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‐chain polystyrene (SCPS) particles sprayed with an atomizer onto freshly cleaved mica surfaces from very dilute solutions of a polydisperse polystyrene sample in good solvents, methylene cloride and benzene, and in poor solvents, CH2Cl2/MeOH 3/1.2 v/v and CH2Cl2/MeOH 3/1.3 v/v. The SCPS particles possess a definite morphology irrespective of the molecular weight but depending on the solvent. The morphology was found to change with time during drying after spraying and to be very sensitive to solvent environment and external forces exerted by the tip of the scanning probe. The particles became oriented due to probe‐tip‐particle interaction during probe scanning. Only qualitative comparison were made for the sizes of the observed images owing to the polydispersity and irregular shape of the particles and uncertainties about the tip convolution effects on the lateral dimensions. Only in the case of spraying the solution in poor solvents particles close to the shape of spheres were observed. In other cases the heights of the particles sprayed were an order of magnitude smaller than the lateral dimensions. AFM imaging has been applied to observe changes in morphology of SCPS particles sprayed from solutions after freeze thaw cycling. The results do not support the idea of cryogenic degradation of PS but the morphology 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°C and then cooled to room temperature the coil size increased with a resulting morphology similar to the morphology observed before freeze thaw cycling.