Developing Scattering Morphology Resolved Total Internal Reflection Microscopy (SMR-TIRM) for Orientation Detection...

Area of Science:

• Colloid and surface science
• Soft matter physics
• Optical microscopy techniques

Background:

• Anisotropic colloidal particles are crucial in various applications.
• Measuring interactions of anisotropic particles at the ~kT scale is challenging.
• Existing techniques lack precise orientation and separation distance measurements for anisotropic colloids.

Purpose of the Study:

• To develop and validate a novel technique, scattering morphology resolved total internal reflection microscopy (SMR-TIRM).
• To demonstrate SMR-TIRM's capability in measuring anisotropic particle orientation and interactions.
• To enable accurate calculation of potential energy landscapes for colloidal ellipsoids.

Main Methods:

• Development of SMR-TIRM for analyzing light scattered from anisotropic particles.
• Utilizing an evanescent wave to probe particle-fluid interactions.
• Fitting scattered light morphologies with 2D Gaussian surfaces to extract orientation and aspect ratio parameters.
• Comparing experimental and simulation data for colloidal ellipsoids at varied orientations.

Main Results:

• Scattering morphology orientation (Mφ) correlates with particle azimuthal angle.
• Scattering morphology aspect ratio (M_AR) is sensitive to particle polar angle.
• Both azimuthal and polar angles are resolved effectively, outperforming bright-field microscopy.
• Integrated scattering intensity is orientation-dependent, requiring careful interpretation.

Conclusions:

• SMR-TIRM successfully resolves both azimuthal and polar angles of colloidal ellipsoids.
• A method is established to interpret orientation-dependent scattering intensity for accurate separation distance determination.
• This technique provides a pathway to precisely map the potential energy landscapes of anisotropic colloids.