Characterization of optically driven fluid stress fields with optical tweezers

Area of Science:

• Rheology
• Soft Matter Physics
• Biophysics

Background:

• Understanding complex fluid behavior is crucial in various scientific and industrial fields.
• Traditional viscometry methods may not capture microscale phenomena or local variations in complex fluids.
• Optical tweezers offer a precise tool for manipulating and probing microscopic entities.

Purpose of the Study:

• To develop and validate a controlled stress microviscometer for analyzing complex fluids.
• To investigate microscopic fluid velocity fields and their relationship to bulk properties.
• To explore local inhomogeneities at the probe particle surface within complex fluids.

Main Methods:

• Utilizing dual beam optical tweezers to generate and measure microscopic fluid velocity fields.
• Employing a controlled stress approach for microviscometry.
• Conducting experiments with water as a baseline and a hyaluronic acid model for complex fluid analysis.
• Integrating optical torque measurements with flow field data.

Main Results:

• Demonstrated the accuracy of the microviscometer in water.
• Observed significant deviations from classical fluid dynamics in a hyaluronic acid model.
• Successfully determined bulk viscosity by analyzing flow field deviations and optical torque.
• Modeled the observed deviations to derive microscopic parameters.

Conclusions:

• The developed microviscometer accurately measures fluid properties at the microscale.
• Complex fluids exhibit non-classical flow behaviors that can be quantified using this technique.
• This method provides insights into both bulk viscosity and microscopic characteristics of complex fluids.