Application of thin films of conjugated polymers in novel light-emitting devices and liquid crystal “light-valves”

Light-emitting electroluminescent diodes and electrochemically-driven electroluminescent devices involving conjugated polymers are described. The effect on the properties of polypyrrole films (deposited from aqueous polymerizing solutions of pyrrole) caused by the hydrophilicity/hydrophobicity of the substrate surface is utilized by a “microcontact printing” technique to form patterned liquid crystal display devices.     

Gradient and patterned polymer brushes by photoinitiated “grafting through” approach

More than 2 decades of active investigations in the field of polymer brushes have revealed continuous and growing interest in different aspects of synthesis, properties, and applications of tethered polymers. In this article, we report on our recent advances in brush synthesis. The method we explore is based on the combination of “grafting through” approach with the functional anchoring polymer layer technique. We introduce the photoinitiated “version” of synthesis of polyacrylamide brushes. Both homogeneous depositions and laterally resolved gradient and patterned samples have been prepared by this technique. The results for flat polymer brushes, that is, thickness, stability, and contact angles, are complimented by kinetic parameters as deducted from analysis of gradient samples obtained by the method of a sliding mask. A microscopic shadow mask is used to fabricate patterned brushes. The microscopically patterned brushes demonstrate high lateral resolution limited by optical phenomena. Finally, we have performed a viability assaying of neuronal cell on both flat and patterned brushes. Sufficient restraint of cell adhesion on polyacrylamide photobrushes and very low cytotoxicity of the brush components (polymer brush itself, anchoring layer) make photografting a promising platform to control cell deposition and surface localization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1616–1622, 2010     

Stability and disturbance of coating films

In the studies of two-roll metering and application systems, two types of disturbances were observed. These were termed “ring type” and “irregular” disturbances. This research established that the physical reason for the appearance of the ring type instability is the competition between surface tension and centrifugal forces at the liquid-air interface. The rings are generated at the surface of the dynamic liquid meniscus, in the gap between the rolls, because of the very large centrifugal forces there. Considering conditions of a constant interfacial pressure difference (pressure jump), one can reduce the problem to one with only one free parameter, viz., the radius of the meniscus, and calculate the wavelength of the disturbances. There is no single formula which will adequately describe the dynamic meniscus. Its curvature depends on the rheological properties of the fluid and on the kinematic conditions in the process. Dimensional analysis is combined with experimental findings to yield a formula for the radius of the meniscus for fluids having a high yield stress for the case of two counter-rotating rolls.The rheological behavior of a flowing starch adhesive in the dynamical meniscus is analyzed. The theoretical and experimental studies show that systems using two counter-rotating rolls practically always produced ring-type instabilities with all types of fluids.The picture is more complex for co-rotating roll systems. When non-Newtonian adhesives are used, ring type disturbances are observed in one zone of roll speed ratios, and irregular disturbances are observed in another zone. The two zones are separated by a speed ratio zone (a “speed window”) where a more or less perfectly stable fluid layer is observed. When Newtonian oils are used, there are two such speed windows. The first one corresponds to very low metering roll speeds and a minimum of liquid transfer to the applicator roll. The second stable zone occurs at high metering roll speeds and yields a maximum of liquid transfer. The physical reason for the high transfer rate in the high speed “window” is considered and shown to be the thin air layer following the surface of the metering roll. The air pumped into the metering gap returns along the applicator roll and accelerates the film on the applicator roll in the process. Under these conditions the fluid-air interface may become unstable, leading to the “irregular” type of disturbance.     

