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Surface tension

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Description of key information

Surface tension [2-(perfluorohexyl)ethyl]triethoxysilane: 72.2 mN/m at 20°C (OECD 115)

Surface tension [2-(perfluorohexyl)ethyl]silanetriol: <22 mN/m at 20°C (OECD 115)

Key value for chemical safety assessment

Surface tension:
in mN/m at 20°C and concentration in mg/L:

Additional information

A measured surface tension value of 72.2 mN/m at 20°C and 10 mg/l was determined for the substance using a relevant test method and in compliance with a known quality system (ISO 17025). The measurements were taken after a solution age of 30 minutes to minimise hydrolysis of the substance. The result is considered to be reliable and is selected as key study. Under the condition of the study, the parent substance, [2-(perfluorohexyl)ethyl]triethoxysilane is considered as not surface active.

In contact with water, [2-(perfluorohexyl)ethyl]triethoxysilane hydrolyse moderately to form [2-(perfluorohexyl)ethyl]silanetriol and ethanol. Therefore, the surface tension of the silanol hydrolysis product, [2-(perfluorohexyl)ethyl]silanetriol was obtained using relevant test method and read-across from octylsilanetriol.

The surface tension study was conducted using an analogue trimethoxy substance [[2-(perfluorohexyl)ethyl]trimethoxysilane, CAS No 85857-16-5]. Under dilute conditions in water, [2-(perfluorohexyl)ethyl]trimethoxysilane hydrolyses faster when compared with the submission substance (CAS No 51851-37-7) with a hydrolysis half-life of 0.4 h at pH 4, 0.4 h at pH 5, 8.8 h at pH 7, 0.1 h at pH 9 and 20-25°C. The product of hydrolysis of the trimethoxy analogue is [2-(perfluorohexyl)ethyl]silanetriol and methanol. The surface tension study uses a test substance concentration of 1 g/l at 20°C and 43 h solution age. At the age of the solution used during the study (43 h), the surface tension result is considered to reflect the silanol hydrolysis product(s) under conditions where the limit of solubility is significantly exceeded. Under these conditions, the hydrolysis product, [2-(perfluorohexyl)ethyl]silanetriol has a measured surface tension value of <22 mN/m at 20°C and 1 g/l. This value is also supported by available measured data for the read-across substance octylsilanetriol.

The surface tension of octylsilanetriol was determined by the addition of octyltrichlorosilane in water. Octyltrichlorosilane (CAS No 5283-66-9) in contact with water reacts very rapidly with a half-life of <1 minute at pH 4, pH 7 and pH 9 and 25°C to form octylsilanetriol and hydrochloric acid. Both buffered (pH 7) and non-buffered solutions with solution age of 3 days and 4 hours respectively. Surface tension of 53 mN/m at 20°C and 100 mg/l using EU Method A.5 was obtained for the buffered solution of octylsilanetriol. The result indicates that octylsilanetriol is potentially surface active.

Therefore, based on the available information and uses of the substance; the silanol hydrolysis product, [2-(perfluorohexyl)ethyl]silanetriolis considered to be surface active.

The corresponding monomeric silanetriol is expected to be surface active based on measured and read across data. The presence of fluorocarbon chains may mean that condensation products could have some surface activity. For these reasons, the effective limits of solubility of both the parent substance and monomeric silanol hydrolysis products are very low and all forms of the substance may have a tendency to enrich at surfaces rather than forming stable evenly dispersed solutions.