Thermal Transport in Polymers: A Review

In this article, we review thermal transport in polymers with different morphologies from aligned fibers to bulk amorphous states. We survey early and recent efforts in engineering polymers with high thermal conductivity by fabricating polymers with large-scale molecular alignments. The experimentally realized extremely high thermal conductivity of polymer nanofibers are highlighted, and understanding of thermal transport physics from molecular simulations are discussed. We then transition to the discussion of bulk amorphous polymers with an emphasize on the physics of thermal transport and its relation with the conformation of molecular chains in polymers. We also discuss the current understanding of how the chemistry of polymers would influence thermal transport in amorphous polymers and some limited, but important chemistry-structural-property relationships. Lastly, challenges, perspectives and outlook of this field are presented. We hope this review will inspire more fundamental and applied research in the polymer thermal transport field to advance scientific understanding and engineering applications.

Unveiling how intramolecular stacking modes of covalently linked dimers dictate photoswitching properties

Covalently linked π-stacked dimers represent the most significant platform for elucidating the relationship between molecular alignments and their properties. Here, we present the one-pot synthesis of two intramolecularly π-stacked dimers and disclose how intramolecular stacking modes dictate photoswitching properties. The dimer, which features cofacially stacked chromophores and geometrically favours intramolecular photochemical [2 + 2] cycloadditions, displays a nearly irreversible photoswitching behaviour. By contrast, the dimer, bearing crosswise stacked chromophores, is geometrically unfavourable for the cycloaddition and exhibits a highly reversible photoswitching process, in which the homolysis and reformation of carbon−carbon single bonds are involved. Moreover, the chiral carbon centres of both dimers endow these photoswitches with chirality and the separated enantiomers exhibit tuneable chiroptical properties by photoswitching. This work reveals that intramolecular stacking modes significantly influence the photochemical properties of π-stacked dimers and offers a design strategy toward chiral photoswitchable materials.

Microstructure evolution and properties of polyimide fibers containing trifluoromethyl units

A series of copolyimide (co-PI) fibers containing trifluoromethyl units were successfully obtained on the molecular design of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, p-phenylenediamine, and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP) via a widely utilized two-step wet-spinning method. Significant variations on the microstructures and properties of the resulting co-PI fibers were observed after the incorporation of HFBAPP moieties. The tensile strength and initial modulus of the fibers decreased from 0.70 GPa to 0.38 GPa and from 69.63 GPa to 9.60 GPa, respectively. However, the dielectric permittivity decreased from 3.62 to 2.85 in the frequency of 10 MHz as a result of the incorporation of trifluoromethyl units. Two-dimensional wide-angle X-ray diffraction showed that the fibers exhibited highly oriented molecular alignments along the fiber direction and low lateral packing degree in the transverse direction. In addition, the co-PI fibers possessed excellent thermal–oxidative stabilities with the 5% weight loss temperature ranging from 532°C to 552°C under nitrogen atmosphere and the glass transition temperature ranging from 312°C to 330°C.

Combined molecular and morphological phylogeny of Myrtlemiris, evolution of endosomal spicules, description of two new species and Neomyrtlemiris, gen. nov. (Insecta : Heteroptera : Miridae : Orthotylinae)

The mirid subfamily Orthotylinae is hyperdiverse in Australia but poorly described; this work is part of a series of papers on the documentation of this fauna. Two new species of the Australian endemic plant bug genus Myrtlemiris Cheng, Mututantri & Cassis (Heteroptera: Miridae: Orthotylinae: Orthotylini) are described as new to science: Myrtlemiris kararensis, sp. nov., and M. lochada, sp. nov. The new Australian genus and species Neomyrtlemiris picta gen. nov. et sp. nov. are also described. Myrtlemiris is analysed phylogenetically using 32 morphology-based characters, as well as molecular alignments (COI, 16S rRNA, 18S rRNA and 28S rRNA; including 1958 base pairs) with the genus found to be monophyletic based on molecular, morphological and combined analyses. Neomyrtlemiris is the sister to Myrtlemiris. Host plant association analysis demonstrated constraints to the myrtaceous tribe Chamelaucieae, with Malleostemon and Calytrix recovered as ancestral host plants. Ancestral state reconstructions were carried out on male genitalic structures, demonstrating the phylogenetic value of endosomal spicules. This work demonstrates that the Orthotylinae are a rich component of Australia’s biodiversity, particularly in the south-west of Western Australia.

Systematic study of the Australian plant bug genus Xasmasoma, gen. nov. (Insecta : Heteroptera : Miridae : Orthotylinae), including host plant and biogeographic analysis, and description of twelve new species

A new Australian genus of Orthotylini, Xasmasoma, gen. nov. is described, with 12 new included species: X. acuminatus, sp. nov., X. agana, sp. nov., X. carrollae, sp. nov., X. celiae, sp. nov., X. chamelaucieaphila, sp. nov., X. mareeba, sp. nov., X. mimae, sp. nov., X. mungallala, sp. nov., X. nillinghoo, sp. nov., X. schuhi, sp. nov., X. silveirae, sp. nov. and X. woodstocki, sp. nov. These species were analysed phylogenetically using 25 morphology-based characters and molecular alignments (COI, 16S, 18S and 28S; 2096 base pairs), with the genus found to be monophyletic based on molecular, morphological and combined analyses. An analysis of host plant associations demonstrated no pattern of co-divergence and limited phylogenetic conservatism, aside from two subclades with respective Calytrix and Myrtaceae preferences. The biogeographic analysis revealed a south-western (South-west Interzone, Western Desert) area relationship, which is in distinction to the orthotyline genus Naranjakotta. The taxonomic component includes an identification key to species and diagnostic characters are illustrated, with detailed documentation of the male genitalia, and the genus uniquely possesses tile-like texture on the apex of the apophysis of the left paramere, and a single endosomal spicule.