Preparation and characterization of carboxylic-containing poly(methyl methacrylate) nanolatexes

Poly(methyl methacrylate) (PMMA)-based latex particles bearing carboxylic groups at the surface were prepared via emulsion polymerization. The polymerization recipe and process were optimized in order to target monodisperse particles with diameters around 100 nm. The polymerizations were performed using 4,4-azobis(4-cyanopentanoic) acid (ACPA) as initiator and sodium dodecyl sulphate (SDS) as surfactant. The polymerization conversion was determined by both gas chromatography and gravimetry. The final latexes were characterized with respect to particle size, size distribution, surface charge density, electrokinetic properties (i.e. electrophoretic mobility vs pH and ionic strength) and colloidal stability (i.e. coagulation rate constants vs pH and stability factor vs ionic strength).     

Viscosity of liquid selenium and selenium-sulphur mixtures

The viscosity of selenium has been studied in the liquid state, and the effect of thallium and sulphur additives was investigated. The rotating cylinder method was used. Experimental measurements show that the viscosity of liquid selenium with sulphur admixtures is higher than that for pure selenium, and a complex molecular structure is formed. The results were explained on the basis of the free volume model and the data for liquid selenium were fitted to the model withE _act=0.6 eV.     

Electrical properties of CuTlSe2 in the liquid state

The electrical conductivity and thermoelectric power of CuTlSe₂ have been investigated as a function of temperature up to 230 °C above its melting point. In the liquid state the experimental data are analyzed in terms of a model developed for the density of states and electrical transport in solid amorphous semiconductors (Mott, 1970). Positive thermoelectric power suggests a large predominance of holes in electrical conduction. It appears that the conduction is due to holes in extended states near the band edge. It is found that the energy gap has a large temperature coefficient =5.5×10^–4eV/K.     

Hopping transport in organic semiconductor system

The electrical conductivity of cupferron and some of its divalent transition metal complexes has been studied in the temperature range 0–150°C, in the amorphous state. An important result was found; namely that the temperature dependence of the conductivity is characteristic of the Mott hopping mechanism and identical with that of layers made by evaporating Ge, Si and carbon. It seems that only the physical structure determines the mechanism of conduction in amorphous materials, while the chemical composition is of minor importance.     

Threshold switching effects in AgTlSe2 and CuTlSe2 films

Switching effects in AgTlSe₂ and CuTlSe₂ chalcopyrite semiconductors films have been investigated. The threshold switching voltage was found to increase linearly with the thickness, moreoverV _th increases exponentially with the temperature. The rapid transition between the highly resistive and conductive states was attributed to an electrothermal origin from Joule's heating of a current channel.     

Polymer mediated peptide immobilization onto amino-containing N-isopropylacrylamide-styrene core-shell particles

Monodisperse cationic core-shell latex particles have been prepared using a shot polymerization process, with N-(3-aminopropyl)-methacrylamide-hydrochloride (APMH) as the functional monomer. The final latexes were characterized with respect to final polymerization conversion, water soluble polymer formation, particle size and size distribution, surface charge density and electrokinetic properties. Then the covalent grafting of maleic anhydride-alt-methyl vinyl ether (MAMVE) copolymer onto aminated latex particles was investigated. The most efficient conditions to obtain derivatised particles with no alteration of the colloidal stability were to control both polymer amount/latex particles concentration ratio and the mixing method of the two species. The charge inversion of the hydrolysed MAMVE functionalized particles was demonstrated by measuring the electrophoretic mobility as a function of pH. Finally, the covalent binding approach was implemented with peptide-MAMVE conjugates, confirming the great potential of this promising methodology for the preparation of reactive latex particles bearing peptides.     

Dielectric relaxation and AC conduction of an AgTlSe2 semiconductor in the solid and liquid states

Measurements of the dielectric properties of AgTlSe₂ in the solid and liquid states were carried out in a wide range of frequencies and temperatures. The material displayed dielectric dispersion, and a loss peak was observed. Cole-Cole diagrams have been used to determine the distribution parameter (a) and the molecular relaxation time (). The process of dielectric relaxation (loss) and ac conduction was attributed to the correlated barrier hopping model suggested by Elliott for amorphous solids, where two carriers simultaneously hop over a barrier between charged defectD ⁺ andD ^– states.     

The determination of thermodynamics of oxygen complexes of anions of sulfur dioxide and fluoronitrobenzenes using atmospheric pressure ionization mass spectrometry

The thermodynamic properties of oxygen complexes of the negative ions of 1-fluoro-2,4-dinitrobenzene (FDNB), 1,5-difluoro-2,4-dinitrobenzene (DFDNB), and sulfur dioxide have been determined by measuring the temperature dependence of the pertinent ion ratios by using a mass spectrometer equipped with a⁶³Ni atmospheric pressure ionization source. The values of -H° and -S°are SO ₂ ^–(O₂), 101 ± 2.1 kJ mole¹ and 121 ± 3.8 J/K-mole; FDNB^–(O₂), 51.5 ±3.4 kJ mole^–1 ± 9.2 J/K-mole; and DFDNB^–(O₂), 65.7 ± 0.4 kJ mole^–2 and 110 ± 5.0 J/K-mole.