MORPHOLOGICAL OBSERVATIONS OF SINGLE-CHAIN GLASSY POLYSTYRENE BY MEANS OF TAPPING MODE ATOMIC-FORCE MICROSCOPY

Tapping mode atomic force microscopy has been used to observe single-c hain poly styrene (SCPS) particles sprayed with an atomizer onto fresh ly cleaved mica surfaces from very dilute solutions of a polydisperse polystyrene sample in good solvents, methylene cloride and benzene, an d in poor solvents, CH2Cl2/MeOH 3/1.2 v/v and CH2Cl2/MeOH 3/1.3 v/v. T he SCPS particles possess a definite morphology irrespective of the mo lecular weight but depending on the solvent. The morphology was found to change with time during drying after spraying and to be very sensit ive to solvent environment and external forces exerted by the tip of t he scanning probe. The particles became oriented due to probe-tip-part icle interaction during probe scanning. Only qualitative comparison we re made for the sizes of the observed images owing to the polydispersi ty and irregular shape of the particles and uncertainties about the ti p convolution effects on the lateral dimensions. Only in the case of s praying the solution in poor solvents particles close to the shape of spheres were observed. In other cases the heights of the particles spr ayed were an order of magnitude smaller than the lateral dimensions. A FM imaging has been applied to observe changes in morphology of SCPS p articles sprayed from solutions after freeze thaw cycling. The results do not support the idea of cryogenic degradation of PS but the morpho logy of PS in solution changed to a smaller coil size during cryogenic freezing which persisted after being brought back to room temperature . When the freeze thaw cycled solution was heated to 100 degrees C and then cooled to room temperature the coil size increased with a result ing morphology similar to the morphology observed before freeze thaw c ycling.