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The impact of four ethylene oxide–propylene oxide block copolymers on the surface tension of dispersions of soils and minerals in water

The impact of four ethylene oxide–propylene oxide block copolymers on the surface tension of dispersions of soils and minerals in water

Hagenhoff, Kerstin, Dong, Jingfeng, Chowdhry, Babur, Torres, Luis and Leharne, Stephen (2012) The impact of four ethylene oxide–propylene oxide block copolymers on the surface tension of dispersions of soils and minerals in water. Physics and Chemistry of the Earth, Parts A/B/C, 37-39. pp. 58-64. ISSN 1474-7065 (doi:10.1016/j.pce.2010.11.002)

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Abstract

A comprehensive series of aqueous solutions of four ethylene oxide–propylene oxide–ethylene oxide block copolymers (EPE) of varying concentrations have been prepared. The EPE molecules are amphiphilic with the P blocks providing the hydrophobic segment of the molecules and the E blocks providing the hydrophilic parts. The surface tension of these solutions has been measured and compared with the surface tension of dispersions of soils (a clay soil and a sandy soil) and minerals (quartz–silica sand, bentonite and kaolinite) in the same aqueous solutions. It is observed that all the block copolymers reduce the surface tension of water; the extent to which it is reduced is determined by the surface activity of the EPE block copolymer, which in turn is related to the balance between the sizes of the P and E blocks. It is further observed that the in the presence of soil the surface tension increases as a result of block copolymer adsorption to the soil/water interface. The extent of adsorption appears to be related to the texture of the soil – the clay soil used in this investigation adsorbs more block copolymer than the sandy soil. In the presence of the mineral phases the surface tension reductions are variable. With bentonite the EPE block copolymers are completely adsorbed at low EPE concentrations as shown by surface tension values that are the same as those measured for pure water. Adsorption to kaolinite is limited and once the adsorption sites have been filled the surface tension of the aqueous phase is approaches the surface tension of the same solution without the presence of bentonite. On the other hand the silica sand is a poor adsorbent. Adsorption to the mineral phases is also dependent upon the relative hydrophobicity of the block copolymer. The more hydrophobic (as inferred by the critical micelle concentration) the copolymer the less readily it is adsorbed by the mineral phases. Thus relatively hydrophobic EPE block copolymers produce a relatively large decrease in surface tension and are less readily adsorbed by the soil and mineral phases. It is concluded that the presence of EPE block copolymers in soils can result in the drainage of soil water from the saturated zone as a result of surface tension reductions. However the extent of drainage is related to the surface activity/molecular composition of the EPE block copolymer; the textural class of the soil and the nature of the minerals present in the soil.

Item Type: Article
Additional Information: [1] Available online 19 November 2010. [2] Published in: Physics and Chemistry of the Earth, Parts A/B/C. Volumes 37–39, 2012, Pages 58–64. Soil and groundwater restoration in tropical and subtropical regions: An international overview of the Latin-American Approach. Edited by Erick R. Bandala and Lius G. Torres.
Uncontrolled Keywords: polyoxyethylene, polyoxypropylene, diblock-copolymers, soil, surface tension
Subjects: Q Science > QD Chemistry
Faculty / Department / Research Group: Faculty of Engineering & Science > Department of Life & Sports Sciences
Faculty of Engineering & Science > Department of Pharmaceutical, Chemical & Environmental Sciences
Related URLs:
Last Modified: 05 Dec 2016 10:50
Selected for GREAT 2016: None
Selected for GREAT 2017: None
Selected for GREAT 2018: None
URI: http://gala.gre.ac.uk/id/eprint/4558

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