ASTM D1331-89(1995)
(Test Method)Standard Test Methods for Surface and Interfacial Tension of Solutions of Surface-Active Agents
Standard Test Methods for Surface and Interfacial Tension of Solutions of Surface-Active Agents
SCOPE
1.1 These test methods cover the determination of surface tension and interfacial tension of solutions of surface-active agents, as defined in Terminology D 459. Two methods are covered as follows:
Method A—Surface Tension.
Method B—Interfacial Tension.
1.2 Method A is written primarily to cover aqueous solutions of surface-active agents, but is also applicable to nonaqueous solutions and mixed solvent solutions.
1.3 Method B is applicable to two-phase solutions. More than one solute component may be present, including solute components that are not in themselves surface-active.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Material Safety Data Sheets are available for reagents and materials. Review them for hazards prior to usage.
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Designation: D 1331 – 89 (Reapproved 1995)
Standard Test Methods for
Surface and Interfacial Tension of Solutions of Surface-
Active Agents
This standard is issued under the fixed designation D 1331; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope shall be not less than 6 cm in diameter, and sufficiently large to
ensure that the contact angle between the ring and the interface
1.1 These test methods cover the determination of surface
is zero.
tension and interfacial tension of solutions of surface-active
agents, as defined in Terminology D 459. Two methods are
4. Preparation of Apparatus
covered as follows:
4.1 Clean all glassware thoroughly. The use of fresh
Method A—Surface Tension.
chromic-sulfuric acid cleaning mixture, followed by a thor-
Method B—Interfacial Tension.
ough rinsing in distilled water, is recommended.
1.2 Method A is written primarily to cover aqueous solu-
4.2 Clean the platinum ring by rinsing thoroughly in a
tions of surface-active agents, but is also applicable to non-
suitable solvent and in distilled water, before taking a set of
aqueous solutions and mixed solvent solutions.
measurements. Allow the ring to dry, and then heat to white
1.3 Method B is applicable to two-phase solutions. More
heat in the oxidizing portion of a gas flame.
than one solute component may be present, including solute
components that are not in themselves surface-active.
5. Calibration of Apparatus
1.4 This standard does not purport to address all of the
5.1 The tensiometer is, in fact, a torsion balance, and the
safety concerns, if any, associated with its use. It is the
absolute accuracy depends on the length of the torsion arm,
responsibility of the user of this standard to establish appro-
which is adjustable. Torsion may be applied to the wire by
priate safety and health practices and determine the applica-
means of either the dial-adjusting screw (which controls the
bility of regulatory limitations prior to use. Material Safety
dial reading) or a rear adjusting screw. Calibration consists
Data Sheets are available for reagents and materials. Review
essentially in adjusting the length of the torsion arm so that the
them for hazards prior to usage.
dial scale will read directly in dynes per centimetre. The
precision tensiometer shall be calibrated in accordance with the
2. Referenced Documents
following: 5.1.1-5.1.3; the interfacial tensiometer shall be
2.1 ASTM Standards:
calibrated in accordance with 5.1.1-5.1.4.
D 459 Terminology Relating to Soaps and Other Deter-
5.1.1 Level the tensiometer. A liquid level of the type
gents
employed on analytical balances may be used. Place the level
3. Apparatus on the table that holds the sample for testing, and adjust the leg
screws of the tensiometer until the table is horizontal. Pull the
3.1 Tensiometer—Either the du Nouy precision tensiometer
torsion wire taut by means of the tension screw, and adjust the
or the du Nouy interfacial tensiometer, equipped with either the
dial reading and the vernier to zero. Insert the platinum ring in
4 or the 6-cm circumference platinum ring, as furnished by the
the holder, and place a small piece of paper across the ring.
manufacturer, may be used. The tensiometer shall be placed on
This will serve as a platform to hold the calibrating weight.
a sturdy support that is free from vibrations and other distur-
Turn the rear adjusting screw of the torsion wire until the index
bances such as wind, sunlight, and heat. The wire of the ring
level of the arm is opposite the reference line of the mirror; this
shall be in one plane, free of bends or irregularities, and
automatically compensates for the weight of the paper plat-
circular. When set in the instrument, the plane of the ring shall
form. Next, place an accurately standardized weight of be-
be horizontal, that is, parallel to the surface plane of the liquid
tween 500 and 800 mg on the paper platform and turn the
being tested.
dial-adjusting screw until the index level of the arm is opposite
3.2 Sample Container—The vessel for holding the liquid
the reference line of the mirror. Record the dial reading to 0.10
divison. Call this “gamma-c.”
