三维吸附紧密高分子单链的力学性质研究

采用PERM(pruned-enriched Rosenbluth method)算法,研究了吸附在界面附近的紧密高分子链力学行为.发现当界面的吸附能比较大时,紧密高分子链从紧贴于吸附界面到逐渐远离的过程中,其外形会经历4种典型的变化.同时紧密高分子链的尺寸大小如/N、xy/N、z/N,形状参数<δ*>,热力学性质如每个键的平均自由能A/N,平均相互作用能/N等,甚至所受外力的大小都会同时做出相应的变化,其出现变化的位置也一致.特别是随着紧密高分子链离开吸附界面的过程中,作用于高分子链上的外力明显出现几个力学平台,这与实验得到的结果完全一致.同时还研究了弱吸附能的情况,在这种情况下实验是很难进行的.

MECHANICS BEHAVIORS OF ADSORBED THREE-DIMENSIONAL COMPACT CHAINS

Elastic behaviors of a single three-dimensional compact chain adsorbed on the attractive surface are investigated using the pruned-enriched-Rosenbluth method (PERM).The size and shape of the chain,such as mean-square end-to-end distance ,mean-square radii of gyration _ xy and _z,and shape factor <δ> are studied with different adsorption interaction energy and different positions of the chain on which the force is exerted.During the elasticity process,the shape factor <δ> first decreases with the shape of chains in a sphere,then increases and the chain extends to be a rod shape along the direction of the force.It decreases again,and at the end it remains a constant value.If the chain is far away from the adsorbing surface,all of the conformational properties remain constant,and there would appear the "jump point".On the other hand,some thermodynamic properties such as the average Helmholtz free energy per bond ,average energy per bond /N,average attraction energy per bond /N,average contact energy per bond /N,elastic force f and energy contribution to elastic force f_U are also calculated during the elasticity process.Different thermodynamic behaviors are obtained when the force acts on different monomers of the chain.Obviously,there exist several long plateaus for elastic force f with strong adsorption interaction,which agrees well with experimental results.We also discuss elastic behaviors of compact chains with weak adsorption interaction,which cannot be obtained from experimental methods.