The method of synthesizing of superhydrophobic surfaces by PECVD

Nowadays the wettability of solid surfaces is a decisive factor in many applications. Control of the hydrophobic or hydrophilic property is a key aspect for microelectronics, antifouling coatings, anti-ice, light industry,... [ view full abstract ]

Nowadays the wettability of solid surfaces is a decisive factor in many applications. Control of the hydrophobic or hydrophilic property is a key aspect for microelectronics, antifouling coatings, anti-ice, light industry, etc. The wettability of the surface generally depends on two factors: surface chemistry and surface roughness. If both parameters are used properly, it is possible to develop superhydrophobic surfaces with a contact angle close to 180°, with very small grazing angle (lotus effect). There are different methods of obtaining hydrophobic surfaces, such as phase separation, CVD, electrochemical deposition, plasma method, crystallization control, wet chemical reaction, sol-gel processing and so on.
In this work, firstly, we got superhydrophobic surfaces using a simple one-step process, based on polymerizing carbonaceous nanoparticles in plasma and deposition on silicon wafer. Nanoparticles arising in plasma polymerization process are typical example of plasma polymers, i.e. materials, which in difference to conventional structured polymers, do not consist of repeating units. In addition, we researched how wetting characteristics were changing when processed in different plasma environments. We focused on the process of growth of nanoparticles and their subsequent deposition. Specific feature of this process is the negative charge of the nanoparticles. Once the particles reach a size of several nanometers, they quickly collect a negative charge (due to the high mobility of the electrons in the plasma). As a result, the particles are held in positive plasma potential, i.e. they are levitating in the discharge, where they continue to grow due to the accumulation of neutral radicals and positive ions. After the plasma turns off, particles lose the negative charge and fall down to the lower electrode. Every time plasma is turned off a certain amount of nanoparticles will fall onto the substrate, which is located on the lower electrode. The SEM image shows that the synthesized materials have a rough surface with contact angles of from 100⁰ to 165⁰, depending on the plasma parameters. Experimentally it has been found, that the number of particles on a silicon substrate depends on the number of cycles, i.e. the film’s hydrophobic feature (contact angle) increases with the number of cycles.