Home About us Contact
|
Home About us Contact | ||
|
|
||
Core-shell Morphology (core-shell + morphology)
Selected AbstractsMorphological and Physical Properties of Triblock Copolymers of Methyl Methacrylate and 2-Ethylhexyl MethacrylateMACROMOLECULAR MATERIALS & ENGINEERING, Issue 9 2006Hormoz Eslami Abstract Summary: Triblock copolymers of methyl methacrylate (MMA) and 2-ethylhexyl methacrylate (EHMA) [that is, poly(MMA,EHMA,MMA)] were prepared by an emulsion atom-transfer radical polymerization. The relationships of their structural, morphological, and physical properties were investigated. The latex particles had core-shell morphologies and the block copolymers experienced phase separation. Small latex particles with a low number of cores could deform and wet silicon-wafer surfaces, but the deformation of large latex particles was restricted by the internal two-phase morphology of the particles. Latex casting produced continuous pinhole-free films, in which hard poly(MMA) (PMMA) cores of different latex particles merged and provided interparticle connections. The morphology of solution-cast films depended on block composition, solvent type, and film thickness. For all the prepared polymer samples, thick films cast in toluene had poly(EHMA) (PEHMA) materials at air surface, whereas those cast in tetrahydrofuran had a sponge-like PMMA surface structure. Thin toluene-cast films from P(MMA,EHMA,MMA) with the block degrees of polymerization () 200,930,200 showed spherical PMMA domains and those from 380,930,380 yielded a protruded worm-like PMMA structure. The copolymer materials were coated on a glass surface for peeling tests. The films gave good hot-melt adhesion properties when the of the PEHMA block was over 600. The peeling strength depended on the lengths of both PEHMA and PMMA blocks. The P(MMA,EHMA,MMA) sample with of 310,930,310 yielded the highest peeling strength of 7.4 kgf,·,inch,1. The developed material is demonstrated to be a good candidate for a solvent-free, hot-melt, pressure-sensitive adhesives for special-purpose applications such as medical tapes and labels. [source] The Thermal Decomposition of Three Magnetic Acetates at Their Autogenic Pressure Yields Different Products.EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2007Abstract We report on the one-stage, reproducible, solvent-free, competent and straightforward approach for the synthesis of fullerene-like Ni@C, Co@C, and Fe3O4@C core-shell nanostructures that can be scaled up. The single precursor reactions of low cost acetates of Fe, Co and Ni are separately conducted at a relatively low temperature (700 °C) in a closed Swagelok reactor, as compared to other methods for the formation of graphitic layers. It is worth mentioning that although identical reaction parameters are employed, using the three acetate precursors, the graphitic carbon is coated on nanosized metallic Ni and Co cores, while Fe tends to form Fe3O4, maintaining the same core-shell morphology. The systematic morphological, compositional, structural characterization and the room temperature magnetic susceptibility measurements of the as-made particles are carried out on a vibrating sample magnetometer. The plausible mechanism is based on the comparison between the dissociation products of three acetate precursors, their obtained experimental data, and calculations on the enthalpy and free energy changes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Small-molecule release from poly(D,L -lactide)/poly(D,L -lactide-co-glycolide) composite microparticlesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2005Emily 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 of oily core-hybrid shell nanocapsules through interfacial free radical copolymerization in miniemulsion: Droplet formation and nucleationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2010Z. H. Cao Abstract Nanocapsules with an oily core and an organic/inorganic hybrid shell were elaborated by miniemulsion (co)polymerization of styrene, divinylbenzene, ,-methacryloyloxy propyl trimethoxysilane, and N -isopropyl acrylamide. The hybrid copolymer shell membrane was formed by polymerization-induced phase separation at the interface of the oily nanodroplets with water. It was shown that the size, size distribution, and colloidal stability of the miniemulsion droplets were extremely dependent on the nature of the oil phase, the monomer content and the surfactant concentration. The less water-soluble the hydrocarbon template and the higher the monomer content, the better the droplet stability. The successful formation of nanocapsules with the targeted core-shell morphology (i.e., a liquid core surrounded by a solid shell) was evidenced by cryogenic transmission electron microscopy. Both nanocapsules and nanoparticles were produced by