The unidirectional liquid spreading without external
energy input
has presently aroused widespread concern. Recently, on the peristome
of Nepenthes alata, a novel 2D unidirectional
liquid spreading has been reported. It has been revealed that its
exquisite superhydrophilic multistage microstructure, overlapping
microcavities with arc-shaped edges and wedge-shaped corners, is the
main reason for this phenomenon. To fabricate a peristome-inspired
surface, a replica molding method is highly efficient and provides
an ideal structure. However, the curved shape of the finally formed
surface cannot be adjusted, and a specific surface shows only one
type of liquid spreading state, greatly limiting its potential application.
Here, we aimed to develop a novel surface-tension-assisted replica
molding method to fabricate an artificial peristome film. The artificial
peristome film was fabricated by pouring styrenic block copolymers
(SBS) dissolved in organic solvents into a negative replica prepared
in polydimethylsiloxane (PDMS), based on the natural peristome.
With volatilizing the organic solvent, the SBS agglomerates formed
an artificial peristome film via surface tension effects. More importantly,
the PDMS-negative replica swelled in the organic solvent and then
returned to the original size, which is conducive for replicating
microstructures. The liquid spreading speed could be dynamically controlled
by stretching the artificial peristome film. We demonstrated that
the microcavity wedge angle decreases with an increasing stretching
ratio. A smaller wedge angle can result in a much stronger unidirectional
liquid spreading ability. This study provides insight into the dynamic
control of unidirectional liquid spreading for novel pump-free medical
microfluidic devices.
Liquid unidirectional spreading without energy input has attracted worldwide attentions owing to its potential applications in various fields. The liquid transfer between the adjacent microcavities on the peristome of Nepenthes alata provides great inspiration in that the concave curvature edge structure has the possibility to induce liquid directional spreading. Herein, the effect of concave curvature edge on liquid spreading is found to be different from that of the solid edge described by the Gibbs inequality condition. In this condition, there exist two liquid transfer states, namely conduction and resistance. Taking the advantages of the concave curvature edge, a new unidirectional liquid spreading channel is designed and fabricated by the traditional machining method, and its liquid directional spreading function is validated. This article provides a theoretical and technical support for the design and fabrication of liquid unidirectional spreading channel without an external energy input.
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