Evaporation‐Directed Crack‐Patterning of Metal–Organic Framework Colloidal Films and Their Application as Photonic Sensors

A straightforward crack‐patterning method is reported allowing the direct formation of periodic cracks in metal–organic framework (MOF) nanoparticle films during dip‐coating deposition. The crack propagation and periodicity can be easily tailored by controlling the evaporation front and the withdrawal speed. Several MOF‐patterned films can be fabricated on large surfaces and on several substrates (flat, curved or flexible) including the inner surface of a tube, not achievable by other lithographic techniques. We demonstrate that the periodic cracked arrays diffract light and, due to the MOF sorption properties, photonic vapor sensors are fabricated. A new concept of “in‐tube”, MOF‐based diffraction grating sensors is proposed with outstanding sensitivity that can be easily tuned “on‐demand” as function of the desired detection range.     

Synthesis of stable “gold nanoparticle–polymeric micelle” conjugates: A new class of star “molecular chimera” that self‐assemble into linear arrays of spherical micelles

Stable and aggregation‐free “gold nanoparticle–polymeric micelle” conjugates were prepared using a new and simple protocol enabled by the hydrogen bonding between surface‐capping ligands and polymeric micelles. Individual gold nanoparticles were initially capped using a phosphatidylthio–ethanol lipid and further conjugated with a star poly(styrene‐block‐glutamic acid) copolymer micelle using a one‐pot preparation method. The morphology and stability of these gold–polymer conjugates were characterized using transmission electron microscopy (TEM) and UV–vis spectroscopy. The self‐assembly of this class of polymer‐b‐polypeptide in aqueous an medium to form spherical micelles and further their intermicelle reorganization to form necklace‐like chains was also investigated. TEM and laser light scattering techniques were employed to study the morphology and size of these micelles. Polymeric micelles were formed with diameters in the range of 65–75 nm, and supermicellular patterns were observed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3570–3579, 2007     

Fabrication of spatially periodic double roughness structures by directional viscous fingering and spinodal dewetting for water-repellent surfaces

Water-repellent and self-cleaning properties of lotus leaves are considered to be due to its double roughness structure, protrusion structure (approximately 20 microm) and hairy structure (0.2-1.0 microm). In this study, attempts to fabricate a spatially periodic double roughness structure by two far-from-equilibrium self-organization phenomena, a directional viscous fingering and a spinodal dewetting, were made. A mixture of an octylsilyl titanium dioxide particle having an average diameter of 35 nm suspended in volatile silicone, decamethyl cyclopentasiloxane, and octyl p-methoxycinnamate was spread on a glass plate by dragging an applicator across the top. Formation of a stripe pattern parallel to the direction of dragging, called directional viscous fingering, was sometimes observed. Influences of spreading conditions on the pattern formation were analyzed. In addition, attempts were made to apply the stripe pattern formation to the preparation of a water repellent surface. We have succeeded in preparing a highly water-repellent surface by immersing a glass plate, on which a spatially periodic stripe pattern having a characteristic wavelength of 200-700 microm was formed, in water, after the completion of evaporation of decamethyl cyclopentasiloxane. In this case, dewetting patterns having a characteristic wavelength at around 5 microm were formed at the bottom part of the stripe patterns. Neither the surface on which only the mesoscopic spatially periodic stripe pattern was formed nor the one on which only the microscopic dewetting pattern was formed showed high water-repellent properties, indicating that the coexistence of the two different scales of patterns increased the water-repellent properties of the hydrophobic surface.     

Developing A “Polysulfide‐Phobic” Strategy to Restrain Shuttle Effect in Lithium–Sulfur Batteries

Inspired by hydrophobic interface, a novel design of “polysulfide‐phobic” interface was proposed and developed to restrain shuttle effect in lithium–sulfur batteries. Two‐dimensional VOPO₄ sheets with adequate active sites were employed to immobilize the polysulfides through the formation of a V?S bond. Moreover, owing to the intrinsic Coulomb repulsion between polysulfide anions, the surface anchored with polysulfides can be further evolved into a “polysulfide‐phobic” interface, which was demonstrated by the advanced time/space‐resolved operando Raman evidences. In particular, by introducing the “polysulfide‐phobic” surface design into separator fabrication, the lithium–sulfur battery performed a superior long‐term cycling stability. This work expands a novel strategy to build a “polysulfide‐phobic” surface by “self‐defense” mechanism for suppressing polysulfides shuttle, which provides new insights and opportunities to develop advanced lithium–sulfur batteries.     

