Direct replication of micro-nanostructures in the fabrication of superhydrophobic silicone rubber surfaces by compression molding

Significance 

The hydrophobicity associated with silicone rubber has made it an interesting research material for various applications, such as high-voltage outdoor insulation. Currently, there are three main sub categories for the aforementioned application: high temperature vulcanized (HTV) silicon rubber, room temperature vulcanized silicone rubber and liquid silicone rubber. HTV is popular as it possesses inherent hydrophobicity as well as superior electrical and mechanical properties. Nonetheless, it is important that HTV possess superhydrophobic and self-cleaning properties in order to withstand the harsh outdoor conditions it is exposed to. To improve its resilience and self-cleaning properties, incorporation of surfaces with micro-nanostructures has been suggested. A noble, cost effective and efficient way of preparing surfaces with micro-nanostructures is by the use of templates; as it favors mass production and is widely acceptable to industries. Polymers are versatile materials, consequently, a number of studies have been published on how to fabricate superhydrophobic polymeric surfaces using thermoplastics as the matrix. Unfortunately, few studies have employed HTV rubber materials to create textured superhydrophobic surfaces.

Recently, University of Quebec researchers: Khosrow Maghsoudi (PhD candidate), Prof. Gelareh Momen, Prof. Reza Jafari and Prof. Masoud Farzaneh presented a facile method for fabricating superhydrophobic HTV silicone rubber surfaces by direct replication using a compression molding system. The research team aspired to produce a micro-nanostructured template using simple chemical etching and subsequent direct replication of micro-nanostructures on the HTV silicone during its vulcanization process. Their work is currently published in the research journal, Applied Surface Science.

The scholars started by fabricating templates. A chemical etching method created micro-nanostructures on an aluminum alloy. The developed samples were later subjected to replication process, where a compression molding system was used to press two platens closer together until the desired pressure was achieved. Lastly, the resultant surface was characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM).

The authors observed that all the samples produced under the various etching conditions displayed water contact angles > 160° and contact angle hysteresis < 3°. Additionally, the replicated samples from inserts produced with an acid concentration of 15% (by weight), demonstrated a slightly higher water repellency level than samples produced from lower and higher acid concentration inserts. Interestingly, SEM images confirmed the successful replication of the templates’ patterns on the rubber samples produced via compression molding. FTIR analysis revealed that fluorinated bonds of the template surfaces did not transfer to the silicone rubber surfaces during the replication process.

In a nutshell direct replication method for fabricating micro-nanostructured superhydrophobic silicone surfaces was successfully developed. Remarkably, the superhydrophobic samples were seen to delay freezing onset confirming the ice-phobic capacity of the produced surfaces. Altogether, the developed HTV silicone rubber surfaces demonstrated a freezing delay and a self-cleaning capacity.

Currently our research team is working on the “Icephobic and self-cleaning ultra-water-repellent silicone rubber surfaces” in which the produced samples are iced under real outdoor conditions. We are also working on a rigorous study to assess the self-cleaning properties of the ultra-water-repellent surfaces under various pollution scenarios. This study can open a new avenue to assess the self-cleaning properties in comprehensive, reliable and real conditions.” said first author, Khosrow Maghsoudi in a statement to Advances in Engineering.

Water-jet impact on the (a) pristine silicone rubber and (b) superhydrophobic silicone rubber surfaces. Inset images show the contact angle hysteresis (CAH) of each surface - Advances in Engineering

Reference

K. Maghsoudi, G. Momen, R. Jafari, M. Farzaneh. Direct replication of micro-nanostructures in the fabrication of superhydrophobic silicone rubber surfaces by compression molding. Applied Surface Science, volume 458 (2018) page 619–628

Go To Applied Surface Science

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