Hypothesis

Grafting nanoparticles surfaces with water-soluble polymers modify interparticle interactions that are pivotal for assembling them into ordered phases. By manipulating salt concentrations of gold nanoparticles (AuNPs) that are grafted with poly(N-isopropylacrylamide) (PNIPAM-AuNPs), we hypothesize that various aggregated phases form at the suspension/vapor interface or in the bulk that depend on the molecular weight (MW) of PNIPAM and on salt concentrations.

Experiments

AuNPs are grafted with thiolated PNIPAM of molecular weights of 3 or 6 kDa, and grafting is confirmed by dynamic light scattering. Liquid-surfaces X-ray reflectivity and grazing incidence small-angle X-ray scattering are used to determine the density profiles of the suspension/vapor interface and their inplane structure as salt is added to the suspensions.

Findings

We find that surface enrichment is induced by adding NaCl to the suspensions, and that at low salt concentrations, the monoparticle layer formed is dispersed, and above a threshold salt concentration, depending on MW of PNIPAM, the PNIPAM-AuNPs order in a hexagonal structure. We show that the lattice constant of the two-dimensional hexagonal structure varies with salt concentration, and more significantly with MW of PNIPAM.

中文翻译：

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蒸气/水界面的聚（N-异丙基丙烯酰胺）接枝的金纳米粒子

假设

用水溶性聚合物接枝纳米颗粒表面可修饰颗粒间相互作用，这对于将它们组装成有序相至关重要。通过操纵接枝有聚（N-异丙基丙烯酰胺）（PNIPAM-AuNPs）的金纳米颗粒（AuNPs）的盐浓度，我们假设在悬浮液/蒸汽界面或本体中会形成各种聚集相，这取决于分子量（ MW）的PNIPAM和盐浓度。

实验

AuNPs接枝了分子量为3或6 kDa的硫醇化PNIPAM，并通过动态光散射证实了接枝。液体表面的X射线反射率和掠入射小角X射线散射用于确定悬浮液/蒸汽界面的密度分布及其在向悬浮液中添加盐时的平面结构。

发现

我们发现，通过向悬浮液中添加NaCl诱导表面富集，并且在低盐浓度下，形成的单颗粒层被分散，并且高于阈值盐浓度，这取决于PNIPAM的MW，PNIPAM-AuNPs呈六边形结构。我们表明，二维六边形结构的晶格常数随盐浓度的变化而变化，并且随PNIPAM的分子量的变化更显着。