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Polymer Shell (polymer + shell)

Distribution by Scientific Domains

Polymers and Materials Science	70%

Selected Abstracts

High Breakdown Field Dielectric Elastomer Actuators Using Encapsulated Polyaniline as High Dielectric Constant Filler

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2010
Martin Molberg
Abstract A novel method allowing rapid production of reliable composites with increased dielectric constant and high dielectric strength for dielectric elastomer actuators (DEA) is reported. The promising approach using composites of conductive particles and insulating polymers generally suffers from low breakdown fields when applied to DEA devices. The present publication shows how to overcome this deficiency by using conductive polyaniline (PANI) particles encapsulated into an insulating polymer shell prior to dispersion. PANI particles are encapsulated using miniemulsion polymerization (MP) of divinylbenzene (DVB). The encapsulation process is scaled up to approximately 20 g particles per batch. The resulting particles are used as high dielectric constant (,,) fillers. Composites in a polydimethylsiloxane (PDMS) matrix are prepared and the resulting films characterized by dielectric spectroscopy and tensile tests, and evaluated in electromechanical actuators. The composite films show a more than threefold increase in ,,, breakdown field strengths above 50 V ,m,1, and increased strain at break. These novel materials allow tuning the actuation strain or stress output and have potential as materials for energy harvesting. [source]

A Delivery System for Self-Healing Inorganic Films,

ADVANCED FUNCTIONAL MATERIALS, Issue 22 2008
Harvey A. Liu
Abstract Multilayer composites that utilize polymeric and brittle inorganic films are essential components for extending the lifetimes and exploiting the flexibility of many electronic devices. However, crack formation within the brittle inorganic layers that arise from defects as well as the flexing of these multilayer composite materials allows the influx of atmospheric water, a major source of device degradation. Thus, a composite material that can initiate self-healing upon the influx of environmental water through defects or stress-induced cracks would find potential applications in multilayer composite materials for permeation barriers. In the present study, the reactive metal oxide precursor TiCl4 is encapsulated within the pores of a degradable polymer, poly(lactic acid) (PLA). Electrospun PLA fibers are found to be reactive to atmospheric water leading to the hydrolysis of the degradable polymer shell and subsequent release of the reactive metal oxide precursor. Release of the reactive TiCl4 from the pores results in hydrolysis of the metal oxide precursor, forming solid titanium oxides at the surface of the fibers. The efficacy of this self-healing delivery system is also demonstrated by the integration of these reactive fibers in the polymer planarization layer, poly(methyl methacrylate), of a multilayer film, upon which an alumina barrier layer is deposited. The introduction of nanocracks in the alumina barrier layer lead to the release of the metal oxide precursor from the pores of the fibers and the formation of titanium dioxide nanoparticles within the crack and upon the thin film surface. In this study the first delivery system that may find utility for the self-healing of multilayer barrier films through the site-specific delivery of metal oxide nanoparticles through smart reactive composite fibers is established. [source]

Poly(,-caprolactone)-Functionalized Carbon Nanotubes and Their Biodegradation Properties,

ADVANCED FUNCTIONAL MATERIALS, Issue 6 2006
H.-L. Zeng
Abstract Biodegradable poly(,-caprolactone) (PCL) has been covalently grafted onto the surfaces of multiwalled carbon nanotubes (MWNTs) by the "grafting from" approach based on in-situ ring-opening polymerization of ,-caprolactone. The grafted PCL content can be controlled easily by adjusting the feed ratio of monomer to MWNT-supported macroinitiators (MWNT-OH). The resulting products have been characterized with Fourier-transform IR (FTIR), NMR, and Raman spectroscopies, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). After PCL was coated onto MWNT surfaces, core/shell structures with nanotubes as the "hard" core and the hairy polymer layer as the "soft" shell are formed, especially for MWNTs coated with a high density of polymer chains. Such a polymer shell promises good solubility/dispersibility of the MWNT,PCL nanohybrids in low-boiling-point organic solvents such as chloroform and tetrahydrofuran. Biodegradation experiments have shown that the PCL grafted onto MWNTs can be completely enzymatically degraded within 4,days in a phosphate buffer solution in the presence of pseudomonas (PS) lipase, and the carbon nanotubes retain their tubelike morphologies, as observed by SEM and TEM. The results present possible applications for these biocompatible PCL-functionalized CNTs in bionanomaterials, biomedicine, and artificial bones. [source]

Small-molecule release from poly(D,L -lactide)/poly(D,L -lactide-co-glycolide) composite microparticles

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2005
Emily J. Pollauf
Abstract Addition of biodegradable polymer shells surrounding polymeric, drug-loaded microparticles offers the opportunity to control drug release rates. A novel fabrication method was used to produce microparticles with precise control of particle diameter and the thickness of the polymer shell. The effect of shell thickness on release of a model drug, piroxicam, has been clearly shown for 2- to 15-µm thick shells of poly(D,L -lactide) (PDLL) surrounding a poly(D,L -lactide-co-glycolide) (PLG) core and compared to pure PLG microspheres loaded with piroxicam. Furthermore, the core-shell microparticles are compared to microspheres containing blended polymers in the same mass ratios to demonstrate the importance of the core-shell morphology. Combining PDLL(PLG) microcapsules of different shell thicknesses allows nearly constant release rates to be attained for a period of 6 weeks. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2013,2022, 2005 [source]

Synthesis and characterization of core,shell-type polymeric micelles from diblock copolymers via reversible addition,fragmentation chain transfer

