Surface tension experimentThe accuracy highly depends on the initial state of the experimental setup. Before the experiment, it is necessary to ensure measurement accuracy through standardized calibration and thoroughly clean to avoid interference from impurities. The following provides detailed operation guidelines from two aspects: device calibration and component cleaning.
1、 Device calibration: Ensure measurement accuracy
Calibration tools and reference materials
Calibration tools: standard weights (used for force sensor calibration), vernier calipers (measuring component dimensions), thermometers (monitoring ambient temperature).
Standard substance: Liquid with known surface tension (such as pure water with a surface tension of 72.8 mN/m at 20 ℃ or ethanol with a surface tension of 22.3 mN/m at 25 ℃).
Calibration steps
Calibration of force sensor (taking the ring method as an example):
Hang the platinum ring on the force sensor and connect it to the data acquisition system.
Hang standard weights (such as 10 mN, 20 mN) and record sensor readings.
If the reading deviates from the weight's gravity by more than ± 1%, adjust the sensor's zero point or gain parameters until the error is ≤ ± 0.5%.
Geometric parameter calibration:
Measure the circumference (C) and radius (r) of the platinum ring with a vernier caliper, and calculate the circumference correction factor of the ring (f=0.7250+0.0403C/r -0.00094C ²/r ²).
If the ring is deformed due to use, it needs to be replaced with a new ring and the parameters need to be measured again.
Temperature calibration:
Place the thermometer probe near the liquid sample and monitor the temperature of the experimental environment.
If the temperature fluctuation is greater than ± 0.5 ℃, a constant temperature water bath or air conditioner should be used to adjust it to a stable value (such as 25 ℃± 0.2 ℃).
Calibration Record
Fill out the calibration form, record the calibration date, standard substance name, sensor reading, correction factor, and environmental temperature and humidity as the basis for tracing experimental data.
2、 Component cleaning: eliminate impurities and interference
Cleaning tools and reagents
Tools: dust-free cloth, soft bristle brush, tweezers, ultrasonic cleaning machine (optional).
Reagents: Analytical pure ethanol, distilled water, acetone (solvent resistant components only).
Key component cleaning process
Platinum ring:
Use tweezers to pick up the ring and avoid direct finger contact that may cause oil stains to adhere.
Rinse with ethanol and distilled water sequentially, and gently brush the surface residue of the ring with a soft bristled brush.
Ultrasonic cleaning for 5 minutes (power ≤ 50W, frequency 40kHz) to remove small particles.
After drying, place it in a clean culture dish for later use.
Glass dish/sample cup:
Soak in ethanol for 10 minutes and wipe the inner wall with a dust-free cloth.
Rinse with distilled water three times, invert and air dry or blow dry with nitrogen gas.
Check if the bottom of the dish is flat, and replace it if there are scratches to prevent affecting the stability of the liquid level.
Elevating platform and fixture:
Wipe metal parts with a dry cloth to remove dust or rust.
Apply a small amount of silicone oil to lubricate the guide rail, ensuring smooth lifting and no jamming.
Cleaning verification
Visual inspection: The surface of the component should be free of visible stains, water marks, or fibers.
Contact angle test (optional): Soak the cleaned component in distilled water and observe if the droplet contact angle is close to 0 ° (completely wetted). If the contact angle is>5 °, it needs to be cleaned again.
3、 Pre experiment checklist
| check item | Qualification Standard | Nonconforming product handling |
| Force sensor calibration | Reading error ≤± 0.5% | Re calibrate or contact the manufacturer for repair |
| Geometric parameters of platinum ring | The deviation between the circumference correction coefficient and the theoretical value is less than ± 1% | Replace the platinum ring |
| Cleanliness of glass dish | After rinsing with distilled water, the contact angle of the droplets is less than 5 ° | Re clean or replace the utensils |
| ambient temperature | 25 ℃± 0.5 ℃ (or the required temperature for the experiment) | Start the thermostatic water bath or adjust the air conditioner |
| Lubrication of lifting platform | Smooth lifting without any lag | Apply silicone oil or replace the guide rail |
4Surface tension experimental apparatusPrecautions
Avoid cross contamination: Thoroughly clean the components between different sample testing rooms, especially for high viscosity or surfactant containing liquids.
Prevent ring deformation: Platinum rings should be stored flat in a dedicated box to avoid compression or collision.
Timely drying: After cleaning, the components need to be completely dried before assembly to prevent moisture residue from causing data fluctuations.
Calibration cycle: It is recommended to calibrate every 3 months or recalibrate after replacing key components.
By standardizing calibration and cleaning, experimental errors can be significantly reduced (usually repeatability errors can be controlled within ± 1%), providing a reliable basis for subsequent surface tension measurements.