Enhancement of the hydrophobicity of recycled polystyrene films using a spin coating unit

What is it about?

This article describes a technique for recycling polystyrene cups (PSr) mixed with poly-butyl-methacrylate (PBMA) to produce PSr/PBMA films and subsequently PSr films by removing PBMA with a selective solvent (acetic acid), with the benefit of a reduction in environmental pollution generated by polystyrene waste. Removal of PBMA increases roughness, which generates a significant increase (~34°) in the water contact angle, reaching its highest value at 128°. By increasing the hydrophobicity of surfaces, properties with important technical applications are acquired such those used in antifouling paints, stain resistant surfaces, and surfaces that avoid the formation and accretion of ice on microelectronic devices. Roughness of PSr/PBMA films is significantly affected by the concentration of both polymers and by the spin rate, reaching its highest value at 2% PSr and 3% PBMA at 2000 rpm. For optimal film deposition, a cheap spin coating unit was designed and built, with a price less than 4% of that of a commercially available spin coating unit. Lastly it was found that the data obtained with our spin coating unit is described by the Meyerhofer model with accuracy of 88±3%.

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Why is it important?

In this work, the manufacturing conditions of thin films improving their hydrophobicity were studied. As a contribution to the reduction in environmental pollution caused by polystyrene cups (PSr), the PSr mixed with poly-butyl-methacrylate (PBMA) were used to produce PSr/PBMA films. Since most methods for manufacturing films involve specialized equipment, an inexpensive alternative for depositing thin films based on the rotation method, was designed and constructed in our laboratory. The unit is stable, with a speed ranging from 1 to 6400 rpm and time from 1 s to 30 h. While commercial spin coaters use vacuum to hold the substrates in place, with the possibility of creating defects in the substrate and therefore on the film, neoprene-coated disks were used to hold the substrate. The effect of the concentration of PSr/PBMA on film roughness was studied, increasing the concentration from 0 to 5% of PSr and decreasing that of PBMA from 5 to 0% in 95% of THF, then the effects of spin rates (1000 to 6400 rpm) on the surface topographies and roughness of 2% PSr/3% PBMA films were investigated. One way of increasing hydrophobicity is to increase film roughness. Therefore, the influence of the demixing process by removal of PBMA on roughness and the water contact angle by removal of PBMA was studied. Furthermore, the thickness of films produced with our spin coating equipment was compared to the thickness predicted using the Meyerhofer model.