Chlorodimethyloctylsilane

Surface tension

Link to relevant study record(s)

Reference

Endpoint:

surface tension

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

Please refer to the attached justification below and the overall justification for grouping of substances attached in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Surface tension:

42.18 mN/m

Temp.:

20 °C

Conc.:

100 mg/L

Remarks on result:

other: Non-buffered result

Surface tension:

52.78 mN/m

Temp.:

20 °C

Conc.:

100 mg/L

Remarks on result:

other: Buffered result at pH 7

Test Conditions (de-ionized water):

When preparing the test solution (100 mg/l), the substance was observed to react rapidly with water with the generation of HCl and a flocculent white precipitate. After stirring for 4 hours and heating to 60°C the precipitate did not disappear. Before measurement at 20°C the precipitate was removed by filtration.

The concentration of the test substance was determined using the method for total carbon in the solution according to DIN EN 1484 H3. No carbon could be detected (detection limit < 3 mg/l). Additionally a 1H-NMR spectrum was measured. There was no signal of CH2Si or CH2 groups of an octyl chain. Therefore there is no indication of the test substance or organic groups as products of hydrolysis in the aqueous solution (detection limit < 10 mg/l).

Due to the very low concenteration of dissolved material, it is difficult to interpret the result of the study.

The test substance was expected to hydrolyse rapidly generating HCl which will lower the pH of the solution. The condensation reaction of the silanol hydrolysis product are expected to be promoted at lower pH. Therefore the study was repeated in a pH 7 buffer solution as test medium.

Table 1: Surface tension result for non-neutralised (non-buffered solution)

No	Time after transferring to the measurement vessel [min]	Measured surface tension [mN/m]	Corrected surface tension [mN/m]
1	30	42.20	-
2	35	42.18	-
3	40	42.15	-
4	45	42.18	-
5	50	42.18	-
Total mean value		42.18	-
Mean value (state of equilibrium)		42.18	-

Test Conditions (pH 7 buffer solution):

When preparing the test solution (100 mg/l) with the buffer solution at pH 7, the substance was observed to react at rapidly with water with flocculent white precipitate being generated. After 3 days the precipitate did not disappear. Before measurement at 20°C the precipitate was removed by filtration.

A 1H-NMR spectrum of the test solution was measured. There was no signal of CH2Si or CH2 groups of an octyl chain. Therefore there is no indication of the test substance or organic groups as products of hydrolysis in the aqueous solution (detection limit < 10 mg/l).

It was assumed that a very small amount of the hydrolysis product of the test substance remained on the surface of the aqueous solution. This was considered a possible reason for the effect of surface tension.

Table 2: Surface tension result for neutralised (buffered solution)

No	Time after transferring to the measurement vessel [min]	Measured surface tension [mN/m]	Corrected surface tension [mN/m]
1	30	52.82	-
2	35	52.78	-
3	40	52.80	-
4	45	52.76	-
5	50	52.76	-
6	55	52.78	-
7	60	52.78	-
Total mean value		52.78	-
Mean value (state of equilibrium)		52.78	-

 

Conclusions:

A surface tension of octylsilanetriol; a hydrolysis product of octyltirchlorosilane was determined as 53 mN/m using a relevant test method. The hydrolysis product (octylsilanetriol) was determined to be potentially surface active using a relevant test method. Significant condensation of the test substance was observed in water and there was no indication of the test substance or organic groups as product of hydrolysis in aqueous solution, thus the result is difficult to interpret. However, the surface activity observed was assumed to be as a result of a very small amount of the hydrolysis product which remained on the surface of the aqueous solution.

Description of key information

Surface tension (Chloro(dimethyl)octylsilane): not relevant

Silanol hydrolysis product approximately 53 mN/m (EU Method A.5), read across from octylsilanetriol

Key value for chemical safety assessment

Surface tension:

53

Additional information

In accordance with Column 2 of REACH Annex VII (Section 7.6), the requirement to test the substance for surface tension is waived because in contact with water the substance hydrolyses rapidly to form dimethyl(octyl)silanol and hydrochloric acid. There are no reliable measured data for the surface tension of dimethyl(octyl)silanol.

For dimethyl(octyl)silanol, it is appropriate to read-across surface tension data from the structurally related substance, octylsilanetriol.

Octadecylsilanetriol was determined to be potentially surface active (surface tension of 53 mN/m) using a relevant test method. Significant condensation of the test substance was observed in water and there was no indication of the test substance or organic group as product of hydrolysis in aqueous solution, thus the result is difficult to interpret. However, the surface activity observed was assumed to be as a result of a very small amount of the hydrolysis product which remained on the surface of the aqueous solution.

The surface activity of the hydrolysis product is observed to be weak and non-ionic, although there is the potential of formation of emulsions and micelles. The critical micelle concentration (CMC) of the substance is assumed to be very high. The polymerisation of the substance is a more pronounced effect than the formation of micelle at high concentration.