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Surface tension

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Reference
Endpoint:
surface tension
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline followed
Principles of method if other than guideline:
Surface tension of aqueous solutions of NaLAS was measured by an automated Lauda TE IC by the duNouy ring method. All solutions were prepared with water passed through a Nanopure water filter system and with sufficient salt to equalize the ionic strength. Solubility of commercial NaLAS was determined by slowly lowering the temperature in a Fisher Isotemp incubator over several days and recording the temperature at which the solutions first turned cloudy (cloud point). Clear points were determined by raising the temperature slowly over several days and recording when the solution cleared. The solubility of the C12 narrow-distribution phenyl isomers was determined by heating a saturated solution to 70°C for 0.5-3 h and then cooling to 5°C. After equilibrating to room temperature overnight, the cloudy mixture was centrifuged, and the clear supernatant drawn off, weighed, and dehydrated to determine percentage solids. The percentage dissolved was then calculated from the weight loss to the supernatant.
GLP compliance:
not specified
Type of method:
ring method
Surface tension:
29.3 - 31.8 other: dynes/cm
Temp.:
25 °C
Conc.:
120 mg/L
Remarks on result:
other: 1 "dyne/centimeter [dyn/cm]" is equivalent to 1 "millinewnon/meter [mN/m]"

Surface activity increased with increasing average alkyl chain length.   Some decrease in surface tension was observed with increasing phenyl isomer number, but the range of phenyl isomer distribution of commercial products is not large enough to significantly alter the surface tension vs. log concentration plot.   Increasing the average alkyl chain length of LAS decreases solubility (i.e., increases cloud point).   The following table shows the critical micelle concentration (CMC) for various chain lengths LAS tested.

                                                

Chain length, isomer composition, dialkyltetralin sulfonate content

CMC (g/L)

Surface Tension (dynes/cm) 

C11 high 2-phenyl, low dialkyltetralinsulfonate

0.120

 31.5

C11 high 2-phenyl, high dialkyltetralinsulfonate

0.120

 31.8

C11 low 2-phenyl, low dialkyltetralinsulfonate

0.120

 31.6

C12 low 2-phenyl, low dialkyltetralinsulfonate

0.105

 30.3

C13 low 2-phenyl, low dialkyltetralinsulfonate

0.038

 29.3

 

Conclusions:
The surface tension was 29.3-31.8 dynes/cm for Sodium dodecylbenzenesulfonate (CAS No. 25155-30-0, EC Number; 246-680-4).
Executive summary:

The surface tension of various components of linear alkyl sulfonates was measured at 25 degree C. The surface tension of the components ranged from 29.3 -31.8 dynes/cm.

Description of key information

The surface tension was 29.3-31.8 dynes/cm.
1 "dyne/centimeter [dyn/cm]" is equivalent to 1 "millinewnon/meter [mN/m]"

Key value for chemical safety assessment

Surface tension:
30
in mN/m at 20°C and concentration in mg/L:
120

Additional information

The surface tension of various components of linear alkyl sulfonates was measured at 25 degree C. The surface tension of the components ranged from 29.3 -31.8 dynes/cm.

Surface activity increased with increasing average alkyl chain length.   Some decrease in surface tension was observed with increasing phenyl isomer number, but the range of phenyl isomer distribution of commercial products is not large enough to significantly alter the surface tension vs. log concentration plot.   Increasing the average alkyl chain length of LAS decreases solubility (i.e., increases cloud point).   The following table shows the critical micelle concentration (CMC) for various chain lengths LAS tested.

                                                

Chain length, isomer composition, dialkyltetralin sulfonate content

CMC (g/L)

Surface Tension (dynes/cm) 

C11 high 2-phenyl, low dialkyltetralinsulfonate

0.120

 31.5

C11 high 2-phenyl, high dialkyltetralinsulfonate

0.120

 31.8

C11 low 2-phenyl, low dialkyltetralinsulfonate

0.120

 31.6

C12 low 2-phenyl, low dialkyltetralinsulfonate

0.105

 30.3

C13 low 2-phenyl, low dialkyltetralinsulfonate

0.038

 29.3