Triethoxyoctylsilane

Surface tension

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

surface tension

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because water solubility is below 1 mg/L at 20°C

Reference 2

Endpoint:

surface tension

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2011-07-01 to 2011-07-04

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

The study was conducted in accordance with an appropriate test method but not in compliance with GLP.

Qualifier:

according to guideline

Guideline:

EU Method A.5 (Surface Tension)

Deviations:

no

GLP compliance:

no

Type of method:

plate method

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 concentration 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 the registered substance was determined as 53mN/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 [triethoxy(octyl)silane]: not relevant due to low water solubility <1 mg/L

Surface tension [octylsilanetriol]: 53 mN/m (EU Method A.5)

Additional information

The surface tension study for triethoxy(octyl)silane (CAS 2943 -75-1) was waived based on low water solubility (i.e. water solubility is <1 mg/L) of the registered substance, but the surface tension of the hydrolysis product was read-across from related substance; octyltrichlorosilane (CAS 5283-66-9).

In contact with water, triethoxy(octyl)silane will hydrolyse moderately rapidly to form octylsilanetriol and ethanol. Similarly, octyltrichlorosilane will hydrolysed very rapidly in contact with water to form octylsilanetriol and hydrochloric acid. Both substances (triethoxy(octyl)silane and octyltrichlorosilane) have the same silanol hydrolysis product; octylsilanetriol. Therefore, since both substances share the same silanol hydrolysis product, it is considered valid to read-across between the two substances.

The hydrolysis product, octylsilanetriol 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 micelles at high concentration.