Heat Transfer Organic Materials: Robust Polymer Films with the Outstanding Thermal Conductivity Fabricated by the Photopolymerization of Uniaxially Oriented Reactive Discogens

Abstract

For the development of advanced heat transfer organic materials (HTOMs) with excellent thermal conductivities, triphenylene-based reactive discogens, 2,3,6,7,10,11-hexakis(but-3-enyloxy)triphenylene (HABET) and 4,4',4″,4‴,4'''',4'''''-(triphenylene-2,3,6,7,10,11-hexaylhexakis(oxy))hexakis(butane-1-thiol) (THBT), were synthesized as discotic liquid crystal (DLC) monomers and cross-linkers, respectively. A temperature-composition phase diagram of HABET-THBT mixtures was first established based on their thermal and microscopic analyses. From the experimental results, it was realized that the thermal conductivity of DLC HTOM was strongly affected by the molecular organizations on a macroscopic length scale. Macroscopic orientation of self-assembled columns in DLC HTOMs was effectively achieved under the rotating magnetic fields and successfully stabilized by the photopolymerization. The DLC HTOM polymer-stabilized at the LC phase exhibited the remarkable thermal conductivity above 1 W/mK. When the DLC HTOM was macroscopically oriented, the thermal conductivity was estimated to be 3 W/mK along the in-plane direction of DLC molecule. The outstanding thermal conductivity of DLC HTOM should be originated not only from the high content of two-dimensional aromatic discogens but also from the macroscopically oriented and self-assembled DLC. The newly developed DLC HTOM with an outstanding thermal conductivity as well as with an excellent mechanical sustainability can be applied as directional heat dissipating materials in electronic and display devices.

Homeotropic Self-Alignment of Discotic Liquid Crystals for Nanoporous Polymer Films

“…The obtained image suggests that the direction of the columns in the planar nonporous sample is apparently perpendicular to the shearing direction of the film ( Figure 9 a), which is in contrast with other examples. 35 − 38 Furthermore, the image shows a persistence length of the columns in the micrometer range. Calculating the Fourier transform of the image ( Figure 9 b), shows a repeating distance of 3.3 nm orthogonal to the columnar director, which corresponds to the d (100) distance of 3.23 nm as determined by X-ray diffraction.…”

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

“…Therefore, increasing the thermal conductivity of the polymers themselves is essential. Kang et al 11 reported a high-thermal-conductive liquid crystalline (LC) polymer, which was photopolymerized using a thiol–ene reaction between disk-shape (discotic) liquid crystal (DLC) molecules. The thermal conductivity of the photopolymerized DLC polymer with a uniaxial orientation was estimated to be 3.0 W m –1 K –1 in the transverse direction of the oriented columnar axis.…”

The Effect of Interfacial Affinity on Thermal Conducting Performance of Liquid Crystalline Composites

“…Therefore, an effective development of innovative heat transfer materials for advanced devices needs a profounder understanding of the interfacial relationship between matrix and additive so that acceptable thermal conducting property can be accomplished even at small amount of filler loading [3]. Motivated by the requirement for a thermal conducting organic matrix, polymerizable liquid crystalline (LC) monomers, LC-ene and LC-thiol, were synthesized [4]. The synthesized LC network was served as a polymeric matrix for heat releasing composites packed with expanded graphite (EG) or hexagonal boron nitride (BN) [5].…”