Sheng Yu-Jane, Cheng Kuang-Ling, Ho Chun-Chih
Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan, Republic of China.
J Chem Phys. 2004 Jul 22;121(4):1962-8. doi: 10.1063/1.1765100.
The effect of solvent quality on the equilibrium structure of a densely branched comb polymer is investigated based on the structure factor analyses by off-lattice Monte Carlo simulations. First, theta temperature (theta(infinity)) must be determined to identify the solvent condition. We locate the characteristic temperature theta(A)(N) at which the second virial coefficient vanishes and the transition temperature theta(R)(N) at which radius of gyration R(g) of the chain varies most rapidly with temperature, i.e., d(2)R(g)/dT(2)|(theta(R)) = 0. N represents the total number of monomers of a comb. As N --> infinity, theta(A) and theta(R) coincide to a point that is identified as the true theta temperature (theta(infinity)). The structure factors of the main chain, the side chain, and the whole polymer are calculated, respectively. It is found that at T = theta(infinity), the structural factors S(qR(g)) for the overall comb polymers match quite well with those of their Gaussian counterparts. When T< theta(infinity), the overall comb polymer assumes collapsed conformations, similar to a homogeneous sphere. However, the structure factor of the side chain indicates that it always remains in an expanded state regardless of the solvent condition. It is attributed to the strong interactions between side chains. The same effect leads to enhanced rigidity of the main chain in comparison to the linear chain, as clearly observed from the rescaled Kratky plot.
基于非晶格蒙特卡罗模拟的结构因子分析，研究了溶剂质量对密集支化梳状聚合物平衡结构的影响。首先，必须确定θ温度（θ(∞)）以识别溶剂条件。我们确定了第二维里系数消失时的特征温度θ(A)(N)以及链的回转半径R(g)随温度变化最快时的转变温度θ(R)(N)，即d(2)R(g)/dT(2)|(θ(R)) = 0。N表示梳状聚合物的单体总数。当N→∞时，θ(A)和θ(R)重合于一点，该点被确定为真实的θ温度（θ(∞)）。分别计算了主链、侧链和整个聚合物的结构因子。研究发现，在T = θ(∞)时，整体梳状聚合物的结构因子S(qR(g))与其高斯对应物的结构因子匹配得非常好。当T < θ(∞)时，整体梳状聚合物呈现塌缩构象，类似于一个均匀的球体。然而，侧链的结构因子表明，无论溶剂条件如何，它始终保持伸展状态。这归因于侧链之间的强相互作用。从重新标度的克拉特基图可以清楚地看出，相同的效应导致主链相对于线性链的刚性增强。
