1. Preliminary preparation: Confirm the environment and instrument status

Environmental control: Stabilize the testing environment temperature at 23 ± 2 ℃, control the relative humidity at 40% -60%, turn off ventilation equipment to avoid airflow interference, clean the workbench to ensure no dust.

Instrument inspection: Turn on the instrument power, start the control software, check if the light source, camera, and drip system (needle, syringe) are normal, and confirm that the syringe has been filled with the liquid to be tested (such as deionized water, which needs to be used and installed immediately).

Liquid preparation: The liquid to be tested is subjected to degassing treatment (to avoid bubbles affecting the droplet shape), and the liquid temperature is recorded (for subsequent data correction). The commonly used liquid volume should be pre-set to 2-5 μ L.

2. Sample processing: Ensure that the sample meets the testing requirements

Sample size: Ensure that the sample size fits the sample stage (e.g. diameter not less than 10mm, thickness not exceeding 5mm). If the sample is too small, it needs to be fixed with a glass slide to avoid displacement during testing.

Surface cleaning: Use a dust-free cloth dipped in anhydrous ethanol or isopropanol to wipe the surface of the sample, remove oil stains, fingerprints, and dust, then place it in a drying oven (50-60 ℃) to dry for 10-15 minutes, cool to room temperature, and then proceed with testing.

Sample fixation: Place the processed sample steadily in the center of the sample stage, adjust the sample position through the sample stage adjustment knob (X/Y/Z axis), and ensure that the testing area is located in the center of the camera field of view.

3. Instrument debugging: Set key parameters

Optical path calibration: Adjust the brightness of the light source (usually 50% -70%) and the focal length of the camera, so that the surface contour of the sample can be clearly presented on the screen without reflection or blurring; Through the software's "calibration function", calibrate the correspondence between image pixels and actual length using standard gauge blocks.

Dropping system debugging: Move the needle directly above the sample surface, adjust the needle height (5-10mm from the sample surface), manually discharge 1-2 drops of liquid through software, confirm that the droplet size is uniform and there are no bubbles, and set the automatic dripping parameters (volume 2-5 μ L, dripping speed 0.5 μ L/s).

Algorithm selection: Select an image analysis algorithm based on the expected shape of the droplet to be tested - for spherical droplets (contact angle>90 °), use the "circle method"; for elliptical droplets (contact angle 30 ° -90 °), use the "ellipse method"; and for irregular droplets (contact angle<30 °), use the "Young Laplace method".

4. Testing operation: Standardized process execution

Pre testing: Click on the software "Single Test" to automatically drop 1 drop of liquid onto the surface of the sample, observe whether the droplet is stable (no offset, no rapid spreading/shrinking), and if there is any abnormality, adjust the sample position or droplet parameters again.

Formal testing: After the pre-test is normal, execute the "multiple tests" mode and drop one drop of liquid on each area of the sample surface (at least 3 points, with a spacing of ≥ 5mm). After each drop of liquid is dropped for 1-3 seconds (to be balanced), the software automatically captures the image and calculates the contact angle.

Exception handling: If there is droplet deformation, needle hanging, or image blurring during testing, the test should be stopped immediately, and the problem should be checked and resolved (such as replacing the needle or cleaning the sample surface) before restarting the test. Any abnormal data that has been generated should be marked and removed.

5. Data processing: Ensure the validity of results

Data filtering: View all test data and remove outliers that deviate significantly from the mean (deviation>5 °). If there are less than 3 valid data sets, retesting is required.

Result calculation: Take the arithmetic mean of the valid data, calculate the standard deviation (reflecting data repeatability), and record the test conditions (liquid type, temperature, humidity, algorithm type).

Report generation: Organize the test results (mean, standard deviation, test conditions) and representative droplet images into a test report, named in the format "Sample Name Test Date Contact Angle Report", and save it to the specified folder.

6. Closing maintenance: Extend instrument lifespan

Instrument cleaning: After the test is completed, wipe the sample table and needle with a dust-free cloth. The remaining liquid in the syringe needs to be emptied, and rinse the syringe and needle with deionized water (to avoid liquid residue blockage). Then turn off the instrument power.

Sample processing: Used samples should be classified and stored (recyclable/waste samples), and the testing table should be cleaned again to ensure that there are no liquid residues or sample debris.

Record filling: Record the testing date, sample name, testing frequency, instrument operating status, and abnormal conditions in the instrument usage log for easy traceability and maintenance.