Investigating the Dynamic Viscoelasticity of Single Polymer Chains using Atomic Force Microscopy

Liang, Xiaobin; Nakajima, Ken

doi:10.1002/polb.24908

Cited by 13 publications

(17 citation statements)

References 53 publications

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“…In the past, the viscoelasticity of single polymer chains has been determined by oscillatory response [ 42 , 43 , 44 ]. As opposed to the present work, these studies used oscillation frequencies close to the resonance of the cantilever and measured dissipation for a polymer from changes in phase lag.…”

Section: Resultsmentioning

confidence: 99%

Quantitative Elasticity of Flexible Polymer Chains Using Interferometer-Based AFM

2022

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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.

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Section: Resultsmentioning

confidence: 99%

Quantitative Elasticity of Flexible Polymer Chains Using Interferometer-Based AFM

2022

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“…In the context of extracting viscoelastic information, oscillatory measurements have been performed on single molecules [50][51][52]. In contrast to the present study, these measurements were performed with oscillation frequencies close to cantilever resonance and have reported dissipation for single molecule.…”

Section: Force-extension Measurementmentioning

confidence: 87%

Elasticity of single flexible polymer chains in good and poor solvents

Ahlawat¹,

Rajput²,

Patil³

2021

Preprint

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Force versus extension curves measure entropic elasticity of single polymer chain in force spectroscopy experiments. A Worm-like Chain model is used to describe force extension experiments with an intrinsic chain parameter called persistence length, which is a measure of local bending flexibility. For flexible polymers, there is a discrepancy in estimates of persistence length in various force regimes. For instance, Atomic Force Microscopy (AFM) based pulling experiments report anomaly low values which are also inconsistent with magnetic tweezers experiments. To understand this, we investigate the role of coupling between microscopic force probe and intrinsic elasticity of polyethylene glycol chain in AFM-based experiments. We perform experiments using oscillatory rheology by providing an external excitation of fixed frequency to the probe. We show that a proper quantification of elastic response measured directly by oscillatory technique deviates significantly from conventional force-extension curves. The persistence length obtained by fitting WLC to stiffness extension data matches well with equilibrium tweezers experiments. In addition, for polystyrene chain in poor solvent no deviation in elastic response is observed between oscillatory and constant velocity pulling experiments. However, such deviation is seen for polystyrene in good solvent. We attribute this to hydrophobic interaction between monomers of polystyrene in water. Our results suggest that oscillatory rheology on single polymer chains provide quantitative estimate of its elastic response. The consistency in values of persistence length using magnetic tweezers experiments in low force regime and the AFM experiments in high force regime suggests that WLC is successful in describing the polymer elasticity in the force range typically probed in AFM experiments.

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“…In this study, to measure the dynamic viscoelasticity of single polymer chains, we equipped an external oscillation control and data acquisition system based on traditional AFM (Figure S1). 34 A lock-in amplifier was introduced into the system to provide flexible experimental control and data acquisition. While the polymer chain was stretched, the AFM cantilever was oscillated at the resonant frequency by an external excitation signal from the lock-in amplifier, as shown in Figure 1b.…”

Section: Materials and Sample Preparationmentioning

confidence: 99%

“…We found that the viscosity of a PS chain was mainly determined by its interaction with the solvent. 34 In this study, we used this dynamic SMFS method to quantitatively measure the dynamic viscoelastic changes in elasticity and viscosity of a single chain at low elongation. By quantitatively analyzing the changes in elasticity and viscosity of a single chain at the low elongation, the interaction of PNIPAM molecules with water was investigated to reveal the hydration mechanism of the single polymer chain.…”

Section: Introductionmentioning

confidence: 99%

Study of the Dynamic Viscoelasticity of Single Poly(N-isopropylacrylamide) Chains Using Atomic Force Microscopy

2022

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Thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) is of great interest in the fields of medicine and pharmacology because its lower critical solubility temperature (LCST) is close to the physiological temperature. The understanding of the phase transfer mechanism of PNIPAM near the LCST is of great significance for the design, development, and application of its derivatives. In this study, a dynamic single-molecule force spectroscopy (SMFS) approach was used to quantitatively assess the dynamic viscoelasticity of single PNIPAM chains at different temperatures. We found that the relationship between the viscoelasticity coefficient of a single polymer chain in the low elongation region and the number of chain segments below the LCST was in accordance with the prediction of the Kirkwood model. Above the LCST, the PNIPAM chains exhibited different viscoelastic behaviors that were determined by their conformations. Importantly, the characterization of dynamic viscoelasticity allowed us to observe the phase transition behavior of single polymer chains in the low elongation region where they are similar to random coils, which helped us to understand the microscopic mechanism of their temperature response. In particular, above the LCST, the PNIPAM chains no longer underwent purely entropic elastic behavior but instead displayed enthalpic viscoelastic behavior dominated by intramolecular hydrogen bonds.

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Investigating the Dynamic Viscoelasticity of Single Polymer Chains using Atomic Force Microscopy

Cited by 13 publications

References 53 publications

Quantitative Elasticity of Flexible Polymer Chains Using Interferometer-Based AFM

Quantitative Elasticity of Flexible Polymer Chains Using Interferometer-Based AFM

Elasticity of single flexible polymer chains in good and poor solvents

Study of the Dynamic Viscoelasticity of Single Poly(N-isopropylacrylamide) Chains Using Atomic Force Microscopy

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