Tailored adhesion at polymer/nonpolymer interfaces

Abstract

AbstractIn this investigation, block copolymers of deuterated polystyrene (dPS) and poly (2‐vinylpyridine) (PVP) have been used to modify the adhesion at polystyrene/soda lime glass interfaces. The fracture energy, Gs of these interfaces was measured using an asymmetric double cantilever beam specimen. The failure mechanism was investigated using forward recoil spectrometry (FRES) and Rutherford backscattering spectrometry (RBS). The areal density, ∑ of the dPS‐PVP block copolymer at the two fracture surfaces, as well as the fraction of the dPS block on the PS side of the fractured sample are measured directly by FRES. The fraction of the PVP block on the glass side of the interface can be found by quaternizing the PVP with methyl iodide and then using RBS to measure the amount of iodine on each fracture surface. Short dPS blocks (NdPS < 175) do not entangle effectively with the PS homopolymer and only very small increases in Gc can be achieved as the dPS block pulls out of the interface. If the dPS block is long (NdPS ≫ 175) and if ∑ is large, crazes can develop in the PS ahead of the crack. The crazed interface fails at low ∑ by breaking the block copolymer close to the styrene/vinylpyridine link. At higher ∑, if the PVP block is relatively short (NPVP = 95), the crazed interface fails by the PVP block being pulled off the glass. If both the PVP and dPS blocks are long (≫ 175), the Gc increases rapidly with increases in ∑, but the interface becomes so strong that the glass on the thinner side of the test specimen breaks. The dPS block and the PVP block are found on opposite sides of the fracture surface with most of the PVP on the glass and most of the dPS on the PS side of the interfaces. Finally, if the glass surface is modified by coating it with a self‐assembled hydrophobic monolayer produced from chlorodimethyloctadecylsilane (CDMOS), the interface becomes very weak and fails by pull‐off of the PVP from the CDMOS‐coated glass. Using these results it is possible to tailor the interfacial adhesion to produce a desired Gc within a wide range of possible values. © 1994 John Wiley & Sons, Inc.