The equilibrium contact angles and line tensions of macroscopic droplets, composed of star-shaped polystyrene (PS) macromolecules, on silicon oxide substrates, are shown to be smaller than their linear analogs, by up ...
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The equilibrium contact angles and line tensions of macroscopic droplets, composed of star-shaped polystyrene (PS) macromolecules, on silicon oxide substrates, are shown to be smaller than their linear analogs, by up to approximately 1 and 2 orders of magnitude, respectively, depending on the size and functionality of the star-shaped molecule. A precursor layer, of lateral dimensions and of thicknesses on the order of nanometers, surrounds each droplet of low molecular weight linear PS chains. Droplets composed of star-shaped molecules possessing a sufficient number of arms, reside on a layer adsorbed to the substrate.
作者：
Bolton, OnasLee, KangwonKim, Hyong-JunLin, Kevin Y.Kim, JinsangDepartment of Materials Science and Engineering
University of Michigan Ann Arbor Michigan 48109 USA
Onas Bolton Kangwon Lee Hyong-Jun Kim & Jinsang Kim
Department of Chemical Engineering University of Michigan Ann Arbor Michigan 48109 USA
Kevin Y. Lin & Jinsang Kim
Departments of Macromolecular Science and Engineering University of Michigan Ann Arbor Michigan 48109 USA
Jinsang Kim
Biomedical Engineering University of Michigan Ann Arbor Michigan 48109 USA
Jinsang Kim
Phosphorescence is among the many functional features that, in practice, divide pure organic compounds from organometallics and inorganics. Considered to be practically non-phosphorescent, purely organic compounds (me...
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Phosphorescence is among the many functional features that, in practice, divide pure organic compounds from organometallics and inorganics. Considered to be practically non-phosphorescent, purely organic compounds (metal-free) are very rarely explored as emitters in phosphor applications, despite the emerging demand in this field. To defy this paradigm, we describe novel design principles to create purely organic materials demonstrating phosphorescence that can be turned on by incorporating halogen bonding into their crystals. By designing chromophores to contain triplet-producing aromatic aldehydes and triplet-promoting bromine, crystal-state halogen bonding can be made to direct the heavy atom effect to produce surprisingly efficient solid-state phosphorescence. When this chromophore is diluted into the crystal of a bi-halogenated, non-carbonyl analogue, ambient phosphorescent quantum yields reach 55%. Here, using this design, a series of pure organic phosphors are colour-tuned to emit blue, green, yellow and orange. From this initial discovery, a directed heavy atom design principle is demonstrated that will allow for the development of bright and practical purely organic phosphors.
Based on our previous work using benzocyclobutene (BCB) moieties in extended-chain polymers [1], it was thought that the construction of unsymmetrical molecules around the BCB unit might result in thermally crosslinka...
Based on our previous work using benzocyclobutene (BCB) moieties in extended-chain polymers [1], it was thought that the construction of unsymmetrical molecules around the BCB unit might result in thermally crosslinkable NLO-active materials. The feasibility of incorporating such a functional system in donor-acceptor molecules without disrupting processability is discussed and demonstrated. The synthesis, processing, and characterization of these molecules was investigated by thermogravimetry, differential scanning calorimetry, and optical microscopy using a specially designed hot stage which makes it possible to apply an in-plane electric field at elevated temperatures. The ability to rapidly and irreversibly crosslink bulk films without the generation of volatile byproducts provides a novel method for sustaining poled optical properties by locking in the desired orientation. The anisotropy of the electrically poled melt and sustained birefringence after BCB crosslinking and cooling demonstrates the achievement of molecular alignment in these new materials.
Electrospinning of pure chitosan or chitosan/poly(vinyl alcohol) (PVA) (blend) was carried out with an optimization of the electrospinning conditions. The electrospinning of the pure chitosan was only possible at a re...
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Electrospinning of pure chitosan or chitosan/poly(vinyl alcohol) (PVA) (blend) was carried out with an optimization of the electrospinning conditions. The electrospinning of the pure chitosan was only possible at a relatively high electric field of 5 kV/cm into fibers with a diameter as thick as 30 ìm, and its reproducibility was very poor. Blending of PVA into chitosan significantly improved the spinnability and the chitosan/PVA blend fiber was electrospun for further characterization. Several target devices were designed and examined to collect aligned nanofibers of chitosan/PVA. The most efficient was a rotating collector having grounded short wire bars arranged on a drum. Over 90 % of electrospun fibers were collected in parallel to the take-up direction with this collector. The fiber alignment was further improved with increasing the collector rotation speed up to a maximum speed of 4.7 m/s. The aligned chitosan/PVA fibers were subjected to drawing to 1.5 times and the crystallization of chitosan fractions was induced without indicating the clear crystal orientation.
Three different kinds of siloxane-containing polybenzamide copolymers have been prepared: a series of siloxane-containing segmented copolymers; a siloxane-poly(benzamide) random copolymer; and a poly(benzamide) - poly...
Three different kinds of siloxane-containing polybenzamide copolymers have been prepared: a series of siloxane-containing segmented copolymers; a siloxane-poly(benzamide) random copolymer; and a poly(benzamide) - poly(dimethylsiloxane) block copolymer. The structures of these copolymers were confirmed using diffuse reflectance FTIR spectroscopy. Dilute solution viscometery showed them to be high polymers. The thermal stabilities of these copolymers were studied using thermal gravimetric analysis. Incorporation of siloxane units via a phenyl link was found to not affect the inherent thermal stability of the poly(benzamide) chain. The solution phase behavior of these copolymers in DMAC/LiCl was studied using an optical microscope fitted with cross-polars. The segmented copolymers and the block copolymer exhibited lyotropic behavior, which was influenced by the amount of siloxane and the overall molecular architecture. Solutions of the random copolymer were isotropic at all concentrations studied.
Novel polyurethane (PU) conducting films consisting of hydroxyl-terminated polybutadienes (HTPB) and carboxyl functionalized multi-walled carbon nanotubes (MWNTs-COOH) were developed by a simple coupling approach base...
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