Maro Publications

Hot Topics

12/7/2011

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Interfacial Basicity-Guided Formation of Polydopamine Hollow Capsules in Pristine O/W Emulsions – Toward Understanding of Emulsion Template Roles
(5105–5110) Chemistry of  Materials 23 #23 (2011)

Xu, Liu and Wang University of South Australia, Australia, and the Max Planck Institute of Colloids and Interface, Germany, used alkane-in-water emulsions as templates for polymerization of 3,4-dihydroxyphenylethylamine (dopamine) and l-3,4-dihydroxyphenylalanine (l-dopa).  The resulting polymer structures are clearly dependent on the concentration of OH ions, i.e., pH, on the surfaces of the oil droplets, while show little dependence on the electrostatic or hydrophobic interactions between the resulting polymers and the surfaces of the oil droplets.  Pristine alkane droplets, stabilized solely by OH ions, have templated formation of hollow capsules due to selective oxidation and self-polymerization of the monomers on the OH ion-rich surfaces of the pristine oil droplets.  In contrast, macroporous structures have been obtained when either cationic or anionic surfactants were used to stabilize alkane droplets to lower the concentration of OH ions on the droplet surfaces.  (RDC 12/6/2011)

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Polyoctahedral Silsesquioxane-Nanoparticle Electrolytes for Lithium Batteries: POSS-Lithium Salts and POSS-PEGs
(5111–5121) Chemistry of  Materials 23 #23 (2011)

Chinnam and Wunder of Temple University, Pennsylvania, prepared nanocomposite electrolytes from mixtures of two polyoctahedral silsesquioxanes (POSS) nanomaterials, each with a SiO_1.5 core and eight side groups.  POSS-PEG₈ has eight polyethylene glycol side chains that have low glass transition (T_g) and melt (T_m) temperatures and POSS-benzyl₇(BF₃Li)₃ is a Janus-like POSS with hydrophobic phenyl groups and −Si–O–BF₃Li ionic groups clustered on one side of the SiO_1.5 cube.  The electron-withdrawing POSS cage and BF₃ groups enable easy dissociation of the Li⁺. In the presence of polar POSS-PEG₈, the hydrophobic phenyl rings of POSS-benzyl₇(BF₃Li)₃ aggregate and crystallize, forming a biphasic morphology, in which the phenyl rings form the structural phase and the POSS-PEG₈ forms the conductive phase.  The −Si–O–BF₃– Li⁺ groups of POSS-benzyl₇(BF₃Li)₃ are oriented toward the polar POSS-PEG₈ phase and dissociate so that the Li⁺ cations are solvated by the POSS-PEG₈.  (RDC 12/6/2011)

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Rapid and Reversible Tuning of Structural Color of a Hydrogel over the Entire Visible Spectrum by Mechanical Stimulation
(5200–5207) Chemistry of  Materials 23 #23 (2011)

Haque et al of Hokkaido University, Japan, formed a rubberlike elastic hydrogel containing microdomains of bilayers periodically stacked into the polymer network that satisfy the Bragg’s law of diffraction.  The rubberlike elastic hydrogel has been synthesized by applying double network principle into a viscoelastic hydrogel containing single-domain macroscopic lamellar bilayer.  The hydrogel is able to tune the magnificent structural color reversibly over the entire wavelength range of visible spectrum as fast as the uniaxial tensile stretching and compressive deformation are applied and released. Owing to the strength, softness, and rubberlike elastic deformability, the tunable hydrogel can be used extensively to design a new class of soft tactile sensor as an advanced stress sensor that is able to detect a local deformation of a complicated force field.  (RDC 12/6/2011)

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Process intensification of encapsulation of functionalized CaCO₃ nanoparticles using ultrasound assisted emulsion polymerization
(1160-1168) Chemical Engineering and Processing 50, #11-12 (2011)