Surface Molding of Microscale Hydrogels with Microactuation Functionality

This work describes the fabrication of numerous hydrogel microstructures (μ‐gels) via a process called “surface molding.” Chemically patterned elastomeric‐assembly substrates were used to organize and manipulate the geometry of liquid prepolymer microdroplets, which, following photo‐initiated crosslinking, maintained the desired morphology. By adjusting the state of strain during the crosslinking process, a continua of structures could be created using one pattern. These arrays of μ‐gels have stimuli‐responsive properties that are directly applicable to actuation where the basis shape and array geometry of the μ‐gels can be used to rationally generate microactuators with programmed motions. As a method, “surface molding,” represents a powerful addition to the soft‐lithographic toolset that can be readily applied to the simultaneous synthesis of large numbers of geometrically and functionally distinct polymeric microstructures.     

“Inverted” Deep Eutectic Solvents Based on Host‐Guest Interactions

Herein, the concept of “inverted” (the mode “molecules mainly interact with cations”) deep eutectic solvents (DESs) is proposed. A strategy to form inverted DESs by host‐guest interactions was developed, and thus numerous DESs could be designed and formed by a combination of host and guest molecules. These liquids are expected to be used as nonaqueous electrolytes in potassium‐ion batteries or other fields for further exploration.     

Solid water at room temperature?

Previously, we have shown that water adjacent to many hydrophilic substances excludes colloidal and molecular solutes. It was labelled “exclusion zone” (EZ) or “fourth phase” water. A salient feature is its characteristic light absorbance at or near 270 nm. In this study, EZ water formed against three chemically distinct surfaces, Nafion, ghee, and Whatman-5 filter paper was extracted, characterized by UV–Visible absorbance spectroscopy, and solidified either by lyophilizing or evaporation in an oven. The resulting highly stable solid was dissolved in water and confirmed as EZ water by its characteristic absorbance at 270–280 nm. We used mass spectroscopy to verify the absence of ionizable contaminants that could reproduce the characteristic “signature EZ” spectra in the three liquid preparations, or in the solids formed from desiccated EZ water that had been reconstituted in deionized water. Hence, a solid form of EZ water may, indeed, exist at room temperature.     

Facile synthesis and responsive behavior of PDMS‐b‐PEG diblock copolymer brushes via photoinitiated “thiol‐ene” click reaction

We present herein a mild and rapid method to create diblock copolymer brushes on a silicon surface via photoinitiated “thiol‐ene” click reaction. The silicon surface was modified with 3‐mercaptopropyltrimethoxysilane (MPTMS) self‐assembled monolayer. Then, a mixture of divinyl‐terminated polydimethylsiloxane (PDMS) and photoinitiator was spin‐coated on the MPTMS surface and exposed to UV‐light. Thereafter, a mixture of thiol‐terminated polyethylene glycol (PEG) and photoinitiator were spin‐coated on the vinyl‐terminated PDMS‐treated surface, and the sequent photopolymerization was carried out under UV‐irradiation. The MPTMS, PDMS, and PEG layers were carefully identified by X‐ray photoelectron spectroscopy, atomic force microscopy, ellipsometry, and water contact angle measurements. The thickness of the polydimethylsiloxane‐block‐poly(ethylene glycol) (PDMS‐b‐PEG) diblock copolymer brush could be controlled by the irradiation time. The responsive behavior of diblock copolymer brushes treated in different solvents was also discussed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Quality evaluation of Eucommiae Cortex processed by different methods and “sweating” conditions based on simultaneous determination of multiple bioactive constituents combined with gray relational analysis

