In cutting-edge fields such as new energy batteries, waterproof coatings, and self-cleaning glass, superhydrophobic materials (contact angle>120The application of (°) is becoming increasingly widespread. However, many laboratories encounter a tricky problem when testing such materials: droplets quickly roll or bounce off the surface of the sample as soon as they come into contact, and traditional seat drop methods cannot capture stable contact angle images at all.

Many process engineers are truly puzzled by the question of how to evaluate wettability even if the contact angle cannot be accurately measured. At this point, choosing a truly knowledgeable device becomes particularly crucial. Users who are looking for manufacturers of high-precision contact angle measuring instruments will find that for such hydrophobic samples, the instrument must have two core capabilities: hanging drop method and high-speed automatic fitting.

Today, starting from the typical superhydrophobic scenario of battery separators, we will explore how to obtain stable and reproducible contact angle data using more scientific testing methods.

1、 Why do superhydrophobic materials require traditional testing'Invalid'?

1、The wetting pain points of battery separators

Taking lithium battery separators as an example, their surfaces usually have microporous structures and low surface energy coatings, with contact angles often exceeding130°. When the needle drips2MLWhen a droplet falls, it cannot stand at all and either rolls away immediately or undergoes elastic bouncing at the moment of contact.

2、 Limitations of the Seat Drop Method

The traditional seat drop method assumes that droplets are stationary and spread on a horizontal surface, but for superhydrophobic materials:

Droplets are difficultSitting steadily, the success rate of manual operation is extremely low

Even with forced contact, the droplet shape is asymmetric, and the difference in left and right contact angles can reach10Above °

Manual tangent fitting has large errors and poor repeatability

Some users have provided feedback:If tested by someone else, the result may be worse15° cannot be used as a process criterion at all. ”

2、 Suspension Drop Method: Born for Superhydrophobic Materials

1、What is the suspended drip method?

The hanging drop method is to suspend a liquid droplet under a needle and indirectly calculate the interfacial tension and contact angle information between liquid and solid by analyzing the contour of the suspended droplet. For superhydrophobic materials, the suspension drop method does not require droplets to be on the surfaceStanding firm fundamentally avoids the problem of droplet bouncing.

2、How to apply the hanging drop method to battery separators?

In practical operation:

After fixing the battery separator sample, the needle should be close to the surface but not in contact

Squeeze out approximately with a microinjection pump0.5MLDroplet, make it just stay at the tip of the needle

Slowly lift the sample stage until the bottom of the droplet lightly touches the surface of the diaphragm and immediately descends

By analyzing the dropletsCalculate the true contact angle based on the contour at the moment of stretching

This process requires high requirements for droplet volume control and motion stability. If the injection pump of the instrument has insufficient suction accuracy orZIf there is vibration during shaft lifting, the data will drift.

3、 Automatic fitting algorithm: turning experience into standards

With good images, smart software is also needed. Many domestic devices are stuck in the final step: manual point selection and fitting.

1、Sub-pixel edge recognition

Excellent automatic fitting algorithms first require sub-pixel level edge recognition capabilities. Conventional algorithms can only treat pixels as the smallest unit, while sub-pixel algorithms can further subdivide between two pixels5-10A 'virtual pixel' greatly improves the smoothness of droplet contours.

2The Young-LaplaceTrue fitting

The most accurate algorithm currently recognized by Gong isYoung-LaplaceEquation fitting. It does not treat droplets as a circular arc, but rather considers their true form under the combined action of gravity and surface tension. For asymmetric suspended droplets, this algorithm can automatically fit the left and right contact angles and provide the mean and deviation.

Guangdong Beidou Instrument The software for the entire range of contact angle measuring instruments is built-in9A fitting algorithm, among whichYoung-LaplaceAutomatic fitting has been optimized specifically for the suspended droplet method. Even if the contact angle is as high as150The superhydrophobic battery separator can also be used in0.5Complete calculations within seconds, with repeatability error controlled within ±0.5Within degrees.

This is exactly the algorithm depth that many users repeatedly compare when asking which domestic contact angle measuring instrument is goodHardware can be replicated, but the iterative experience and targeted optimization of algorithms require a large number of real sample tests to precipitate.

4、 Practical case: Suspension drop method testing process for battery separators

1、Sample preparation

crop5×5 cmBattery separator, keep the surface clean, do not touch the test area

Select ultrapure water as the testing liquid, and control the droplet volume within0.5–1.0 ML

2、Test steps

1.Install the diaphragm and adjust the level（Sample table levelness ＜01°

2.Clean the needle, pre drip3time（Avoid needle tip residue）

3.Droplets suspended from the needle tip（volume06ML, Stable2second）

4.Slowly lift and touch the sample（speed005 mm/s）

5.Automatically trigger shooting and fitting（frame rate≥100 fps）

6.Repeat at different positions5Take the average of the second time（interval≥5 mm）

3、Interpretation of results

If the difference in left and right contact angles is less than2° indicates good uniformity of the diaphragm coating

If the standard deviation of multiple measurements is greater than1.5°, it is necessary to check whether there are defects on the surface of the sample or whether the needle is contaminated

When a laboratory decides to purchase or replace equipment, the real focus is often on these three aspects:

1、Accuracy of microinjection system

Can the output be stable0.2MLGrade of droplets? Ordinary manual syringes are difficult to achieve and require automatic injection pumps controlled by micro stepper motors.

2、Frame rate and synchronization of high-speed cameras

The suspended droplet method capturesTouch-The image at the moment of separation requires a camera frame rate of at least100 fpsAnd it should be in line withZAxis motion triggers signal synchronization.

3、Compatibility of software algorithms with non ideal droplets

Superhydrophobic surface droplets often appear needle shaped or have small tails, and ordinary circle fitting may result in errors. Only supportYoung-LaplaceOnly software that automatically fits and allows manual adjustment of the fitting range can cope.

As a high-precision contact angle measuring instrument manufacturer that has been deeply involved in the field of interface testing for many years, Guangdong Beidou Instrument has mature solutions in all three dimensions mentioned above. From the materials laboratory of Xiamen University to BYD's new energy research and development center, Beidou equipment has undergone verification through tens of thousands of sets of superhydrophobic sample tests.

Returning to the original question: as your sample becomes more and more'Slippery', when traditional testing methods fail, the hanging drop method+Automatic fitting is currently the most reliable technological path. It does not rely on the "feel" of the operator, and uses precise control and intelligent algorithms to minimize subjective factors.

It is recommended that engineers who are screening equipment use a few typical difficult to measure superhydrophobic samples (such as homemade ones) firstPDMSOr use a commercial diaphragm to test and let the sample speak for you.

If you are looking for a good domestic contact angle measuring instrument, or hoping to obtain Guangdong Beidou Instrument The actual test report and demonstration video of the contact angle measuring instrument for superhydrophobic materials can be directly contacted with the manufacturer's technical support team to schedule a prototype trial.

True technical strength is not afraid of the most demanding samples.