Search Results

You are looking at 1 - 2 of 2 items for :

  • "tensioactives" x
  • All content x
Clear All

Abstract  

The critical micelle concentrations and the enthalpies of micellization of alkyltrimethylammonium bromides having dodecyl, tetradecyl and hexadecyl hydrocarbon chains have been studied using surface tension and calorimetry measurements as a function of temperature. As expected, the change of critical micelle concentrations is very small with an increase of temperature of 10 deg whereas we observe a drastic change of the enthalpies of micellization. As it has been found by applying the Van't Hoff law to thecmc values at different temperatures, the calorimetric measurements show that the enthalpy of micellization, exothermic above a minimal temperature, becomes endothermic below this temperature.

Restricted access

Abstract  

Because of the energy loss of α-particles by self-absorption, α-spectrometry requires thin, uniform, and nearly weightless samples. Several methods exist for sample preparation, e.g., electrodeposition or co-precipitation. Unfortunately, the methods yielding the best energy resolution are not always quantitative and are usually relatively demanding and time-consuming. This fact makes application of α-spectrometry for screening tests with radiotracers complicated. For its simplicity and fastness, the possibility to prepare samples for α-spectrometry by direct evaporation of simple aliquots of aqueous or organic solutions and the influence of the presence of volatile organic diluent or tensioactive agent was investigated. Also, the influence of coating the samples with Mylar film was evaluated. The sample preparation techniques were compared based on the counting efficiency and energy resolution achieved. The performance of the selected method was tested on assessment of the efficiency of americium extraction by BTBP (bis-triazine-bipyridine) extractant.

Restricted access