There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Core/Shell Nanoparticles: Classes, Properties, Synthesis Mechanisms, Characterization, and Applications

Structural engineering of polyurethane coatings for high performance applications

Metal-mediated reductive hydrodehalogenation of organic halides.

Latex film formation, the process by which an aqueous dispersion of polymer particles is transformed into a continuous material, has a direct bearing on the final film morphology and properties. Each of the primary stages of film formation (evaporative drying and ordering; particle deformation; and polymer interdiffusion) have been studied experimentally. Recently-developed non-invasive techniques, including direct nonradiative energy transfer, atomic force microscopy, small angle neutron scattering, environmental scanning electron microscopy, and various optical techniques have greatly enhanced the study of these stages. Even so, the exact cause (or causes) of particle deformation is still a topic of considerable debate. Several factors are experimentally known to influence latex film formation: the ambient conditions; the presence of surfactants, plasticizers and pigments; and latex particle structure. An important aim in the study of latex film formation is to understand the mechanisms by which these and other factors affect the process. New challenges lie in the study of film formation of core-shell latices, latex blends and new compositions.

Film formation of latex

A theoretical analysis and a morphological prediction of polyacrylate (PA)/polysiloxane (PSi) latex particles with core/shell morphologies were first conducted based on interfacial tensions and relative volumes of the two polymers in the latex system. The results indicated that the normal core/shell morphology particles (PSi/PA), with hydrophobic polysiloxane as the core and with hydrophilic polyacrylate as the shell, can be easily formed. Although the inverted core/shell morphology particles (PA/PSi) with polyacrylate as the core could not be formed in most cases, even if the fraction volume of polysiloxane was larger than 0.872, which is the smallest value of forming a PA/PSi particle, the PSi/PA particles were unavoidably formed simultaneously with PA/PSi particle formation. The synthesis of PA/PSi particles containing equal amounts of polyacrylate and polysiloxane was then carried out using seeded emulsion polymerization. Before the cyclosiloxane cationic polymerization, 3-methacryloyloxypropyl trimethoxysilane (MATS) was introduced into the polyacrylate seed latex to form an intermediate layer and chemical bonds between the core and the shell polymers. The characterization by transmission electron microscopy (TEM) demonstrated that the perfect PA/PSi core/shell particle is successfully synthesized when both the core and the shell polymers are crosslinked. The experiments showed that both the hardness and water adsorption ratio characteristics of latex films of the PA/PSi particles are in good agreement with those of the polysiloxane film. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2251–2258, 2001

Morphological prediction and its application to the synthesis of polyacrylate/polysiloxane core/shell latex particles

Copolymer latices of styrene–butyl acrylate–silicone were prepared using a semicontinuous addition process and batch and monomer emulsion addition processes. The results showed that a stable latex with narrow particle size dispersion and a high monomer conversion can be obtained only by the semicontinuous addition process. The simultaneous free-radical and ionic copolymerization mechanisms were discussed. 3-Methacryloyloxypropyl trimethoxysilane in this work was used as a coupling agent to form a chemical bond between vinyl polymer and polysiloxane. It was found that the copolymerization reaction and the properties of latex and latex film were obviously influenced by silicone content. When the silicone content was less than 25 wt %, copolymerization proceeded readily and a stable latex could be prepared. With increasing silicone content, monomer conversion, latex stability, film hardness, and tensile strength decreased, whereas the water resistance and impact strength increased. Results of Soxhlet extraction, silicon analysis, and dynamic mechanical properties of latex polymer confirmed the occurrence of copolymerization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3194–3200, 2001

Study on the preparation and properties of styrene–butyl acrylate–silicone copolymer latices

The precipitation polymerization of styrene-trihydroxymethyl propane triacrylate has been carried out using ethanol and an ethanol/water mixture as the solvent. Uniform microspheres with high monomer conversion are achieved within 4 h, a much shorter polymerization time than that reported for the precipitation polymerization of divinyl benzene-styrene in acetonitrile. The results clearly demonstrate that use of water as a co-solvent is indeed very effective to promote the polymerization to high conversion and to obtain uniform microspheres. With no water under the otherwise same experimental conditions, only about 57% of monomer conversion is obtained; while the monomer conversion is remarkably increased to 96% when 12 vol.-% of water is used.

Precipitation Polymerization in Ethanol and Ethanol/Water to Prepare Uniform Microspheres of Poly(TMPTA-styrene).

Porous polyurea (PPU) is prepared through a simple protocol by reacting toluene diisocyanate (TDI) with water in a binary solvent of water–acetone, and the process is optimized. Porosimetric tests demonstrate that PPU possesses typical properties of porous materials. The structure of the material is characterized by Fourier transform infrared (FTIR), NMR (1H & 13C) and X-ray diffraction (XRD). FTIR analysis shows that TDI is fully reacted. Microstructure analysis of PPU by NMR reveals that PPU consists of short polyurea chains with a degree of polymerization about 15. The presence of crystallinity in PPU is confirmed by XRD, which shows three diffraction peaks, for which the corresponding chain conformations, based on interplanar spaces owing to different hydrogen-bonds, are depicted. TGA analysis demonstrates that PPU has high thermal stability, and no degradation is seen before 270 °C. The DSC test reveals that no obvious glass transition is observed owing to intensive hydrogen-bonding.

One step preparation of porous polyurea by reaction of toluene diisocyanate with water and its characterization

In a mixed solvent of water and ethanol, polystyrene/titanium dioxide (PSt/TiO2) composite particles of core-shell structure were prepared by hydrolysis of tetrabutyl titanate in the presence of cationic PSt particles or anionic PSt particles surface-treated using γ-aminopropyl triethoxysilane. Hollow TiO2 particles were obtained through calcination of the PSt/TiO2 core-shell particles to burn off the PSt core or through dissolution of the core by tetrahydrofuran (THF). An alternative process constituted of preheating the PSt/TiO2 particles at 200°C to allow partial crystallization followed by calcination or PSt dissolution by THF. The outcome TiO2 particles thus prepared were examined by TEM, and hollow TiO2 particles were observed. The crystalline phase structure and phase transformation were characterized, which revealed that preheating before the removal of the PSt core was useful to achieve the desired hollow TiO2 particles, and the calcination process was beneficial to the formation of anatase and rutile structures. The tests of TiO2 particles as catalyst in the photodegradation of Rhodamine B demonstrated that a much higher catalytic activity was observed with the TiO2 hollow particles prepared through calcination combined with preheating.

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Preparation of hollow TiO2 nanoparticles through TiO2 deposition on polystyrene latex particles and characterizations of their structure and photocatalytic activity

Xiang Zheng Kong

Papers

Morphological prediction and its application to the synthesis of polyacrylate/polysiloxane core/shell latex particles

Study on the preparation and properties of styrene–butyl acrylate–silicone copolymer latices

Precipitation Polymerization in Ethanol and Ethanol/Water to Prepare Uniform Microspheres of Poly(TMPTA-styrene).

One step preparation of porous polyurea by reaction of toluene diisocyanate with water and its characterization

Preparation of hollow TiO2 nanoparticles through TiO2 deposition on polystyrene latex particles and characterizations of their structure and photocatalytic activity