Nanofoaming dynamics in biopolymers by femtosecond laser irradiation

We have recently shown that irradiation of self-standing films of the biopolymers collagen and gelatine with single femtosecond laser pulses produces a nanofoaming layer with regular bubble size which can be controlled by wavelength selection. Following these initial studies, here we report on the temporal evolution of the foaming effect by measurements in situ and in real time of the change in the transmittance of a cw probe HeNe laser through the irradiated films. Self standing films of the biopolymers were irradiated with 90 fs laser pulses at 800, 400, and 266 nm. For fluences below and above the modification threshold a permanent attenuation of the transmission occurs (increasing with fluence). The initial decay of the transmission is fast (around few tens of ns), and is followed by dynamics in the longer timescale (micro and milliseconds). The temporal evolution of the transmission measured upon fs laser irradiation is similar with that determined in the irradiation of the biopolymer films at 248 nm with 25 ns laser pulses. The method allows separating in time the different processes occurring after irradiation that lead to a permanent nanofoaming structure, while the results allow us to understand the mechanisms of femtosecond laser processing of the biopolymers and their interest in biomedical applications.     

Microstructure characterization of titanium dioxide nanodispersions and thin films for dye-sensitized solar cell devices

This article reports on the microstructure characterization of titanium dioxide nanodispersions and thin films made thereof for dye-sensitized solar cell devices. Structure–property relationships have been investigated mainly using electron microscopy to assess how microstructure (crystalline structure, defects) and morphological (e.g. heterogeneities, inclusions, voids) features in the electron transport element of the solar cell device correlate with electrical performance, namely, short-circuit photocurrent density (J_sc). This work shows that for a nanodispersion synthesized in the laboratory different electrical performances are measurable depending on the thin film forming process, more specifically, heat-sintering at 450 °C or pressure-sintering at 500 bar. For the heat-sintered device J_sc is about 7.3 mA/cm² whereas for the pressure-sintered one this value is much lower, this difference being attributed to the existence of inclusions in the titanium dioxide matrix, which are spatially isolated from the rest of the electron transport element thereby limiting the charge transport process by promoting their premature recombination. PACS 68.37.Lp; 73.61.Le; 81.40.-z; 84.60.Jt     

Correlation between the Soret coefficient and the static structure factor in a polymer blend

Mutual mass diffusion and thermal diffusion has been investigated in poly(dimethylsiloxane)/ poly(ethylmethylsiloxane) (PDMS/PEMS) polymer blends of equal weight fractions. Molar masses ranged from below 1 to over 20 kg/mol. Both the mutual mass (D) and the thermal diffusion (D_T) coefficient contain a thermally activated factor with an activation temperature of 1415 K. The molar mass dependence of D_T is due to an end-group effect of the local friction coefficient. The thermal diffusion coefficient in the limit of long chains and infinite temperature is D_T^0, = - 1.69×10^-7cm²(sK)^-1. The Soret coefficient S_T of blends far enough away from a critical point is proportional to the static structure factor S(q = 0).     

Resonant-cavity light-emitting diodes: quantum noise and spatial emission characteristics

We demonstrate the interplay between the intensity noise and the spatial emission characteristics of resonant-cavity light-emitting diodes. First, we find that the total aperture intensity noise exhibits a sub-shot noise behavior in a quite large pumping regime. Second, we investigate the angular, spectral, and spatial emission characteristics of the devices by controlling the shape and width of the angular intensity distribution via temperature detuning of the quantum well wavelength and the cavity resonance wavelength. Finally, the angular and aperture resolved intensity noise exhibit a super-shot noise behavior in contrast to that of the total emission. We explain this difference with anticorrelations between various radial components which increase with the temperature-tuned extension of the spatial emission. PACS 85.60.Jb; 42.50.L; 23.20.En     

Phase behaviour of <Emphasis Type="Italic">n</Emphasis>-hexane/perfluoro-<Emphasis Type="Italic">n</Emphasis>-hexane binary thin wetting films

We present X-ray reflectivity investigations of the concentration distribution in binary liquid thin films on silicon substrates. The liquid-vapor coexistence of the binary mixture investigated, hexane and perfluorohexane, is far from criticality. Therefore, a sharp interface separates the liquid film from the vapor. The data reveal a separation of the film in layers parallel to the substrate. A phase diagram is constructed as a projection to the (composition difference, temperature) space, covering a temperature range corresponding to the one-phase and the two-phase regime of the bulk liquid. Although the composition data indicate a mixing gap similar to that of the bulk system, there are two major differences: i) only the near-surface phase changes its composition significantly, and ii) a composition gradient in the film exists also at higher temperatures where in the bulk system the one-phase regime exists.Received: 28 April 2004, Published online: 21 September 2004PACS: 61.10.Kw X-ray reflectometry (surfaces, interfaces, films) - 64.75. + g Solubility, segregation, and mixing; phase separation - 68.15. + e Liquid thin films     

Bio-Organometallic Derivatives of Antibacterial Drugs

Overuse and misuse of antibacterial drugs has resulted in bacteria resistance and in an increase in mortality rates due to bacterial infections. Therefore, there is an imperative necessity of new antibacterial drugs. Bio-organometallic derivatives of antibacterial agents offer an opportunity to discover new active antibacterial drugs. These compounds are well-characterized products and, in several examples, their antibacterial activities have been studied. Both inhibition of the antibacterial activity and strong increase in the antibiotic activity of the parent drug have been found. The synthesis of the main classes of bio-organometallic derivatives of these drugs, as well as examples of the use of structure–activity relation (SAR) studies to increase the activity and to understand the mode of action of bio-organometallic antimicrobial peptides (BOAMPs) and platensimicyn bio-organometallic mimics is presented in this article.     

Purity assessment using the mass balance approach for inorganic in-house certified reference material production at Inmetro

Accreditation and Quality Assurance - The production of Certified Reference Materials (CRMs) is one of the essential activities of the National Institute of Metrology, Quality and Technology...