Controlling Crystal Orientation in Films of Conjugated Polymers by Tuning the Surface Energy

Area of Science:

• Materials Science
• Polymer Science
• Crystallography

Background:

• Controlling molecular orientation in conjugated polymer films is essential for optimizing their electronic and optical properties.
• Understanding the interplay between surface energy and crystal growth is key to achieving desired film morphologies.

Purpose of the Study:

• To investigate how surface energies influence the crystal orientation of conjugated polymers.
• To develop a method for controlling the molecular orientation in polythiophene films for device applications.

Main Methods:

• Systematic modification of polythiophene side chains by attaching polar groups to alter surface energy.
• Crystallization of modified polythiophenes on various substrates (graphene, amorphous surfaces).
• Analysis of crystal orientation using techniques sensitive to molecular arrangement.

Main Results:

• Increasing the surface energy of edge-on crystals suppressed their formation at the vacuum interface.
• Achieved uniform face-on crystal orientation in polythiophene films up to 200 nm thick, even on amorphous surfaces.
• Demonstrated the ability to switch crystal orientation by altering crystallization conditions when interfacial interactions compete.

Conclusions:

• Surface energy is a fundamental factor dictating equilibrium crystal orientation in conjugated polymer films.
• Tailoring polymer side chains offers a route to control molecular packing for enhanced film properties.
• This work provides a foundational understanding for designing and fabricating high-performance conjugated polymer-based devices.