SFM characterization of poly(isocyanodipeptide) single polymer chains in controlled environments:: Effect of tip adhesion and chain swelling

Isolated slightly hydrophilic chains of poly(isocyanodipeptides) (PICs) adsorbed on mica were studied by intermittent contact mode-scanning force microscopy (IC-SFM) in an ambient atmosphere controlled both with respect to the relative humidity (RH) and the presence of CHCl3 vapor. SFM revealed that the average chain height increases up to more than an order of magnitude with decreasing RH, leading to the highest value at RH = 0%. This is due to both a minimization of the capillary forces between the SFM tip and the hydrophilic substrate surface and a collapse of the side chains in the poor solvent. In a saturated CHCl3 vapor atmosphere, the chain heights increase up to twice this value, which is close to the polymer diameter measured by powder X-ray diffraction. This indicates that the PIC chains are solvated by CHCl3 molecules, causing the swelling of the single polymers. Achieving a control over the thickness of the polymer chains is fundamental for their optimal observation by SFM. Moreover, the understanding of the conformational properties of single macromolecules adsorbed on surfaces under different environmental conditions is of importance for unraveling their physicochemical properties and their dynamics, including their reactivity.