Bhanvase et al, India, showed the cavitational effects produced due to the use of ultrasonic irradiations enhanced the dispersion of functional nano-inorganic particles into the monomer during polymerization process.  The model system is based on the nanocomposite of poly(methyl methacrylate)/calcium carbonate (PMMA/CaCO₃) which has been synthesized by ultrasound assisted semibatch emulsion polymerization. CaCO₃ nanoparticles were pretreated with myristic acid in order to improve the compatibility of the monomer with the inorganic particles. TEM image of PMMA/CaCO₃ composite particles with well-defined core–shell structure give direct evidence of encapsulation. Effect of encapsulation of CaCO₃ particles on thermal properties has been evaluated using thermo-gravimetric methods and it has been observed that the nanocomposites have better thermal stability as compared to the PMMA.  (RDC 12/6/2011)

“Micro-encapsulation is a process in which tiny particles or droplets are surrounded by a coating to give small capsules many useful properties. In a relatively simplistic form, a microcapsule is a small sphere with a uniform wall around it. The material inside the microcapsule is referred to as the core, internal phase, or fill, whereas the wall is sometimes called a shell, coating, or membrane. Most microcapsules have diameters between a few micrometers and a few millimeters.”

“The definition has been expanded, and includes most foods. Every class of food ingredient has been encapsulated; flavors are the most common. The technique of microencapsulation depends on the physical and chemical properties of the material to be encapsulated.”

“Many microcapsules however bear little resemblance to these simple spheres. The core may be a crystal, a jagged adsorbent particle, an emulsion, a suspension of solids, or a suspension of smaller microcapsules. The microcapsule even may have multiple walls.”

(Wikipedia, Microencapsulation, 12/7/2011)

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Villermaux–Dushman protocol for experimental characterization of micromixers
( 979-990) Chemical Engineering and Processing 50, #10 (2011)

Commenge and Falk, of Nancy University, France, presents the detailed protocol of the iodide/iodate test method, with different concentration sets and a general protocol to determine mixing times in micromixers.  (RDC 12/6/2011)

“The ability to mix liquids in microchannel networks is fundamentally important in the design of nearly every miniaturized chemical and biochemical analysis system. Here, we show that enhanced micromixing can be achieved in topologically simple and easily fabricated planar 2D microchannels by simply introducing curvature and changes in width in a prescribed manner. This goal is accomplished by harnessing a synergistic combination of (i) Dean vortices that arise in the vertical plane of curved channels as a consequence of an interplay between inertial, centrifugal, and viscous effects, and (ii) expansion vortices that arise in the horizontal plane due to an abrupt increase in a conduit's cross-sectional area. We characterize these effects by using confocal microscopy of aqueous fluorescent dye streams and by observing binding interactions between an intercalating dye and double-stranded DNA. These mixing approaches are versatile and scalable and can be straightforwardly integrated as generic components in a variety of lab-on-a-chip systems.” [Sudarsan and Ugaz. Proc Natl Acad Sci 103 #19: 7228–7233.(2006)]

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A Dynamic Transient Model to Simulate the Time Dependent Pultrusion Process of Glass/Polyester Composites
(585-601) Applied Composite Materials 18 #6 (2011)

Shokrieh and Aghdami of the Iran University of Science and Technology, Iran, developed a novel dynamic transient model to simulate the time dependent pultrusion process of glass/polyester composites.  It is shown that in liquid and gel-solid phases, some of the resin physical properties have significant role in heat transfer phenomenon and affect simulation results.  The components of the model are integrated in a finite element method. As case studies, the process of pultrusion of circular, rectangular and I cross-sections are simulated by the model. The results show that the model is able to simulate the pultrusion process very well.  (RDC 12.6.2911)

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Monolithic, Hierarchical Surface Reliefs by Holographic Photofluidization of Azopolymer Arrays: Direct Visualization of Polymeric Flows
( 4412–4422) Advanced Functional Materials 21  #23 (2011)

