Senanayake Manjula, Perahia Dvora, Grest Gary S
Department of Chemistry, Clemson University, Clemson, South Carolina 29634, USA.
Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
J Chem Phys. 2021 Feb 21;154(7):074903. doi: 10.1063/5.0038097.
A small number of associating groups incorporated onto a polymer backbone have dramatic effects on the mobility and viscoelastic response of the macromolecules in melts. These associating groups assemble, driving the formation of clusters, whose lifetime affects the properties of the polymers. Here, we probe the effects of the interaction strength on the structure and dynamics of two topologies, linear and star polymer melts, and further investigate blends of associative and non-associating polymers using molecular dynamics simulations. Polymer chains of approximately one entanglement length are described by a bead-spring model, and the associating groups are incorporated in the form of interacting beads with an interaction strength between them that is varied from 1 to 20 kT. We find that, for all melts and blends, interaction of a few kT between the associating groups drives cluster formation, where the size of the clusters increases with increasing interaction strength. These clusters act as physical crosslinkers, which slow the chain mobility. Blends of chains with and without associating groups macroscopically phase separate for interaction strength between the associating groups of a few kT and above. For weakly interacting associating groups, the static structure function S(q) is well fit by functional form predicted by the random phase approximation where a clear deviation occurs as phase segregation takes place, providing a quantitative assessment of phase segregation.
少量连接到聚合物主链上的缔合基团对熔体中大分子的迁移率和粘弹性响应有显著影响。这些缔合基团聚集在一起，促使簇的形成，簇的寿命影响聚合物的性能。在此，我们通过分子动力学模拟探究相互作用强度对两种拓扑结构（线性和星形聚合物熔体）的结构和动力学的影响，并进一步研究缔合聚合物与非缔合聚合物的共混物。大约一个缠结长度的聚合物链由珠簧模型描述，缔合基团以相互作用的珠子形式引入，它们之间的相互作用强度在1至20 kT之间变化。我们发现，对于所有熔体和共混物，缔合基团之间几kT的相互作用会促使簇的形成，其中簇的尺寸随着相互作用强度的增加而增大。这些簇充当物理交联剂，减缓链的迁移率。对于缔合基团之间相互作用强度为几kT及以上的情况，有缔合基团和无缔合基团的链的共混物在宏观上会发生相分离。对于弱相互作用的缔合基团，静态结构函数S(q)能很好地拟合由随机相位近似预测的函数形式，随着相分离的发生会出现明显偏差，从而对相分离进行定量评估。
