Multiscale orientational order and in-plane thermal transport in dip-coated filamentous virus liquid-crystalline films

Achieving high in-plane thermal transport in compliant, bioderived coatings without inorganic fillers remains challenging. Here, we examine how multiscale orientational order in dip-coated liquid-crystalline films of filamentous M13 bacteriophages is related to lateral heat spreading. Films were prepared on glass, polyimide, and poly(L-lysine)-coated glass with varying withdrawal speed (10–80 µm min −1 ) and solution pH (5, 7, or 11). The orientational order was quantified from 30 × 30 µm 2 atomic force microscopy height images using two-dimensional Fourier analysis to obtain tile-averaged and whole-image order parameters. For polyimide-supported films at pH 7, the tile-averaged parameter ( S ) increased from 0.318 to 0.544 as the withdrawal speed increased from 10 to 80 µm min −1 . In-plane thermal conductivity along the coating direction was measured for polyimide-supported films by scanning laser-heating photothermal radiometry and extracted using differential two-layer analysis, yielding 3.1 ± 1.1, 4.2 ± 2.0, and 9.3 ± 1.2 W m −1 K −1 at 10, 50, and 80 µm min −1 , respectively. These results support an initial structure–property correlation between enhanced alignment and increased in-plane thermal transport in supported virus films, and they highlight the need for nonequivalent metrics to describe mesoscale alignment.