Photothermocapillary Method for the Nondestructive Testing of Solid Materials and Thin Coatings.

Aleksandr Zykov,Marina Kuimova,Vladimir Vavilov

doi:10.3390/s21196671

Abstract

The photothermocapillary (PTC) effect is a deformation of the free surface of a thin liquid layer on a solid material that is caused by the dependence of the coefficient of surface tension on temperature. The PTC effect is highly sensitive to variations in the thermal conductivity of solids, and this is the basis for PTC techniques in the non-destructive testing of solid non-porous materials. These techniques analyze thermal conductivity and detect subsurface defects, evaluate the thickness of thin varnish-and-paint coatings (VPC), and detect air-filled voids between coatings and metal substrates. In this study, the PTC effect was excited by a “pumped” Helium-Neon laser, which provided the monochromatic light source that is required to produce optical interference patterns. The light of a small-diameter laser beam was reflected from a liquid surface, which was contoured by liquid capillary action and variations in the surface tension. A typical contour produces an interference pattern of concentric rings with a bright and wide outer ring. The minimal or maximal diameter of this pattern was designated as the PTC response. The PTC technique was evaluated to monitor the thickness of VPCs on thermally conductive solid materials. The same PTC technique has been used to measure the thickness of air-filled delaminations between a metal substrate and a coating.

Highlights

By analyzing the relationship between the material thermal conductivity and the PTC pattern diameter, it was found that the dependence Dst (Ks ) can be expressed by the
The PTC technique was developed to monitor the thickness of varnish-and-paint coatings (VPC) on thermally conductive solid materials by measuring a specific PTC parameter Dst
This study establishes the main features of the PTC method for the detection of subsurface defects and the evaluation of coating thickness, as well as the determination of material thermal properties

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Microfluidics involves the manipulation of small volumes of liquids. The use of microfluidics in engineering, chemistry, and biology, including thermocapillary-based sensors and devices, has increased in recent years and has been summarized by Karbalaei et al [1]. A review of digital microfluidic devices was presented by Shiyu Chen et al [2]. Jasińska and Malecha described the proposed microfluidic modules with integrated microwave components [3]

Methods

Results

Discussion

Conclusion