Homeotropically Aligned Monodomain-like Smectic-A Structure in Liquid Crystalline Epoxy Films: Analysis of the Local Ordering Structure by Microbeam Small-Angle X-ray Scattering

Abstract

For the development of functional thin films with high thermal conductivity, the local ordering structure of a cured liquid crystalline epoxy resin (LCER) droplet was investigated by using synchrotron radiation microbeam small-angle X-ray scattering. The cured LCER in the vicinity of a substrate with low surface free energy was revealed to form a polydomain smectic-A (SmA) structure in which the normal direction of the layers was random in each domain, although the alignment was planar near the air interface. On the other hand, the cured LCER on a substrate with high surface free energy formed a homeotropically aligned SmA structure in the region within 21 μm from the surface of the substrate. Therefore, a 20 μm thick LCER film was fabricated and found to form a homeotropically aligned monodomain-like SmA structure throughout the whole film with a high thermal conductivity (0.81–5.8 W m –1 K –1 ). This film with a high thermal conductivity is expected to be applicable for adhesion and precoating materials for electrical and electronic devices.

Thermal Conducting Thermosets Driven by Molecular Structurally Enhanced Mesogen Interactions

“…Hence, the thermal conductivity of pure thermosetting resins for preparing a polymer composite can be considered valuable if it can secure a thermal conductivity of 1–2 W/m·K. , Particularly, regarding epoxy resins (ERs), which consist of tricyclic LC epoxy, phenol resin, and triphenylphosphine, their maximum reported isotropic thermal conductivity value is 1.16 W/m·K . Additionally, the same research group revealed that the same epoxy achieved up to 5.8 W/m·K conductivity after a surface treatment in an amine curing system, although the value was the anisotropic maximum . These studies were greatly significant because they represent a breakthrough for the limits of organic matter.…”

“…These studies were greatly significant because they represent a breakthrough for the limits of organic matter. However, the global utilization of the materials was limited by the high conductivity values obtained by the film, as well as the fact that most of them required special processing. − ,− To the best of our knowledge, the maximum thermal conductivity of epoxy bulk systems, which could be utilized globally, must be <0.5 W/m·K; those with relatively high values are LC materials. , …”

“…43 Additionally, the same research group revealed that the same epoxy achieved up to 5.8 W/m•K conductivity after a surface treatment in an amine curing system, although the value was the anisotropic maximum. 44 These studies were greatly significant because they represent a breakthrough for the limits of organic matter. However, the global utilization of the materials was limited by the high conductivity values obtained by the film, as well as the fact that most of them required special processing.…”

Forming a Homeotropic SmA Structure of Liquid Crystalline Epoxy Resin on an Amine-Modified Surface

“…TM/DAN on G1 had not been prepared in this study because GISAXS measurements of it had already been reported in our previous paper. 18,19 3. RESULTS AND DISCUSSION 3.1.…”

Highly anisotropic thermal conductivity of mesogenic epoxy resin film through orientation control

“…Previous studies 34,42 found that LC epoxy resins spontaneously form planar or homeotropic alignments depending on the surface free energy of the substrates on which the LC epoxy monomer is polymerized. Specifically, the cured product obtained from the LC epoxy monomer was revealed to form a homeotropically aligned smectic A structure on a substrate possessing a relatively high surface free energy (73 mN/m), and the cross-linked LC epoxy resin showed a maximum thermal conductivity of 5.8 W m À1 K À1 in the molecular chain direction.…”