Facile fabrication of superhydrophobic poly(methyl methacrylate) substrates using ultrasonic imprinting

Abstract

Superhydrophobic surfaces (SHSs) have received increasing attention in the last decade, and have been generally developed from hydrophobic materials. In this study, a facile fabrication method based on ultrasonic imprinting is proposed to develop SHSs from a hydrophilic polymer, poly(methyl methacrylate) (PMMA). To fabricate SHSs on PMMA substrates, micro electrical discharge machining, micromachining and ultrasonic imprinting were sequentially used. The ultrasonic imprinting was performed for various channel designs and imprinting conditions, and the resulting water contact angles were measured for the replicated samples. As a result, superhydrophobic characteristics could be obtained on a hydrophilic PMMA replica without any chemical treatments. The effects of nanoscale roughness on the replicated channel as well as composition change are discussed with respect to the analyses using an atomic force microscope, x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.

Tools for ultrasonic hot embossing

“…The patterns were uniform and they were fabricated in one minute [35]. Superhydrophobic surfaces with micro channels (width: 30 µm, depth: 50 µm) were also produced by an ultrasonic imprinting system and a maximum contact angle of the embossed surface from PMMA of 152.2° had been achieved [36]. [17], (b) micro V shape channels [39].…”

“…Figure 2.7 a) [36]. For producing predetermined breaking points in polymer yarns, a sonotrode with a single protruding bar (width: 500 µm and height: 800 µm) was used [44] and is shown in Figure 2 [36], Repringted with permission from IPO publishing; (b) single bar [46] A lot of research has been done on injection molding and hot embossing, but the exploration of ultrasonic hot embossing is still at its beginning. There is no doubt that the ultrasound is assisting to melt the polymer and reducing the cycle time [15].…”

“…Best results have been obtained with PVDF filling only half of the height of the LIGA tool, while other polymers were filling only about 30% of the depth of the embossing tool. In ultrasonic hot embossing applying more embossing energy would improve polymer melting and better filling of the tool can be achieved, which were also investigated by [36,121]. Polymers with high melting temperature and stiffness are harder to emboss.…”

“…where θ 0 is the contact angle on a flat surface, r is defined as the surface roughness factor, which is calculated by [36]: According to the above formulas, when in the Wenzel state the surface roughness factor is increased, the contact angle is decreased. While in Cassie-Baxter state, increasing the void between structures, e.g., increasing n and decreasing m, results in a smaller surface fraction and the contact angle is increased.…”

“…Baxter contact state, the contact angle θ c is calculated by[124]:Where h is called the surface fraction under the water drop, which is contacting the liquid. The h is expressed by[36]:…”