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.

力与延伸曲线在力谱实验中测量单个聚合物链的熵弹性。类蠕虫链模型用于描述具有称为持久长度的内在链参数的力扩展实验，该参数是局部弯曲灵活性的度量。对于柔性聚合物，在各种力状态下对持续长度的估计存在差异。例如，基于原子力显微镜 (AFM) 的拉动实验报告异常低值，这也与磁镊子实验不一致。为了理解这一点，我们在基于 AFM 的实验中研究了微观力探针与聚乙二醇链的固有弹性之间耦合的作用。我们通过向探头提供固定频率的外部激励来使用振荡流变学进行实验。我们表明，通过振荡技术直接测量的弹性响应的适当量化与传统的力-延伸曲线显着不同。通过将 WLC 拟合到刚度扩展数据获得的持久长度与平衡镊子实验非常匹配。此外，对于在不良溶剂中的聚苯乙烯链，在振荡和等速拉伸实验之间没有观察到弹性响应的偏差。然而，这种偏差在良好溶剂中的聚苯乙烯中可见。我们将此归因于水中聚苯乙烯单体之间的疏水相互作用。我们的结果表明，单个聚合物链上的振荡流变学提供了对其弹性响应的定量估计。