Quantification of the Dissolved Inorganic Carbon Species and of the pH of Alkaline Solutions Exposed to CO₂ under Pressure: A Novel Approach by Raman Scattering

Dissolved inorganic carbon (DIC) content of aqueous systems is a key function of the pH, of the total alkanility (TA), and of the partial pressure of CO₂. However, common analytical techniques used to determine the DIC content in water are unable to operate under high CO₂ pressure. Here, we propose to use Raman spectroscopy as a novel alternative to discriminate and quantitatively monitor the three dissolved inorganic carbon species CO₂(aq), HCO₃^–, and CO₃^2– of alkaline solutions under high CO₂ pressure (from <i>P</i> = 0 to 250 bar at <i>T</i> = 40 °C). In addition, we demonstrate that the pH values can be extracted from the molalities of CO₂(aq) and HCO₃^–. The results are in very good agreement with those obtained from direct spectrophotometric measurements using colored indicators. This novel method presents the great advantage over high pressure conventional techniques of not using breakable electrodes or reference additives and appears of great interest especially in marine biogeochemistry, in carbon capture and storage and in material engineering under high CO₂ pressure

Concentration Mediated Structural Transition of Triblock Copolymer Ultrathin Films

X-ray reflectivity, atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle measurement techniques are used to study the structural changeover as a function of concentration of poly­(ethylene oxide)-poly­(propylene oxide)-poly­(ethylene oxide) (PEO-PPO-PEO) triblock copolymer diluted in toluene spin-coated as ultrathin films on hydrophilic Si substrate. A lamellar structure made of three alternating incomplete bilayers is observed until the concentration of copolymer solution attains a threshold value of about 3.6–4 g/L. Around this concentration and beyond, the entanglement of polymer chains takes place during drying and the growth of a homogeneous film made of complete bilayers on Si substrate is observed. The strong hydrophilic nature of the Si substrate dictates the growth of this amphiphilic copolymer. We evidence that the lower part of the films is made of hydrophilic PEO blocks attached to the substrate while the hydrophobic PPO blocks are directed toward air

Using Three-Dimensional 3D Grazing-Incidence Small-Angle X‑ray Scattering (GISAXS) Analysis To Probe Pore Deformation in Mesoporous Silica Films

In the past decade, remarkable progress has been made in studying nanoscale objects deposited on surfaces by grazing-incidence small-angle X-ray scattering (GISAXS). However, unravelling the structural properties of mesostructured thin films containing highly organized internal three-dimensional (3D) structures remains a challenging issue, because of the lack of efficient algorithms that allow prediction of the GISAXS intensity patterns. Previous attempts to calculate intensities have mostly been limited to cases of two-dimensional (2D) assemblies of nanoparticles at surfaces, or have been adapted to specific 3D cases. Here, we demonstrate that highly organized 3D mesoscale structures (for example, porous networks) can be modeled by the combined use of established crystallography formalism and the Distorted Wave Born Approximation (DWBA). Taking advantage of the near-zero intensity of symmetry-allowed Bragg reflections, the casual extinction or existence of certain reflections related to the anisotropy of the form factor of the pores can be used as a highly sensitive method to extract structural information. We employ this generic method to probe the slightly compressed anisotropic shape and orientation of pores in a mesoporous silica thin film having <i>P</i>6₃/<i>mmc</i> symmetry

Anisotropic One-Dimensional Aqueous Polymer Gel Electrolyte for Photoelectrochemical Devices: Improvement in Hydrophobic TiO₂–Dye/Electrolyte Interface

Aqueous photoelectrochemical devices have emerged recently as promising area because of their economic and ecological friendliness. In the present work, we have expedited surface active amphiphilic quasi-solid aqueous polymer gel electrolyte (PGE) with hydrophobic sensitizer SK3 in water-based dye sensitized solar cell (DSSC). PGE was prepared from amphiphilic block copolymer (PEO)–(PPO)–(PEO) with iodide–triiodide couple in pure aqueous media without any organic solvent. This block copolymer, with iodide-triiodide salt exhibits 1D-lamellar microcrystalline phase which shows stability in the temperature range of 25–50 °C. Parallel (||^al) and perpendicular (⊥^ar) alignment of anisotropic lamellar microcrystalline phase pertaining by PGE were characterized and applied in quasi-solid DSSC. Temperature dependency of ionic conductivity, triiodide diffusion, differential scanning calorimetry, viscosity, and 1-D lamellar anisotropic behavior were studied. Surface active effect of PGE at the hydrophobic dye sensitized photoanode was investigated and compared with liquid water based electrolyte. Because of the amphiphilic nature and thermoreversible sol–gel transition of PGE at a lower temperature (0 to −2 °C) allowing PGE to penetrate efficiently inside the hydrophobic surface of dye–TiO₂ and resulted in a fused contact between dye–TiO₂/PGE interface. This aqueous PGE successfully enhances the performance of DSSCs over liquid water based devices by improving their <i>V</i>_oc and stability. Under 0.5 sun illumination, DSSC with 1-D lamellar perpendicularly align PGE shows an efficiency of 2.8% and stability up to 1000 h at 50 °C

Nonionic Fluorinated Surfactant Removal from Mesoporous Film Using sc-CO₂

Surfactant templated silica thin films were self-assembled on solid substrates by dip-coating using a partially fluorinated surfactant R₈^F(EO)₉ as the liquid crystal template. The aim was 2-fold: first we checked which composition in the phase diagram was corresponding to a 2D rectangular highly ordered crystalline phase and second we exposed the films to sc-CO₂ to foster the removal of the surfactant. The films were characterized by in situ X-ray reflectivity (XRR) and grazing incidence small angle X-ray scattering (GISAXS) under CO₂ pressure from 0 to 100 bar at 34 °C. GISAXS patterns reveal the formation of a 2-D rectangular structure at a molar ratio R₈^F(EO)₉/Si equal to 0.1. R₈^F(EO)₉ micelles have a cylindrical shape, which have a core/shell structure ordered in a hexagonal system. The core contains the R₈^F part and the shell is a mixture of (EO)₉ embedded in the silica matrix. We further evidence that the extraction of the template using supercritical carbon dioxide can be successfully achieved. This can be attributed to both the low solubility parameter of the surfactants and the fluorine and ethylene oxide CO₂-philic groups. The initial 2D rectangular structure was well preserved after depressurization of the cell and removal of the surfactant. We attribute the very high stability of the rinsed film to the large value of the wall thickness relatively to the small pore size