Water-Polymer Slide Electrification in Polyethylene Films Coated with Amphiphilic Compounds and Its Connection to Surface Properties Dependent on Water-Polymer Interactions.

Slide electrification experiments were performed on low-density polyethylene films (PE) and PE sprayed with five amphiphilic compounds, including antistatic and slip additives. Drops of aqueous solutions were delivered on the films and after sliding spontaneously acquired a net electrical charge (Qdrop), which is dependent on the pH and ionic strength. The slide electrification was detected in pristine PE films and those with five additives. An acid-base equilibrium model, based on the adsorption of hydroxides and protons on surface sites, accounted for the dependence of Qdrop on pH, allowing recovery of the acid-base equilibrium constants and the density of adsorption sites. The model was modified to account for ionic strength effects through activity factors. The surface conductivity, wettability, and friction coefficients were strongly modified by the additives. However, the observed trends are different from those observed in slide electrification, which better correlated with zeta potential determinations. This suggests that the interaction mechanisms among surface water, the considered additives, and the polymer, which are involved in slide electrification and the generation of zeta potential, are different from those associated with other surface processes involving surface water. Although additives are required for changing surface resistivity, friction coefficients, and wettability, the generation of sliding electrical charges in polyethylene is a spontaneous and highly effective process. For one specific additive, a simultaneous decrease in friction coefficients, zeta potential, and Qdrop was observed, assigned to the blockade of hydroxide adsorption sites and water repulsion by the compound.

Liquid-polymer triboelectricity: chemical mechanisms in the contact electrification process.

Liquid-polymer contact electrification between sliding water drops and the surface of polytetrafluoroethylene (PTFE) was studied as a function of the pH and ionic strength of the drop as well as ambient relative humidity (RH). The PTFE surface was characterized by using SEM, water-contact-angle measurements, FTIR spectroscopy, XPS, and Raman spectroscopy. The charge acquired by the drops was calculated by detecting the transient voltage induced on a specifically designed capacitive sensor. It is shown that water drops become positively charged at pH > pHzch (pHzch being the zero charge point of the polymer) while they become negatively charged for pH < pHzch. The addition of non-hydrolysable salts (NaCl or CaCl2) to water decreases the electrical charge induced in the drop. The charge also decreases with increasing RH. These results suggest proton or hydroxyl transfer from the liquid to the hydrophobic polymer surface. A proposed thermodynamic model for the ion transfer process allows explaining the observed effects of RH, pH and ionic strength.

Formation of HCO+ and HCS+ Ions in the Photodissociation of CH3OC(S)SCH3 under VUV Synchrotron Radiation.

Synchrotron-based total ion yield and photoelectron-photoion-coincidence spectra have been applied to investigate the electronic structure and the dissociative ionization of gaseous O,S-dimethyl xanthate, CH3OC(S)SCH3, in the shallow-core S 2p region. The spectral assignment and the electronic structure are interpreted in terms of the most stable synperiplanar conformer in the Cs symmetry point group. The use of tunable synchrotron radiation allows for a selective excitation of sulfur atoms at different photon energy values, including resonance transitions and ionization around the S 2p level. The fragmentation patterns show that the title molecule is well suited as a laboratory precursor of ionic species found in the interstellar medium, especially formyl and thioformyl cations, HCO+ and HCS+, respectively.

The Structure and Conformation of (CH3 )3 CSNO.

The gas-phase molecular structure of (CH3 )3 CSNO was investigated by using electron diffraction, allowing the first experimental geometrical parameters for an S-nitrosothiol species to be elucidated. Depending on the orientation of the -SNO group, two conformers (anti and syn) are identified in the vapor of (CH3 )3 CSNO at room temperature, the syn conformer being less abundant. The conformational landscape is further scrutinized by using vibrational spectroscopy techniques, including gas-phase and matrix-isolation IR spectroscopy, resulting in a contribution of ca. 80:20 for the anti:syn abundance ratio, in good agreement with the computed value at the MP2(full)/cc-pVTZ level of approximation. The UV/Vis and resonance Raman spectra also show the occurrence of the conformational equilibrium in the liquid phase, with a moderate post-resonance Raman signature associated with the 350 nm electronic absorption.

