Search

The influence of the nonionic surfactant lauryl alcohol ethoxylate with 12 moles ethylene oxide (LAE-12OE) was evaluated on the Stratum corneum model biomembrane (SCMM) of shed snake skin (Bothrops jararaca and Spilotes pullatus) through the biophysical techniques Fourier transform Raman spectroscopy (FT-Raman) and Fourier transform infrared photoacoustic spectroscopy (PAS-FTIR). The surfactant was used in aqueous solutions above and below the critical micelle concentration (cmc), 50.0 and 0.21 g/L, respectively. The SCMM samples were pre-treated for periods of 8 h (whole SCMM) and for 12 h (SCMM after tape stripping procedure). The LAE-12OE did not promote increase in the hydration of the B. jararaca and S. pullatus SCMM but exhibited some action as far as lipid extraction., Colegio de Farmacéuticos de la Provincia de Buenos Aires

Texto completo. Acesso restrito. p. 569-577 Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-08-01T20:06:35Z No. of bitstreams: 1 666666666666666666666.pdf: 154172 bytes, checksum: 52ac4df86246ddb5c33fd36947d46cba (MD5) Made available in DSpace on 2013-08-01T20:06:35Z (GMT). No. of bitstreams: 1 666666666666666666666.pdf: 154172 bytes, checksum: 52ac4df86246ddb5c33fd36947d46cba (MD5) Previous issue date: 1999 The thermal behavior of Nafion-117 membranes was investigated by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). TG measurements revealed that the mechanism of thermal degradation of a Nafion membrane in the acid form is different from that of Nafion in the sodium form. The DSC curves for the first heating, for both acid and salt forms, display two endothermic peaks, near 120 and 230oC. The high-temperature peak was assigned to the crystalline domains melting in Nafion, and the low-temperature peak was attributed to a transition into ionic clusters, since this transition exhibits significant changes depending on the nature of the counterion and the degree of hydration. Salvador

Texto completo: acesso restrito. p.291–297 Submitted by Suelen Reis (suelen_suzane@hotmail.com) on 2013-01-30T16:53:02Z No. of bitstreams: 1 Almeida.pdf: 256655 bytes, checksum: ae6894bbfb431ccc20c12dff89071449 (MD5) Made available in DSpace on 2013-01-30T16:53:02Z (GMT). No. of bitstreams: 1 Almeida.pdf: 256655 bytes, checksum: ae6894bbfb431ccc20c12dff89071449 (MD5) Previous issue date: 1998 The effects of X-ray radiation on Nafion-117 membrane were investigated by electron paramagnetic resonance spectroscopy (EPR), photoacoustic infrared spectroscopy (PAS), Raman scattering and ultraviolet-visible electronic absorption spectroscopy. EPR spectrum of irradiated Nafion membrane reveals the presence of peroxy free radical similar to that found in irradiated polytetrafluoroethylene. The Raman and infrared (IR) spectra of irradiated samples show the appearance of new bands at 1458, 1700 and 1773 cm−1, that can be associated with the presence of C=O and C=C groups. In addition, Raman and IR spectra show a band intensity change associated with the stretching modes of C–O, C–S and SO3-, indicating scissions of C–S and C–O bonds and SO2 liberation. UV-Vis spectra of irradiated samples exhibit bands at 196, 230 and 273 nm, whose intensities increase with irradiation doses and with aging time.

Texto completo: acesso restrito. p.1307–1311 Submitted by Suelen Reis (suelen_suzane@hotmail.com) on 2013-01-31T13:07:03Z No. of bitstreams: 1 Almeida.pdf: 441717 bytes, checksum: c3ef34290898eaa2156d5457729581cc (MD5) Made available in DSpace on 2013-01-31T13:07:03Z (GMT). No. of bitstreams: 1 Almeida.pdf: 441717 bytes, checksum: c3ef34290898eaa2156d5457729581cc (MD5) Previous issue date: 1997 The effect of pre-treatment, counterion and electrolyte concentration, temperature and aging of Nafion 117 membrane was investigated by electronic absorption spectroscopy. The band at 196 nm is sensitive to the cluster environment. Its intensity decreases with increasing water content and increases with various countercations according to increasing ionic radius, increase of electrolyte concentration, temperature and time of aging. This behavior may be associated with structural changes induced by membrane hydration.