Morphology and film formation of poly(butyl methacrylate)–polypyrrole core–shell latex particles

 Core–shell latex particles made of a poly(butyl methacrylate) (PBMA) core and a thin polypyrrole (PPy) shell were synthesized by two-stage polymerization. In the first stage, PBMA latex particles were synthesized in a semicontinuous process by free-radical polymerization. PBMA latex particles were labeled either with an energy donor or with an energy acceptor, in two different syntheses. These particles were used in a second stage as seeds for the synthesis of the core–shell particles. The PPy shell was polymerized around the PBMA core latex in an oxidative chemical in situ polymerization. Proofs for the success of the core–shell synthesis were obtained using nonradiative energy transfer (NRET) and atomic force microscopy (AFM). NRET gives access to the rate of polymer chain migration between adjacent particles in a film annealed at a temperature above the glass-transition temperature T _g of the particles. Slower chain migration of the PBMA polymer chains was obtained with the PBMA–PPy core–shell particles compared to rate of the PBMA polymer chain migration found with the pure, uncoated PBMA particles. This result is due to the coating of PBMA by PPy, which hinders the migration of the PBMA polymer chains between adjacent particles in the film. This observation has been confirmed by AFM measurements showing that the flattening of the latex film surface is much slower for the core–shell particles than for the pure PBMA particles. This result can again be explained by the presence of a rigid PPy shell around the PBMA core. Thus, these two complementary methods have given evidence that real core–shell particles were synthesized and that the shell seriously hinders film formation of the particles in spite of the fact that it is very thin (thickness close to 1 nm) compared to the size (750 and 780 nm in diameter) of the PBMA core. Transparency measurements confirm the results obtained by NRET and AFM. When the films are placed at a temperature higher than the T _g of PBMA, the increase in transparency is faster for films made with the uncoated PBMA particles than for films made with the coated PBMA particles. This result indicates again that the presence of the rigid PPy layer around the PBMA core reduces considerably the speed at which the structure of the film is modified when heated above the T _g of PBMA. Received: 02 September 1999 Accepted: 21 December 1999     

SYNTHESIS OF BOWL-LIKE PARTICLES BY EMULSION POLYMERIZATION AND RELEASE BEHAVIOR OF SOLVENT FROM THE PARTICLES

1. INTRODUCTION Hollow particles have been produced usually by the alkali swelling procedure (ASP), dynamic swelling method (DSM), and water-in-oil-in-water (w/o/w) emulsion polymerization [1]. Because particles can reserve various chemicals in their hollow, they could be used as reservoir and release material [2]. But almost all the work was to make hollow spheres. One kind of hollow particles, the bowl-shaped polymer particles have some advantages because of their special shape [3~6]…     

SYNTHESIS OF BOWL-LIKE PARTICLES BY EMULSION POLYMERIZATION AND RELEASE BEHAVIOR OF SOLVENT FROM THE PARTICLES

Poly(styrene-glycidyl methacrylate) particles having bowl-shaped hollow structures were synthesized by swollen seed emulsion polymerization. The PS emulsion synthesized through soap-free emulsion polymeri:ation was swollen by toluene, and then the mixture of second monomers was added under polymerization condition So a thin shell of poly(styrene-glycidyl methacrylate) cross-linked by triethylene glycol diacrylate was formed around the swollen PS particle. The bowl-shaped particles were obtained after the collapsing of the thin shell when the toluene emanated from the particles, but the shapes were effected by the degrees of cross-linking. The shape of the particles was observed by SEM. The release behavior of solvent from the particles was examined by TG     

Facile fabrication of hollow mesoporous silica nanospheres for superhydrophilic and visible/near-IR antireflection coatings

A series of hierarchically mesostructured silica nanoparticles (MSNs) less than 100 nm in size were fabricated by means of a one-step synthesis using dodecanethiol (C(12)-SH) and cetyltrimethylammonium bromide (CTAB) as the dual template, and trimethylbenzene (TMB) as the swelling agent. Silica nanoparticles with varied morphologies and structures, including mesoporous silica nanoparticles with tunable pore size, mesoporous silica nanoparticles with a thin solid shell, hollow mesoporous silica nanoparticles with tunable cavity size, and hollow mesoporous silica nanoparticles with a thin solid shell, were obtained by regulating the TMB/CTAB molar ratio and the stirring rate with the assistance of C(12)-SH. Silica particulate coatings were successfully fabricated by using MSNs with varied morphologies and structures as building block through layer-by-layer dip-coating on glass substrates. The thickness and roughness of the silica particulate coatings could be tailored by regulating the deposition cycles of nanoparticles. The silica particulate coatings composed of hollow mesoporous silica nanoparticles with a thin shell (S2) increased the maximum transmittance of slide glass from 90 to 96%, whereas they reduced its minimum reflection from 8 to 2% at the optimized wavelength region that could be adjusted from visible to near-IR with a growing number of deposition cycles. The coatings also exhibited excellent superhydrophilic and antifogging properties. These mesostructured silica nanoparticles are also expected to serve as ideal scaffolds for biological, medical, and catalytic applications.     

聚乙二醇包裹羰基铁核壳粒子的制备及水基磁流变液的性能

以羰基铁粉(CI)为原料用共溶胶-凝胶反应制备CI/聚乙二醇核壳复合粒子，并将其与水组成了磁流变液. 用SEM、TEM、FT-IR和VSM表征了核壳复合粒子的微观结构和静磁特性，并测试了水基磁流变液的性能. 结果表明，核壳复合粒子表面有SiO_x和聚乙二醇的包覆层，它有较好的亲水性和优良的软磁特性，用它组成的水基磁流变液具有抗沉降性优良、零场粘度低、磁流变效应显著等特点.     

