Investigating the origin of the far-field reflection interference fringe (RIF) of microdroplets

Journal Article · Wed May 22 00:00:00 EDT 2024 · Journal of Applied Physics

DOI:https://doi.org/10.1063/5.0211245· OSTI ID:2472758

Kim, Iltai Isaac ^[1]; Lie, Yang ^[2]; Park, Jaesung ^[1]; Kim, Hyun-Joong ^[3]; Kim, Hong-Chul ^[3]; Yoon, Hongkyu ^[4]

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1. Texas A & M Univ., Corpus Christi, TX (United States)
2. Texas A & M Univ., Corpus Christi, TX (United States); Pro-Lab Diagnotics, Round Rock, TX (United States)
3. CEKO Co., Ltd. (Korea, Republic of)
4. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

We show that the reflection interference fringe (RIF) is formed on a screen far away from the microdroplets placed on a prism-based substrate, which have low contact angles and thin droplet heights, caused by the dual convex–concave profile of the droplet, not a pure convex profile. The geometric formulation shows that the interference fringes are caused by the optical path difference when the reflected rays from the upper convex profile at the droplet–air interface interfere with reflection from the lower concave profile at oblique angles lower than the critical angle. Analytic solutions are obtained for the droplet height and the contact angle out of the fringe number and the fringe radius in RIF from the geometric formulation. Furthermore, the ray tracing simulation is conducted using the custom-designed code. The geometric formulation and the ray tracing show excellent agreement with the experimental observation in the relation between the droplet height and the fringe number and the relation between the contact angle and the fringe radius. This study is remarkable as the droplet's dual profile cannot be easily observed with the existing techniques. However, the RIF technique can effectively verify the existence of a dual profile of the microdroplets in a simple setup. In this work, the RIF technique is successfully developed as a new optical diagnostic technique to determine the microdroplet features, such as the dual profile, the height, the contact angle, the inflection point, and the precursor film thickness, by simply measuring the RIF patterns on the far-field screen.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: NA0003525
• OSTI ID: 2472758
• Report Number(s): SAND--2024-13781J
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 20 Vol. 135; ISSN 0021-8979
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
Geometrical optics
Goniometers
Interferometry
Liquid solid interfaces
Microcontact printing
Microdroplets
Optical interference
Thin films