Preparation and Swelling Properties of Poly(NIPAM) "Minigel" Particles Prepared by Inverse Suspension Polymerization

The characterization of temperature- and pH-sensitive poly-N-isopropylacrylamide (poly-NIPAM) microgel particles, produced by surfactant-free emulsion polymerization, has been extensively reported. In the work described here poly(NIPAM) gel particles, cross-linked with N-N'-methylenebisacrylamide (BA), have been produced using inverse suspension polymerization. These particles have been termed "minigels" here since they are somewhat larger than conventional microgels. Results suggest that minigel particles are formed as a dilute suspension, within the aqueous dispersed (droplet) phase. The hydrodynamic diameter of the minigel particles produced in this work is 相似文献   

Preparation of Copolymerized Phenylsilsesquioxane-Benzylsilsesquioxane Particles

Copolymerized phenylsilsesquioxane-benzylsilsesquioxane particles were prepared from their corresponding organotriethoxysilanes by the sol-gel method. Transparent thick films of a few microns in thickness have been successfully prepared on glass substrates coated with indium tin oxide (ITO) by heat-treating the copolymerized particles which had been electrophoretically deposited on the substrates. The on-set temperature for thermal sintering of the copolymerized particles decreased from 150 to 50°C with increasing the benzylsilsesquioxane content. These on-set temperatures for thermal sintering of the particles were found to be higher by 10 to 50°C than the glass transition temperatures of the particles of the corresponding composition. The thermal sintering of the particles should occur due to a large decrease in viscosity of the particles at temperatures higher than the glass transition temperatures. The decrease in the on-set temperature with composition for thermal sintering as well as in the glass transition temperature of the particles can be related with the decreases in average molecular weight and in distribution of the molecular weight of the particles with an increase in the benzylsilsesquioxane content.     

Evaporation‐Driven Self‐Assembly of Colloidal Silica Dispersion: New Insights on Janus Particles

The evaporation driven self‐assembly of novel colloidal silica Janus particles was evaluated by scanning electron microscopy in comparison to unfunctionalized silica particles. The cyclodextrin‐ and azobenzene‐modified compound was obtained utilizing Pickering emulsion approach, in which the particles were immobilized on solidified wax droplets and subsequently functionalized. Silica particles were modified with 3‐aminopropyl trimethoxysilane and afterward reacted with tosyl‐β‐CD or phenylazo(benzoic acid), respectively. Mesoscopic structures of the colloidal dispersions, as dried films from aqueous solution, have been investigated by scanning electron microscopy and dynamic light scattering. Interestingly, it has been observed that the Janus particles show a significantly different evaporation‐induced assembly than the unmodified particles.     

超细金属铁颗粒的高分子修饰及其悬浮液的磁流变性能

报道以γ射线辐照方法合成出具有良好分散性的高分子复合金属铁粒子.分别选择十二烷基硫酸钠、溴化十六烷基三甲基铵、Tween-80、TritonX-200和OP-10等表面活性剂和有机单体、无机铁颗粒一起制备乳状液,通过对这种含有超细金属铁颗粒乳状液稳定性的比较,以寻求合适的乳化剂.并对以TritonX-200为乳化剂时合成出的高聚物复合铁颗粒进行了XRD、TEM和IP表征.还将实验中所获得的高聚物复合铁粒子与粒径相同的未经修饰的纯铁粒子分别制成了悬浮液,对两者的悬浮性能进行了比较,同时,也将高聚物复合铁粒子制成的悬浮液与Fe3O4-PMMA复合粒子悬浮液两者的屈服应力随磁场变化情况进行比较研究.     

Size-selective synthesis and stabilization of gold organosol in C(n)TAC: enhanced molecular fluorescence from gold-bound fluorophores

Gold nanoparticles of variable sizes have been synthesized in toluene employing two-phase (water-toluene) extraction of AuCl4- followed by its reduction with sodium borohydride in the presence of a series of cationic surfactants of a homologous series having the general formula C(n)TAC. The solubility features of the gold particles in the organic solvent have been accounted qualitatively by calculating the van der Waals interaction potential between the particles. The effect of thermal energy and medium dielectric constant on the stability of metal particles has been studied by measuring the surface plasmon resonance. The stabilization of surfactant-mediated gold particles as hydrosol or organosol has been elucidated by considering the double-layer interaction as a function of the dielectric constant of the solvent medium. The influence of the counterion of the phase transfer reagent and stabilizing ligand on the photochemical stability of the gold colloids has been investigated. The fluorescence probe 1-methylaminopyrene (MAP) was considered for the surface functionalization of the gold particles, and it has been found that there is an enhancement of molecular fluorescence from the gold-probe assembly.     

