18 research outputs found
Influence of thermal and optical properties on the visibility of liquid-crystal phase transitions in photoacoustic spectroscopy
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Caging interactions between a dopant chromophore and the solâgel matrix
The successful incorporation of chromophores in a solâgel matrix requires a careful study of their interaction with the gel environment. Photoacoustic spectroscopy is used to probe chemical changes in the direct neighborhood of dopant molecules in a silica-based solâgel during times of evolution up to 100 times the gelation time. Studies of different chromophores such as ÎČ-carotene (ÎČ-Car.) and copper phthalocyanine (Cu-Pht.) show a size dependent steric hindrance effect as well as chromophore relaxation phenomena within the gel pores. Three main phases of evolution of the medium are distinguished. The stability of the chromophores is discussed and the results compared to FTIR spectra over time
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A SunscreenâTanning Compromise: 3D Visualization of the Actions of Titanium Dioxide Particles and Dihydroxyacetone on Human Epiderm
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Hydrolysis/Condensation Reactions at the SolâGel/Air Interface:â Pure Titania Alkoxide Exposed to AirâWater Molecules
Solâgel alkoxides are very often sensitive to the surrounding air humidity, especially when the chemical evolution of the sol is operating at time scales comparable to the water-molecule diffusion from the surrounding air inside the medium and their interaction with the alkoxide molecules. The present study reports the in situ observation and interpretation of hydrolysis/condensation reactions occurring within the surface layers of pure titanium(IV) butoxide exposed to air, which illustrates the interest of the methodology for studies of near-surface chemistry in sol gel evolutions and thin films
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Visualisierung von OberflĂ€chengelierungen bei einem dotierten SolâGelâGlas
Gepulste Photoakustikspektroskopie ermöglichte tiefenaufgelöste InâsituâUntersuchungen der chemischen VerĂ€nderungen, die bei SolâGelâProzessen auftreten. Unter Verwendung von ÎČâCarotin als SondenmolekĂŒl, das zur Bestimmung der Effizienz der WĂ€rmeĂŒbertragung auf die unmittelbare molekulare Umgebung in dĂŒnnen und dicken Filmen genutzt wurde, lieĂen sich OberflĂ€chengelierungen und Gelierungen im Inneren von SolâGelâMaterialien verfolgen
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Direct Evidence of the LiquidâSolid Transition of a SolâGel Material Using Photoacoustic Spectroscopy
The gelation process of a solâgel material is monitored for the first time in a detailed manner by use of a photoacoustic spectroscopy derived methodology. Measurements of the acoustic response spectrum of a solâgel material during the transition permits a clear monitoring of the solâgel evolution as well before macroscopic gelation as afterward. Different phases are inferred corresponding to the three first proceeding steps of the material formation
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A comparative study on chromophore diffusion inside porous filters by pulsed photoacoustic spectroscopy
In the context of investigations on drug diffusion into human skin, first examples of using porous filters as model bio-membranes to understand the role of physical and chemical parameters on the penetration of chromophores. The diffusion of small molecules has been investigated in porous filters of different pore sizes by using pulsed photoacoustic spectroscopy. An analogy is made between the model membranes and human skin concerning the influence of the filter structure and the hydrophilic nature of the matrix support material. Finally, first data are presented on the effect of a modified surface filter structure on the diffusion pattern, thus opening the field to the potential use of these filters as model membrane of adjustable structural and chemical parameters
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Visualization of Surface Gelation Processes in a Doped Sol-Gel Glass
Hydrolysis/Condensation Reactions at the SolâGel/Air Interface:Â Pure Titania Alkoxide Exposed to AirâWater Molecules
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Photoacoustic Spectroscopy Applied to Biological Materials
The conventional method of analysis used to investigate properties of molecules inside a medium consists of measuring the transmission and reflection coefficients of the material in order to determine the absorption of a given chromophore in the medium. However, this classical technique only gives access to an average value over the thickness of the material being investigated. It does not allow for the establishment of a depth profile of the density of chromophores in the material, i.e. their local concentration. In addition, this technique necessitates good optical quality of the medium in the range of the optical wavelengths used which makes it less suited to amorphous biological tissues because these are often subject to strong light diffusion, diffraction or a too high absorption. In contrast to this technique, photoacoustic spectroscopy (PAS) allows for the in-depth characterization of either homogenous or heterogenous non-transparent materials.1â4 This spectroscopy has already been applied to study complex biological media like leaves (photosynthesis)5â7, eye retina (vision)8â9 or human skin (membrane permeability).10â1