Physico-Chemical nanomaterials science
Dependence of rheological behavior of PEG solutions and PEG-BTC aqueous mixtures from molecular weight of PEG
A.V. Sachko1, A. Slobodian1, V.P. Zakordonskiy2
1 Biology, Chemistry and Bioresourses Institute, Yuriy Fedkovych Chernivtsi National University, Kotsyubynsky 2, 58012,Chernivtsi, Ukraine
E-mail: an.sachko@chnu.edu.ua
2 Chemistry Faculty, Ivan Franko National University of Lviv, Universytetska St, 1, 79000, L'viv, Lviv, Ukraine. E-mail:vzakordonskiy@ukr.net

The main purpose of this work was to study the influence of polyethylene glycol (PEG) molecular mass (Mm (PEG) = 400 - 4500) and the concentration on the viscosity of aqueous solutions of PEG and its mixtures with cationic surfactant benzethonium chloride (BTC).
It was shown that for aqueous solutions of individual PEGs of different molecular weight in the region of low concentrations (C PEG <0.05 M) anomalous nature of the change in viscosity occurs, namely, the viscosity of the solutions is lower than the water viscosity. This fact indicate on the influence of PEG additives on the water molecular structure. The viscosity decreasing is the greater the smaller the molecular weight of PEG, unlike ethylene glycol solutions, for which the effect of lowering the relative viscosity is insignificant and weakly expressed (observed in the area of experimental error). With further increasing of PEG concentration (CPEG > 0.05 M) take place a natural growing in the solutions viscosity, and the viscosity value is the greater, the higher the molecular weight of PEG.
The viscosity isotherms of the PEG-BTC binary solutions (СPEG = 0.1 M) in the premicellar concentration range of BTC (CBTC <0.002 M) is characterized by a marked decreasing of mixtures relative viscosity in comparison with respective concentration of BTC. Generally, the increasing in the BTX concentration in system is accompanied with increasing in viscosity, especially in the region of BTC concentrations 0.005-0.01 M. In the region of the BTC micellar concentrations, the dependence of the system viscosity on the PEG molecular weight was clearly observed. The higher the molecular weight of PEG is, the higher the viscosity of the mixtures for fixed BTC concentration. The increasing of the viscosity of PEG solutions in the case of addition of cationic benzethonium chloride could be connected with the increasing in the degree of structuring of the system because of the intermolecular associates formation.
Depending on the BTC/PEG concentrations, two processes can occur in such systems: the BTC-PEG association and the formation of free micelles of BTC. The ratio of these processes determines the total result of the concentration factor influence on the rheological behavior of binary PEG-BTC mixtures.