These test methods are under the jurisdiction of ASTM Committee D-12 on
5.1.2 Calculate what the reading “gamma-c” obtained in
Soaps and Other Detergents and are the direct responsibility of Subcommittee
5.1.1 should be when the tensiometer is properly adjusted, as
D12.15on Physical Testing.
follows (Note 1):
Current edition approved May 26, 1989. Published July 1989. Originally
published as D 1331 – 54 T. Last previous editions D 1331 – 56(1986).
g 5 ~M 3 g!/2L (1)
c
Annual Book of ASTM Standards, Vol 15.04.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 1331
the water. Care should be taken that the solution is physically homoge-
where:
neous. Measurements made near or above the cloud point or other critical
M 5 weight placed on the paper platform, g,
solubility points can be in serious error. This is particularly true when the
g 5 gravity constant (Note 2), cgs units, and
solute is a surface-active material.
L 5 mean circumference of the ring (furnished by the
6.3 Lower the platform slowly, at the same time applying
manufacturer with each ring).
torsion to the wire by means of the dial-adjusting screw. These
If the recorded dial reading “gamma-c” is greater than the
simultaneous adjustments must be carefully proportioned so
calculated value, the torsion arm should be shortened. If
that the ring system remains constantly in its zero position. As
“gamma-c” is less than the calculated value, the torsion arm
the breaking point is approached, the adjustments must be
should be lengthened. Repeat the calibration procedure, read-
made more carefully and more slowly. Record the dial reading
justing the zero position after each change in the length of the
when the ring detaches from the surface.
torsion arm, until the dial reading agrees with the calculated
6.4 Make at least two measurements. Additional measure-
value. Each unit of the scale now represents a pull on the ring
ments shall be made if indicated by the over-all variation
of 1 dyne/cm. Note that a conversion factor, F (see 5.1.3), must
obtained, the total number of readings to be determined by the
be multiplied by the scale reading to give corrected surface
magnitude of that variation.
tension in dynes per centimetre.
6.5 Record the temperature of the solution and the age of the
NOTE 1—Example—If M is exactly 0.600 g and L is 4.00 cm:
surface at the time of testing. Since the submerging of the ring
g 5 (0.600 3 980.3)/(2 3 4.00) 5 73.52 dynes/cm
c
(6.2) may constitute a significant disturbance of the surface,
NOTE 2—The gravity constant is 980.3 at Chicago; in other localities it
take the age as the elapsed time between submersion and
will differ very slightly from this value.
breakaway of the ring. The accuracy of this time observation
5.1.3 After the tensiometer has been calibrated, it is conve-
may be indicated in the usual manner. In most cases an
nient to calculate the number of grams total pull on the ring that
accuracy of 65 s is reasonable, and sufficient for this test
is represented by each scale division. This is done simply by
method.
dividing the scale reading into the weight used for calibration
(Note 3). This value is used in the calculation of the conversion 7. Calculation and Report
factor, F, mentioned in 5.1.2.
7.1 The dial reading, obtained from a measurement carried
out in the foregoing manner with a calibrated instrument, is
NOTE 3—In the example given in Note 1, each scale unit after
calibration represents: actually the pull per linear centimetre on the ring (both inner
and outer circumference being considered) at the break-point,
0.600/73.52 5 0.008161 g (2)
expressed in dynes. This value, called the uncorrected surface
5.1.4 Interfacial Tensiometer—With the interfacial tensiom-
...
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