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2006
Ping Zhang
Abstract A method was developed to enable the formation of nanoparticles by reversible addition,fragmentation chain transfer polymerization. The thermoresponsive behavior of polymeric micelles was modified by means of micellar inner cores and an outer shell. Polymeric micelles comprising AB block copolymers of poly(N -isopropylacrylamide) (PIPAAm) and poly(2-hydroxyethylacrylate) (PHEA) or polystyrene (PSt) were prepared. PIPAAm- b -PHEA and PIPAAm- b -PSt block copolymers formed a core,shell micellar structure after the dialysis of the block copolymer solutions in organic solvents against water at 20 °C. Upon heating above the lower critical solution temperature (LCST), PIPAAm- b -PHEA micelles exhibited an abrupt increase in polarity and an abrupt decrease in rigidity sensed by pyrene. In contrast, PIPAAm- b -PSt micelles maintained constant values with lower polarity and higher rigidity than those of PIPAAm- b -PHEA micelles over the temperature range of 20,40 °C. Structural deformations produced by the change in the outer polymer shell with temperature cycles through the LCST were proposed for the PHEA core, which possessed a lower glass-transition temperature (ca. 20 °C) than the LCST of the PIPAAm outer shell (ca. 32.5 °C), whereas the PSt core with a much higher glass-transition temperature (ca. 100 °C) retained its structure. The nature of the hydrophobic segments composing the micelle inner core offered an important control point for thermoresponsive drug release and the drug activity of the thermoresponsive polymeric micelles. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3312,3320, 2006 [source]

Surface-initiated nitroxide-mediated polymerization: a tool for hybrid inorganic/organic nanocomposites ,in situ' synthesis

POLYMER INTERNATIONAL, Issue 10 2006
Leïla Ghannam
Abstract Hybrid silica particles comprised of an inorganic core and an organic polymer shell can be synthesized by surface-initiated nitroxide-mediated polymerization (SINMP) in the presence of a grafted alkoxyamine as initiator. The layer of initiator molecules attached or adsorbed to the particles surface is based on a nitroxide group. The synthesis and characterization of these alkoxyamine structures are briefly described. The grafted initiator particles are studied in order to determine the nature of the anchorage sites and the grafting density. With a stable radical or nitroxide as chain-growth moderator tethered to the inorganic core, it was demonstrated that the grafting from or to SINMP exhibits a control character with a very low polydispersity and good agreement between theoretical/experimental molecular weights. A comparative review of different alkoxyamines with a bimolecular system based on a grafted azoic initiator in the presence of an acyclic ,-phosphonylated nitroxide called SG1 is also described. Moreover, original methods for the synthesis of alkoxyamine grafted surface by in situ trapping of carbon radicals and some new developments for colored pigments will be reported. These topics could be one of the directions of the field in the next years. Copyright © 2006 Society of Chemical Industry [source]

Polymersomes as viral capsid mimics

DRUG DEVELOPMENT RESEARCH, Issue 1 2006
Fariyal Ahmed
Abstract Polymersomes are self-assembled polymer shells composed of block copolymer amphiphiles. These synthetic amphiphiles have a similar amphiphilicity to lipids, but they have much larger molecular weights and so for this reason, plus many others reviewed here, comparisons of polymersomes to viral capsids composed of large polypeptide chains seem increasingly more appropriate. The wide range of polymers being used to make polymersomes is summarized together with descriptions of physical properties such as stability and permeability. Emerging studies of in vivo stealthiness and programmed disassembly for controlled release are also elaborated here together with a summary of targeting in vitro. Comparisons of polymersomes to viral capsids are shown to encompass many aspects of current designs. Drug Dev. Res. 67:4,14, 2006. © 2006 Wiley-Liss, Inc. [source]

Small-molecule release from poly(D,L -lactide)/poly(D,L -lactide-co-glycolide) composite microparticles

"Click" Dielectrics: Use of 1,3-Dipolar Cycloadditions to Generate Diverse Core-Shell Nanoparticle Structures with Applications to Flexible Electronics

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 18 2008
Meghann A. White
Abstract We have synthesized a "universal ligand" incorporating a phosphonate surface anchor and a terminal alkyne moiety which binds to TiO2 nanoparticles and exhibits excellent dispersity in organic solvents. The alkyne functionality permits attachment of azide terminated polymer shells using "click" chemistry. Thus TiO2 core nanoparticles have been encapsulated with both polystyrene and poly(t -butyl acrylate) shells. The TiO2 -poly(t -butyl acrylate) core shell nanoparticles are amenable to further chemical transformation into TiO2 -poly(acrylic acid) nanoparticles through ester hydrolysis. These TiO2 -polyacrylic acid nanoparticles are dispersible in aqueous solution. The resulting core-shell nanoparticles have been incorporated as high K dielectric films in capacitor and organic thin film transistor devices and are promising new materials for flexible electronics applications. [source]

Surface-graft hyperbranched polymer via self-condensing atom transfer radical polymerization from zinc oxide nanoparticles

POLYMER ENGINEERING & SCIENCE, Issue 9 2007
Peng Liu
We present the synthesis of hyperbranched polymer grafted zinc oxide (ZnO) hybrid nanoparticles by self-condensing vinyl polymerization (SCVP) via surface-initiated atom transfer radical polymerizations (SI-ATRP) from ZnO surfaces. ATRP initiators were covalently linked to the surfaces of ZnO particles, followed by SCVP of an initiator-monomer ("inimer") which has both a polymerizable group and an initiating group in the same molecule. Well-defined polymer chains were grown from the surfaces to yield hybrid nanoparticles comprised of ZnO cores and hyperbranched polymer shells having multifunctional chlorobenzyl functional end groups. The percentage of grafting (PG%) achieved 429% in 6 h, calculated from the elemental analysis results. The hybrid nanoparticles were also characterized using Fourier transform infrared spectroscopy, UV,vis absorption spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, and transmission electron microscopy. POLYM. ENG. SCI., 47:1296,1301, 2007. © 2007 Society of Plastics Engineers [source]