Nanosecond laser ablation and deposition of silver,copper, zinc and tin

Nanosecond pulsed laser deposition of different metals (Ag, Cu, Sn, Zn) has been studied in high vacuum at a laser wavelength of 355 nm and pulse length of 6 ns. The deposition rate is roughly similar for Sn, Cu and Ag, which have comparable cohesive energies, and much higher for the deposition of Zn which has a low cohesive energy. The deposition rate for all metals is strongly correlated with the total ablation yield, i.e., the total mass ablated per pulse, reported in the literature except for Sn, for which the deposition rate is low, but the total ablation yield is high. This may be explained by the continuous erosion by nanoparticles during deposition of the Sn films which appear to have a much rougher surface than those of the other metals studied in the present work.     

Comparative rheological study of ionic semi-IPN composite hydrogels based on polyacrylamide and dextran sulphate and of polyacrylamide hydrogels

Ionic semi-interpenetrating polymer networks composite hydrogels were synthesized by free-radical polymerization using dextran sulphate (DxS), acrylamide as monomer and N,N′-methylene(bis)acrylamide as cross-linking agent. The viscoelastic properties of these composite hydrogels were investigated by oscillatory shear measurements under small deformation conditions comparative with those of polyacrylamide gels. Changes of the rheological properties of composite hydrogels have been studied in terms of polymerization temperature, cross-linker ratio, initial monomer concentration and molar mass of DxS. The results showed that the stability of the composite hydrogels obtained at room temperature (22?°C) was relatively low because the storage modulus (G′) was only eight times higher than the loss modulus (G″), while for those obtained by cryopolymerization (?18?°C), the stability was improved, the G′ values being about 30 times higher than those of G″. This behaviour indicated that, by conducting the synthesis of hydrogels below the freezing point of the reaction solutions, an enhancement of the hydrogels elasticity was achieved. The network parameters, i.e. the average molecular weight between two cross-links and the cross-link density of the composite hydrogels prepared at ?18?°C, were estimated from rheological data.     

Dynamics of Water Near Oxidized Polystyrene Films

Atomistic MD simulations of water in the vicinity of oxidized amorphous atactic polystyrene are presented. The changes in the orientational and translational dynamics of water near polymer surfaces with different hydrophilicity are studied. Two main orientational relaxation processes of water molecules are distinguished: a process on a fs timescale, associated with the ballistic motion of water molecules, and a process on a ps timescale, associated with the self‐diffusion of water. The fast process is not affected by the presence of the polymeric surface. The second relaxation process differs at the interface from that in the bulk in that the dynamics of water molecules is more heterogeneous in the first. The effect of the representation of polystyrene films on the water dynamics is discussed.

     

Synthesis of Coenzyme Q<Subscript>10</Subscript> and β-carotene by Yeasts Isolated from Antarctic Soil and Lichen in Response to Ultraviolet and Visible Radiations

The effect of different doses of visible (Vis), ultraviolet-А (UVA), and mixed light (UVA + Vis) upon coenzyme Q₁₀ (CoQ₁₀) and β-carotene synthesis and biomass yield by the Sporobolomyces salmonicolor AL₁, Cryptococcus albidus AS₅₅, Cryptococcus laurentii AS₅₆, and C. laurentii AS₅₈ strains isolated from Antarctic samples was investigated. The β-carotene concentration in the red strain biomass increased by 52% under irradiation with 11 J/cm² Vis, and the CoQ₁₀ concentration rose by 37% in relation to the control quantity obtained through dark cultivation. Under irradiation with 6 J/cm² UVA, the S. salmonicolor AL₁ strain synthesized 15% more β-carotene; C. albidus AS₅₅, 22%; C. laurentii AS₅₆, 44%; and C. laurentii AS₅₈, 35% in relation to the control quantity. Irradiation with a low UVА + Vis dose significantly stimulated β-carotene biosynthesis by the strains of the Cryptococcus genus (87%, 138%, and 100%), whereas S. salmonicolor AL₁ increased the β-carotene content to a smaller degree (55%). Higher doses of all three irradiation types inhibited β-carotene accumulation. Vis suppressed CoQ₁₀ biosynthesis in the Cryptococcus strains, whereas UVА and UVА + Vis inhibited it in all four strains. The S. salmonicolor AL₁ strain pre-treated with 0.02 J/cm² UVA synthesized twice as much CoQ₁₀ and β-carotene when cultivated in the presence of Vis light in an 11-J/cm² dose.     

