Ordered layered pore structures are typically created by replicating a template, which can be separated into soft and hard template methods based on whether the template is rigid or soft. Precursors either fill the spaces within the template or cover the template surface in both procedures; after the precursor material has cured, the template can be removed to get a well-defined porous structure. The use of a combination of soft and hard template techniques can result in structural hierarchy and changes in the fine view structure.
Alfa Chemistry uses a variety of template approaches to modify pore hierarchy and morphology. The elements that influence pore structure and how pore structure impacts the function of the resulting porous surface are the subject of this study. Below are some of the precise methods we use to construct porous surfaces.
Soft Template Method
Macroscopic foams, micron-sized droplets, and even nanoscale micelles are examples of soft templates. The orderliness of the final structure is ensured by the self-assembly of these soft templates. Evaporation is the most typical cause of soft template self-assembly. The soft templates suspended in the precursor solution progressively form organized crystal-like structures as the solvent evaporates. After solidifying the precursor and removing the soft template, an ordered porous structure can be formed, with the pore morphology adjustable by altering the soft template.
Fig 1. Dome-shaped octopus-inspired architectures formed by multiple soft-template method. a,b) Photograph and schematic of the inspiration source: an octopus suction cup; c) schematic and SEM images of fabricated octopus-inspired architectures, cylindrical pillars, perforated cylinders, and cylindrical holes based on the soft solid template method. (Baik S, et al. 2017)
In the multitemplate process, air microbubbles are used as soft templates to mimic the dome-shaped protrusions found in octopus suckers. A prepolymer solution is poured and pressed into silica molds with microporous patterns of various sizes. The prepolymer solution partially wets the gap between the bubbles and the micropores, trapping air microbubbles within each hole. The prepolymer solution is subsequently cured into a perforated cylindrical array, which serves as the second molding's polymer mask. The polymer mask is molded into a dome-shaped octopus-like structure as well as other conventional columnar forms. In both water and oil, the micro-dome structure improves suction and demonstrates robust, reversible, and repeatable wet adherence.
The hydrophobic porous surface can be further salted or fluorinated to obtain a lubricant-infused surface, which results in high repellency to all liquids.
Hard Template Method
The hard template method is a replication technique that duplicates the template structure accurately. Monodisperse colloidal nanoparticles are the most often used hard templates for ordered porous surfaces. A slide is dipped in a colloidal dispersion and subsequently withdrawn to generate a crystal-like structure of monodisperse colloids. The colloid on the slide has an opal structure, which is a homogenous structure.
The negative replica of the opal structure is the anti-opal structure, and the water contact angle of the colloid is 155° after fluorination. Reconstruction of a recessed microstructure on the skin of the pop tail followed by reactive ion etching with SF6 gas can be used to make silicon dioxide anti-opal molds. The etched surface is transformed into an array of triangular microcolumns with a recessed profile, and the structure is fluorinated using SF6 gas, resulting in a ubiquitous structure, has strong mechanical stability, and is chemically resistant to organic solvents.
Fig 2. A typical example of a hard-template method. a) Assembling, filling, and sintering of colloids to form a porous surface, followed by soaking of fluorinated oil as lubricant. b) Self-healing of a lubricant-infused surface by resoaking the lubricant. c) Lubricant-infused porous surfaces that can repel water, octane, and blood. d) Wiping, tape-peeling, and scratching with sandpaper (from left to right) could not reduce the liquid repellency. (Vogel N, et al. 2013)
Colloidal hard templates are also utilized to create transparent porous surfaces with liquid repellency and self-healing capabilities for lubricant injection. Silica colloidal opals have well-defined nanopores that are easily tunable from tens to hundreds of nanometers and can be easily surface changed. The liquid repellency may be maintained for more than 9 months and remains even after damage because of the interconnected honeycomb structure.
References
- Baik S, et al. (2017). "A Wet-Tolerant Adhesive Patch Inspired by Protuberances in Suction Cups of Octopi." Nature. 546(7658): 396-400.
- Vogel N, et al. (2013). "Transparency and Damage Tolerance of Patternable Omniphobic Lubricated Surfaces Based on Inverse Colloidal Monolayers." Nat. Commun. 4: 2176.
