Determination of critical micelle concentration by dynamic light scattering

Significance of the topic

Detergent critical micelle concentration is a key parameter in colloid and surface chemistry affecting applications from drug delivery to formulation. Dynamic light scattering offers a non-perturbing and rapid technique to pinpoint micelle formation without probe interference.

Objectives and Study Overview

This study aimed to determine the CMC of Triton X-100 in salt-free conditions using dynamic light scattering, comparing results with established methods.

Methodology and Instrumentation

Measurements were performed on a Wyatt DynaPro DLS/SLS system at 90° scattering angle, using 45 µL quartz cuvettes and 0.1 µm filtered samples. Dynamic and static detectors monitored scattering intensity and hydrodynamic radius across increasing surfactant concentrations.

Main Results and Discussion

The scattering intensity increased markedly at ~0.26 mM Triton X-100, coinciding with the emergence of particles with an average hydrodynamic radius of ~3.8 nm, indicating micelle onset above 0.27 mM. Aggregation numbers and molecular weights derived from DLS closely matched values from fluorescence and ultracentrifugation.

Benefits and Practical Applications

• Non-perturbing measurement preserving native surfactant behavior
• Rapid and straightforward operation suitable for routine analysis
• Simultaneous determination of size, polydispersity, molecular weight, and concentration
• Adaptable to various solution conditions and surfactant systems

Future Trends and Potential Applications

Advancements may include integration with microfluidic platforms for real-time CMC monitoring, combining DLS/SLS data with machine learning for predictive modeling, and expanding to diverse surfactant and polymer assemblies in formulation science.

Conclusion

Dynamic light scattering provides a versatile and accurate approach to determine surfactant CMC and micelle characteristics, matching established techniques while offering enhanced ease of use. This method supports broad applications in research and quality control of colloidal systems.

Used Instrumentation

• Wyatt DynaPro DLS/SLS instrument with separate optimized detectors at 90°
• 45 µL quartz cuvette and 0.1 µm filtration system