solvent). PS(3.3K)- b-P4VP(18.7K) (asymmetric, longer P4VP) showed multiple morphologies with transitions from spheres to cylinders and finally to vesicles with an increase in phi. PS(19.6K)- b-P4VP(5.1K) (asymmetric, longer PS) showed spherical micelles only at the narrow ranges of 90 wt % 相似文献