Eucommiae Cortex is a classical traditional Chinese medicine, which needs to be processed by “sweating” methods. To select the suitable processing method and “sweating” processing condition for Eucommiae Cortex, in this study, the quality of Eucommiae Cortex was evaluated based on simultaneous determination of multiple bioactive constituents combined with gray relational analysis. The contents of lignans, iridoids, penylpropanoids, flavonoids, and phenols in samples were simultaneously determined using ultra‐fast performance liquid chromatography coupled with triple quadrupole‐linear ion trap tandem mass spectrometry. The chromatographic separation was performed on a Synergiۛ Hydro‐RP 100 Å column (100 mm × 2.0 mm, 2.5 μm) at 30°C with a gradient elution of acetonitrile with 0.1% formic acid/0.1% aqueous formic acid as the mobile phase. Furthermore, gray relational analysis was performed to evaluate and sort the samples according to the contents of 14 constituents by calculating the relative correlation degree of each sample. The results demonstrated that the quality of Eucommiae Cortex “sweating” at source area was better and the better “sweating” condition was to scrape off the cork layer before “sweating” with straw covering and sun drying. The developed method could provide the foundation and support for “sweating” processing method of Eucommiae Cortex in normalization and standardization.     

Smart Microdevices Laying “Breadcrumbs” to Find the Way Home: Chemotactic Homing TiO2/Pt Janus Microrobots

Synthetic microrobots or micromotors are known to show “intelligent” behavior such as magnetotaxis, phototaxis, chemotaxis, active detection, and chemical communication. Herein, we present the concept of micromotors laying “breadcrumbs”; that is, these micromachines can move/return to a home position without external guidance after their external energy input is stopped. As a demonstration, TiO₂/Pt Janus micromotors that move forward with UV light can return back following the previous path when the UV light is turned off. Such autonomy of motion opens the door for truly independent applications of micromotors in the “deliver‐and‐return” fashion.     

The influence of electrostatic forces on protein adsorption

In this paper we investigate the importance of electrostatic double layer forces on the adsorption of human serum albumin by UV-ozone modified polystyrene. Electrostatic forces were measured between oxidized polystyrene surfaces and gold-coated atomic force microscope (AFM) probes in phosphate buffered saline (PBS) solutions. The variation in surface potential with surface oxygen concentration was measured. The observed force characteristics were found to agree with the theory of electrical double layer interaction under the assumption of constant potential. Chemically patterned polystyrene surfaces with adjacent 5 microm x 5 microm polar and non-polar domains have been studied by AFM before and after human serum albumin adsorption. A topographically flat surface is observed before protein adsorption indicating that the patterning process does not physically modify the surface. Friction force imaging clearly reveals the oxidation pattern with the polar domains being characterised by a higher relative friction compared to the non-polar, untreated domains. Far-field force imaging was performed on the patterned surface using the interleave AFM mode to produce two-dimensional plots of the distribution of electrostatic double-layer forces formed when the patterned polystyrene surfaces is immersed in PBS. Imaging of protein layers adsorbed onto the chemically patterned surfaces indicates that the electrostatic double-layer force was a significant driving force in the interaction of protein with the surface.     

“Push‐pull” supramolecular chromophores supported on cyclopolymers

Well‐defined macromolecules have been obtained through free‐radical cyclopolymerization and cyclocopolymerization of difunctional and acrylic‐like monomers, which contained “push‐pull” supramolecular chromophores, able to form 1:1 complexes with Eu³⁺ ions in solution. The monomeric molecular modules are built around bismalonate crown ethers in a convergent fashion, in which one of the malonate moiety is derivatized as the ylidene malonate push‐pull fragment, and the other malonate moiety is elaborated to introduce two polymerizable and acrylic‐like substituents. The free‐radical induced cyclopolymerization of these monomers, or their cyclocopolymerization with UV/Vis “silent” but structurally related monomers, afforded macromolecular architectures characterized by GPC, NMR and DSC techniques. UV/Vis titration studies, performed with Eu(OTf)₃ as the supramolecular probe, revealed how adjacent chromophores within the polymeric backbone are virtually independent from each other, and how the binding ability towards the probe of these multivalent, highly packed cyclopolymeric architectures, although reduced, is still clearly detectable. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5202–5213, 2008     

