Chandran Sivasurender, Saw Shibu, Kandar A K, Dasgupta C, Sprung M, Basu J K
Department of Physics, Indian Institute of Science, Bangalore 560012, India.
Centre for Condensed Matter Theory, Indian Institute of Science, Bangalore 560012, India.
J Chem Phys. 2015 Aug 28;143(8):084902. doi: 10.1063/1.4929438.
We present the results of combined experimental and theoretical (molecular dynamics simulations and integral equation theory) studies of the structure and effective interactions of suspensions of polymer grafted nanoparticles (PGNPs) in the presence of linear polymers. Due to the absence of systematic experimental and theoretical studies of PGNPs, it is widely believed that the structure and effective interactions in such binary mixtures would be very similar to those of an analogous soft colloidal material-star polymers. In our study, polystyrene-grafted gold nanoparticles with functionality f = 70 were mixed with linear polystyrene (PS) of two different molecular weights for obtaining two PGNP:PS size ratios, ξ = 0.14 and 2.76 (where, ξ = Mg/Mm, Mg and Mm being the molecular weights of grafting and matrix polymers, respectively). The experimental structure factor of PGNPs could be modeled with an effective potential (Model-X), which has been found to be widely applicable for star polymers. Similarly, the structure factor of the blends with ξ = 0.14 could be modeled reasonably well, while the structure of blends with ξ = 2.76 could not be captured, especially for high density of added polymers. A model (Model-Y) for effective interactions between PGNPs in a melt of matrix polymers also failed to provide good agreement with the experimental data for samples with ξ = 2.76 and high density of added polymers. We tentatively attribute this anomaly in modeling the structure factor of blends with ξ = 2.76 to the questionable assumption of Model-X in describing the added polymers as star polymers with functionality 2, which gets manifested in both polymer-polymer and polymer-PGNP interactions especially at higher fractions of added polymers. The failure of Model-Y may be due to the neglect of possible many-body interactions among PGNPs mediated by matrix polymers when the fraction of added polymers is high. These observations point to the need for a new framework to understand not only the structural behavior of PGNPs but also possibly their dynamics and thermo-mechanical properties as well.
我们展示了在存在线性聚合物的情况下，对聚合物接枝纳米颗粒（PGNP）悬浮液的结构和有效相互作用进行的实验与理论（分子动力学模拟和积分方程理论）相结合的研究结果。由于缺乏对PGNP的系统实验和理论研究，人们普遍认为这种二元混合物中的结构和有效相互作用与类似的软胶体材料——星型聚合物非常相似。在我们的研究中，将官能度f = 70的聚苯乙烯接枝金纳米颗粒与两种不同分子量的线性聚苯乙烯（PS）混合，以获得两种PGNP:PS尺寸比，ξ = 0.14和2.76（其中，ξ = Mg/Mm，Mg和Mm分别为接枝聚合物和基体聚合物的分子量）。PGNP的实验结构因子可以用一种有效势（模型X）来建模，该有效势已被发现广泛适用于星型聚合物。同样，ξ = 0.14的共混物的结构因子可以得到合理的建模，而ξ = 2.76的共混物的结构则无法被捕捉，特别是对于添加聚合物的高密度情况。基体聚合物熔体中PGNP之间有效相互作用的模型（模型Y）也未能与ξ = 2.76且添加聚合物高密度的样品的实验数据很好地吻合。我们初步将对ξ = 2.76的共混物结构因子建模中的这种异常归因于模型X在将添加聚合物描述为官能度为2的星型聚合物时的可疑假设，这在聚合物 - 聚合物和聚合物 - PGNP相互作用中都有体现，特别是在添加聚合物的比例较高时。模型Y的失败可能是由于在添加聚合物比例较高时，忽略了基体聚合物介导的PGNP之间可能的多体相互作用。这些观察结果表明需要一个新的框架来不仅理解PGNP的结构行为，还可能理解它们的动力学和热机械性能。
