Integrated plasma processes for Superhydrophobic pattern construction on the polyamide surface

Abstract

A method largely employed to tailor the thermodynamical properties of polymers is the delineation of patterns on their surfaces. Different and sophisticate approaches are normally associated to micro/nanometric patterning a surface, attaining complexity and high costs to the process. This project aims to develop integrated plasma methodologies for the production of surfaces with super repelency towards water by the construction of fakir-like structures on the polymer surfaces. The polyamide, a widely diffused engineering thermoplastic was selected since it still presents some practical restrictions related to its natural hydrophilicity. Regularly and randomly distributed patterns will be delineated on the surface of commercial polyamide plates using different plasma processes or their associations. In the first research line, post-like structures will be created on the polyamide surface chemically ablating material from specific points of the surface using oxygen plasmas. Prior to that, oxygen resistant organometallic masks will be prepared from hexamethyldisiloxane, HMDSO, and argon plasma mixtures with the aid of commercial membranes containing pores with appropriate geometries and dimensions. This methodology is proposed to replace the conventional photoresist, thus eliminating the necessity of photolithography. After the delineation of the mask, the system will be submitted to the ablation process. It will be investigated the effect of the oxygen plasma pressure, power and exposure time on the surface properties of the polyamide. A still simpler methodology is proposed in the second research line: to grow tridimensional structures on the polyamide surface by plasma deposition. Mixtures of HMDSO and O2, the same compounds employed for the mask preparation, will be used to excite the depositing plasmas once hydrophobic materials and high deposition rates can be obtained from that. The deposition will be conducted with the aid of porous membranes to allow the creation of post-like structures. It will be investigated the influence of the deposition time, pressure, power and compounds proportions on the final surface properties. In the third and simplest procedure, the polymer will be exposed, without any kind of mask, to plasmas generated from argon. It will be investigated the effect of the low energy ion bombardment on the selective removal of material from less resistant regions of the polyamide. The natural selectivity of this material to the plasma should generate structures on the surface, as already obtained for the PVC. The treatment will be conducted for different times in plasmas excited with different powers and pressures. In the three research lines it will be evaluated the influence of the plasma parameters on the geometry and dimensions of the patterns using scanning electron microscopy. The receptivity of the surfaces towards water will be investigated by the sessile drop technique while roughness will be determined by the topographic profiles taken by atomic force microscopy. The chemical composition of the surfaces will be analyzed by X-ray photoelectron spectroscopy. Associating the morphology, topography and chemical composition results, the theoretical model which explains the wettability data should be determined, allowing a deeper knowledge on the polyamide thermodynamical properties. (AU)