SURFACE TENSION,STICKINESS AND ENGULFMENT

The thermodynamic conditions for the engulfment of one set of particles by another has been given in terms of interfacial energies. Experimentally, it has been shown that a polymer with a high glass transition temperature can be engulfed by a particle of low glass transition temperature; also, that Inorganic particles can be engulfed by polymer particles. As a precursor to the engulfment stage heterocoagulation can be used for bringing the particles together in a ‘sticking’ mode. This appears to be a general process which is applicable to a number of scientific areas, e.g. in biology, phagocytosis, and in material science for the preparation of composite particles.     

Poly(vinylpyridine) core/poly(N-isopropylacrylamide) shell microgel particles: their characterization and the uptake and release of an anionic surfactant

The use of microgel particles for controlled uptake and release of active species has great potential. The compatibility of microgel particles with their environment and the functionality of the particles can be achieved by modification of the core microgel through the addition of a shell. In this work, core-shell microgel particles, with a pH-responsive core (polyvinylpyridine) and a temperature-responsive shell (poly-N-isopropylacrylamide), have been prepared and characterized. The uptake and release of an anionic surfactant from the microgels has been investigated as a function of solution pH and temperature. The results indicate that electrostatic attraction between the anionic surfactant and the cationically charged core of the microgel particles is the dominant mechanism for absorption of the surfactant into the core-shell microgel particles.     

Electroadhesive properties of polymer particles in contact with the photoconductor surface

The electroadhesive properties of polymer particles 5 to 30 μm in diameter have been assessed by the values of their individual charges after tearing off, and by the force of their adhesion to a solid surface. It has been established that the electroadhesion properties of polymer particles are largely determined by the donor-acceptor interaction between the main functional groups of polymers and the solid surface.

The electroadhesive properties of particles in contact with the surface of a photoconductor have been found to be affected by exposure to light. The spectral dependence of the adhesion force of particles and the variation in the distribution of the torn-off particles with regard to a charge sign under the effect of exposure to light are related to a variation in the density of the double electric layer at their interface with the solid surface.

The results obtained are interpreted on the basis of notions on the preponderant role of the forces of electrostatic nature, which are attributable to the effect of the double electric layer at the interface, in the adhesion interaction of the particles with the solid surface.     

Synthesis of Organic-Inorganic Hybrid Particles by Sol-Gel Chemistry

The synthesis of ORganically MOdified SILica (ORMOSIL) particles has been carried out using both the hydrolytic and non-hydrolytic sol-gel routes. The hybrid (nano)composites are organically modified with an alkyl or aryl group covalently bonded to silicon. Hybrids have been synthesised in an aqueous sol-gel process by a modified Stöber route, producing spherical nanoparticles with diameters in the range 50–300 nm. The size of the particles can be controlled by control of certain reaction parameters. Smaller ormosil nanoparticles can be synthesised by a base-catalysed emulsion polymerisation route, by varying the type and concentration of surfactant and precursor feed rate. In this case, particles in the size range 3.5–10 nm can be obtained. Hybrids have been synthesised from hyperbranched polyesters by encapsulation in a silica matrix using the hydrolytic sol-gel route. Optimisation of the reaction conditions allows the hybrids to be produced as isolated sub-micron spherical particles. Ormosil particles have also been synthesised using the non-hydrolytic sol-gel route, which may lead to products of different morphologies because of the different polarity of the reaction medium. Different reaction conditions were studied in order to optimise the size and shape of the particles, including choice of solvent, use of surfactants and addition of polystyrene. Dimethylsulfoxide acts as a novel oxygen donor for the catalyst-free formation of colourless silsesquioxanes.     

