Zhou Jie, Ou-Yang Zhong-Can, Zhou Haijun
Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100080, People's Republic of China.
J Chem Phys. 2008 Mar 28;128(12):124905. doi: 10.1063/1.2842064.
It has been revealed by mean-field theories and computer simulations that the nature of the collapse transition of a polymer is influenced by its bending stiffness epsilon(b). In two dimensions, a recent analytical work demonstrated that the collapse transition of a partially directed lattice polymer is always first order as long as epsilon(b) is positive [H. Zhou et al., Phys. Rev. Lett. 97, 158302 (2006)]. Here we employ Monte Carlo simulation to investigate systematically the effect of bending stiffness on the static properties of a two-dimensional lattice polymer. The system's phase diagram at zero force is obtained. Depending on epsilon(b) and the temperature T, the polymer can be in one of the three phases: crystal, disordered globule, or swollen coil. The crystal-globule transition is discontinuous and the globule-coil transition is continuous. At moderate or high values of epsilon(b) the intermediate globular phase disappears and the polymer has only a discontinuous crystal-coil transition. When an external force is applied, the force-induced collapse transition will either be continuous or discontinuous, depending on whether the polymer is originally in the globular or the crystal phase at zero force. The simulation results also demonstrate an interesting scaling behavior of the polymer at the force-induced globule-coil transition.
平均场理论和计算机模拟表明，聚合物塌缩转变的性质受其弯曲刚度ε(b)的影响。在二维情况下，最近的一项分析工作表明，只要ε(b)为正，部分定向晶格聚合物的塌缩转变总是一级的[H. Zhou等人，《物理评论快报》97, 158302 (2006)]。在此，我们采用蒙特卡罗模拟系统地研究弯曲刚度对二维晶格聚合物静态性质的影响。得到了零力下系统的相图。根据ε(b)和温度T，聚合物可以处于三种相之一：晶体、无序球状体或溶胀线团。晶体 - 球状体转变是不连续的，球状体 - 线团转变是连续的。在ε(b)为中等或较高值时，中间的球状体相消失，聚合物只有不连续的晶体 - 线团转变。当施加外力时，力致塌缩转变将是连续的或不连续的，这取决于聚合物在零力时最初处于球状体相还是晶体相。模拟结果还表明了聚合物在力致球状体 - 线团转变时有趣的标度行为。
