Study of micro and nano surface structures from UV irradiated urethane/urea elastomers

Area of Science:

• Materials Science
• Polymer Science
• Surface Science

Background:

• Urethane/urea copolymers are versatile materials with tunable properties.
• Understanding structure formation under external stimuli is crucial for material design.

Purpose of the Study:

• To investigate the formation of micro and nanostructures on free-standing flexible urethane/urea copolymer films.
• To analyze the effect of ultraviolet (UV) radiation exposure time on surface morphology and roughness.

Main Methods:

• Synthesis of a urethane/urea copolymer film (120 microm) from a polypropylene oxide-based prepolymer (PU) and polybutadienediol (PBDO).
• Exposure of film samples to UV radiation (λ=254 nm) for varying durations (23-49 h).
• Characterization using polarizing optical microscopy (POM), small-angle light scattering (SALS), and atomic force microscopy (AFM) before and after toluene extraction.

Main Results:

• Initially flat surfaces (Ra=0.59 nm) developed corrugated, wrinkled structures after 25 h of UV exposure and toluene extraction.
• Surface roughness (Ra) increased significantly, reaching up to 515.4 nm after 49 h of exposure.
• A non-monotonous time-dependent growth of wrinkled surfaces was observed, with a notable increase in peak-to-valley height and roughness between 26 and 31 h exposure.

Conclusions:

• UV radiation induces the formation of micro/nanostructured wrinkled surfaces on urethane/urea copolymer films.
• The development of these wrinkled surfaces is dependent on UV exposure time and correlated with uniaxial stretching effects.
• The study highlights a non-monotonous behavior in surface morphology evolution under UV irradiation.