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- Studying the PEG familyPublication . Sequeira, Maria Carolina; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.The main goal of this line of research is the realisation of experimental measurements of thermophysical properties of a homologous series of ethylene and polyethylene glycols [H(OCH2CH2)nOH], and the development of correlation methods, with an accuracy adequate for the applications. Ethylene glycols and poly (ethylene) glycols (PEG) are widely used in many industrial applications as green solvents and as components of important sustainable processes as they are considered environmentally acceptable compounds [1,2]. Liquid Poly(ethyleneglycols) [PEGs] are in general considered as green solvents. They are non-volatile; their toxicity is very low, such that they are being used as food additives [3]. PEGs have been found to be biodegradable by bacteria in soil or sewage, but the ability of bacteria to biodegrade PEG decreases with increasing molecular weight [3]. The study of this series of compounds is important in many respects, not only because it is aimed at the study of PEGs which have innumerable practical applications but also because this study can be useful to monitor the degree of polymerization in the production of PEGs, themselves. In the present work, the viscosity of three ethylene glycols, namely diethylene, triethylene and tetraethylene glycols [4] and PEG 400 were measured with high accuracy using the vibrating wire technique at moderately high pressures. Complementary experimental density, surface tension and rheological behavior were obtained for the same liquids. One of the aims of the work is to analyse the relation of the present results with those obtained before for CO2 saturated PEG400 mixtures
- Viscosity measurements of compressed ionic liquid EMIM OTfPublication . Sequeira, Maria Carolina; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.Ionic liquids have attracted considerable interest in recent years, as they can be used for multiple aims, namely, as antistatic agents, electrolytes, solvents, lubricants, and CO2 absorbents [1]. The use of ionic liquids in industrial processes require their thermophysical properties, in particular, the viscosity and the thermal conductivity. However, transport properties are scarce due to the difficulty of the measurements, particularly at pressures higher than the atmospheric pressure. Our group has developed a programme of measurements aiming at obtaining rigorous results for the viscosity of ionic liquids using the vibrating wire method. This technique, although very accurate for molecular, non-conducting liquids, could have some difficulties with ionic liquids due to their electrical conductivity [2]. As we were planning to use the vibrating wire method in the forced mode of oscillation, the method requires the acquisition of the frequency response of the wire in a range of frequencies containing the velocity resonance for the transverse oscillations of the wire. Therefore, it is important to verify if the ionic liquid sample is a good electrolytic conductor in the range of frequencies that matter for the measurement of viscosity. The problematic of measuring the viscosity of ionic liquids both in general and in particular, using the vibrating wire technique was studied [3]. Pardal et al. [4] have used 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIMOTf) mixed with water as the electrolyte to successfully reduce CO2 at high pressure. The objective of this work is to contribute with viscosity data in the pressure and temperature range of the work performed by those authors. Therefore, we present new ionic viscosity results for temperatures between 298 K and 347 K and pressures up to 50 MPa.