SCANNING FORCE MICROSCOPY OF NANOFIBRILLAR STRUCTURE OF DRAWN POLYETHYLENE TAPES .2. MEASUREMENTS UNDER WATER

Atomic force microscopy studies of drawn ultra high molecular weight polyethylene tapes were conducted under water, where the operating repulsive forces and the contact area between probe and sample are smaller than in ambient conditions measurements. In this way a higher image resolution allows to identify nanofibrils with widths of 15-25nm, which are formed during stretching, Numerous linear features with separation of 5-8 nm were resolved on the surfaces of nanofibrils in a tape with draw ratio 70. Periodical contrast variations along the stretching direction with a repeat distance of ca. 25 nm - long period - were found on drown tapes only at stronger operation forces, This finding indicates that these features are related not to the surface topography but to differences in surface hardness. From the molecular scale images it is evident that the harder parts of nanofibrils consist of crystalline domains of extended polymer chains, while no ordered features were found between the elevated image patterns.