Single-Molecule Measurement of the Strength of a Siloxane Bond

Abstract

Increasing the mechanical stability of artificial polymer materials is an important task in materials science, and for this a profound knowledge of the critical mechanoelastic properties of its constituents is vital. Here, we use AFM-based single-molecule force spectroscopy measurements to characterize the rupture of a single silicon-oxygen bond in the backbone of polydimethylsiloxane as well as the force-extension behavior of this polymer. PDMS is not only a polymer used in a large variety of products but also an important model system for highly flexible polymers. In our experiments, we probe the entire relevant force range from low forces dominated by entropy up to the rupture of the covalent Si-O bonds in the polymer backbone at high forces. The resulting rupture-force histograms are investigated with microscopic models of bond rupture under load and are compared to density functional theory calculations to characterize the free-energy landscape of the Si-O bond in the polymer backbone.

Chemomechanics: chemical kinetics for multiscale phenomena

“…8,50,75 The latter strategy was used in a careful study of mechanical properties of polydialkylsiloxanes, which demonstrated the lack of a correlation between the estimated barrier lowering of the Si-O bond dissociation and the strain energy (either total or per Si-O bond) and the absence of a unique fit of the experimental data to standard models of force-dependent kinetics. 41 The latter findings are consistent with calculations presented in Section 2a (Fig. 11A).…”

“…In practice, rapid detachments are observed at forces of a few nN. 8,41 In a less common configuration, a macromolecule is stretched rapidly to a desired restoring force and maintained at such a force until it ruptures. 50 This approach is best suited to a bimolecular reaction, whose rates can be controlled by the concentration of a reagent in solution.…”

“…(1) chemical and/or structural heterogeneity of multipolymeric assemblies and different reactivity of chemical bonds at the polymer/solid interface and within the polymer, 41,79 (2) biased estimates of F t * due to limited statistics, 78 the lack of internal mechanical equilibrium prior to the reaction 26 or Chem. Soc.…”

From Biological towards Artificial Molecular Motors

“…An ideal molecule where the cis state had an elasticity as high as the trans state could reach 100 % efficiency if it could hold and switch against forces of 8 nN, but such a force cannot be reached as covalent bonds already break at few nN forces. [61,62] How does this compare to biological molecular motors? The efficiency of the bacteriophage f29 is more than 50 % and this at low forces compared to the synthetic molecular motor.…”

Mechanochemistry: One Bond at a Time

“…Both experimental and theoretical investigations suggest the pulling force necessary to break a chemical bond be a few nanonewtons1, 37-39 while rupturing structures maintained by non-covalent bonds, such as unfolding of proteins, overcoming protein-ligand interactions and unraveling a single base-pair in double-stranded DNAs, requires forces at least one order of magnitude smaller 40-43. A few reports37, 38 have been published on bonding the molecule covalently at both ends before the pulling experiments, while in the majority of experiments, the molecule is picked up randomly through non-specific interactions. Consequently, the adhesion between the AFM tip and the molecule, or between the molecule and the substrate surface, is weak compared with the force required to break a chemical bond, but probably comparable to the hydrogen bonds and hydrophobic interactions maintaining the secondary and tertiary structure of a protein (without disulfide bonds).…”