Highly Oriented Liquid Crystalline Epoxy Film: Robust High Thermal-Conductive Ability

Area of Science:

• Materials Science
• Polymer Science
• Surface Science

Background:

• Liquid crystalline epoxy resins (LCERs) offer potential for advanced materials.
• Controlling molecular orientation is key to tailoring material properties.
• Thermal conductivity in polymers is an area of active research for electronic applications.

Purpose of the Study:

• To investigate the effect of molecular orientation of LCER on thermal conductivity.
• To understand the role of substrate surface free energy in controlling LCER alignment.
• To explore the potential of LCERs as high-thermal-conductive materials.

Main Methods:

• Modification of amorphous soda-lime-silica glass substrates with varying surface free energies.
• Investigation of LC epoxy monomer alignment using optical microscopy and X-ray analyses.
• Calculation of orientational order parameter using grazing incidence small-angle X-ray scattering (GISAXS).
• Estimation of thermal conductivity in the direction of the Smectic A (SmA) layer normal.

Main Results:

• LC epoxy monomer exhibited homeotropic alignment on high surface free energy substrates (71.3-72.7 mN m⁻¹) and planar alignment on low surface free energy substrates (46.3 mN m⁻¹).
• Cross-linking on high surface energy substrates resulted in a homeotropically aligned SmA structure with an orientational order parameter of 0.73-0.75.
• The cross-linked LCER achieved remarkable thermal conductivity values of 2.0 W m⁻¹ K⁻¹ (average) and 5.8 W m⁻¹ K⁻¹ (maximum) along the SmA layer normal.

Conclusions:

• Substrate surface free energy significantly influences the molecular orientation of LCER.
• Homeotropic alignment of LCER leads to substantially enhanced thermal conductivity.
• LCERs with controlled molecular orientation show promise for high-thermal-conductive adhesives and packaging in electronic devices.