Section on Quantitative Imaging and Tissue Sciences, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
J Chem Phys. 2021 Oct 7;155(13):134905. doi: 10.1063/5.0064835.
We investigate the conformational properties of "ideal" nanogel particles having a lattice network topology by molecular dynamics simulations to quantify the influence of polymer topology on the solution properties of this type of branched molecular architecture. In particular, we calculate the mass scaling of the radius of gyration (R), the hydrodynamic radius, as well as the intrinsic viscosity with the variation of the degree of branching, the length of the chains between the branched points, and the average mesh size within these nanogel particles under good solvent conditions. We find competing trends between the molecular characteristics, where an increase in mesh size or degree of branching results in the emergence of particle-like characteristics, while an increase in the chain length enhances linear polymer-like characteristics. This crossover between these limiting behaviors is also apparent in our calculation of the form factor, P(q), for these structures. Specifically, a primary scattering peak emerges, characterizing the overall nanogel particle size. Moreover, a distinct power-law regime emerges in P(q) at length scales larger than the chain size but smaller than R of the nanogel particle, and the R mass scaling exponent progressively approaches zero as the mesh size increases, the same scaling as for an infinite network of Gaussian chains. The "fuzzy sphere" model does not capture this feature, and we propose an extension to this popular model. These structural features become more pronounced for values of molecular parameters that enhance the localization of the branching segments within the nanogel particle.
我们通过分子动力学模拟研究了具有晶格网络拓扑结构的“理想”纳米凝胶粒子的构象性质，以量化聚合物拓扑结构对这种支化分子结构类型在溶液中性质的影响。具体来说，我们在良溶剂条件下，计算了不同支化度、支链间链长和平均网格尺寸下的回转半径（R）、流体力学半径以及特性粘数的质量标度。我们发现分子特性之间存在竞争趋势，网格尺寸或支化度的增加会导致粒子状特征的出现，而链长的增加则会增强线性聚合物状特征。这种极限行为之间的交叉也体现在我们对这些结构的形式因子 P(q)的计算中。具体来说，会出现一个主要的散射峰，表征整个纳米凝胶粒子的大小。此外，在比链尺寸大但比纳米凝胶粒子的 R 小的长度尺度上，P(q) 中出现明显的幂律区，并且随着网格尺寸的增加，R 的质量标度指数逐渐趋近于零，与高斯链无限网络的标度相同。“模糊球”模型无法捕捉到这一特征，我们提出了对该流行模型的扩展。对于增强支化段在纳米凝胶粒子内局域化的分子参数值，这些结构特征变得更加明显。