Kang, Lee and Park of the Korea Advanced Institute of Science and Technology, South Korea, demonstrated a deterministic and scalable fabrication of hierarchically ordered, monolithic surface reliefs by holographic photofluidization of azopolymer line arrays.  In particular, it is shown that the structural features of monolithic surface reliefs including shapes and modulation heights can be deterministically tunable by adjusting the polarization and irradiation time of the holographic interference pattern.  Moreover, by a direct visualization of azopolymeric flow according to the light polarization, a long-standing question about the origin of surface-relief-grating formation on azopolymer film is addressed in terms of polymeric flows.  (RDC 12/6/2011)

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“Cancer /kænsər/ known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the body through the lymphatic system or bloodstream.  Not all tumors are cancerous.  Benign tumors do not grow uncontrollably, do not invade neighbouring tissues, and do not spread throughout the body.”

“Healthy cells control their own growth and will destroy themselves if they become unhealthy.  Cell division is a complex process that is normally tightly regulated. Cancer occurs when problems in the genes of a cell prevent these controls from functioning properly. These problems may come from damage to the gene or may be inherited, and can be caused by various sources inside or outside of the cell. Faults in two types of genes are especially important: oncogenes, which drive the growth of cancer cells, and tumor suppressor genes, which prevent cancer from developing.”

(Wikipedia, Cancer, 12/7/2011)

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Molecular Weight-Induced Structural Transition of Liquid-Crystalline Polymer Semiconductor for High-Stability Organic Transistor
( 4442–4447) Advanced Functional Materials 21  #23 (2011)

Kim et al, South Korea and California, fabricated polymer field-effect transistors (PFETs) with high electrical stability under bias-stress, by minimizing the density of charge trapping sites caused by the disordered regions.  Here we report PFETs with excellent electrical stability comparable to that of single-crystalline organic semiconductors by specifically controlling the molecular weight (MW) of the donor-acceptor type copolymer semiconductors, poly (didodecylquaterthiophene-alt-didodecylbithiazole).  We found that MW-induced thermally structural transition from liquid-crystalline to semi-crystalline phases strongly affects the device performance (charge-carrier mobility and electrical bias-stability) as well as the nanostructures such as the molecular ordering and the morphological feature. This enhancement of the electrical bias-stability can be attributed to highly ordered liquid-crystalline nanostructure of copolymer semiconductors on dielectric surface via the optimization of molecular weights. (RDC 12/6/2011)

“A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit.  A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be much more than the controlling (input) power, a transistor can amplify a signal.  Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.”

“The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. Following its release in the early 1950s the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios calculators, and computers, among other things.”

“The essential usefulness of a transistor comes from its ability to use a small signal applied between one pair of its terminals to control a much larger signal at another pair of terminals. This property is called gain. A transistor can control its output in proportion to the input signal; that is, it can act as an amplifier. Alternatively, the transistor can be used to turn current on or off in a circuit as an electrically controlled switch, where the amount of current is determined by other circuit elements.”

“There are two types of transistors, which have slight differences in how they are used in a circuit. A bipolar transistor has terminals labeled base, collector, and emitter. A small current at the base terminal (that is, flowing from the base to the emitter) can control or switch a much larger current between the collector and emitter terminals.  For a field-effect transistor, the terminals are labeled gate, source, and drain, and a voltage at the gate can control a current between source and drain.

 (Wikipedia, Transistors, 12/6/2011)

The field-effect transistor (FET) is a transistor that relies on an electric field to control the shape and hence the conductivity of a channel of one type of charge carrier in a semiconductor material. FETs are sometimes called unipolar transistors to contrast their single-carrier-type operation with the dual-carrier-type operation of bipolar (junction) transistors (BJT). The concept of the FET predates the BJT, though it was not physically implemented until after BJTs due to the limitations of semiconductor materials and the relative ease of manufacturing BJTs compared to FETs at the time.  (Wikipedia, Field Effect Transistors, 12/7/2011)

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Improved Performance of Polymer:Polymer Solar Cells by Doping Electron-Accepting Polymers with an Organosulfonic Acid
(4527–4534) Advanced Functional Materials 21  #23 (2011)

