Theoretical and Experimental Analysis of Nanoparticle-Nanoparticle and Nanoparticle-Surface Interactions and Their Role in Defining Nanoparticle Stability and Mobility

Abstract

The use of nanocrystals in a number of technological areas, such as in environmental remediation, oil fields illumination or even in situ cancer treatment, creates a challenge to the complete understanding of the transport of these nanoparticles in various types of porous media - soil, sandstone matrixes or tissue material, respectively. Even though nanocrystals present breakthrough possibilities in these various applications, their feasible use would be compromised without reaching the area of interest. As the library of nanoparticles is growing at a considerable rate over time, it is of great importance that efficient screening methods are developed and used routinely to assess their mobility. The central challenge of this work was to fully understand the phenomena behind nanoparticle interactions with other nanoparticles and with surfaces and, based on this knowledge, to characterize mobility and thus nanoparticle transport in different environments. The core of this analysis was explored outside neutral situations, i.e. nanoparticles in aqueous suspensions. We looked closely into how the mobility behavior of nanoparticles was affected by the influence of various chemistries, such as a broad range of ionic strength, different surrounding ionic valences, pH and also at distinct physical properties where temperature influence was also verified. We took advantage of our in-house production capability of narrow size distributed nanoparticles, of the many core compositions available and also the many coatings attainable in our laboratory library. Distinct sets of nanoparticles were analyzed using an extremely accurate and precise instrument, known as a quartz crystal microbalance (QCM-D), and characterized using a number of well-known techniques that would later make it possible for us to compare these experimental results with our own simulations taking into account electrostatic and Van der Waal forces. The results of this theoretical-experimental analysis clearly suggest that nanoparticles interact among themselves and with surfaces in the same fashion that has been previously described by traditional colloidal science and the approach and techniques here applied present an effective method for screening nanoparticle stability and transport.