Structure and stability of silica particle monolayers at horizontal and vertical octane-water interfaces

Monolayers of silica particles at horizontal and vertical octane-water interfaces have been studied by microscopy. It is found that their structure and stability depend strongly on the particle hydrophobicity. Very hydrophobic silica particles, with a contact angle of 152 degrees measured through the water, give well-ordered monolayers at interparticle distances larger than 5 particle diameters which are stable toward aggregation and sedimentation. In contrast, monolayers of less-hydrophobic particles are disordered and unstable. Two-dimensional particle sedimentation has been observed in the case of vertical monolayers. The results have been analyzed with a simple two-particle model considering the sedimentation equilibrium as a balance between the long-range electrostatic repulsion through the oil, the gravity force, and the capillary attraction due to deformation of the fluid interface around particles. The value of the charge density at the particle-octane interface, 14.1 muC/m(2), found for the most hydrophobic particles is reasonable. It drastically decreases for particles with lower hydrophobicity, which is consistent with the order-disorder transition in monolayer structure reported by us before. The pair interactions between particles at a horizontal octane-water interface have been analyzed including the capillary attraction due to undulated three-phase contact line caused by nonuniform wetting (the contact angle hysteresis). The results are in agreement with the great stability of very hydrophobic silica particle monolayers detected experimentally, even at low pH at the point of zero charge of the particle-water interface, and with the aggregated structure of hydrophilic particle monolayers.     

Fabrication of carbon/silica hybrid materials using cationic polymerization and the sol-gel process

Silica particles with different morphology have been functionalized with carbon shells by different synthetic procedures. In the key step, the bare silica particles are functionalized by a specific cationic surface polymerization with furfuryl alcohol (FA). The polyfurfuryl alcohol (PFA)/silica hybrid particles have been also post-functionalized with maleic anhydride (MSA) by a Diels Alder reaction. Simultaneously occuring cationic polymerization of FA and sol-gel process with TEOS has been used for producing interpenetrating carbon-silica hybrid materials. The thermal transformation of the PFA component on silica into the carbon phase has been carried out under argon atmosphere in a temperature range from 700°C to 900°C. The influence of the former morphology of the silica on the homogenity of the resulting carbon layer is shown by zetapotential measurements and electron microscopic investigations.     

Synthesis and properties of latex particles with polyaniline shells

Core–shell polyaniline–latex particles have been obtained via oxidative polymerization of aniline hydrochloride in the presence of charged polystyrene latex. The polymerization conditions have been determined under which polyaniline is predominantly formed on the surface of latex particles to yield closed shells. The dependence of the electrical conductivity of the resulting particles on the initial concentration of aniline hydrochloride in the polymerization medium has been studied. Stable aqueous dispersions of polyaniline–latex particles have been prepared by modifying the particles with sodium 3-mercaptopropane sulfonate.     

Study of sulfur heterogeneous nucleation from supersaturated vapor on tungsten oxide and sodium chloride seed particles. Determination of contact angle of critical sulfur nuclei

A procedure has been developed for determining the contact angle of a critical nucleus formed on seed particles during the heterogeneous nucleation of a vapor in a flow chamber. The procedure comprises the determination of the fraction of enlarged particles, as well as the selective separation of nanoparticles over sizes to locate the zone of intense nucleation. The concentration and size distribution of aerosol particles have been measured with a diffusion spectrometer of aerosols. Vapor concentration distributions and supersaturation fields have been determined by solving the mass-transfer problem. The calculated supersaturation fields are in good agreement with the location of the intense nucleation zone experimentally found with the help of selective separation. The fractions of enlarged particles have been determined as functions of supersaturation in the chamber. A formula has been derived for calculating the fraction and size distribution function of enlarged particles at known supersaturation and temperature fields and a preset contact angle. The contact angles are selected in a manner such that the calculated fraction of enlarged particles coincides with that measured experimentally. It has been revealed that the contact angle of critical sulfur nuclei formed on tungsten oxide seed particles with average radii 〈R _p〉 ≈ 5.8?4.4 nm is in a range of 21.2?20.5°, while, in the case of sodium chloride seed particles with 〈R _p〉 ≈ 6.0?4.4 nm, the contact angle is 20.4?17.4°. The size of a critical nucleus has been found to be proportional to calculated average radius of a seed particle 〈R _p〉 in both cases.     

Depth-resolved investigation of the element and compound inventory of aerosol particles from outdoor air

Plasma-based SNMS has been employed to perform a depth-resolved elemental analysis of aerosol particles collected in a suburban area near Karlsruhe. Two classes of particles could be distinguished. Both of them exhibited a significant depth structure. Submicron particles have been found with a 15 nm deep ammonium sulphate surface layer on carbon rich cores. The other class consisted of coarse particles of several m size which even showed a double layer system enclosing geogenic cores. For depth-scaling a new internal calibration procedure has been tested and found to be suitable for the complex environmental material. Dynamic SIMS measurements have been used to investigate especially the carbon compounds of the particles by evaluation of small cluster ion signal patterns.     

