Reaction product of castor oil with glycerol

Surface tension

Link to relevant study record(s)

Reference

Endpoint:

surface tension

Type of information:

experimental study

Adequacy of study:

key study

Study period:

25-Jul to 02-Aug-2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

EU Method A.5 (Surface Tension)

Deviations:

yes

Remarks:

Due to the complex composition of the test item, it was not possible to follow the EC A.5 and OECD 115 guidelines with regard to sample preparation. Therefore the surface tension at a conc. of 90% of the critical micelle concentration was calculated.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 115 (Surface Tension of Aqueous Solutions)

Deviations:

yes

Remarks:

Due to the complex composition of the test item, it was not possible to follow the EC A.5 and OECD 115 guidelines with regard to sample preparation. Therefore the surface tension at a conc. of 90% of the critical micelle concentration was calculated.

GLP compliance:

no

Type of method:

ring method

Surface tension:

40.9 mN/m

Temp.:

20 °C

Conc.:

44 mg/L

Results

The concentration (mg/L), log10 [concentration (mg/L)] and mean surface tension values for the sample solutions are shown in the following table:

 

Concentration (mg/L)	Log10 Concentration	Mean Surface Tension (mN/m)	Solution pH
5.021 x 10^3	3.701	36.5	7.6
1.004 x 10^3	3.002	37.5	6.9
301.2	2.479	38.7	6.4
100.4	2.002	40.7	6.0
30.12	1.479	44.2	5.8
10.04	1.002	52.2	5.9
3.012	0.479	62.7	5.8
1.004	0.002	66.5	5.8
0.3012	-0.521	70.5	5.8
0.1004	-0.998	72.0	5.8

 

The results were used to plot log10 [concentration (mg/L)] versus surface tension (mN/m).

Line 1 was generated from linear regression of 3 sample solution concentrations for which the surface tension was shown to be concentration dependent and Line 2 was generated from linear regression of 2 sample solution concentrations for which the surface tension was observed to be essentially independent of concentration. The intersection of

these two lines gave the critical micelle concentration and was calculated by solving the two equations:

Line1 equation:  y = -18.5x+71.3

Line 2 equation: y = -1.78x +43.0

 

The sample solution at 100.4 mg/L was not used in generating the two lines. At this concentration the surface tension appeared to be transitioning to Line 2 at a shallower gradient than Line 1.

 

The sample solutions at 1.004, 0.3012 and 0.1004 mg/L were not used in generating the two lines. At this concentration the surface tension was only slightly affected and was approaching that of purified water.

The CMC was determined to be 48.9 mg/L.

 

The surface tension at a concentration of 90% of the CMC (44.0 mg/L) was calculated to be 40.9 mN/m using the equation for Line 1.

Discussion

The critical micelle concentration (CMC) is an important characteristic of a surfactant. At low concentrations of surfactant, the surface tension of water is only slightly affected. Increasing the concentration but before reaching the CMC, the surface tension changes significantly. After reaching the CMC and above, the surface tension remains relatively constant or changes with a much more gradual slope.

 

Below the CMC, a surfactant is considered to be thermodynamically soluble in the water; whereas above the CMC, the solubility of a surfactant in water has been exceeded and the excess surfactant aggregates to form micelles. These micelles have significantly less effect on the surface tension of a solution and are considered not to be in solution. Thus, the water solubility of a surfactant may be expressed in terms of the CMC.

 

According to criteria stated in EC Method A.5, substances showing a surface tension lower than 60 mN/m under the conditions of this method should be regarded as being surface active.

Conclusion

The critical micelle concentration of the test item was determined to be 49 mg/L at 20.0 ± 0.5 °C.

 

The surface tension at a concentration of 90% of the CMC (44.0 mg/L) was calculated to be 40.9 mN/m at 20.0 +/- 0.5 °C. The test item was considered to be surface active.

Description of key information

40.9 mN/m at 20 °C (calculated from of 90% of the critical micelle concentration, OECD 115).

Key value for chemical safety assessment

Surface tension:

40.9