Registration Dossier
Registration Dossier
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EC number: 253-930-6 | CAS number: 38436-16-7
Surface tension
Administrative data
Link to relevant study record(s)
Description of key information
Surface tension [2-(perfluorobutyl)ethyl]dichloro(methyl)silane: Not relevant
Surface tension [2-(perfluorobutyl)ethyl]methylsilanediol: <22 mN/m at 20°C (OECD 115)
Key value for chemical safety assessment
Additional information
The requirement to conduct a surface tension study for the submission substance is waived in accordance with Section 2 of REACH Annex XI, because in contact with water, the substance reacts rapidly to form [2-(perfluorobutyl)ethyl]methylsilanediol and hydrochloric acid. Therefore, the surface tension of the silanol hydrolysis product, [2-(perfluorobutyl)ethyl]methylsilanediol has been read-across from [2 -(perfluorohexyl)ethyl]silanetriol and octylsilanetriol.
A surface tension study was conducted using a structurally-related trimethoxy substance, [2-(perfluorohexyl)ethyl]trimethoxysilane] (CAS No 85857-16-5), under conditions in which the results would reflect the surface tension of the hydrolysis product. Under dilute conditions in water, the analogue substance [2-(perfluorohexyl)ethyl]trimethoxysilane has hydrolysis half-lives 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 forming [2-(perfluorohexyl)ethyl]silanetriol and methanol. The surface tension study used 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), hydrolysis would have occurred and the surface tension result is considered to reflect the silanol hydrolysis product(s) under conditions where the limit of solubility is significantly exceeded. Therefore, the study results are considered to indicate that 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 to 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 ages of 3 days and 4 hours respectively were used during the study. A 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.
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.
Therefore, the silanol hydrolysis product, [2-(perfluorobutyl)ethyl]methylsilanediol is considered to be surface active.
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