Poly(<Emphasis Type="SmallCaps">d,l</Emphasis>-lactic acid) nanoparticle preparation and colloidal characterization

Nano size-ranged poly(d,l-lactic acid) (PLA) particles were obtained from 2 and 10 w% PLA solution in water-saturated ethyl acetate by the emulsification-diffusion method. An increase in the PLA solution concentration resulted in an increase of the particle mean size from ca 260 nm to 530 nm with a broadening of the distribution. After fractionation by centrifugation, the particle mean size was 980 nm. The Pluronic F68 used in the formulations at concentration ranging from 0.5 to 5% w/v, was shown to adsorb at the interface at 0.5 mg/m ² for both particle sizes. The molecular occupied area of 24 nm ²/molecule suggested an expanded conformation of the surfactant at the interface, though an incomplete coverage could not be excluded. Coagulation kinetics measurements revealed a critical coagulation concentration (CCC) of 1.5 M sodium chloride, indicating a steric stabilization of the colloids by the adsorbed triblock copolymer. Nonetheless, variations in zeta potential with increasing salt concentration were observed, suggesting that the surface carboxylate groups were still accessible for further modifications.     

Structure of adsorbed n-dodecyl-beta-D-maltoside layers on hematite

The composition, structure, and thickness of n-dodecyl-beta-D-maltoside self-assembled layers on hematite have been evaluated using infrared external reflection spectroscopy and spectral simulation techniques. From the qualitative and quantitative analysis of the reflection spectra of the same sample recorded at different specific angles of incidence and two polarizations, the orientation of the sugar ring and hydrocarbon chain were obtained. Both of these molecular groups are positioned parallel to hematite surface, the adsorbed molecules being at low (2.2-nm-thick layer) as well as higher (11-nm) coverages. The maltoside is adsorbed through interaction of sugar ring OH groups with hematite surface hydroxyl groups. The adsorption of maltoside is not very strong and desorption takes place easily from acidic and low-basic solutions but with more difficulty from strong-basic solution.     

Sorption of uranium (VI) species on zircon: structural investigation of the solid/solution interface

This work is an investigation of the mechanisms of interaction between uranium (VI) ions and zirconium silicate. The speciation of uranium (VI) sorbed on zircon was studied using four complementary techniques as probes of the local structure around the uranium atom: laser spectrofluorimetry, X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier-transformed (DRIFT) spectroscopy, and EXAFS spectroscopy. The sorption of uranyl on zirconium oxide was also studied to allow structural comparisons. Spectrofluorimetry and XPS results allowed an identification of the silicate sorption sites on the solid. These methods associated with spectrofluorimetry and DRIFT led to a characterization of the sorbed surface complexes, taking into account the influence of the nature of the background salt and of the pH on the structure of the U(VI) surface species. EXAFS measurements, either on air-dried samples or in situ, were then carried out on well-characterized samples and allowed identification of the sorption mechanism on zircon as the formation of an inner-sphere polydentate surface complex.     

Electrical properties of the AgTlSe2 semiconductor in the liquid state

The electrical conductivity and thermoelectric power of AgTlSe₂ have been investigated as a function of temperature from 390° C up to 590° C. The experimental data are analyzed in terms of a model developed for the density of states and electrical transport in solid amorphous semiconductors [12]. Positive thermoelectric power suggests a large predominance of holes in electrical conduction. It appears that the conduction is due to holes in localized states near the band edge.     

Adsorption of oligonucleotides on PMMA/PNIPAM core-shell latexes: polarity of the PNIPAM shell probed by fluorescence

The adsorption of a rhodamine X labeled oligonucleotide composed of 25-mers of thymine (dT(25)-ROX) onto the thermosensitive shell of PMMA/PNIPAM core-shell latex particles was studied at 22 and 40 degrees C, below and above the T(VPT) (volume phase transition temperature) of the PNIPAM shell, respectively. The experimental binding isotherms were well fitted with the cooperative Hill model. The Hill coefficient is lower than 1 at both temperatures showing that the adsorption is anticooperative. The polarity of the shell was probed by both the lifetimes and solvatochromic shifts of the zwitterionic form of rhodamine X. For temperatures below the shell T(VPT) has a polarity similar to that of water, while for temperatures above the transition the polarity is equivalent to that of a water/dioxane mixture with 30% (v/v) water.     

Impact of defects on the surface chemistry of ZnO(0001 macro)-O

Scanning tunneling microscopy and core level photoelectron spectroscopy measurements have been used to investigate the morphology of ZnO(0001 macro)-O, and its reactivity with carbon monoxide and carbon dioxide, as a function of surface preparation. Real space images of the surface indicate that increasing the substrate anneal temperature during preparation significantly reduces the surface step density. Surface defect concentration is also monitored by employing formic acid as a chemical probe, which is shown to adsorb dissociatively (HCOOH --> [HCOO](-) + H(+)) only on zinc cations at step edges. Carbon 1s X-ray photoelectron spectra show that carbon monoxide and carbon dioxide both react to form surface carbonate species. Spectra, recorded both as a function of surface preparation and following coadsorption, demonstrate that the carbonate formed from either reactant molecule is located at oxygen vacancies at step edges, evidencing the significant role that defects can play in the surface chemistry of ZnO(0001 macro)-O.     

The influence of the structure of thin antimony films on their electrical conductivity

The eletrical conductivity of antimony films of different thicknesses was studied at different temperatures. For small thicknessd, whereL is the electron mean-free path, the film resistances varies asd ^?n , wheren=2. However, ford?L the value ofn becomes smaller than 2 which is in agreement with the theory.     

Catalyzed Autoxidation of Hydrogensulfite by Cobalt(II) (2,3,9,10-tetramethyl-1,4,8,11-tetraaza-cyclotetradeca-1,3,8,10-tetraene) (H 2 O) 2 2+

The catalytic autoxidation of hydrogensulfite (hydrogentrioxosulfate(1-)) in the presence of Co(tim)(H 2 O) 2 2+ (tim=2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) was studied. Dioxygen reacts with excess sulfite in the presence of Co(tim)(H 2 O) 2 2+ in a complex process (a minimum of five kinetic steps can be identified) to produce Co(tim)(SO 3 ) x (3 m 2 x )+ ( x =1 or 2) ( u max at 350 nm) and sulfate. Seventy turnovers over 4 h were attained in a system where dioxygen and sulfite were supplied constantly. The Co(III) product formed reacts only slowly with dioxygen to produce sulfate. A mechanistic analysis of the results implies the involvement of a Co(tim)-dioxygen adduct, stabilized by an axial sulfite ligand.