Abstract
Two methods, the first physical and the other chemical, were investigated to modify the surface roughness of polydimethylsiloxane (PDMS) films. The physical method consisted of dispersing multi-walled carbon nanotubes (MWCNTs) 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-irradiating. The characterizing techniques included scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, optical microscopy, atomic force microscopy (AFM) and magnetic force microscopy (MFM). The surface roughness was quantitatively analyzed by AFM. In the physical method, the random dispersion of MWCNTs (1% w/w) and magnetic nanoparticles (2% w/w) generated 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. SEM, AFM and MFM showed that the magnetic particles always remained attached to the carbon nanotubes, and the effect on the roughness was interpreted as being due to a rupture of dispersion randomness and a 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 were close to 100 μm2 and depths of up to 500 nm. The observations of AFM images and FTIR spectra were in agreement with the hypothesis of etching by Br radicals generated by UV on the polymer chains. Both methods induced important changes in the surface roughness (the chemical method generated the greatest changes due to the formation of surface wells), which are of great importance in superficial technological processes.
Highlights
The modification of polymer surfaces finds applications in many relevant areas, such as the development of super-hydrophobic membranes for oil–water separation [1,2], activation surfaces for microfluidics [3], the attachment of biomolecules for biosensors [4], self-replenishing coatings [5], and anti-bacterial and fouling release coatings [6,7,8]
The presence of multi-walled carbon nanotubes (MWCNTs) was detected in PDMS/MWCNT films by optical microscopy (Figure 2) and scanning electron microscopy (SEM) (Figure 3)
The two methods explored in this work led to an increase in the surface roughness, which was Thetwo two methods explored inInthis work to an of increase inphysical the surface roughness, The explored work ledled to an increase in the surface roughness, whichwhich was quantified bymethods the parameter
Summary
The modification of polymer surfaces finds applications in many relevant areas, such as the development of super-hydrophobic membranes for oil–water separation [1,2], activation surfaces for microfluidics [3], the attachment of biomolecules for biosensors [4], self-replenishing coatings [5], and anti-bacterial and fouling release coatings [6,7,8]. Some of the authors have reported that the incorporation of very low amounts (0.5% w/w) of multi-walled carbon nanotubes (MWCNTs) into the silicone matrix spectacularly improves the physical and rheological behavior of the PDMS resin [10]. This was found to trigger significant changes in the nanocomposite surface topography, concomitant with variations in the wettability behavior upon immersion in water. The obtained results suggest that, independently of the bulk mechanical performances, the surface properties significantly affect the fouling-release behavior of the filled materials
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