Unfolding of a Single Polymer Chain from the Single Crystal by Air-Phase Single-Molecule Force Spectroscopy: Toward Better Force Precision and More Accurate Description of Molecular Behaviors

Abstract

Understanding the mechanisms of the mechanical deformation of lamellar crystals at the molecular level is of prime importance to rational design of advanced crystalline polymer materials. Single-molecule force spectroscopy (SMFS) can directly characterize molecular behavior and kinetic parameters that are masked in ensemble measurements. However, current SMFS approach cannot sufficiently manipulate a single molecule in air, which is the real working condition for most crystalline polymer materials. Here, we establish an air-phase atomic force microscopy (AFM)-based SMFS method that allows the unfolding of a single helical poly(ethylene oxide) (PEO) chain from the single crystal in air. Our results show that the mechanostability of PEO stem and unfolding potential are significantly enhanced in air compared with the case in liquid. The airphase SMFS method can achieve a much better force precision of 4 pN even at rapid stretching velocity of ∼100 μm/s. Moreover, some intermediate states (e.g., the movement of helical loop within the crystal phase), which were not detectable by using liquid-phase SMFS, have been identified by air-phase SMFS. Therefore, this proposed approach opens new ways for investigating the nanomechanical properties and corresponding molecular mechanism of polymer materials used in solvent-free state.

The molecular mechanisms underlying mussel adhesion

“…AFM-based SMFS has been widely used to study the mechanical strength of chemical bonds, ligand-receptor interactions, protein-protein interactions and adhesive molecule-surface interactions. [59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74] AFM measurement is complementary to SFA measurement and can directly quantify the strength of single adhesion bonds with an extremely high resolution of 10 À9 N on force and 10 À10 m on separation. Representative interaction strengths measured by SMFS are summarized in Table 1.…”

Force‐induced melting of a single polyethylene oxide chain from single crystal: Molecular behavior and influencing factors

“…Gaussian fitting gives the most probable forces: 44 ± 3 pN in amyl acetate, 48 ± 4 pN in eucalyptol, 46 ± 4 pN in butyl butyrate, 56 ± 4 pN in dihexyl ether, 56 ± 6 pN in α‐pinene, 63 ± 4 pN in octane, 64 ± 4 pN in hexadecane, and 109 ± 7 pN in air. To further examine the relationship between the melting force and interfacial free energy, we calculated PEO‐solvent interfacial tension (Table ) according to the Wu's equation . The surface tensions of solvent can be calculated from Hansen solubility parameters, which is developed by Beerbower and Panzer (Table ).…”

Static and Dynamic Mechanical Properties of Single Polymer Chains

“…Some of the force curves that have been studied 19) . SMFS also enables direct measurements of intraand intermolecular interactions at the molecular level, providing information about the molecular conformation and structure of synthetic polymers and biopolymers 20,21) . In addition, SFMS can measure individual molecules under a variety of controlled conditions (solvent, temperature, pH, etc.)…”