Wetting phenomena, i.e. the spreading of a liquid over a dry solid surface, are important for understanding how plants and insects imbibe water and moisture and for miniaturization in chemistry and biotechnology, among other examples. They pose fundamental challenges and possibilities, especially in dynamic situations. The surface chemistry and micro-scale roughness may determine the macroscopic spreading flow. The question here is how dynamic wetting depends on the topography of the substrate, i.e. the actual geometry of the roughness elements. To this end, we have formulated a toy model that accounts for the roughness shape, which is tested against a series of spreading experiments made on asymmetric sawtooth surface structures. The spreading speed in different directions relative to the surface pattern is found to be well described by the toy model. The toy model also shows the mechanism by which the shape of the roughness together with the line friction determines the observed slowing down of the spreading.
Nanocellulose is regarded as a green and renewable nanomaterial
that has attracted increased attention. In this study, we demonstrate
that nanocellulose materials can exhibit high thermal conductivity
when their nanofibrils are highly aligned and bonded in the form of
filaments. The thermal conductivity of individual filaments, consisting
of highly aligned cellulose nanofibrils, fabricated by the flow-focusing
method is measured in dried condition using a T-type measurement technique.
The maximum thermal conductivity of the nanocellulose filaments obtained
is 14.5 W/m-K, which is approximately five times higher than those
of cellulose nanopaper and cellulose nanocrystals. Structural investigations
suggest that the crystallinity of the filament remarkably influence
their thermal conductivity. Smaller diameter filaments with higher
crystallinity, that is, more internanofibril hydrogen bonds and less
intrananofibril disorder, tend to have higher thermal conductivity.
Temperature-dependence measurements also reveal that the filaments
exhibit phonon transport at effective dimension between 2D and 3D.
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