pH-responsive fatty acid self-assembly transition induced by UV light.

Area of Science:

• Supramolecular Chemistry
• Materials Science

Background:

• Fatty acids are natural surfactants with pH-responsive properties.
• Solution pH can be modulated by external stimuli like CO2 or light.
• Photoacid generators (PAGs) enable light-induced pH changes in aqueous systems.

Purpose of the Study:

• To investigate photoresponsive systems using fatty acids and a PAG.
• To characterize the impact of UV-induced pH decrease on fatty acid self-assembly.
• To evaluate the effect of altered self-assembly on foaming properties.

Main Methods:

• Utilized a multi-scale approach combining molecular and microscopic characterization.
• Employed pH and infrared spectroscopy to determine fatty acid ionization state.
• Applied small-angle neutron scattering and microscopy to analyze self-assembled structures.

Main Results:

• UV irradiation of PAG-containing fatty acid solutions decreased pH, altering molecular ionization.
• This pH shift induced a transition from spherical micelles to vesicles or lamellar phases.
• Foam stability was significantly enhanced post-UV irradiation due to changes in self-assembly.

Conclusions:

• Fatty acid self-assembly and foaming properties can be controlled by light-induced pH changes.
• The observed transitions are dependent on fatty acid chain length.
• This photoresponsive strategy is extensible to other pH-responsive surfactants.