Conformational properties of ethyl- and 2,2,2-trifluoroethyl thionitrites, (CX3CH2SNO, X = H and F).

The simple 2,2,2-trifluoroethyl thionitrite molecule, CF3CH2SNO, has been prepared in good yield for the first time using CF3CH2SH and NOCl in slight excess. The vapor pressure of the red-brown compound CF3CH2SNO follows, in the temperature range between 226 and 268 K, the equation log p = 12.0-3881/T (p/bar, T/K), and its extrapolated boiling point reaches 51 °C. Its structural and conformational properties have been compared with the ethyl thionitrite analogue, CH3CH2SNO. The FTIR spectra of the vapor of both thionitrites show the presence of bands with well-defined contours, allowing for a detailed conformational analysis and vibrational assignment on the basis of a normal coordinate analysis. The conformational space of both thionitrite derivatives has also been studied by using the DFT and MP2(full) level of theory with extended basis sets [6-311+G(2df) and cc-pVTZ]. The overall evaluation of the experimental and theoretical results suggests the existence of a mixture of two conformers at room temperature. The relative abundance of the most stable syn form (N═O double bond syn with respect to the C-S single bond) has been estimated to be ca. 79 and 75% for CF3CH2SNO and CH3CH2SNO, respectively.

Immobilization of alkyl-pterin photosensitizer on silicon surfaces through in situ SN2 reaction as suitable approach for photodynamic inactivation of Staphylococcus aureus.

The tuning of surface properties through functionalization is an important field of research with a broad spectrum of applications. Self-assembled monolayers (SAMs) allow the surface tailoring through the adsorption of molecular layers having the appropriate functional group or precursor group enabling in situ chemical reactions and thus to the incorporation of new functionalities. The latter approach is particularly advantageous when the incorporation of huge groups is needed. In this study, we report the immobilization of pterin moieties on 11-bromoundecyltrichlorosilane-modified silicon substrates based on the in situ replacement of the bromine groups by pterin (Ptr), the parent derivative of pterins, by means of a nucleophilic substitution reaction. The modified surface was structurally characterized through a multi-technique approach, including high-resolution XPS analysis, contact angle measurements, and AFM. The designed synthesis method leads to the functionalization of the silicon surface with two compounds, O-undecyl-Ptr and N-undecyl-Ptr, with a higher proportion of the N-derivative (1:8 ratio). The alkyl-pterins immobilized via the proposed strategy, retain their photochemical properties, being able to inhibit Staphylococcus aureus growth under irradiation (84.3 ± 15.6 % reduction in viable cells). Our results open the possibility for the modification of several materials, such as glass and metal, through the formation of SAMs having the proper head group, thus allowing the design of photosensitive surfaces with potential microbiological self-cleaning properties.

Fluorescent silica nanoparticles with chemically reactive surface: Controlling spatial distribution in one-step synthesis.

The encapsulation of fluorescent dyes inside silica nanoparticles is advantageous to improve their quality as probes. Inside the particle, the fluorophore is protected from the external conditions and its main emission parameters remains unchanged even in the presence of quenchers. On the other hand, the amine-functionalized nanoparticle surface enables a wide range of applications, as amino groups could be easily linked with different biomolecules for targeting purposes. This kind of nanoparticle is regularly synthesized by methods that employ templates, additional nanoparticle formation or multiple pathway process. However, a one-step synthesis will be an efficient approach in this sort of bifunctional hybrid nanoparticles. A co-condensation sol-gel synthesis of hybrid fluorescent silica nanoparticle where developed. The chemical and morphological characterization of the particles where investigated by DRIFTS, XPS, SEM and SAXS. The nanoparticle fluorescent properties were also assessed by excitation-emission matrices and time resolved experiments. We have developed a one-pot synthesis method that enables the simultaneous incorporation of functionalities, the fluorescent molecule and the amino group, by controlling co-condensation process. An exhaustive characterization allows the definition of the spatial distribution of the fluorescent probe, fluorescein isothiocyanate, inside the particle and reactive amino groups on the surface of the nanoparticle with diameter about 100nm.