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Observation of a crossover in kinetic aggregation of Palladium colloids

机译：钯胶体动力学聚集的交叉观察

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We use field emission scanning electron microscope (FE-SEM) to investigate the growth of palladium colloids over the surface of thin films of WO3/glass. The film is prepared by Pulsed Laser Deposition (PLD) at different temperatures. A PdCl2 (aq) droplet is injected on the surface and in the presence of steam hydrogen the droplet is dried through a reduction reaction process. Two distinct aggregation regimes of palladium colloids are observed over the substrates. We argue that the change in aggregation dynamics emerges when the measured water drop Contact Angel (CA) for the WO3/glass thin films passes a certain threshold value, namely CA approximate to 46 degrees, where a crossover in kinetic aggregation of palladium colloids occurs. Our results suggest that the mass fractal dimension of palladium aggregates follows a power-law behavior. The fractal dimension (D-f) in the fast aggregation regime, where the measured CA values vary from 27 degrees up to 46 according to different substrate deposition temperatures, is D-f = 1.75(+/- 0.02) - the value of Df is in excellent agreement with kinetic aggregation of other colloidal systems in fast aggregation regime. Whereas for the slow aggregation regime, with CA=58 degrees, the fractal dimension changes abruptly to D-f = 1.92(+/- 0.03). We have also used a modified Box-Counting method to calculate fractal dimension of gray-level images and observe that the crossover at around CA approximate to 46 degrees remains unchanged. (C) 2015 Elsevier B.V. All rights reserved.
机译：我们使用场发射扫描电子显微镜（FE-SEM）研究WO3 /玻璃薄膜表面上钯胶体的生长。该膜通过在不同温度下的脉冲激光沉积（PLD）制备。将PdCl2（aq）液滴注入表面，在存在蒸汽氢的情况下，该液滴通过还原反应过程进行干燥。在基底上观察到钯胶体的两种不同的聚集方式。我们认为，当WO3 /玻璃薄膜的水滴接触天使（CA）测得的某个阈值超过某个阈值，即CA接近46度时，就会发生聚集动力学的变化，此时钯胶体的动态聚集发生了交叉。我们的结果表明钯聚集体的质量分形维数遵循幂律行为。在快速聚集状态下，分形维数（Df）为Df = 1.75（+/- 0.02），根据不同的衬底沉积温度，CA的测量值从27度变化到46度。与其他胶体系统在快速聚集状态下的动态聚集。而对于CA = 58度的慢速聚集机制，分形维数突然变化为D-f = 1.92（+/- 0.03）。我们还使用了一种改进的Box-Counting方法来计算灰度图像的分形维数，并观察到CA周围大约46度的分频点保持不变。 （C）2015 Elsevier B.V.保留所有权利。

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