Triazene UV-triggered photogeneration of silver/gold nanoparticles in block copolymer templates

Journal of Nanoparticle Research - Synthesis of yttrium oxide nanoparticles in a specially designed radio frequency thermal plasma reactor is reported. Good crystallinity, narrow size distribution,...     

On the feasibility of chemical reactions in the presence of siloxane-based surfactants

Siloxane-containing surfactants have been tested as stabilizers for the preparation of polymer nanoparticles by three types of chemical reactions. Two crosslinking reactions were used to obtain silicone elastomers particles: one involved HO-terminated polydimethylsiloxane and tetraethoxysilane, while the other one was a crosslinking via polyhydrosilylation. The third reaction was a linear polycondensation between a diamine and a siloxane dialdehyde. The monitoring of the reactions has been made by infrared spectroscopy and the resulting particles have been analyzed in dispersion by light scattering and in dry state by electron microscopy and atomic force microscopy. The particles size was of hundreds of nanometers and their spherical shape was generally maintained after drying. The spectral and microscopy data proved efficient stabilization, which allowed the reactions to evolve after the formation of the particles.     

Parabanic polymers obtained by the cyclocondensation reaction of polyureas containing 2,6-pyridyl structure

The polymers containing 1,3-imidazolidine-2,4,5-trione rings on the macromolecular backbone are known for a few years and named poly(parabanic acid)s. The paper presents some polymers and model compounds with urea and/or parabanic structures, as a result of the cyclocondensation reaction of the urea derivatives containing 2,6-pyridyl rest, with the oxalyl chloride. The 2,6-pyridyl radical has an acid acceptor character that determines an important distinct influence on the cyclocondensation reaction. The influence of the reaction conditions (temperature, time, beside of the presence or absence of pyridine (Py)) on the progress of the cyclocondensation was studied. The advance of the reaction was followed by IR spectra. The products were characterized by the elemental analysis, ¹H NMR and IR spectra, solubilities and viscosity measurements. Thermal properties were determined by thermogravimetric analyses and differential scanning calorimetry. The analytical and spectral data demonstrated that, in absence of Py, the cyclocondensation performed almost completely only in the case of the aliphatic polyureas, while, in the same conditions, the aromatic polymers were only partly transformed. By using the Py as catalyst, both aromatic and aliphatic polyureas can be transformed into parabanic polymers at above 90% transformation degree (TD). A calculation method of the TD based on the IR spectroscopy was discussed.     

Synthesis and Characterization of Fluorescent,Nonionic, Water Self-Dispersible Oligothiophenes

Two α-septithiophenes substituted at the third position of the middle ring with polyethyleneglycol of different molecular weights (PEG 1000 and PEG 2000) were synthesized using Suzuki condensation. Their structural characterization was performed by ¹H NMR and FT-IR. The thermal behavior of the new synthesized oligothiophenes was investigated by differential scanning calorimetry (DSC) and thermogravimetrical (TGA) analysis. Photophysical properties in solutions were evaluated by UV-vis and fluorescence measurements using different solvents. The amphiphilic nature of the synthesized oligothiophenes and the presence of the PEG side chains induced self-dispersibility in water and the possibility of fluorescent nanoparticles forming by self-assembling. The size of nanoparticles in water was assessed by DLS and AFM investigations.     

Photocatalytic synthesis of silver nanoparticles using polysilane initiator

This study shows that the exposure to visible light of the poly[diphenylsilane-co-methyl(H)silane] solution together with a silver salt, initiates a photocatalytic process which leads to the formation of metal nanoparticles. This phenomenon is a consequence of close-range interactions between the methylhydrosilyls’ σ-conjugated segments and the metal ions at the salt surface. Due to the weak charge transfer complexes thin films casted from solution show a specific morphology with microdomains of various dimensions and shapes in relation with the stage of the process. The polymethylhydrosilane copolymer stabilizes the synthesized nanoparticles in a similar manner as the conventional surfactants do. The polymer chemical structure is not affected during the photocatalytic process and the optical and electronic properties of polysilanes are well preserved.     

Morphological Investigation of Poly[methyl(H)silane-co-diphenylsilane] Irradiated by XeCl Excimer Laser

The morphological properties of poly[methyl(H)silane-co-diphenylsilane] copolymer (PSH) under XeCl (308 nm) laser irradiation were investigated. For this purpose, PSH films were exposed to XeCl excimer laser, 308 nm, at various UV doses (122 and 366 mJ/cm²), with 11 and 33 mJ/pulse and 1 Hz pulse repetition rate. The morphology of the PSH film surface was investigated by the atomic force microscopy (AFM) technique. AFM identifies that the films of the copolymer form a wormlike morphology before irradiation and conical defects are created on the polymer surface and grow with the laser irradiation.