CQFM-Centro de Química-Física Molecular, IN-Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, Lisboa, Portugal.
J Colloid Interface Sci. 2013 Jul 1;401:14-22. doi: 10.1016/j.jcis.2013.03.002. Epub 2013 Mar 16.
We prepared water-dispersible core-shell nanoparticles with a perylenediimide-labeled silica core and a poly(butyl methacrylate) shell, for application in photoactive high performance coatings. Films cast from water dispersions of the core-shell nanoparticles are flexible and transparent, featuring homogeneously dispersed silica nanoparticles, and exhibiting fluorescence under appropriate excitation. We characterized the film formation process using nanoparticles where the polymer shell has been labeled with either a non-fluorescent N-benzophenone derivative (NBen) or a fluorescent phenanthrene derivative (PheBMA). We used Förster resonance energy transfer (FRET) from PheBMA to NBen to follow the interparticle interdiffusion of the polymer anchored to the silica surface that occurs after the dried dispersions are annealing above the glass transition temperature of the polymer. By calculating the evolution of the FRET quantum efficiency with annealing time, we could estimate the approximate fraction of mixing (fm) between polymer from neighbor particles, and from this, the apparent diffusion coefficients (Dapp) for this process. For long annealing times, the limiting values of fm are slightly lower than for films of pure PBMA particles at similar temperatures (go up to 80% of total possible mixing). The corresponding diffusion coefficients are also very similar to those reported for films of pure PBMA, indicating that the fact that the polymer chains are anchored to the silica particles does not significantly hinder the diffusion process during the initial part of the mixing process. From the temperature dependence of the diffusion coefficients, we found an effective activation energy for diffusion of Ea=38 kcal/mol, very similar to the value obtained for particles of the same polymer without the silica core. With these results, we show that, although the polymer is grafted to the silica surface, polymer interdiffusion during film formation is not significantly decreased by the silica core. This explains the excellent properties of the photoactive high performance coatings formed from the core-shell nanoparticles.
我们制备了具有苝二酰亚胺标记的硅核和聚（正丁基甲基丙烯酸酯）壳的水分散核壳纳米粒子，用于光活性高性能涂料。从核壳纳米粒子的水分散体浇铸的薄膜是柔性和透明的，具有均匀分散的硅纳米粒子，并在适当的激发下显示荧光。我们使用聚合物壳已用非荧光 N-苯甲酮衍生物（NBen）或荧光菲衍生物（PheBMA）标记的纳米粒子来表征成膜过程。我们使用来自 PheBMA 到 NBen 的Förster 共振能量转移（FRET）来跟踪在干燥分散体在高于聚合物玻璃化转变温度的温度下退火后，固定在硅表面上的聚合物的粒子间互扩散。通过计算随退火时间的 FRET 量子效率的演化，我们可以估计相邻粒子之间的聚合物的混合分数（fm）的近似值，并且可以从该值计算出该过程的表观扩散系数（Dapp）。对于较长的退火时间，fm 的极限值略低于在相似温度下的纯 PBMA 粒子的薄膜（高达总可能混合的 80％）。相应的扩散系数也与纯 PBMA 薄膜报道的值非常相似，这表明聚合物链固定在硅颗粒上的事实不会在混合过程的初始部分显著阻碍扩散过程。从扩散系数的温度依赖性，我们发现扩散的有效活化能为 Ea=38 kcal/mol，与具有相同聚合物但没有硅核的粒子的活化能非常相似。有了这些结果，我们表明，尽管聚合物接枝到硅表面，但在成膜过程中，聚合物的互扩散不会因硅核而显著降低。这解释了由核壳纳米粒子形成的光活性高性能涂料的优异性能。
