Recently, many studies have investigated additive manufacturing of hierarchical surfaces with high surface area/volume (SA/V) ratios, and their performance has been characterized for applications in next-generation functional devices. Despite recent advances, it remains challenging to design and manufacture high SA/V ratio structures with desired functionalities. In this study, we established the complex correlations among the SA/V ratio, surface structure geometry, functionality, and manufacturability in the Two-Photon Polymerization (TPP) process. Inspired by numerous natural structures, we proposed a 3-level hierarchical structure design along with the mathematical modeling of the SA/V ratio. Geometric and manufacturing constraints were modeled to create well-defined three-dimensional hierarchically structured surfaces with a high accuracy. A process flowchart was developed to design the proposed surface structures to achieve the target functionality, SA/V ratio, and geometric accuracy. Surfaces with varied SA/V ratios and hierarchy levels were designed and printed. The wettability and antireflection properties of the fabricated surfaces were characterized. It was observed that the wetting and antireflection properties of the 3-level design could be easily tailored by adjusting the design parameter settings and hierarchy levels. Furthermore, the proposed surface structure could change a naturally-hydrophilic surface to near-superhydrophobic. Geometrical light trapping effects were enabled and the antireflection property could be significantly enhanced (>80% less reflection) by the proposed hierarchical surface structures. Experimental results implied the great potential of the proposed surface structures for various applications such as microfluidics, optics, energy, and interfaces.
With the recent threat of climate change and global warming,
ensuring
access to safe drinking water is a great challenge in many areas worldwide.
Designing functional materials for capturing water from natural resources
like fog and mist has become one of the key research areas to maximize
the production of clean water. From this aspect, nature is a great
source for designing bioinspired functional materials as some of the
plant leaves and animal exoskeletons can harness water and then store
it to save themselves from arid, xeric conditions. Inspired by the Stenocara beetle, we have designed a composite surface structure
with periodic islands made of aluminum microparticles surrounded by
poly(dimethylenesiloxane) (PDMS). An acoustic tweezer-based method
was used to fabricate the bioinspired composite structures, where
surface acoustic waves at specific frequencies and amplitudes are
applied to align the microparticles as islands in the polymer matrix.
An oxygen plasma etching step was applied to expose the microparticles
on the PDMS surface. The average water harvesting efficiencies for
structures made with 120 and 80 kHz acoustic frequencies and 1 hour
etching time were found to be 9.41 and 8.84 g cm–2 h–1, respectively. The acoustically patterned
biomimetic composite surface showed higher water harvesting efficiency
compared with completely hydrophobic PDMS and hydrophilic aluminum
surfaces, demonstrating the advantages of the bioinspired composite
material design and acoustic-assisted manufacturing technique. The
biomimetic fog water harvesting material is a promising avenue to
fulfill the demand for a cost-effective, sustainable, and energy-efficient
solution to safe drinking water.
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