Increased Surface Roughness in Polydimethylsiloxane Films by Physical and Chemical Methods

CABRERA, JORGE; RUIZ, MARIANO; FASCIO, MIRTA; D?ACCORSO, NORMA; MINCHEVA, ROSICA; DUBOIS, PHILIPPE; LIZARRAGA, LEONARDO; NEGRI, R.

Polymers

MDPI

Año: 2017 vol. 9

Two methods, one physical and other chemical, were investigated to modify the surface roughness of PDMS films. The physical method consisted in dispersing multi-walled carbon nanotubes (MWCNT) and magnetic cobalt ferrites (CoFe2O4) prior to thermal cross-linking and curing the composite system in the presence of a uniform magnetic field H. The chemical method was based on exposing the films to bromine vapours and then UV irradiated. Characterization techniques included SEM, EDS, FTIR, optical microscopy, AFM and MFM. Surface roughness was quantitatively analyzed by AFM. In the physical method, the random dispersion of MWCNT (1% w/w) and magnetic nanoparticles (2% w/w) generates a roughness increase of about 200% (with respect to PDMS films without any treatment), but that change was 400 % for films cured in the presence of H perpendicular to the surface. Since SEM, AFM and MFM showed that the magnetic particles always remain attached to the carbon nanotubes, and the effect on the roughness is interpreted as due to a rupture of dispersion randomness and possible induction of structuring in the direction of H.In the chemical method, the increase in roughness was even greater (1000%). Wells were generated with surface areas that can be close to 100 m2 and depths up to 500 nm. The observations of AFM images and FTIR spectra are in agreement with the hypothesis of etching by Br radicals generated by UV on the polymer chains. Both methods induce important changes in surface roughness (the chemical one generates the greatest changes with formation of surface wells), which are of great importance in superficial technological processes.