Water droplet unidirectional transport on the asymmetric superhydrophobic surface has attracted much interest in theory analysis and applications, such as self-cleaning, antifogging, anti-icing, heat transfer, and so on. Different from the symmetrical performance on the uniform topographies, the droplets acting on the asymmetric surface exhibit an anisotropic state and easily roll off the surface along the special direction. This phenomenon is indicated by natural butterfly wings. The flexible asymmetrically arranged microstep induces the droplet to release along the outside radial (RO) direction and to pin against the RO direction. Here, inspired by butterfly wings, a kind of surface for superhydrophobic and unidirectional droplet transport is achieved by integrating the methods of soft lithography and enhanced crystal growth. The water droplet shows the anisotropic state on the biofabricated surface, and it rolls off easily along the step direction. The droplet is unidirectionally driven off the surface by the asymmetric surface tension force generated by the microstep topography. This experiment is significant for designing self-cleaning surfaces.
Semiconducting
conjugated polymers possess attractive optoelectronic
properties and low-cost solution processability and are inherently
mechanically flexible. However, the device performance is susceptible
to the fabrication methods because of the relatively weak intermolecular
interaction of the polymers and their inherent conformational and
energetic disorder. An efficient fabrication technique for large-scale
integration of high-quality polymer architectures is essential for
realizing high-performance optoelectronic devices. Here, we report
an efficient method for fabrication of polymer nanowire arrays with
a precise position, a smooth surface, a homogeneous size, high crystallinity,
and ordered molecular packing. The controllable dewetting dynamics
on a template with asymmetric wettability permits the formation of
discrete capillary bridges, resulting in the ordered molecular packing
arising from unidirectional recession of the three-phase contact line.
The high quality of nanowire architectures is evidenced by the morphological
characteristics and hybrid edge-on and face-on molecular packing with
high crystallinity. On the basis of these high-quality nanowire arrays,
photodetectors with a responsivity of 84.7 A W–1 and detectivity of >1012 Jones are realized. Our results
provide a platform for integration of high-quality polymer architectures
for use in high-performance optoelectronic devices.
Hemiwicking has been introduced to describe the wetting state in which a liquid film surrounds a drop. To fully understand this special wetting state, we performed energy analysis and systematic lattice Boltzmann (LB) simulations on the wetting state through spreading liquid droplets on pillared hydrophilic substrates. Although the energy analysis shows that the hemiwicking is energetically unfavorable, droplets in stable hemiwicking are indeed observed in our LB simulations. This observation led us to conclude that we have obtained a result that is the same as the result obtained in the published experiment and theory: hemiwicking is dynamically trapped by the pinning of the imbibition front during invasion of the substrate texture by the liquid film. Our simulations show that the special wetting state is always found to emerge near the phase boundary between the liquid film and the Wenzel state. For the morphology of the droplet, strong deviation of the apparent contact angle from hemiwicking is observed when the contact line of the liquid imbibition film is close to the spherical caplike droplet. We also show that there exist at least two different kinetic pathways for the formation of hemiwicking, including spreading and evaporation.
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