Angle‐resolved XPS of fluorinated and semi‐fluorinated side‐chain polymers

Abstract

AbstractAngle‐resolved XPS data (elemental quantification and high‐energy‐resolution C 1s) are presented for ten polymers with side‐chains of the form OCO(CF2)yF, COO(CH2)2OCO(CF2)yF (y = 1, 2, 3) and COO(CH2)x(CF2)yF (x = 1, y = 1, 2, 3; x = 2, y = 8). Particular attention was paid to charge compensation and speed of data acquisition, with co‐addition from multiple fresh samples to give spectra with good energy resolution and good signal‐to‐noise ratio free from the effects of x‐ray‐induced degradation. Water contact angles for the polymers are also reported. The XPS data demonstrate preferential surface segregation of fluorine‐containing groups for all but the shortest side‐chain polymer, where the OCOCF3 side‐chain either does not surface segregate or is too short for surface segregation to be detectable by angle‐resolved XPS. In the other polymers studied the relative positions of functional groups in the side‐chains correlate with the angle‐resolved behaviour of the corresponding C 1s components. This shows that the surface side‐chains are oriented towards the polymer surface. For the COO(CH2)2OCO(CF2)yF (y = 1) side‐chain, the angle‐resolved C 1s data suggest reduced ordering and linearity compared with y = 2 and 3. For any particular series of polymers, e.g. COO(CH2)x(CF2)yF, the water contact angles increase with y, consistent with burying of the hydrophilic ester groups as y increases. For any particular value of y the sequence of water contact angles is COO(CH2)x(CF2)yF > OCO(CF2)yF ∼ COO(CH2)2OCO(CF2)yF, suggesting greater ordering and density of fluorocarbon species at the surface of the COO(CH2)x(CF2)yF side‐chain polymers compared with the other polymers studied. For the COO(CH2)2(CF2)8F polymer a water contact angle of 124° is measured, which is greater than that of poly(tetrafluoroethene). The COO(CH2)2OCO(CF2)F polymer is unusual in that it shows a particularly low water contact angle (83° ), suggesting that the probe fluid is able to sense both ester groups, consistent with the reduced ordering of the side‐chain detected by angle‐resolved XPS. Copyright © 2004 John Wiley & Sons, Ltd.