单分散核／壳结构导电高分子复合材料的研究（Ⅰ）——单分散核／壳结构聚苯乙烯／聚吡咯的结构表征

导电高分子在光、电、磁等领域表现出的广泛应用前景 ,使它成为材料科学的研究热点 .然而 ,早期发现的导电高分子的不溶不熔性 ,使它在可加工性和机械性能等方面仍面临许多挑战 .核 /壳结构导电高分子与单分散技术的结合 ,无疑为这一领域的研究带来新的生机和活力 .目前仅有的少量文献主要集中报道微米和亚微米级单分散核 /壳导电高分子复合材料的研究 ,大多采用种子乳液聚合法合成 .微米级的种子乳液通常采用以醇为分散介质的分散聚合方法制备 [1～ 3] ,由于种子分散体系要经反复离心分离 ,除去醇类 ,重新分散在水相中再进行核 /壳导电高分…     

Preparation and Chromatographic Features of Fibrous Core–Shell HPLC Packing Material

In this study, fibrous core–shell silica particles were successfully synthesized via a one-step oil–water biphase stratification coating strategy. The core–shell silica particles were composed of 3-µm non-pore silica cores and thin shells (50–100 nm), which have radial-like direct channels and a large pore size (19.89 nm). The fibrous core–shell silica particles were further modified by n-octadecyltrichlorosilane and used as stationary-phase media in high-performance liquid chromatography (HPLC). The chromatographic properties of the particles were systematically studied in small-molecule and protein separation processes. The results showed that the back pressure was as low as 8.5 MPa under the 1.0-mL min^?1 flow velocity. Furthermore, fibrous core–shell silica particles with an 80-nm shell were used for separating seven small molecules within 10 min and six proteins within 6 min. This work demonstrates that the fibrous core–shell silica particles could be used as an HPLC stationary phase with good performance and low back pressure, and that they have great potential for application to HPLC separation in the future.     

Two‐dimensional non‐close‐packed arrays of nanoparticles via core‐shell nanospheres and reactive ion etching

Nanosized PTFE/polystyrene core‐shell particles were prepared by seed emulsion polymerization technique starting from PTFE seeds of 20 nm. At the end of the reaction, no residual PTFE nor secondary nucleation was observed and by appropriately choosing the ratio between the monomer and the PTFE seed it was possible to obtain particles, with predetermined size in the range 60–100 nm, featuring an extremely narrow size distribution. These particles were successfully employed as building blocks for the preparation of large scale nanosized monolayers through the floating technique. Reactive ion etching was further applied to modulate the size characteristics of the resulting 2D ordered nanostructure. Although for relatively short RIE times a peculiar continuous morphology was observed in which the particles are interconnected through thin arms, on further increasing the RIE time a well‐organized 2D arrangement of particles with size of about 30 nm was obtained. Considering the shell as an expendable ordering and spacing tool, the use of core‐shell nanospheres allows a wide variety of controlled morphologies to be designed and prepared thus opening new perspectives for nanostructure fabrication processes through nanosphere lithography (NSL). Copyright © 2011 John Wiley & Sons, Ltd.     

ZnS:Mn2+/聚苯乙烯核壳及ZnS:Mn2+中空球的制备和光谱性质

ZnS:Mn2+ polystyrene (PS) core-shell structures and ZnS:Mn2+ hollow spheres were prepared by a sonoehemical deposition approach. Transmission electron micrograph (TEM) studies show that the PS surface is covered by a thin shell consisted of ZnS: Mn2+ nanoparticles with an average size of 9 nm. ZnS: Mn2+ hollow spheres were obtained by heating the core-shell particles in air at 500 ℃ to drive off PS. The photoluminescence spectrum for the emission band of Mn2+ peaked at 540 nm, and a 45 nm blue shift compared to that of corresponding bulk sample, was discussed based on the Mn-O octahedral distortion induced by shell structure.     

Encapsulation of emulsion droplets by organo-silica shells

Surfactant-stabilized emulsion droplets were used as templates for the synthesis of hollow colloidal particles. Monodisperse silicone oil droplets were prepared by hydrolysis and polymerization of dimethyldiethoxysiloxane monomer, in the presence of surfactant: sodium dodecyl sulphate (SDS, anionic) or Triton X-100 (non-ionic). A sharp decrease in the average droplet radius with increasing surfactant concentration was found, with a linear dependence of the droplet radius on the logarithm of the surfactant concentration. The surfactant-stabilized oil droplets were then encapsulated with a solid shell using tetraethoxysilane, and hollow particles were obtained by exchange of the liquid core. The size and polydispersity of the oil droplets and the thickness of the shell were determined using static light scattering, and hollow particles were characterized by electron microscopy. Details on the composition of the shell material were obtained from energy-dispersive X-ray analysis. In the case of sodium dodecyl sulphate, the resulting shells were relatively thin and rough, while when Triton X-100 was used, smooth shells were obtained which could be varied in thickness from very thick ( approximately 150 nm) to very thin shells ( approximately 17 nm). Finally, hexane droplets were encapsulated using the same procedure, showing that our method can in principle be extended to a wide range of emulsions.