Single-Molecule AFM Study of Polystyrene Grafted at Gold Surfaces

ABSTRACT

Single-molecule studies under poor solvent conditions show that atomic force microscopy (AFM) measurements of contour lengths of polystyrene 12K and 17K relate well to gel permeation chromatography (GPC) data when grafting concentrations are low (not greater than 0.7 mM). Contact angles and ellipsometry have been used to characterize the surfaces and indicate low grafting densities at this grafting concentration. Persistence lengths (p) of different length polystyrene chains, when fitted to a WLC (worm-like chain) model, show values of p = 0.23 nm±0.10 nm and p = 0.25 nm±0.13 nm, for 12 K and 17 K polystyrene, respectively, when the persistence lengths are fitted to log-normal distributions. These values are close to the expected theoretical value of 0.23 nm and further confirm that mostly single molecules were studied on these polystyrene surfaces. Higher grafting concentrations (≥1 mM) resulted in pulling multiple molecules.

Keywords:

• AFM
• Atomic force microscopy
• GPC
• Polydispersity
• Polystyrene
• Single molecule

Notes

Note: Also shown is the distribution of percentages of the data that fit well to the WLC model and those that do not (Figure 2).

One of a collection of papers honoring Manoj K. Chaudhury, the February 2005 recipient of The Adhesion Society Award for Excellence in Adhesion Science, sponsored by 3M.