Ultrasonic Studies of Solid Azobenzene-Decorated Polymer Thin Films

Area of Science:

• Polymer Science
• Photochemistry
• Materials Science

Background:

• Azobenzene derivatives are known for their photoisomerization properties.
• Controlling isomer conformation in solid polymer films is crucial for advanced materials.
• Ultrasound's potential for inducing solid-state molecular transformations is an emerging area.

Purpose of the Study:

• To investigate the efficiency of ultrasound in inducing cis-to-trans isomerization of azobenzene in polymer films.
• To differentiate between direct ultrasonic agitation and ultrasound-induced heating effects on isomerization.
• To compare the kinetics and energy barriers of ultrasound-induced isomerization with other methods.

Main Methods:

• Synthesis of methyl methacrylate and methacryloyloxyazobenzene copolymers [P(MMA/MOAB)].
• Application of ultrasonic agitation to solid polymer films.
• Utilizing ultraviolet-visible and 1H nuclear magnetic resonance spectroscopies for analysis.
• Comparative studies involving heat and visible light irradiation.

Main Results:

• Ultrasound induced a 46% cis-to-trans isomerization through direct agitation.
• An additional 46% cis-to-trans conversion was attributed to localized ultrasound-induced heating.
• Ultrasound exposure required longer times for cis-to-trans switching compared to heat or visible light.
• The activation energy for cis-to-trans conversion was comparable to previously reported values.

Conclusions:

• Ultrasound is a viable method for inducing cis-to-trans isomerization in azobenzene-containing polymer films.
• Both mechanical agitation and thermal effects contribute to ultrasound-mediated isomerization.
• While effective, ultrasound is kinetically slower than photothermal or direct photoisomerization for this system.
• Polymer incorporation influences isomerization kinetics but not the fundamental conformational change energy barriers.