Combined XPS and contact angle studies of flat and rough ethylene‐vinyl acetate copolymer films

Abstract

Flat and rough thin films were prepared by dip coating using LDPE, PVAc, and EVA polymers containing 12-40% VA contents. Surface free energy of flat films was determined by measuring contact angles. Surface atomic composition was investigated by XPS at 0 and 60 take-off angles. XPS results show that hydrophobic PE component was found to enrich at the near-surface region for all EVA samples for a depth of $ 5 nm for both flat and rough surfaces, whereas hydrophilic VA component was enriched on the surface when VA < 18% for only at 10 nm depth. The difference between the XPS results of the flat and rough surfaces was not significant for EVA samples except EVA-33 surface where the atomic oxygen content decreased 15-20% for rough surfaces. Contact angle hysteresis values for the rough samples were much larger than that of the flat samples for LDPE and EVA-12 surfaces due to the presence of partial trapping of air pockets on these rough surfaces. A good agreement was obtained between surface concentration of atomic oxygen in the 5 nm outermost layer and c À S surface free energy component especially for the samples having high VA contents.

Combined XPS and contact angle studies of ethylene vinyl acetate and polyvinyl acetate blends

“…The surface oxygen atomic concentrations measured at 90 • take-off angle for a depth of 8 nm, were 1-19% lower than the theoretical values calculated from the bulk copolymer composition for all the pure EVA copolymers. This is in agreement with the previous reports indicating that PE segments are more enriched at the surface than VA segments for EVA copolymers by dip or spin coating [20,24].…”

“…As seen in this figure the change of VA content on the surface for a depth of 8 nm (at 90 • take-off angle) was not significant when all the data points were considered indicating that neither PE nor VA enrichment occurred. We also determined that similar to the previous findings [20,24], PE segments were more enriched at the surface for a depth of 8 nm for pure EVA copolymers as shown in Fig. 3b where the surface atomic oxygen concentrations were 1-19% lower than the theoretical values calculated from the bulk copolymer.…”

“…Hydrophobic PE component was found to enrich in the near-surface region for all flat and rough EVA samples for a depth of around 5 nm. The difference between the XPS results of the flat and rough surfaces was not significant for EVA samples except EVA-33 surface where the atomic oxygen content decreased 15% for 10 nm and 20% for 5 nm depth due to its very low molecular weight [24].…”

“…In a previous study, we investigated the surface chemical structure and wetting properties of both flat and rough EVA copolymer films by varying the concentration and temperature of the dip coating solution [24]. A solution concentration of 40 mg/ml was used for the flat coatings and up to 100 mg/ml for the rough coatings and the temperatures changed from room temperature to 125 • C. XPS analysis at 0 • and 60 • take-off angles (approximately 10 nm and 5 nm depths, respectively) was applied and contact angle measurements were carried out by increasing the VA content of the bulk EVA copolymer.…”

Selective adsorption of L1210 leukemia cells/human leukocytes on micropatterned surfaces prepared from polystyrene/polypropylene-polyethylene blends

“…Polymer blends which are the physical mixtures of the independent polymers can preferably be used for this purpose because blending may provide optimization of the desired properties of the final surface [32]. Solvent evaporation rate, phase separation, solvent diffusion, and SFE of the polymers have substantial effects on surface morphology of the polymer blends [31,[33][34][35]. Micropatterned surfaces can also be prepared using polymer blends [36,37].…”