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

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