5 research outputs found
Quantification of the Dissolved Inorganic Carbon Species and of the pH of Alkaline Solutions Exposed to CO<sub>2</sub> 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 CO<sub>2</sub>. However, common analytical techniques
used to determine the DIC content in water are unable to operate under
high CO<sub>2</sub> pressure. Here, we propose to use Raman spectroscopy
as a novel alternative to discriminate and quantitatively monitor
the three dissolved inorganic carbon species CO<sub>2</sub>(aq), HCO<sub>3</sub><sup>â</sup>, and CO<sub>3</sub><sup>2â</sup> of alkaline solutions under high CO<sub>2</sub> 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 CO<sub>2</sub>(aq) and HCO<sub>3</sub><sup>â</sup>. 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
CO<sub>2</sub> 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
polyÂ(ethylene oxide)-polyÂ(propylene oxide)-polyÂ(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 3.6â4 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 Xâray 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>6<sub>3</sub>/<i>mmc</i> symmetry
Anisotropic One-Dimensional Aqueous Polymer Gel Electrolyte for Photoelectrochemical Devices: Improvement in Hydrophobic TiO<sub>2</sub>âDye/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)â(PPO)â(PEO) with iodideâtriiodide
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 25â50
°C. Parallel (||<sup>al</sup>) and perpendicular (â„<sup>ar</sup>) 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
solâgel transition of PGE at a lower temperature (0 to â2
°C) allowing PGE to penetrate efficiently inside the hydrophobic
surface of dyeâTiO<sub>2</sub> and resulted in a fused contact
between dyeâTiO<sub>2</sub>/PGE interface. This aqueous PGE
successfully enhances the performance of DSSCs over liquid water based
devices by improving their <i>V</i><sub>oc</sub> 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-CO<sub>2</sub>
Surfactant templated
silica thin films were self-assembled on solid
substrates by dip-coating using a partially fluorinated surfactant
R<sub>8</sub><sup>F</sup>(EO)<sub>9</sub> 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-CO<sub>2</sub> 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 CO<sub>2</sub> pressure from 0 to 100 bar at 34 °C. GISAXS
patterns reveal the formation of a 2-D rectangular structure at a
molar ratio R<sub>8</sub><sup>F</sup>(EO)<sub>9</sub>/Si equal to 0.1. R<sub>8</sub><sup>F</sup>(EO)<sub>9</sub> micelles have a cylindrical
shape, which have a core/shell structure ordered in a hexagonal system.
The core contains the R<sub>8</sub><sup>F</sup> part and the shell is a mixture of (EO)<sub>9</sub> 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 CO<sub>2</sub>-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