Testing Principle and Difference between Platinum Plate Method and Platinum Ring Method for Surface Tension

Platinum plate method

When the sensing platinum plate is immersed in the measured liquid, surface tension will be applied around the platinum plate, and the surface tension of the liquid will pull the platinum plate down as far as possible. When the surface tension of the liquid and other related forces and balance forces are balanced , the sensing platinum plate will stop immersing into the liquid. At this point, the instrument's balance sensor measures the depth of immersion and converts it into a value for the surface tension of the liquid.

In the specific test process, the test steps of the platinum plate method are: (1) gradually immerse the platinum plate in the liquid; (2) in the state of being immersed in the liquid surface, the balance value is sensed by the sensor; (3) the sensed balance value is Converted to surface tension values ​​and displayed.

P = mg + Lγ･cosθ – shρg

Balance force = gravity of the platinum plate + sum of surface tension – buoyancy force on the platinum plate

(up) (down) (up)

m : the weight of the platinum plate

g: Gravity (9.8N/Kg)

L : Perimeter of platinum plate

γ: surface tension of the liquid

θ: contact angle between liquid and platinum plate

s : cross-sectional area of ​​the platinum plate

h : depth of immersion of the platinum plate

ρ: density of the liquid

hardware

When the platinum plate touches the sample liquid, the surface tension of the sample liquid will pull the platinum plate down. The digital detection system based on high-precision electronic balance detects this tiny force and transmits it to the microprocessor for processing.

software

The special control and analysis software converts the detected micro force into the surface tension value through a series of calculations by the microprocessor.

Display and Output Devices

The LCD digital display screen outputs the surface tension value in real time, and if necessary, it can be connected to a printer to print data or collect corresponding data through a computer.

Platinum Tour de France

This method is also known as the du Nouy method because it is widely used in du Nou tensiometers, and is widely used because of its ease of operation . The Platinum Ring method is so called because a ring is formed between the test part and the liquid sample .

The measurement method of the platinum ring method is: (1) gently immerse the platinum ring in the liquid; (2) slowly lift the platinum ring up about 5mm to 6mm, that is, the liquid level drops relatively, so that A column of liquid forms below the platinum ring and eventually separates from the platinum ring. The platinum ring method is to sense a highest value, and this highest value is formed when the platinum ring and the liquid sample are close to each other. The accuracy with which this highest value is converted to a surface tension value depends on the viscosity of the liquid.

F in the above equation is a set value, its size depends on the diameter of the ring and the nature of the liquid. This correction is important because the downward force is not always vertical, and the behavior of the liquid pulled up with the platinum ring is complicated.

In general, F-values ​​are calculated by the Zuidema & Waters equation:

a : 0.7250

b : 0.09075 m-1  s2

c : 0.04534 – 1.679 r／R

r : radius of the platinum wire

R : Inner diameter of the platinum ring (the distance between the centers of the two wires)

ρ : density of the liquid

 Platinum Plate vs. Platinum Ring Comparison

The du Nouy platinum ring method has been used to measure surface tension for 40 years before the relevant measuring equipment is researched and produced.

years of history. In comparison, the Wilhelmy platinum plate method is only 20 years old. However, now more and more

Many people use the platinum plate method to measure surface tension. This is mainly due to the following deficiencies in the Platinum Ring:

1) It is difficult to measure the surface tension value of high-viscosity samples;

This is mainly due to the greater downward resistance of the sample on the inner side of the platinum ring

2) It is not easy to measure the surface tension value that changes with time;

This is mainly because the platinum ring can only measure the surface tension value at the point in time when the ring leaves the liquid.

3) It is difficult to maintain the accuracy of the instrument;

Platinum rings are easily deformed, and their varying sizes can affect surface tension measurements.

◆ paint

Place goo on top of the ring and measure

◆ Solutions containing surfactants

The surfactant concentration is low, and the surfactant is continuously dispersed.