(648a) Experimental Insight on Non-Newtonian Liquid Extended Thin Film

The study of extended thin films plays a significant role in advancement of microfluidics domain. Many essential applications such as microscale heat pipes, falling film reactors are heavily influenced by the physical phenomena occurring in the extended thin film region near the three-phase contact line. The study of three phase contact line region is crucial, to understand the interfacial transport dynamics within these systems. Over the years, numerous experimental efforts have been undertaken to explore the complex interactions among the forces acting in this area, with the goal of modulating them to enhance the efficiency and effectiveness of mass and energy transfer in this region.

Despite this progress, there remains substantial potential for deeper and more rigorous investigation, particularly concerning thin films that arise during spreading of complex fluids. A notable gap exists in the literature limiting the understanding of non-Newtonian fluid behaviour in extended thin film region. The impact of strong viscous forces, on the formation and characteristics of extended thin films is a less explored query. The answer to this query is crucial for polymeric or colloidal fluids applications, where thin film behavior deviates significantly from those of simple Newtonian fluids.

To address these gaps, the present study focuses on a series of controlled experiments involving shear-thinning polymeric solution of sodium carboxymethyl cellulose (NaCMC) water solution. Surfactant is incorporated to alter the surface tension of the solution. The combined effects of surfactant and polymer concentration is examined by conducting detailed rheological study.

Furthermore, using an interferometric technique, the thickness of the extended thin film is measured across various polymer concentrations. These thickness profiles are then analyzed to determine the slope and curvature of the film, from which the Hamaker constant is calculated. This constant is a key parameter that quantifies van der Waals interactions and spreading characteristic of the polymer solution. Building upon these experimental insights, a theoretical model is developed based on a fundamental force balance and an augmented version of the Young-Laplace equation. This model is solved for polymer solutions of different concentrations. The results from the model shows a strong correlation with the experimental data, confirming its validity and usefulness.

Overall, this study provides a meaningful contribution toward understanding the behavior of extended thin films in non-Newtonian, sheer thinning fluid systems. The findings not only deepen the knowledge of the physics governing thin film formation and dynamics but also have practical implications for the design and optimization of microfluidic devices. These insights could support the development of more efficient, cost-effective, and scalable technologies in areas ranging from thermal management to chemical processing.