Calibration of Polarization-Sensitive and Dual-Angle Laser Light Scattering Methods Using Standard Latex Particles

A polarization-sensitive laser light scattering (PSLLS) method and a dual-angle laser light scattering (DALLS) method have been studied for in situ measurement of submicrometer hydrosol and aerosol particles. By using standard monodisperse polystyrene latex particles suspended in water and air as test particles, calibration of systems built based on the above methods have been performed. The effects of light scattered by agglomerated aerosol particles (multiplets) were corrected by considering the fraction of multiplets as determined with an aerosol measurement technique using a differential mobility analyzer. The change in the measured intensities of scattered light with particle diameter was then determined by calculations based on Mie theory. It was shown that the PSLLS system can determine particle diameters as small as approximately 60 nm for the test hydrosol particles and approximately 100 nm for test aerosol particles, respectively. The DALLS system can determine smaller diameters than the PSLLS system for test particles with no light absorption. The change in scattered light intensities with particle diameter was also investigated by theoretical calculations with various refractive indexes and scattering angles. The PSLLS and DALLS systems promise to become routine measurement tools for absorbing and nonabsorbing particles, respectively. Copyright 2001 Academic Press.     

STM observation of Au fine-particles on graphite

Gold particles deposited on graphite in vacuum have been studied by STM observation in air. Liquid-like coalescence between small gold-particles has been observed near room temperature. Preparation of small particles in vacuum is discussed. Small particles are formed in nucleation process if the degree of coalescence of particles is reduced. Over 400 Au particles of 5 nm in diameters with a narrow size-distribution with FWHM 2 nm and a high density of 3×10¹²/cm² is prepared by evaporating gold in a vacuum of about 2×10^?5 Torr and at the substrate (HOPG) temperature of 20°C.     

Synthesis and characterization of magnetic and non-magnetic core-shell polyepoxide micrometer-sized particles of narrow size distribution

Core polystyrene microspheres of narrow size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. Uniform polyglycidyl methacrylate/polystyrene core-shell micrometer-sized particles were prepared by emulsion polymerization at 73 degrees C of glycidyl methacrylate in the presence of the core polystyrene microspheres. Core-shell particles with different properties (size, surface morphology and composition) have been prepared by changing various parameters belonging to the above seeded emulsion polymerization process, e.g., volumes of the monomer glycidyl methacrylate and the crosslinker monomer ethylene glycol dimethacrylate. Magnetic Fe(3)O(4)/polyglycidyl methacrylate/polystyrene micrometer-sized particles were prepared by coating the former core-shell particles with magnetite nanoparticles via a nucleation and growth mechanism. Characterization of the various particles has been accomplished by routine methods such as light microscopy, SEM, FTIR, BET and magnetic measurements.     

Synthesis of fluorescent silica-coated gibbsite platelets

We describe the fluorescent labeling of gibbsite particles. Gibbsite particles are first stabilized with polyvinyl pyrrolidone. Subsequently the particles are covered with a silica layer in which a fluorescent dye is incorporated. Both fluorescein and rhodamine dyes have been used. The fluorescent labeling is applicable to gibbsite particles of various sizes. Particles are transferred to dimethyl formamide by vacuum distillation after dialysis. These particles are used for confocal scanning laser microscopy and confocal fluorescence-recovery after photobleaching.     

Composite Particles: Design of Hybrid Materials on the Nano-Scale

Summary: In the last decade there has been a steady increased interest in the techniques providing design of nano-structured materials. It has been demonstrated that colloidal polymeric particles can be successfully used for the deposition of different functional nano-materials. Due to their numerous attractive properties polymeric particles have been used as templates for the synthesis, storage and transportation of nanostructured materials. This contribution demonstrates the synthetic ways for the preparation of hybrid particles by effective control over the size, morphology and distribution of the non-miscible phases. Developed methods allow design of the composite particles on the nanometer scale and opens new possibilities for the preparation of the materials with advanced properties. The synthesis, characterization and applications of hybrid particles are discussed in detail.