Reaction mass of N,N,N',N'-tetrabutylmethylenediamine and dibutylamine

Surface tension

Link to relevant study record(s)

Reference

Endpoint:

surface tension

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

March 2022 to February 2023

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method A.5 (Surface Tension)

Version / remarks:

Commission Regulation No 440/2008

Qualifier:

according to guideline

Guideline:

OECD Guideline 115 (Surface Tension of Aqueous Solutions)

Version / remarks:

1995

GLP compliance:

not specified

Type of method:

ring method

Remarks:

Critical micelle concentration by ring tensiometer method

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source (i.e. manufacturer or supplier) and lot/batch number of test material: Sigma-Aldrich; Batch No: SHBL0699.
- Purity: 99.69%


STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: 1-5°C
- Solubility and stability of the test material in the solvent/vehicle and the exposure medium: water solubility of the test substance is 156 mg/L
- Reactivity of the test material with the incubation material used (e.g. plastic ware): NS.
The measurement vessel was cleaned carefully. It was washed with hot chromo-sulfuric acid and subsequently with syrupy phosphoric acid (83 to 98% by weight of H3PO4), thoroughly rinsed in tap water, then washed with ultrapure water (osmotic water passed through UV photo-oxidation reactor and deionizer/absorber kit) until a neutral reaction was obtained (observed with a pHmeter) and subsequently dried.
The ring was firstly immersed in chromosulfuric acid and rinsed thoroughly with ultra-pure water until a neutral reaction was obtained, then immersed in acetone and finally briefly heated with a methanol flame.

Key result

Remarks on result:

not determinable

Remarks:

The surface tension did not stabilise up until the highest micellar concentration tested. The critical micellar concentration was determined to be above 3.8 g/L, which is the highest water solubility concentration

The surface tension of both methanol and butanol-1 were measured twice, once on 11 March when the eight first solutions were measured and the other time on 30 March with the two last solutions (9 and 10).

The surface tension of the reference substance methanol was measured before the first solution determination. Surface tensions of 22.3 mN/m and then 22.6 mN/m were registered and meet the validation criteria of 22.5 +/- 0.2 mN/m.

The surface tension of the reference substance butanol-1 was measured after the last solution determination. Surface tensions of 24.4 mN/m and then 24.1 mN/m were registered and meet the validation criteria of 24.3 +/- 0.2 mN/m.

The surface tensions of solutions 1 to 8 were measured on 11 March 2022. The surface tension of two additional solutions (9 and 10) were measured on 30 March. 

The following surface tensions were obtained:

 

Table 2. Surface tension measurements of test substance

Solution	Concentration (mg/L)	Log Concentration	Surface tension (mN/m)
			1	2	3	4	5	Mean
1	1.16	0.06	69.9	69.9	69.9	69.8	69.8	69.9
2	5.00	0.70	69.8	69.8	69.7	69.7	69.6	69.7
3	12.52	1.10	68.2	68.2	68.3	68.4	68.4	68.3
4	49.48	1.69	67.6	67.7	67.7	67.5	67.6	67.6
5	101.96	2.01	66.2	66.3	66.2	66.2	66.4	66.3
6	491.84	2.69	54.0	54.1	53.9	54.1	54.0	54.0
7	1081.92	3.03	48.1	48.2	48.2	48.1	48.1	48.1
8	2063.6	3.31	41.6	41.7	41.8	41.7	41.7	41.7
9	2985.64	3.48	39.5	39.4	39.5	39.5	39.5	39.5
10	3800.76	3.58	36.8	36.8	36.8	36.7	36.8	36.8

The mean surface tension obtained with each solution was plotted against the logarithm of the concentration (See graph attached).

The surface tension decreases as the concentration increases but no stabilisation of the surface tension is observed up to the maximum concentration tested (3.8 g/L).

Therefore, the Critical Micelle Concentration is no lower than the solubility concentration (3.8 g/L).

Conclusions:

Study was carried out according to OECD guideline 115, ISO 304 (1985-12-15) – Surface Active Agents – Determination of surface tension by drawing up liquid films. The Critical Micelle Concentration and thus surface tension could not be determined

Executive summary:

The purpose of this test was to determine the critical micelle concentration of the reference substance dibutylamine by measuring the surface tension of solutions at different concentrations. The test design described in this protocol was performed in accordance with the following guidelines: OECD TG 115; EU Method A.5 and ISO 304 (1985-12-15).

The measurement of the surface tension by the ring tensiometer method is restricted to aqueous solutions with a dynamic viscosity of less than 200 mPa.s, and substances having a water solubility higher than 1 mg/L.

The principle of the method is the following: when surfactants are brought into an aqueous solution, a higher concentration of surfactants is found at the surface than in the bulk. This decreases the surface tension of the solution, as a function of the total surfactant concentration. Once the surface of the solution is saturated with surfactant molecules, no more molecules can join the surface layer, irrespective of the concentration of surfactant reached. This means that no further decrease in surface tension is detected. Beyond this point agglomerates, called micelles, are formed within the bulk solution. This point is called “the Critical Micelle Concentration”. All measurements were made at 21.2+/- 0.5 °C.

Two reference substances, methanol and butanol-1were used. The surface tension of methanol was measured before the first solution determination and butanol-1 was measured after the last. The measurements of both resulted in values that met the validation criteria. 

The measurement procedure was repeated for each concentration of the test substance so that five consecutive values with the same surface tension (+/- 0.1 mN/m of the mean) are obtained. The arithmetic mean of the five measurements gives the surface tension value for the considered solution. Temperature was measured at the end of the determination.

The surface tension decreased as the concentration increased, as expected, but no stabilisation of the surface tension was observed up to the maximum concentration tested (3.8 g/L). The Critical Micelle Concentration is therefore no lower than the solubility concentration (3.8 g/L) and the surface tension for the substance could not be established.

Description of key information

Surface tension not determinable; OECD 115; Noel, Y. (2023)

Additional information

The purpose of this test was to determine the critical micelle concentration of the substance dibutylamine, which is a major constituent of the test item, by measuring the surface tension of solutions at different concentrations in line with OECD TG 115.

All measurements were made at 21.2+/- 0.5°C.

Two reference substances, methanol and butanol-1 were used. The measurements of both resulted in values that met the validation criteria.

The surface tension decreased as the concentration increased, as expected, but no stabilisation of the surface tension was observed up to the maximum concentration tested (3.8 g/L). The Critical Micelle Concentration is therefore not lower than the solubility concentration (3.8 g/L) and the surface tension for the substance could not be established.

The test further supports that this substance as a whole is not or weakly surface active as dibutylamine would be the driver behind surface activity. 

The test also supports the methods employed for water solubility.  Dibutylamine is known to be surface active and therefore critical micelles below the water solubility may impact water solubility interpretation. The surface tension result using EU Method A.5 of 57.2 mN/m is thought to be driven below the surface activity cut-off due to dibutylamine, not N,N,N',N' tetrabutylmethylenediamine as the formers surface tension measure is 50.2 mN/m.  No critical micelles were formed below the water solubility of dibutyamine, this effect would not effect interpretation of the results for water solubility.  Moreover, in this mixture, dibutylamine's water solubility was < 1000 mg/L, thus no critical micelles would have formed. The test was also conducted to ensure that water solubility was the most relevant parameter to use during exposure assessment. It also meant that if any micelles formed below 3.8 g/L that this could be attributed to N,N,N',N' tetrabutylmethylenediamine. Based on the result the conduct of water solubility testing was most relevant for this substance.