Thomas Beuvier

Synthesis of hollow vaterite CaCO3 microspheres in supercritical carbon dioxide medium

We here describe a rapid method for synthesizing hollow core, porous crystalline calcium carbonate microspheres composed of vaterite using supercritical carbon dioxide in aqueous media, without surfactants. We show that the reaction in alkaline media rapidly conducts to the formation of microspheres with an average diameter of 5 µm. SEM, TEM and AFM observations reveal that the microspheres have a hollow core of around 0.7 µm width and are composed of nanograins with an average diameter of 40 nm. These nanograins are responsible for the high specific surface area of 16 m2 g−1 deduced from nitrogen absorption/desorption isotherms, which moreover confers an important porosity to the microspheres. We believe this work may pave the way for the elaboration of a biomaterial with a large potential for therapeutic as well as diagnostic applications.

Densification and Depression in Glass Transition Temperature in Polystyrene Thin Films

Ellipsometry and X-ray reflectivity were used to characterize the mass density and the glass transition temperature of supported polystyrene (PS) thin films as a function of their thickness. By measuring the critical wave vector (qc) on the plateau of total external reflection, we evidence that PS films get denser in a confined state when the film thickness is below 50 nm. Refractive indices (n) and electron density profiles measurements confirm this statement. The density of a 6 nm (0.4 gyration radius, Rg) thick film is 30% greater than that of a 150 nm (10Rg) film. A depression of 25 °C in glass transition temperature (Tg) was revealed as the film thickness is reduced. In the context of the free volume theory, this result seems to be in apparent contradiction with the fact that thinner films are denser. However, as the thermal expansion of thinner films is found to be greater than the one of thicker films, the increase in free volume is larger for thin films when temperature is raised. Therefore, the free volume reaches a critical value at a lower Tg for thinner films. This critical value corresponds to the onset of large cooperative movements of polymer chains. The link between the densification of ultrathin films and the drop in their Tg is thus reconciled. We finally show that at their respective Tg(h) all films exhibit a critical mass density of about 1.05 g/cm(3) whatever their thickness. The thickness dependent thermal expansion related to the free volume is consequently a key factor to understand the drop in the Tg of ultrathin films.

Stability of Polymer Ultrathin Films (<7 nm) Made by a Top-Down Approach

In polymer physics, the dewetting of spin-coated polystyrene ultrathin films on silicon remains mysterious. By adopting a simple top-down method based on good solvent rinsing, we are able to prepare flat polystyrene films with a controlled thickness ranging from 1.3 to 7.0 nm. Their stability was scrutinized after a classical annealing procedure above the glass transition temperature. Films were found to be stable on oxide-free silicon irrespective of film thickness, while they were unstable (<2.9 nm) and metastable (>2.9 nm) on 2 nm oxide-covered silicon substrates. The Lifshitz-van der Waals intermolecular theory that predicts the domains of stability as a function of the film thickness and of the substrate nature is now fully reconciled with our experimental observations. We surmise that this reconciliation is due to the good solvent rinsing procedure that removes the residual stress and/or the density variation of the polystyrene films inhibiting thermodynamically the dewetting on oxide-free silicon.

Synthesis and characterization of CaCO3–biopolymer hybrid nanoporous microparticles for controlled release of doxorubicin

Doxorubicin (Dox) is a hydrophilic drug extensively used for treatment of breast, lung, and ovarian cancer, among others; it is highly toxic and can cause serious side effects on nontargeted tissues. We developed and studied a hybrid nanoporous microparticle (hNP) carrier based on calcium carbonate and biopolymers derivatized with folic acid (FA) and containing Dox as a chemotherapeutic drug model. The hNPs were characterized by X-ray diffraction, and Raman and Fourier transform infrared (FTIR) spectroscopies. The X-ray diffraction patterns of calcium carbonate particles showed about 30-70% vaterite-calcite polymorphisms and up to 95% vaterite, depending on the absence or the presence of biopolymers as well as their type. Scanning electron microcopy images revealed that all types of hNPs were approximately spherical and porous with average diameter 1-5 μm, and smaller than CaCO3 microparticles. The presence of biopolymers in the matrices was confirmed after derivatization with a fluorescein isothiocyanate probe by means of confocal microscopy and FTIR synchrotron beamline analysis. In addition, the coupling of lambda carrageenan (λ-Car) to FA in the microparticles (FA-λ-Car-hNPs) increased the cancer-cell targeting and also extended the specific surface area by up to ninefold (26.6 m2 g(-1)), as determined by the Brunauer-Emmett-Teller isotherm. A nanostructured porous surface was found in all instances, and the FA-λ-Car-hNP pore size was about 30 nm, as calculated by means of the Barrett-Joyner-Halenda adsorption average. The test of FA-λ-Car-hNP anticancer activity on human osteosarcoma MG-63 cell line showed cell viabilities of 13% and 100% with and without Dox, respectively, as determined by crystal violet staining after 24 h of incubation.

Small‐angle X‐ray scattering analysis of porous powders of CaCO3

The results of small-angle and ultra-small-angle X-ray scattering on porous CaCO3 microparticles of pulverulent vaterite made by a conventional chemical route and by using supercritical CO2 are presented. The scattering curves are analysed in the framework of the Guinier–Porod model, which gives the radii of gyration of the scattering objects and their fractal dimension. In addition, the porosity and the specific surface area are determined by using the Porod invariant, which is modified to take into account the effective thickness of the pellet. The results of this analysis are compared with those obtained by nitrogen adsorption.