Morphological and electrical characteristics of amino acid–AuNP nanostructured two-dimensional ensembles

The interaction between amino acids (l-cysteine, l-lysine) and gold nanoparticle layers deposited on ITO glasses was investigated. The citrate capped gold nanoparticles (AuNP) were first deposited as a thin layer onto silanized ITO and subsequently linked with an amino acid, due to strong affinity of thiol and amine groups to gold. The gold nanoparticles had an elliptical shape, with size varying between 7 and 14 nm, as indicated by TEM analysis. After deposition on ITO substrate, the nanoparticles self-assembled into large aggregates with poor contact between, as revealed by AFM. After linking l-cysteine or l-lysine to the surface of nanoparticles layer, a change in morphology occured. A better contact between the gold aggregates boundary developed, which improved the conducting properties of the nanostructured layer. The electrical resistance of the AuNPs layer, obtained from I–V measurements, was very high (2.8 × 10¹³ Ω) and slightly decreased after linking the NPs with amino acids.     

New Polymeric Adsorbents Functionalized with Aminobenzoic Groups for the Removal of Residual Antibiotics

In this paper, we present the synthesis of new polymeric adsorbents derived from macroporous chloromethylated styrene–divinylbenzene (DVB) copolymers with different cross-linking degrees functionalized with the following aminobenzoic groups: styrene—6.7% DVB (PAB1), styrene—10% DVB (PAB2), and styrene—15% DVB (PAB3). The new polymeric products, PAB1, PAB2, and PAB3, were characterized by FTIR spectroscopy, thermogravimetric analysis, and EDX, SEM, and BET analysis, respectively. The evolution of the functionalization reaction was followed by FTIR spectroscopy, which revealed a decrease in the intensity of the γCH₂Cl band at 1260 cm⁻¹, and, simultaneously, the appearance of C=O carboxylic bands from 1685–1695 cm⁻¹ and at 1748 cm⁻¹. The thermal stability increased with the increase in the cross-linking degree. The data obtained from the EDX analysis of the novel cross-linked copolymers confirmed the functionalization with aminobenzoic groups through the presence and content of nitrogen, as follows: PAB1: N% = 0.47; PAB2: N% = 0.85; and PAB3: N% = 1.30. The adsorption performances of the novel polymeric adsorbents, PAB1, PAB2, and PAB3, were tested in the adsorption of three antibiotics, tetracycline, sulfamethoxazole, and amoxicillin, from aqueous solutions, by using extensive kinetic, equilibrium, and thermodynamic studies. The best adsorption capacity was demonstrated by the tetracycline. Amoxicillin adsorption was also attempted, but it did not show positive results.     

Nonstoichiometric interpolyelectrolyte complexes as colloidal dispersions based on NaPAMPS and their interaction with colloidal silica particles

Preparation and characterization of some nonstoichiometric interpolyelectrolyte complexes (NIPECs) as stable colloidal dispersions by the interaction between poly(sodium 2-acrylamido-2-methylpropanesulfonate) (NaPAMPS) and three strong polycations bearing quaternary ammonium salt centres in the backbone, poly(diallyldimethylammonium chloride) (PDADMAC) and two polycations containing N,N-dimethyl-2-hydroxypropyleneammonium chloride units (PCA₅ and PCA₅D₁), have been followed in this study as a function of the polycation structure and polyelectrolyte concentration. Complex characteristics were followed by polyelectrolyte titration, turbidity and quasi-ellastic light scattering. Almost monodisperse NIPECs nanoparticles with a good storage stability were prepared when total concentration of polyelectrolyte was varied in the range 0.85-6.35 mmol/L, at a ratio between charges (n⁻/n⁺) of 0.7. NIPECs as a new kind of flocculants were used to flocculate a stable monodisperse silica suspension. The main advantage of NIPECs as flocculants is the broad flocculation window, which is a very important aspect for industrial applications.