Environment dependence of single polymer chain stretching and application to molecular spring

点击翻译按钮获取中文摘要

It is well known that a restoring force by entropic elasticity is acted on the ends of a polymer chain upon stretching a flexible poly* chain in a random coil state. The atomic force microscope (AFM) has enabled direct stretching measurement for single polymer chains * which both the ends of a polymer chain could be adsorbed at an AFM probe tip and substrate surfaces. In this study, an entro* elasticity of a stretched single polystyrene chain was directly measured with AFM in a dilute solution of mono-disperse polystyrene(* and the relationship between applied force and end-to-end distance of PS chain with different molecular weights was investigated.Each end of mono-disperse PS was modified with a carboxyl group which can form a linkage to an amino group on the surfaces * probe tip and a substrate. The shape of the force-distance curve could be explained by the model of freely jointed segments which * elastically deformable during stretching. The magnitude of the maximum stretching fo … More rce ranged 200-500 pN, which could correspo* to the breaking force of hydrogen bonding formed between a PS chain end and the probe tip or the substrate surface. The maxim* extension was found to be longer with increasing molecular weight. The average of the experimental maximum extensions was ab* 60〜70 % as long as of the molecular contour length. From analogy of simulations with the freely jointed chain model, the observ* curves could result from entropic elasticity of an elongated random coil. The extension of a PS chain in a methanol solution * smaller than that in a toluene one, though the Mn of a PS chain in each solution was same. Generally, the dimension of a random * of a polymer chain in a poor solvent is smaller than that in a good solvent. Since methanol is much poorer solvent to PS compared * toluene, a radius of gyration of a PS chain in a methanol solution should be much smaller than that in a toluene solution. Therefore* larger force was required to stretch a PS chain in a methanol solution in comparison with that in a toluene solution. Less