Aggregation of ionic surfactants to block copolymer assemblies: a simple fluorescence spectral study

Area of Science:

• Physical Chemistry
• Polymer Science
• Colloid and Surface Chemistry

Background:

• Copolymer-surfactant interactions are crucial in various applications.
• Understanding these interactions requires precise methodologies.
• Fluorescence spectroscopy offers a sensitive probe for molecular interactions.

Purpose of the Study:

• To develop a simple fluorescence-based method for studying copolymer-surfactant interactions.
• To elucidate the interaction mechanisms across different concentration regimes.
• To investigate the general applicability of the method for diverse systems.

Main Methods:

• Steady-state fluorescence spectral measurements using coumarin 153 as a probe.
• Analysis of spectral parameters like full width at half-maximum and fluorescence intensity.
• Varying the molar ratio of ionic surfactant to triblock copolymer (n).

Main Results:

• Three distinct concentration regions identified based on spectral changes.
• At low n, copolymer-rich micelles dominate; at high n, surfactant-rich micelles form.
• Two interaction mechanisms (Type I and Type II) described for the transition, with Type II prevalent for nonionic copolymers and Type I for nonionic surfactants.

Conclusions:

• The fluorescence method effectively characterizes copolymer-surfactant complexation.
• Interaction mechanisms are dependent on surfactant and copolymer types and concentrations.
• The study provides insights into micelle formation and transformation processes.