February 23, 2017

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Liquid Crystalline Epoxy Resins

Photos of the resins cured at different temperatures showing different optical properties. LCERs are opaque indicating their semicrystalline structure. From left to right: 170oC; 180oC; 190oC; 200oC

The goal of this research is to investigate various liquid crystalline epoxy resins (LCERs) and identify the most promising systems to be used as polymer matrices for high performance composites.

LCERs are a relatively new class of thermosetting materials. The liquid crystalline (LC) phase formed upon curing of low molecular weight, multifunctional monomers can be retained by the three dimensional crosslinked networks that form during polymerization. The versatility of traditional epoxy resins, such as good mechanical properties, excellent chemical resistance, and low shrinkage upon curing can be further improved by introducing the LC phase into the networks.

Polarized optical microscope images of isothermal curing study of an LCER resin at different temperatures. The fan-shaped focal-conic texture is a characteristic of smectic LC phase. The cure temperatures are (a) 170oC; (b) 180oC; (c) 190oC; (d) 200oC.

LCERs may be obtained using monomers with rigid aromatic groups with functional end groups that facilitate crosslinking reactions. Fully cured LCERs exhibit a semicrystalline structure with individual LC domains distributed in an amorphous matrix. The ordered and rigid structure of LC domains can bring desirable thermomechanical characteristics such as low coefficient of thermal expansion (CTE) and high glass transition temperature. In addition, the fracture toughness of the resins can be greatly improved due to the presence of LC domains. Another interesting aspect of LCERs is their ability to be oriented under magnetic field. The resulting resins are expected to have substantial reduction in CTE and better thermomechanical properties than the unoriented materials.

People Involved

Yuzhan Li, Prashanth Badrinarayanan, Michael Kessler