polymerization of the miniemulsion droplets. The proportion of nanoparticles increased with increasing monomer concentration in the oil phase. These undesirable nanoparticles were presumably formed by homogeneous nucleation as we showed that micellar nucleation could be neglected under our experimental conditions even for high surfactant concentrations. The introduction of ,-methacryloyloxy propyl trimethoxysilane was considered to be the main reason for homogeneous nucleation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 593,603, 2010 [source] Synthesis and characterization of poly(methyl methacrylate)/casein nanoparticles with a well-defined core-shell structureJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2003Junmin Zhu Abstract Well-defined, core-shell poly(methyl methacrylate) (PMMA)/casein nanoparticles, ranging from 80 to 130 nm in diameter, were prepared via a direct graft copolymerization of methyl methacrylate (MMA) from casein. The polymerization was induced by a small amount of alkyl hydroperoxide (ROOH) in water at 80 °C. Free radicals on the amino groups of casein and alkoxy radicals were generated concurrently, which initiated the graft copolymerization and homopolymerization of MMA, respectively. The presence of casein micelles promoted the emulsion polymerization of the monomer and provided particle stability. The conversion and grafting efficiency of the monomer strongly depended on the type of radical initiator, ROOH concentration, casein to MMA ratio, and reaction temperature. The graft copolymers and homopolymer of PMMA were isolated and characterized with Fourier transform infrared spectroscopy and differential scanning calorimetry. The molecular weight determination of both the grafted and homopolymer of PMMA suggested that the graft copolymerization and homopolymerization of MMA proceeded at a similar rate. The transmission electron microscopic image of the nanoparticles clearly showed a well-defined core-shell morphology, where PMMA cores were coated with casein shells. The casein shells were further confirmed with a zeta-potential measurement. Finally, this synthetic method allowed us to prepare PMMA/casein nanoparticles with a solid content of up to 31%. Thus, our new process is commercially viable. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3346,3353, 2003 [source] Preparation of Polystyrene-Poly(N -isopropylacrylamide) (PS-PNIPA) Core-Shell Particles by Photoemulsion PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 14 2006Yan Lu Abstract Summary: Monodisperse thermosensitive PS-NIPA core-shell particles composed of a PS core and a cross-linked PNIPA shell can be successfully synthesized by a novel method: photoemulsion polymerization. Cryo-TEM images indicate clearly the core-shell morphology of the PS-NIPA particles: A homogeneous regular PNIPA shell has been affixed on the spherical PS core. DLS measurements indicate that the obtained PS-NIPA latex particles are thermosensitive. The shell of PNIPA networks with different cross-linking densities can shrink and re-swell with temperature and the volume transition temperature is around 32,°C in all cases. Cryo-TEM image of PS-NIPA core-shell particles. [source] Effect of cooling field strength and ferromagnetic shell shape on exchange bias in nanoparticles with inverted ferromagnetic,antiferromagnetic core-shell morphologyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2010Yong Hu Abstract The dependence of exchange bias (EB) effects on cooling field strength and particle shape in nanoparticles with antiferromagnetic (AFM) interfacial coupling and inverted AFM core with a fixed radius and ferromagnetic (FM) shell with various thicknesses are investigated by using a modified Monte Carlo Metropolis method. It is found that with the increase of cooling field, field-cooled exchange bias field (HE) fluctuates in the range of negative values initially, and then has an abrupt jump from the negative value to the positive value, finally levels off. However, HE decreases as the FM shell shape varies from No. 1 to No. 13 regardless of the strength of cooling field. Coercivity is affected by cooling fields and shapes indicating distinct behaviors. Because the AFM core is almost unaffected by shape and frozen completely during measuring hysteresis loops, the effect of ferromagnets on EB, negligible in most of other systems, is ambiguously manifested in such an unconventionally structural system. Moreover, the phenomena are interpreted well by presenting the snapshots of microscopic spin energy distributions, which make us observe directly and vividly the movement of domains and the competition of energies. This work will shed new light into the microscopic origin of peculiar magnetic properties of nanoparticles with special structures. [source] | |||||||||||||