Thermal and solutal non-equilibrium fluctuations in a polymer solution

Area of Science:

• Soft matter physics
• Polymer science
• Transport phenomena

Background:

• Non-equilibrium fluctuations (NEFs) are crucial in understanding complex fluid dynamics.
• Investigating simultaneous thermal and solutal NEFs provides insights into coupled transport processes.

Purpose of the Study:

• To investigate simultaneous thermal and solutal non-equilibrium fluctuations (NEFs) in a dilute polymer solution using shadowgraphy.
• To extract diffusive transport coefficients from observed NEFs.

Main Methods:

• Performed shadowgraphy experiments on a dilute polymer solution subjected to a temperature gradient.
• Analyzed gravitational quenching of NEFs at small q-vectors to define thermal and solutal roll-off wavevectors.
• Extracted data from static structure functions and time correlation functions.

Main Results:

• Successfully extracted thermal and solutal roll-off wavevectors using two distinct methods, showing good agreement.
• Observed a ∼10% larger static solutal roll-off wavevector, consistent with prior literature.
• Determined polymer diffusion, thermodiffusion, and Soret coefficients, along with solution thermal diffusivity.

Conclusions:

• Developed an alternative method to measure diffusive transport coefficients using NEFs and roll-off wavevectors.
• This method bypasses the need for explicit optical contrast factor knowledge.
• Acknowledged potential for unfavorable error propagation in this novel measurement technique.