Doubly Re-entrant Microstructures for Universal Liquid Repellency
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Solution Overview
Problem
Existing liquid-repellent surfaces fail to effectively repel fluorinated solvents due to their low surface tension and strong wetting behavior on conventional materials, and slippery liquid-infused porous surfaces (SLIPS) are limited in repelling liquids that are immiscible with the lubricating fluid and have surface tensions greater than the lubricating fluid.
Innovation Solution
A surface with a doubly re-entrant topology and a low liquid-solid contact fraction, featuring microstructures with a cap portion and a downwardly extending lip, is created using top-down or bottom-up methods, allowing for the repulsion of all liquids by maximizing the liquid-gas contact area and minimizing the liquid-solid contact area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional superhydrophobic surfaces with simple microscale roughness are used, then water repellency is achieved, but fluorinated solvents with low surface tension cannot be repelled
Solution Approach 1:
The surface is segmented into multiple hierarchical levels: microscale roughness features and nanoscale re-entrant structures. This multi-level segmentation creates increasingly effective liquid suspension, where each level addresses different liquid properties. The microscale features provide initial suspension while nanoscale re-entrant structures provide the overhanging geometry needed to suspend low surface tension fluorinated solvents through enhanced upward surface tension forces.
Solution Approach 2:
The invention transitions from simple microscale roughness to a hierarchical structure incorporating nanoscale re-entrant features that extend in multiple dimensions. The re-entrant topology creates three-dimensional overhanging structures with negative curvature that conventional two-dimensional roughness cannot provide. This dimensional complexity enables the surface to generate sufficient upward surface tension forces to counteract the low surface tension of fluorinated solvents.
2Reliability
If SLIPS with lubricating liquid are used, then aqueous and hydrocarbon liquids are repelled, but fluorinated solvents cannot be repelled due to miscibility and surface tension criteria
Solution Approach 1:
The invention eliminates the need for a lubricating liquid intermediary by using purely geometric surface structures. Instead of relying on a liquid layer to provide repellency, the doubly re-entrant microstructures directly suspend all liquids through geometric confinement and upward surface tension forces. This removes the miscibility and surface tension compatibility requirements that limit SLIPS functionality.
Solution Approach 2:
The invention replaces the liquid-based mechanical system of SLIPS with a solid geometric structure system. Rather than using a lubricating liquid layer to provide the repellent effect, the patent uses rigid microscale and nanoscale re-entrant structures that mechanically suspend liquids through their geometry. This substitution eliminates the chemical compatibility constraints of SLIPS while maintaining the liquid suspension function.
3Reliability
If re-entrant microstructures are used to suspend liquids, then liquid-gas contact area increases, but manufacturing precision requirements increase
Solution Approach 1:
The complex doubly re-entrant structure is segmented into two fabrication stages: first creating microscale features, then adding nanoscale re-entrant details. This segmentation allows each stage to be optimized for its specific precision requirements, with the microscale stage providing the overall geometry and the nanoscale stage providing the critical re-entrant overhangs. This hierarchical segmentation makes the overall high-precision structure achievable through sequential, less-demanding processes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The doubly re-entrant surface achieves robust liquid repellency, suspending and repelling liquids with varying surface tensions, including fluorinated solvents, by utilizing surface tension for suspension force, even for perfectly wetting liquids, and maintaining repellency under external pressures.
Implementation Method 1
utilizing surface tension for suspension force, even for perfectly wetting liquids
Data Source
AI summary
An artificial surface is disclosed where super-repellency is obtained solely from surface roughness regardless of the material's intrinsic wettability. The surface is able to repel all known liquids. The surface contains thereon a plurality of microstructures having a doubly re-entrant topology and a liquid-solid contact fraction of less than 50%. In one embodiment, the doubly re-entrant topology includes a cap portion and downwardly extending lip extending from the periphery of the cap portion. The surface withstands high temperatures and resists surface changing phenomenon such as biofouling and chemical scaling.