Preliminary study of the thermally stimulated blue luminescence of ulexite

In this paper, novel results on the blue thermally stimulated luminescence (TSL) emission of ulexite (NaCaB₅O₆(OH)₆·5H₂O) have been studied. The four maxima appearing at 60, 110, 200 and 240°C on the TSL glow curves of this borate could be respectively associated to: (i) the first dehydration (NaCaB₅O₆(OH)₆·5H₂O→NaCaB₅O₆(OH)₆·3H₂O), (ii) the creation-annihilation of the three-hydrated phase, (iii) the Na-coordinated chains dehydroxylation and the starting point of the alkali self-diffusion through the lattice and (iv) the amorphisation of the lattice. These results are fairly well correlated with the differential thermal analyses (DTA), in situ thermal observations under environmental scanning electron microscope (TESEM) and thermal X-ray diffraction (TXRD) techniques.     

In situ UV-vis absorbance measurements for Langmuir films of poly[4'-[[2-(methacryloyloxy)-ethyl]ethylamino]-2-chloro-4-nitroazobenzene] (HPDR13) azopolymer

In situ UV-vis absorbance measurements are used to investigate aggregation in Langmuir films from the azopolymer poly[4'-[[2-(methacryloyloxy)-ethyl]ethylamino]-2-chloro-4-nitroazobenzene] (HPDR13), a methacrylate derivative of DR13. The level of aggregation in a Langmuir film is intermediate between that of HPDR13 in chloroform solution and in a deposited LB film, as expected. Absorption is negligible at large areas per monomer, and starts to increase at a critical area that is the same as the one obtained in surface potential isotherms, being close to twice the area per monomer for a condensed film. This indicates that the onset for light absorption coincides with a critical packing density where monolayer structuring occurs and there is a sharp change in the effective dielectric constant of the film/water interface. Consistent with a featureless pressure-area isotherm for HPDR13, denoting no significant molecular rearrangement upon film compression, the UV-vis spectra did not vary with the surface pressure. The intensity of absorbed light increased, though, as the film was compressed owing to a higher density of chromophores. At higher subphase temperatures, larger flexibility of HPDR13 chains led to a more compact arrangement, causing the area per monomer to decrease and the absorbed light to increase-with approximately opposite trends.     

Two-photon induced anisotropy in PMMA film doped with Disperse Red 13

In this paper we present optical anisotropy induced by 150-fs laser pulses operating at 775 nm in poly(methyl methacrylate) (PMMA) films doped with Disperse Red 13 (DR13). Two-photon absorption of DR13 induces reversible birefringence in the sample, a feature associated with the molecular orientation caused by isomerization of the azochromophores. No irreversible anisotropy, associated with photobleaching of the chromophore was observed. The slope of 2 obtained for the induced birefringence as a function of the excitation irradiance corroborates the two-photon nature of the process.     

Interaction of chitosan and mucin in a biomembrane model environment

Thermoplastics have been increasingly used for fabricating microfluidic devices because of their low cost, mechanical/biocompatible attributes, and well-established manufacturing processes. However, there is sometimes a need to integrate such a device with components made from other materials such as polydimethylsiloxane (PDMS). Bonding thermoplastics with PDMS to produce hybrid devices is not straightforward. We have reported our method to modify the surface property of a cyclic olefin copolymer (COC) substrate by using corona discharge and grafting polymerization of 3-(trimethoxysilyl)propyl methacrylate; the modified surface enabled strong bonding of COC with PDMS. In this paper, we report our studies on the surface modification mechanism using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and contact angle measurement. Using this bonding method, we fabricated a three-layer (COC/PDMS/COC) hybrid device consisting of elastomer-based valve arrays. The microvalve operation was confirmed through the displacement of a dye solution in a fluidic channel when the elastomer membrane was pneumatically actuated. Valve-enabled microfluidic handling was demonstrated.     

Titanium Dioxide/Electrolyte Solution Interface: Electron Transfer Phenomena

Electron transfer between a titanium dioxide/electrolyte solution interface has been studied. As found by other researchers of similar interfaces (TiO(2)- and ZnO-electrolyte solution), a slow consumption of OH(-) ions takes place in this type of interface. A theoretical model has been developed for calculating the change in the Fermi energy of both electrolyte solution and semiconductor, showing that ion consumption from the solution is favoured by the decrease of the difference between their Fermi energies. A kinetic constant (upsilon) is found to characterise the consumption process, its value increasing with electrolyte and semiconductor mass concentrations. Furthermore, this process may be used to estimate the point of zero charge of a titanium dioxide colloidal dispersion. Copyright 2000 Academic Press.