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

众所周知，在无规卷曲状态下拉伸柔性聚 * 链时，由熵弹性产生的恢复力作用在聚合物链的末端。原子力显微镜（AFM）能够直接测量聚合物单链的拉伸，聚合物链的两端可以吸附在AFM探针尖端和基底表面。在本研究中，用原子力显微镜（AFM）直接测量了单分散聚苯乙烯（PS）在稀溶液中拉伸时的内弹性，并研究了不同分子量的PS链在拉伸过程中所受作用力与链端间距的关系。探针尖端和衬底。力-距离曲线的形状可以用自由连接的节段模型来解释，这些节段在拉伸过程中发生弹性变形。最大拉伸力的大小 ...更多信息 rce在200-500 pN之间，这与PS链端与探针针尖或基底表面形成氢键的断裂力相对应。发现随着分子量的增加，最大延伸时间更长。实验最大延伸的平均值为分子轮廓长度的ab* 60 ~ 70%。从模拟与自由连接链模型的类比，Ekv * 曲线可以由伸长的无规卷曲的熵弹性产生。PS链在甲醇溶液中的延伸小于在甲苯溶液中的延伸，尽管两种溶液中PS链的Mn相同。通常，聚合物链在不良溶剂中的无规尺寸小于在良溶剂中的无规尺寸。由于甲醇是比甲苯差得多的PS的溶剂，所以PS链在甲醇溶液中的回转半径应该比在甲苯溶液中的回转半径小得多。因此，与在甲苯溶液中相比，在甲醇溶液中拉伸PS链需要更大的力。少

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