Thermal Induced Instability of Thin Polymer Films: A Study by Atomic Force Microscopy

Systematic studies of thin-film stabilities of random copolymers consisting of decyl methacrylate (DMA)/methyl methacrylate (MMA) units on a polystyrene (PS) layer tethered to silicon wafer have been carried out by atomic force microscopy (AFM) as functions of molecular weight and chemical composition. Upon annealing at an elevated temperature above the glass transition temperature ( Tg), the initially flat polymer films break up into small holes, and finally form macroscopic droplets. The tethered PS layer was found to be dense enough to inhibit penetration of the copolymers into the lower layer during the annealing process. AFM studies at an early stage showed that the velocity of the hole growth was dependent upon both the molecular weights and chemical compositions of the copolymers. However, the equilibrium contact angles of the copolymer droplets formed on the PS layer were more dependent on the chemical compositions than on the molecular weights.

Nanotribological Properties of Poly(ether ketone ketone) (PEKK) and Sulfonated Poly(ether ketone ketone) (S-PEKK) Thin Films

An atomic force microscope (AFM) was used to determine the nanotribological properties of poly(ether ketone ketone) (PEKK) and sulfonated poly(ether ketone ketone) (S-PEKK) thin films, by sliding the AFM tip on the polymer surfaces and stepwise increasing the loading forces on the cantilever. For comparison, a polystyrene (PS) film with surface roughness comparable to those of the PEKK and S-PEKK was also examined using the same procedure. It was found that the S-PEKK film exhibits much higher values of both the coefficient of friction and the adhesive force than the PEKK film, which exhibits slightly higher values than the PS film. The surface topographies of the polymer films captured after frictional measurements suggest that PEKK has much better wear resistance than PS, whereas S-PEKK displays some visco-elastic character.