distribution in the surface layer (a thin liquid layer contacting gas ) is sparser than internal.
Intermolecular repulsion in surface layer decreases as the distance between each other
increases. Intermolecular attraction prevails in surface layer. Mutual traction of any two
parts in surface layer prompts a shrinking trend in surface layer. The liquid surface tends
to reduce as much as possible due to the effect of surface tension, so the small droplet in
the air is in sph
erical shape.
1.2 Platinum plate method)
When the platinum plate is immersed in the liquid to be measured, the surface tension will
occurs around the platinum plate. The surface tension of the liquid will try to pull plate
down. When surface tension of the liquid and other related stress are equal to the
equilibrium force, the platinum plate will stop. At this time, the balance sensor will measure
the immersion depth, and convert it to the liquid surface tension values.
Steps:
(1) Raise the platform;
(2) When the bottom of the platinum plate contacts with the liquid surface, the equilibrium
value is measured by the sensor and converted to the surface tension value to display.
1.3 Platinum ring method
A circular membrane between testing part and the liquid sample will be formed with this
method.
Steps:
(1) Immerse the platinum ring gently into liquid inside.
(2)The platform descends and then a bubble film forms below the platinum ring and
eventually leaves it.
(3)The equilibrium value is measured by the sensor and converted to the surface tension
value to display.
1.4 Comparison
①
The platinum plate method measures the change of liquid surface (or interface) tension
over time. Platinum plate is always contacting with the liquid to be tested and as long as
the liquid surface tension changes, the test value will change. The curve of surface
tension over time can be observed with data processing software.
②
The platinum plate method can easily measure the surface tension of medium and high
viscosity liquid; The platinum ring method requires the ring to ascend and the ring is acted
upon surface tension and viscous force in that process.
③
The platinum plate method has high precision. Platinum plate is harder to be deformed
than ring. Irregular and uneven round ring may affect test precision.