Synthesis of a Novel Oligoaniline: “Dumbbell‐Shaped” Oligoaniline

Summary: A new kind of aniline oligomer with a “dumbbell” shape was synthesized through a simple oxidative coupling reaction with a new rigid aromatic amine as starting material. The oligomer was characterized with mass spectrometry, IR and NMR spectroscopies. Its redox property was checked by cyclic voltammetry and chemical oxidation/reduction process was monitored by UV spectroscopy. We found it has a reversible electrochemical property like common oligoanilines. Combined with its well‐defined structure, it is expected to act as a model compound for a molecular electronic switch.

The “dumbbell‐shaped” oligoaniline compound synthesized here.     

Synthesis of Novel Core Cross‐Linked Star‐Based Polyrotaxane End‐Capped via “CuAAC” Click Chemistry

The first example of core cross‐linked star (CCS) polyrotaxane was prepared using the poly(ϵ‐caprolactone) (PCL) CCS three‐dimensional (3D) scaffold. The 3D CCS polymer was firstly prepared through the “arm‐first” approach. Then, the “arms” of the resultant PCL CCS polymer were threaded with α‐cyclodextrins (α‐CDs). The threaded α‐CDs were permanently locked by the “click” reaction of terminal alkyne functionalities of the star polymers with the azide‐functionalized end caps to afford the CCS polyrotaxanes. All analytical results confirm the formation of the CCS polyrotaxanes and reveal their characteristics, including fluorescence under UV, a channel‐type crystalline structure, a two‐step thermal decomposition, and a unique core‐shell structure in great contrast to the polymer precursors.     

Investigation of the tensile properties of “epoxy resin‐monomer” systems using cationic UV‐crosslinkable blends

The compatibility of cycloaliphatic and aromatic multifunctional epoxides with several epoxide resins allows the development of a wide range of cationic radiation‐curable formulations. The influence of different “epoxide resin‐monomer” systems UV‐cured in the presence of suitable cationic photoinitiators on the resulting physicochemical film properties was studied, and the results are stated. Copyright © 2004 John Wiley & Sons, Ltd.     

On the “Wolfsberg–Helmholz Conjecture” of “Extended‐Hückel Theory”

After having reviewed some pioneer integral approximations closely related to Rüdenberg's expansions of one‐ and two‐electron orbital products, we apply the previously described “Implicit Multi‐Center Integration” techniques on Roothaan's “restricted” Fock‐matrix components over standard atomic orbital bases. The resulting compact forms are very similar to the well‐known “Wolfsberg–Helmholz Conjecture” of “Extended‐Hückel Theory,” which relates the various off‐diagonal matrix elements of “restricted” Fock‐type to their corresponding diagonal counterparts. In this way, a “nonempirical Extended‐Hückel Theory” can be created. © 2012 Wiley Periodicals, Inc.     

Encapsulation of Bovine Serum Albumin in Temperature‐Programmed “Shell‐in‐Shell” Structures

A novel approach to load a hydrophilic bovine serum albumin into drug carriers was proposed in terms of temperature‐programmed “shell‐in‐shell” structures, which were fabricated with poly(N‐isopropylacrylamide), poly(lactide), poly(ethylene glycol), and Au nanoparticles. Spherically well‐defined “shell‐in‐shell” structures were constructed by a modified‐double‐emulsion method (MDEM). The lower critical solubility temperature of the structures was manipulated to 36.4 °C which was confirmed by UV/Vis spectroscopy and DSC (Differential Scanning Calorimetry).

TEM image of the Au@PLLA‐PEG@PNIPAAm‐PDLA structure.