Lysozyme encapsulation into nanostructured CaCO3 microparticles using a supercritical CO2 process and comparison with the normal route

The aim of the present work was to assess the merits of supercritical CO2 (SC-CO2) as a process for protein encapsulation into calcium carbonate microparticles. Lysozyme, chosen as a model protein, was entrapped during CaCO3 precipitation in two different media: water (normal route) and SC-CO2. The particles were characterized and compared in terms of size, zeta potential, morphology by SEM, crystal polymorph and lysozyme encapsulation. Fluorescent and confocal images suggested the encapsulation and core-shell distribution of lysozyme into CaCO3 obtained by the SC-CO2 process. A high encapsulation efficiency was reached by a supercritical CO2 process (50%) as confirmed by the increased zeta potential value, lysozyme quantification by HPLC and a specific bioassay (M. lysodeikticus). Conversely, lysozyme was scarcely entrapped by the normal route (2%). Thus, supercritical CO2 appears to be an effective process for protein encapsulation within nanostructured CaCO3 particles. Moreover, this process may be used for encapsulation of a wide range of macromolecules and bioactive substances.

Swelling of Poly(n-butyl methacrylate) Films Exposed to Supercritical Carbon Dioxide: A Comparative Study with Polystyrene

We report here the swelling and relaxation properties of confined poly(n-butyl methacrylate) (PBMA) films having thicknesses of less than 70 nm under supercritical carbon dioxide (scCO2) using the X-ray reflectivity technique. Swellability is found to be dominant in thinner films compared to thicker ones as a consequence of the confinement-induced densification of the former. Swellability is proportionately increased with the density of the film. PBMA films exhibit a more significant swelling than do PS films, and their differences become more prominent with the increase in film thickness. A comparison between the results obtained for polystyrene (PS) and PBMA ultrathin films reveals that the swellability is dependent upon the specific intermolecular interaction between CO2 and the chemical groups available in the polymers. Owing to strong Lewis acid-base interactions with scCO2 and the lower glass-transition temperature (bulk Tg ≈ 29 °C), PBMA films exhibit a greater amount of swelling than do PS films (bulk Tg ≈ 100 °C). Though they reach to the different swollen state upon exposition, identical relaxation behavior as a function of aging time is evidenced. This unprecedented behavior can be ascribed to the strong bonding between trapped CO2 and PBMA that probably impedes the release of CO2 molecules from the swollen PBMA films manifested in suppressed relaxation.

Role of a phenothiazine/phenoxazine donor in solid ionic conductors for efficient solid state dye sensitized solar cells

Efficient electron donors, phenothiazine (PTZ)/phenoxazine (POZ) substituted imidazolium (IMI) and benzimidazolium (BIMI) iodide solid organic ionic conductors (SOICs) possessing good thermal stability and high conductivity are synthesized. The high conductivity arises due to the presence of the effective electron donor moiety PTZ/POZ and hence, these SOICs were used as single component solid electrolytes in solid state dye sensitized solar cells (ss-DSSCs). The ss-DSSC devices operate proficiently without any post-treatment to dye loaded TiO2 and additives in the electrolyte matrix. The presence of unsaturation and hetero-atoms in PTZ/POZ is responsible for the hole mobility and enhancement in light harvesting properties. Hence, when SOICs were excited along with a metal-free sensitizer, SK 1,the higher LUMO levels of SOICs increased the total electron injection in the TiO2 interface with the electrons of SK 1. Under illumination of solar light (100 mW cm−2 with an AM1.5G filter), ss-DSSCs with POZ substituted IMI and BIMI as single component solid electrolytes showed power conversion efficiency (PCE) of about 5.7%, which is quite comparable with the conventional imidazolium/benzimidazolium salt based liquid electrolytes and SK 1 sensitizer. The ss-DSSC devices with all four SOICs exhibit good long-term stability (∼1000 h) under 1 sun illumination and ambient humidity conditions. The present report paves the way for the development of single component solid organic ionic conductors having high electronic conductivity and better light harvesting ability as well as thermal stability.

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 P = 0 to 250 bar at T = 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.

Radiolytic Conversion of Platinum, Rhodium, Osmium and Palladium Salts into Metal Coatings and Metal Nanoparticles

Email: *tmadima@yahoo.com, **alain.gibaud@univ-lemans.fr We herein report on the effect of gamma ray radiation on platinum, osmium, rhodium and palladium salt solutions for synthesis of nanoparticles. Pt, Os, Rh and Pd salt solutions were exposed to intense gamma ray irradiation with doses varying from 70 to 120 kGy. The metal ion salt solutions were easily converted into metal nanoparticles using this radiolysis method. The radiolytic conversion effect produced metal nanoparticles suspended in solution. For Pt, Pd and Rh a metal coating on the edges of the polypropylene tube used as a container was unexpectedly observed but not for the Os solution. X-Ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) analyses confirmed that both the coating and the metal nanoparticles correspond to the pure metal coming from the reduction of the initial salt. Quantitative analysis of the XRD patterns shows information about the size and stress of the converted metals. The production of a metal coating on polypropylene plastic tubes by gamma ray irradiation presents an interesting alternative to conventional techniques of metal deposition especially for coating the inner part of a tube.