Nam et al, South Korea, improved the performance of polymer:polymer solar cells that are made using blend films of poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene-co- benzothiadiazole (F8BT) by doping the F8BT polymer with an organosulfonic acid [4-ethylbezenesulfonic acid (EBSA)].  The F8BT-EBSA films exhibit huge photoluminescence quenching, ionization potential shift toward lower energy, and greatly enhanced electron mobility. The short-circuit current density of solar cells is improved by ca. twofold (10 wt.% EBSA doping), while the open-circuit voltage increases by ca. 0.4 V. Consequently, the power conversion efficiency was improved by ca. threefold, even though the optical density of the P3HT:F8BT-EBSA blend film is reduced by 10 wt.% EBSA doping due to the nanostructure and surface morphology change.  (RDC 12/6/2011)

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Exploiting Microphase-Separated Morphologies of Side-Chain Liquid Crystalline Polymer Networks for Triple Shape Memory Properties
( 4543–4549) Advanced Functional Materials 21  #23 (2011)

Ahn and Kasi of the University of Connecticut, Connecticut, used side-chain liquid crystalline (SCLC) type random terpolymer networks (XL- TP-n), where n is the length of flexible methylene spacer (n = 5, 10, and 15) to link backbone and mesogen for a triple-shape memory material.  A lower glass transition temperature (T_g = T_low) and a higher liquid crystalline clearing temperature (T_cl = T_high) of XL-TP-n serve as molecular switches to trigger a shape memory effect (SME).  Two different triple shape creation procedures (TSCPs), thermomechanical treatments to obtain temporary shapes prior to the proceeding recovery step, are used to investigate the triple shape memory behavior of XL-TP-n.  The discrete T_g and T_cl as well as unique microphase-separated morphologies (backbone-rich and mesogen-rich domains) within smectic layers of XL-TP-n enables triple shape memory properties.  Motional decoupling between backbone-rich and mesogen-rich domains is also critical to determine the resulting macroscopic shape memory properties.  (RDC 12/6/2011)

“Liquid crystals (LCs) are a state of matter that have properties between those of a conventional liquid and those of a solid crystal.  For instance, an LC may flow like a liquid, but its molecules may be oriented in a crystal-like way.  There are many different types of LC phases, which can be distinguished by their different optical properties (such as birefringence). When viewed under a microscope using a polarized light source, different liquid crystal phases will appear to have distinct textures.  The contrasting areas in the textures correspond to domains where the LC molecules are oriented in different directions. Within a domain, however, the molecules are well ordered. LC materials may not always be in an LC phase (just as water may turn into ice or steam).”

“Liquid crystals can be divided into thermotropic, lyotropic and metallotropic phases. Thermotropic and lyotropic LCs consist of organic molecules. Thermotropic LCs exhibit a phase transition into the LC phase as temperature is changed. Lyotropic LCs exhibit phase transitions as a function of both temperature and concentration of the LC molecules in a solvent (typically water). Metallotropic LCs are composed of both organic and inorganic molecules; their LC transition depends not only on temperature and concentration, but also on the inorganic-organic composition ratio.”

“Examples of liquid crystals can be found both in the natural world and in technological applications. Most modern electronic displays are liquid crystal based. Lyotropic liquid-crystalline phases are abundant in living systems. For example, many proteins and cell membranes are LCs. Other well-known LC examples are solutions of soap and various related detergents, as well as the tobacco mosaic virus.”

(Wikipedia, Liquid Crystal Materials, 12/6/2011)

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Roger D. Corneliussen
Editor
www.maropolymeronline.com

Maro Polymer Links
Tel: 610 363 9920
Fax: 610 363 9921
E-Mail: cornelrd@bee.net   

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Copyright 2011 by Roger D. Corneliussen.
No part of this transmission is to be duplicated in any manner or forwarded by electronic mail without the express written permission of Roger D. Corneliussen
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** Date of latest addition; date of first entry is 10/19/2010.