The proton conductivity of radiation-grafted ethylenetetrafluoroethylene-grafted-poly(styrene sulfonic) acid (ETFE-g-PSSA) and Nafion 117 membranes between 25 and -37 degrees C is reported. The freezing of water in the membranes, which strongly depends on the internal acid concentration, results in a 4-fold decrease in proton conductivity. The activation energies before and after the freezing of the membranes are approximately 0.15 and 0.4 eV, consistent with proton transport through liquid water and strongly bound water, respectively. Differential scanning calorimetry data show that up to 14 H(2)O molecules per H(+)/SO(3)(-) group remain unfrozen at subzero temperatures and are believed to be responsible for the low temperature conductivity that is observed. These results indicate that proton conductivity in membranes may be achieved via strongly bound and highly polarized water.
Novel polymers with controlled microstructures were prepared and studied to further advance the understanding of structure-property relationships of proton conducting membranes. PAN-g-macPSSA membranes, which contained poly(styrenesulfonic acid) (PSSA) grafts of defined graft length, are compared with PVDF-g-PSSA membranes, prepared by radiation-grafting, and Nafion 1 117. The intrinsic properties of PAN-g-macPSSA membranes are insensitive to the macromonomer graft length but are highly dependent on the ion exchange capacities (IEC). Increasing the IEC increases the content of free water absorbed by the membrane. Self-diffusion coefficients of water in water-swollen PAN-g-macPSSA were found to be similar to that of N117, despite PAN-g-macPSSA's higher water content. Of the polymers studied, PAN-g-macPSSA exhibited the lowest methanol permeability, which is explained on the basis of it containing a more tortuous ionic network. Methanol permeability decreased with decreasing volume of free water.
Background: Colorectal cancer (CRC) is one of the main five causes of morbidity and mortality by oncologic diseases in our country and worldwide. Recently, fecal immunochemical test (FIT) has proven to be a non-invasive screening test that allows to select patients most likely to have a pre-malign lesion to perform a colonoscopy. Objective: The aim of the study was to report the findings of a CRC screening program using FIT in our country population. Method: A multicentric study was performed, by inviting open population older than 50 years to participate in a CRC screening. Quantitative FIT specific for human hemoglobin was used, with a cut point of 100 ng/mL or higher to consider as positive. Those patients with positive results were asked to undergo a colonoscopy. In the cases where polypoid lesions were found, biopsies were performed. Results: In total, 751 FIT was processed, and 51 (6.8) of those were positive, with a rate of 15.9 premalign lesions for 1000 individuals, and 1.3 patients with CRC for every 1000. Conclusions: The present study matches worldwide reports, supporting the initiative of establishing a formal and standardized CRC screening program in the public health sector.
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