A contact angle measuring instrument is a precision instrument specifically designed to measure the contact angle formed by a liquid on a solid surface. The contact angle is a key physical parameter for measuring the wettability of a liquid on a solid surface, providing information about the surface energy, surface tension, and properties of the solid-Important information on liquid interface interactions.

Core functions and principles

1. Definition of contact angle: contact angle(θ)It's fixed-liquid-The angle between the tangent line along the droplet contour and the solid surface at the contact point of the three-phase gas.

2. Measurement principle:

Instruments typically operate in controlled environments (temperature, humidity).

Carefully deposit a precise volume of test liquid (usually deionized water, but other liquids can also be used) onto a clean, flat surface of the solid sample through a microsyringe or automatic drip system.

Using high-resolution optical systems（CCDorCMOSA camera is used in conjunction with a uniform backlight or front light source to capture the side profile image of liquid droplets on a solid surface.

Image analysis software identifies droplet contours, baselines (solid surfaces), and three-phase contact points, and applies selected mathematical models (such as tangent method, circle fitting method, ellipse fitting method)Young-LaplaceAutomatically calculate the value of contact angle using methods such as equation fitting.

Main components of the instrument

1. Light source system：Provide uniform and stable lighting (usuallyLEDCold light source ensures clear and sharp droplet contours with high contrast. Common sources include backlight and front light.

2. Sample stage: precise adjustable position（X, Y, ZA platform with axis translation, sometimes with tilt and rotation functions, used for placing and positioning test samples. It may have a temperature control device.

3. Liquid injection unit:

Manual injector: The operator manually controls the droplet formation.

Automatic injection system: precisely controlled by stepper motors or piezoelectric ceramics, achieving precise control of droplet volume and automatic titration (especially important for dynamic measurement).

4. Image acquisition system: A high-resolution digital camera (usually equipped with a long working distance microscope lens) is used to capture droplet images.

5. Environmental chamber (optional but important): used to control the temperature, humidity, or atmosphere of the measurement environment (such as inert gases), reduce the impact of environmental fluctuations on the results, especially for volatile liquids or sensitive materials.

6. Image analysis software: the core brain of the instrument. be responsible for:

Image processing (noise reduction, edge detection, baseline recognition).

Apply mathematical models to calculate contact angles (left contact angle, right contact angle, average contact angle).

Calculate surface free energy and its components (byOWRK, Fowkes, van Oss-Chaudhury-GoodWaiting for theoretical models).

Perform dynamic contact angle analysis (forward angle, backward angle, rolling angle, contact angle hysteresis).

Data storage, analysis, and report generation.

Main measurement methods

1. Static drip method: commonly used. Measure the contact angle of a stationary liquid droplet on a solid surface. Suitable for most flat surfaces.

2. Suspension Drop Method: Measuring the contour of a droplet suspended from an injection needle tip, mainly used to measure the surface tension of a liquid/Interface tension, but it can also be indirectly used for estimating the apparent contact angle of irregular samples such as powders or fibers (requiring a special sample stage).

3. Capture bubble method: Capture a bubble on a solid surface immersed in liquid and measure the contact angle between the bubble and the solid surface. Suitable for measuring surfaces with strong hydrophobicity (such as underwater).

4. Dynamic contact angle measurement:

Tilt plate method: gradually tilt the sample stage until the droplets start rolling, and measure the forward angle, backward angle, and rolling angle when rolling occurs.

Droplet volume adjustment method: Slowly increase or decrease the droplet volume at a fixed position through an automatic injection system, and measure the forward and backward angles.