Abstract

Contact angle goniometers and drop shape analysis systems are widely used in the study of surface wettability, interfacial properties, cleanliness evaluation, and surface treatment effects. The TrueDrop® and RealDrop® series developed by KINO Scientific Instruments integrate optical, mechanical, and 3D structural analysis modules based on conventional contact angle and surface tension testing methods. This paper introduces the principles, functional components, and model classifications of these drop shape analysis systems, as well as their applications in liquid cleanliness testing, surface contamination recognition, and complex interfacial analysis. By combining first-principles modeling, mechanical measurement techniques, and image processing algorithms, the TrueDrop®/RealDrop® platform offers a comprehensive and quantitative solution for interfacial characterization in both scientific research and industrial applications.

1. Fundamentals and Trends of Contact Angle and Drop Shape Analysis Systems

1.1 Scientific Importance of Contact Angle Measurement

Contact angle reflects the interfacial interactions between liquids and solids and is a key indicator for assessing wettability, surface energy, and treatment efficacy. It plays an essential role in materials characterization, surface coatings, microfluidics design, and biomedical interfaces.

1.2 Evolution of Drop Shape Analysis Systems

Traditional drop shape analysis systems, mainly based on the sessile drop method, are simple and intuitive but face limitations in identifying contamination and analyzing complex surfaces. Recent developments emphasize integrated platforms that combine optical imaging, mechanical tension measurement, and 3D analysis to meet diverse demands in modern surface science.

2. System Structure and Principles of the TrueDrop®/RealDrop® Platform

2.1 Optical Contact Angle and Interfacial Tension Module

Using high-resolution cameras and contour recognition algorithms, this module extracts drop profiles and calculates contact angles and interfacial tension via ADSA® (Advanced Dynamic and Static Analysis) modeling of the Young-Laplace equation. Unlike conventional image-fitting algorithms constrained to Bond numbers between 0.4 and 0.75, ADSA® supports robust modeling across a wider range of droplet shapes.

2.2 Mechanical Surface Tension Measurement Module

Based on the Wilhelmy plate method, this module records buoyancy and adhesion forces to calculate surface tension accurately. It enables precise detection of changes caused by organic residues, surfactants, or cleaning agents, enhancing reliability in cleanliness evaluation of liquids and solid surfaces.

2.3 Top-View and 3D Structural Analysis Module

By incorporating top-down imaging and 3D modeling, this module provides full topological analysis of the contact region, enabling directional contact angle mapping and advanced analysis of functional or microstructured surfaces.

3. Cleanliness Analysis: Integrated Evaluation of Liquids and Solids

3.1 Liquid Cleanliness: Pendant Drop Analysis for Water Contamination

Through pendant drop testing and Young-Laplace modeling, the system accurately detects deviations in surface tension caused by contaminants. Compared to conventional methods that assume constant water surface tension, TrueDrop®/RealDrop® offers enhanced reliability in assessing liquid purity.

3.2 Solid Surface Cleanliness: Reverse Analysis via Droplet Tension

On solid surfaces with possible residues such as oils or detergents, platinum plate measurements enable reverse estimation of surface states through observed water droplet tension changes. This is particularly valuable for evaluating cleaning efficacy where visual inspection is insufficient.

4. Advanced Measurement Strategies for Complex and Functional Surfaces

4.1 Top-View Imaging and Directional Contact Angle Mapping

With top-view imaging and directional contour analysis, the system generates full-angle distribution maps that reveal wettability anisotropy, supporting microstructure design validation, coating uniformity inspection, and localized performance analysis.

4.2 3D Morphology Coupled with Contact Angle Mapping

The C60 model combines structured light or confocal techniques for microtopography acquisition with drop contour analysis. This enables identification of Cassie-Baxter and Wenzel wetting states, particularly useful for superhydrophobic or interfacially engineered materials.

5. Model Comparison and Application Scenarios

6. Conclusion and Outlook

As essential tools for surface characterization, contact angle and drop shape analysis systems are evolving toward multifunctionality and high precision. The TrueDrop®/RealDrop® platform integrates optical, mechanical, and morphological modules to deliver comprehensive analysis of complex wettability behaviors.
With increasing demand across material research and engineering, the system is expected to find broader application in microfluidics, biointerfaces, and smart surface development. Modular design and intelligent operation will continue to guide future upgrades.