Agglomeration of nanoparticles

The direct electrochemical deposition methods for the preparation of electrocatalysts allow to localize the catalyst particles on the top surface of the carbon support, as close as possible to the solid polymer electrolyte and does not need heat (oxidative and/or reducing) treatment, as most of the chemical methods do, in order to clean the catalytic particles from surfactant contamination [27,28], This will prevent catalyst sintering due to the agglomeration of nanoparticles under thermal treatment. 

TEM micrographs of bimetallic catalysts revealed the presence of randomly accessible ordered domains as well as the partly disordered mesostructure of silica films (Figure 4). The nanoparticles of Ru-Pt have a mean size of 1.4 nm with a narrow particle size distribution (Figure 5). However, the TEM image also shows the small agglomeration of nanoparticles due to the absence of a local mesostructure. 

Capillary pressure is the major cause leading to cracking of the gel skeletons or agglomeration of nanoparticles during drying [21] ... 

At present, there are no generally accepted views on the formation of hard agglomerates of nanoparticles. There are several representative theories proposed, e.g., including crystal bridge theory, capillary pressure theory, hydrogen bond theory, chemical bond theory, etc. [21]. We shall only mention the essential concept of each theory. 

For the production of polymeric nanocomposites, in many cases a pretreatment and a functionalization of the nanomaterials are necessary [ 13] in order to allow a break up of agglomerates of nanoparticles and to gain adhesion to the matrix and distinct improvement of mechanical properties. This is achieved through various means such as plasma treatment in the presence of certain gasses, which is a well known and widely used process. Various treatments in the liquid phase are also known and applied [7]. 

Platinum based catalysts supported on carbon black allowed to significantly increase the power density per electrode area as compared to platinum black type catalysts. The pore system of the support material allows to increase the platinum dispersion and partially prevents migration and the agglomeration of nanoparticles thus leading to a higher specific surface area. 

Flesch, J., Kemer, D., Riemenschneider, H., and Reimert, R. 2008. Experiments and modeling on the deacidification of agglomerates of nanoparticles in a fluidized bed. Powder Technol. 183 467-479. 

For nanoparticle/polymer composites using melt blending, the particles are difficult to disperse in the matrix due to strong van der Waals forces and the agglomeration of nanoparticles. The effect of different synthesis conditions (such as temperature, rotation, and time) on the mechanical properties has an impact on the dispersion of nanoparticles. 

C. Sauter, M.A. Emin, H.P. Schuchmann, S. Tavman, Influence of hydrostatic pressure and soimd amplitude on the ultrasound induced dispersion and de-agglomeration of nanoparticles. Ultrasonics Sonochem. 15(4), 517-523 (2008). doi 10.1016/j.ultsonch.2007.08.010... 

Probably it is connected with the difference in polyelectrolyte shells structure and capsules size. More drastic increase in the sensitivity to a laser beam at the further increase of adsorbed nanoparticles quantity was observed for capsules formed on CaCOs rather than for the ones formed on polystyrene cores. Apparently, the agglomeration of nanoparticles occurs at this quantity of nanoparticles. 

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