Key Takeaways & Executive Findings
- •• • The SiO2 'bridge' layer enables grafting of PDMS brushes onto shape memory epoxy, achieving low adhesion to liquids with surface tensions as low as ~20 mN/m, overcoming limitations of superhydrophobic surfaces that only repel high-surface-tension liquids. • • Precise control of SiO2 layer thickness and grafting conditions yields surfaces with both shape memory and quasi-liquid properties, enabling reversible anisotropic/isotropic droplet sliding control for water and organic droplets. • • The coating demonstrates anti-fouling and self-cleaning properties on diverse substrates, with potential for applications requiring durable, low-maintenance surfaces. • • The combination of shape memory polymer and PDMS brushes offers programmable droplet manipulation, addressing the issue of lubricant loss in SLIPS and structural fragility in superhydrophobic surfaces.
Abstract
Shape memory droplet manipulation platforms have attracted significant attention due to their programmable droplet control capabilities. Current research primarily focuses on superhydrophobic surfaces and slippery lubricant-infused porous surfaces (SLIPS); however, these approaches suffer from vulnerable surface micro/nanostructures and loss of lubricant oils. Here, we report a shape memory quasi-liquid polydimethylsiloxane (PDMS) brush surface that overcomes these limitations. The surface is fabricated by introducing a SiO2 layer as a 'bridge' on a shape memory epoxy substrate, providing abundant functional groups for grafting PDMS brushes. By precisely controlling the SiO2 layer thickness and grafting conditions, the surface exhibits good shape memory properties and low adhesion to diverse liquids with varying surface tensions. Reversible anisotropic/isotropic droplet sliding control for both water and organic droplets is demonstrated through dynamic introduction/removal of groove structures, proving excellent droplet manipulation based on the combination of shape memory and low adhesion of PDMS brushes. Furthermore, the material can be applied as a functional coating on diverse substrates to impart anti-fouling and self-cleaning properties. This work introduces a nanoscale SiO2 layer as a 'bridge', offering a strategy to graft PDMS brushes onto polymer surfaces. Given the advantages of quasi-liquid PDMS brushes and programmable controllability of shape memory polymers, this work provides fresh ideas for developing droplet manipulation platforms.
1. Introduction
Droplet manipulation platforms are critical in bioanalysis, green printing, and microreactors. Existing technologies, such as superhydrophobic surfaces and SLIPS, face fundamental limitations: superhydrophobic surfaces rely on fragile micro/nanostructures and are ineffective for low-surface-tension liquids, while SLIPS suffer from lubricant depletion and are only effective for liquids immiscible with the lubricant. These drawbacks hinder long-term reliability and broad applicability.
PDMS brush surfaces offer a promising alternative due to their low glass transition temperature and low surface energy, providing low adhesion to a wide range of liquids without the need for infused lubricants. However, grafting PDMS brushes onto polymer substrates is challenging. This work introduces a nanoscale SiO2 layer as a 'bridge' to facilitate grafting, enabling the creation of a shape memory quasi-liquid surface that combines programmable shape memory with the low adhesion of PDMS brushes, thereby addressing the bottlenecks of existing platforms.
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Xuan Zhang, Deping Ma, Liang Geng, Yuan Chen, Yuyan Liu, Hua Lai, Zhimin Xie, Zhongjun Cheng, Lei Jiang (2026). Shape Memory Quasi-Liquid Slippery Surface for Programmable Droplet Manipulation. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-4100-9
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Frequently Asked Questions
What is the maximum surface tension range of liquids that can be manipulated on this surface?
The surface exhibits low adhesion to diverse liquids with different surface tensions, including both water and organic droplets. While specific surface tension values are not provided in the abstract, the design aims to handle low-surface-tension liquids, which are problematic for superhydrophobic surfaces.
How does the SiO2 'bridge' layer affect the grafting density and stability of PDMS brushes?
The SiO2 layer provides abundant functional active groups for grafting PDMS brushes. By precisely controlling the thickness of the SiO2 layer and grafting conditions, the surface achieves good shape memory and low adhesion, indicating that the grafting density is sufficient for quasi-liquid behavior. The stability is implied by the durability of the coating, though specific quantitative data are not provided.
What is the mechanism for reversible anisotropic/isotropic droplet sliding control?
The mechanism relies on the shape memory property of the epoxy substrate. By dynamically introducing/removing groove structures on the surface, the surface topography changes between anisotropic (grooved) and isotropic (flat) states, which alters the sliding behavior of droplets. This is achieved through the shape memory effect, which allows the surface to recover its original shape upon external stimuli.
Can this coating be applied to flexible substrates without compromising its performance?
The abstract states that the material can be used as a functional coating for diverse substrates, implying applicability to flexible substrates. However, the specific mechanical flexibility and adhesion to flexible substrates are not detailed. Further testing would be required to confirm performance under bending or stretching.
What are the potential industrial applications of this shape memory quasi-liquid surface?
Potential applications include anti-fouling coatings, self-cleaning surfaces, and programmable droplet manipulation platforms for bioanalysis, microreactors, and green printing. The combination of shape memory and low adhesion offers unique capabilities for on-demand droplet control, which could be valuable in lab-on-a-chip devices and smart surface technologies.
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