Quantitative Elasticity of Flexible Polymer Chains Using Interferometer-Based AFM

Abstract

We estimate the elasticity of single polymer chains using atomic force microscope (AFM)-based oscillatory experiments. An accurate estimate of elasticity using AFM is limited by assumptions in describing the dynamics of an oscillating cantilever. Here, we use a home-built fiber-interferometry-based detection system that allows a simple and universal point-mass description of cantilever oscillations. By oscillating the cantilever base and detecting changes in cantilever oscillations with an interferometer, we extracted stiffness versus extension profiles for polymers. For polyethylene glycol (PEG) in a good solvent, stiffness–extension data showed significant deviation from conventional force–extension curves (FECs) measured in constant velocity pulling experiments. Furthermore, modeling stiffness data with an entropic worm-like chain (WLC) model yielded a persistence length of (0.5 ± 0.2 nm) compared to anomaly low value (0.12 nm ± 0.01) in conventional pulling experiments. This value also matched well with equilibrium measurements performed using magnetic tweezers. In contrast, polystyrene (PS) in a poor solvent, like water, showed no deviation between the two experiments. However, the stiffness profile for PS in good solvent (8M Urea) showed significant deviation from conventional force–extension curves. We obtained a persistence length of (0.8 ± 0.2 nm) compared to (0.22 nm ± 0.01) in pulling experiments. Our unambiguous measurements using interferometer yield physically acceptable values of persistence length. It validates the WLC model in good solvents but suggests caution for its use in poor solvents.

Toughening and stabilizing MOF crystals via polymeric guest inclusion

“…This can be ascribed to the increased flexibility of PEG with respect to its chemical structure. 28,29…”

“…This can be ascribed to the increased flexibility of PEG with respect to its chemical structure. 28,29 Motivated by the above findings, we also compared the mechanical properties of 1 . PSt and 1 .…”

The average magnetic anisotropy of polystyrene in polymersomes self-assembled from poly(ethylene glycol)-b-polystyrene

“…These few monomers are expected to be at the edge of the membrane, where the polymer is forced to be orientated perpendicular to the membrane and the bending stiffness is the largest. Recent research showed that the bending stiffness (persistence length) of PS is 1 monomer, 34 which implies that the rest of the PS monomers are expected to be coiled up. To determine the degree of coiling, Δ χ PS is calculated as a function of the fraction of the maximal extension of PS in the polymersome membrane, assuming that phenyls are free to rotate around the bonds connecting them to the PS backbone (for more details on this calculation see the Supporting Information 2 and Fig.…”

Recent Advances in Aptamer-Based Sensors for Sensitive Detection of Neurotransmitters

“…Since polymers are composed of repeatedly connected units, they can be fabricated so as to have flexible forms [ 102 , 103 , 104 , 105 ]. In addition, polymers have physical variables that determine their physical properties, and thus each polymer can be used in various ways [ 106 , 107 ].…”