Wettability and surface microstructure of polyamide 6 coated with SiOXCYHZ films.

Polyamide, PA, is a thermoplastic very used in practical applications once it associates a series of convenient properties. However, its affinity towards water promotes swelling and thus dimensional changes, a drawback for most of the applications. There exist alternative polymers but the fully bulk replacement is hindered by costs. In this sense, the modification of polymer surfaces using a versatile, simple and low cost methodology emerges as an important tool. In this work, low pressure plasmas were employed to adjust the surface properties of the commercial polyamide 6 aiming to decrease its affinity to water. Organosilicon films were deposited from hexamethyldisiloxane, HMDSO, oxygen and argon plasma mixtures. The plasma reactor was pumped down to 3.0 Pa and HMDSO, oxygen and argon were admitted to the reactor establishing the pressure of 24 Pa. In each one of the four deposition cycles, the HMDSO proportion was fixed at 70% while those of oxygen (0 to 30%) and argon (30 to 0%) were varied in opposite ways. The plasma was ignited by the application of radiofrequency power (13.56 MHz, 150 W) to the lowermost sample holder, earthening the top electrode. Deposition was conducted for 1800 s. It was specifically investigated if the receptivity of the organosilicon film to water can be further reduced by adjusting its topography. Infrared spectroscopy was used to determine the molecular structure of the samples while water wettability was measured by the contact angle approach. Surface microstructure was inspected by scanning electron microscopy and atomic force microscopy. Elemental composition was derived from energy dispersive spectroscopy. Films are in general organosilicon with methyl functionals connected to the SiOSi backbone as lateral groups and/or chain termination in a more crosslinked way than the conventional silicone. A granular structure composed by agglomerates of different diameters was generated. Roughness is affected by the proportion of the dilution gases since it influences the deposition kinetics and then the rate of polymerization in the plasma phase. Independently of the oxygen and argon proportions used in the plasma polymerization process, the bare hydrophilic PA was converted into hydrophobic upon film deposition. [ABSTRACT FROM AUTHOR]