Effect of molecular weight distribution on the thermal adhesion of polystyrene and PMMA brushes

Abstract

The effect of the molecular weight distribution (MWD) and graft density of polymer brushes on the adhesion strength of flat substrates was investigated using polystyrene (PS) and poly(methyl methacrylate) (PMMA) brushes with variations in the molecular weight, MWD, and graft density. Two silicon wafers covered with polymer brushes were bound in a 0.5 cm2 contact area using 5 μL of toluene and a pinchcock Hoffman clamp and then annealed at 408 K in a vacuum oven for 3 h. PS brushes with a MWD narrower than Mw/Mn = 1.20 yielded an adhesion strength lower than 0.1 MPa. In contrast, PS brushes having a broad MWD (Mw/Mn = 1.3–1.4) were successfully joined to afford a lap shear adhesion strength of 1.2 MPa despite high graft density due to the intermixing of longer chains of the opposite brushes. Similar results were also obtained in the case of PMMA brush.