Estridge Carla E, Jayaraman Arthi
Department of Chemistry and Biochemistry, University of Colorado, 215 UCB, Boulder, Colorado 80309, USA.
Department of Chemical and Biological Engineering, University of Colorado, 596 UCB Boulder, Colorado 80309, USA.
J Chem Phys. 2014 Apr 14;140(14):144905. doi: 10.1063/1.4870592.
In this work, we use coarse-grained molecular dynamics simulations to study spherical nanoparticles functionalized with AB diblock copolymer chains at low grafting density, to obtain a design library linking copolymer composition, monomer-monomer interaction strengths, graft lengths, particle sizes, and monomer solvent-philicity to the two stages of nanoparticle assembly: the initial formation of patches within the copolymer-grafted particles from attractive monomers aggregating, and then the (equilibrium) assembled cluster formation. With regards to patch formation, as the fraction of the solvent-phobic (A or B) block decreases along the graft and the interaction strength decreases, the propensity to form patches on the particles decreases. As the fraction of the solvent-phobic block increases, the time for patch formation decreases, in particular if the inner A block is solvent-phobic. As the ratio of graft length to particle size increases the propensity to form fewer patches increases due to inter-graft monomer aggregation. For all compositions, the assembled clusters formed in B-selective solvents (solvent-phobic A block) have a higher fraction of particles at smaller inter-particle distances than in A-selective solvents (solvent-phobic B block). In an A-selective solvent at low interaction strengths, as the graft length to particle diameter ratio is increased, the tendency to form isotropic clusters at equilibrium is increased, and intermediate anisotropic chain-like assembly is observed. When these anisotropic intermediate states are observed, they accelerate the formation of equilibrium isotropic clusters. With increasing strength of interaction between solvent-phobic B monomers, the intermediate states disappear from the assembly pathway. At low and intermediate interaction strengths, as fraction of A block increases, the clusters' outer shell of solvent-philic A monomers which surrounds the patch of solvent-phobic B monomers becomes dense, hindering addition of more particles to the cluster leading to smaller overall clusters. In a B-selective solvent, predominantly anisotropic clusters form, and show an increase in shape anisotropy with increasing monomer interaction strength. In both cases of monomer solvent-philicity, with an increase in the graft length to particle diameter ratio we see a decrease in anisotropic cluster formation. And, in both cases of monomer solvent philicity, with increasing monomer interaction strength the average cluster size and tendency to form anisotropic clusters is increased.
在这项工作中，我们使用粗粒度分子动力学模拟来研究以低接枝密度用AB二嵌段共聚物链功能化的球形纳米颗粒，以获得一个设计库，将共聚物组成、单体-单体相互作用强度、接枝长度、颗粒尺寸和单体溶剂亲合性与纳米颗粒组装的两个阶段联系起来：在共聚物接枝颗粒内由吸引性单体聚集形成斑块的初始阶段，以及随后（平衡）组装簇的形成。关于斑块形成，随着溶剂疏水性（A或B）嵌段沿接枝方向的比例降低且相互作用强度降低，在颗粒上形成斑块的倾向降低。随着溶剂疏水性嵌段的比例增加，斑块形成的时间减少，特别是当内部A嵌段为溶剂疏水性时。随着接枝长度与颗粒尺寸的比率增加，由于接枝间单体聚集，形成较少斑块的倾向增加。对于所有组成，在B选择性溶剂（溶剂疏水性A嵌段）中形成的组装簇在颗粒间距离较小时比在A选择性溶剂（溶剂疏水性B嵌段）中具有更高比例的颗粒。在低相互作用强度的A选择性溶剂中，随着接枝长度与颗粒直径的比率增加，在平衡时形成各向同性簇的倾向增加，并观察到中间各向异性链状组装。当观察到这些各向异性中间状态时，它们会加速平衡各向同性簇的形成。随着溶剂疏水性B单体之间相互作用强度的增加，中间状态从组装途径中消失。在低和中等相互作用强度下，随着A嵌段比例的增加，围绕溶剂疏水性B单体斑块的溶剂亲合性A单体的簇外壳变得致密，阻碍更多颗粒添加到簇中，导致总体簇较小。在B选择性溶剂中，主要形成各向异性簇，并随着单体相互作用强度的增加而显示出形状各向异性增加。在单体溶剂亲合性的两种情况下，随着接枝长度与颗粒直径比率的增加，我们看到各向异性簇形成减少。并且，在单体溶剂亲合性的两种情况下，随着单体相互作用强度的增加，平均簇尺寸和形成各向异性簇的倾向增加。
