Full View of Single-Molecule Force Spectroscopy of Polyaniline in Oxidized, Reduced, and Doped States

Abstract

The macroscopic mechanical properties of polyaniline (PANI) lie mainly on two factors, the structure of molecular aggregations of polymers and the mechanical properties of a single polymer chain. The former factor is well revealed; however, the latter is rarely studied. In this article, we have employed atomic force microscopy-based single-molecule force spectroscopy to investigate the mechanical properties of a kind of water-soluble PANI at a single-molecular level. We have carried out the study comparatively on single-chain-stretching experiments of oxidized, reduced, and doped PANI and obtained a full view of the single-chain elasticity of PANI in all these states. It is found that oxidized and reduced PANI chains are rigid, and the oxidized PANI is more rigid than the reduced PANI. Such a difference in single-chain elasticity can be rationalized by the molecular structures that are composed of benzenoid diamine and quinoid diimine in different proportions. The doped PANI has been found to be more flexible than the oxidized and reduced PANI, and the modified freely jointed chain parameters of doped PANI are similar with those of a common flexible-chain polymer. The results have explained the molecular-level origin of the outstanding flexibilities of materials made of doped PANI.

Surface and Biomolecular Forces of Conducting Polymers

“…shows a non-linear increase in force with increasing distance 50 , which is typical behaviour for Figure 5B) 49 . In contrast to the weaker interactions via heparin domains, this electrochemically induced adhesion is stronger and non-specific but can be reversibly switched to smaller piconewton adhesion forces by applying an opposite negative bias to the polymer.…”

Large Mechanical Response of Single Dendronized Polymers Induced by Ionic Strength

“…To use single polymers as building blocks in molecular machines and devices,2, 14 one must be able to control their mechanical response 6. 8, 9, 12, 15 For elastic proteins, impressive changes in their elongation by factors of 2–3 were reported in the force range 0.1–0.3 nN as a result of unfolding of individual domains 3–5. Amylose shows changes in its elongation of 10–20 % in a similar force range.…”

“…These changes were interpreted in terms of conformational transitions of the pyranose rings 6. 8 Although synthetic polymers can be tuned in a reversible fashion by optical excitation,12 redox properties,15 and the nature of the solvent,9 the changes in the elongation that were obtained are only 5–15 % and were observed for forces below 0.1 nN. Synthetic polymers featuring a more significant response, especially at larger forces, have not been described so far.…”

Frequency Dispersion of Double Layer Capacitance of Polyaniline-Coated Electrodes Under the Conducting State

“…The feasibility may be related with microscopic Young's modulus of PANi. The mechanical properties such as macroscopic moduli of PANi films have been discussed in the context of the redox states (Mohamoud, et al, 2007;Valentová, et al, 2010;Han, et al, 2004;Yu, et al, 2009). The Young moduli of the oxidized state are smaller than those of the reduced one (Valentová, et al, 2010).…”

“…The curves varied with locations of touching a cantilever with the film, but they were always composed of two lines with a critical point. Two lines with a junction have been exhibited in most PANi films (Mohamoud, et al, 2007;Valentová, et al, 2010;Han, et al, 2004;Yu, et al, 2009;Passeri, et al, 2011) although complicated curves appeared in a single polymer chain (Yu, et al, 2009). The slope of force against the depth, proportional to the Young modulus, of the oxidized form (8.8±3.8 mV nm -1 ) is smaller than that of the reduced one (10.5±5.9 mV nm -1 ), where these values were averaged for 46 curves at different locations, and the errors mean the standard deviation.…”