Theory-Guided Targeted Delivery of Nanoparticles inAdvective Environmental Porous Media

For near-neutrally buoyant colloids, retention on surfaces is dramatically reduced for radii in the range from approximately 100 nm to 1 mu m (i.e., n-mu transition) under unfavorable conditions (energy barrier present). Given that unfavorable conditions are predominant in the environment, the above-described characteristic is underutilized in strategies for targeted delivery of nano- to microscale particles (colloids) in porous media. We present herein, a strategy that involves tuning colloid size within the n-mu transition range to minimize retention in non-target porous media, followed by solution chemistry-triggered disaggregation to yield nanoscale colloids and promote retention in target porous media. Toward this purpose we examined the transport properties of aggregated and disaggregated carboxylate-modified latex (CML) nanospheres (55 nm radius) and novel shell cross-linked knedel-like (SCK) nanoparticles (10-50 nm radius). Colloid retention was measured on soda-lime glass (silica) in an impinging jet system representing upstream sides of porous media grains. Continuum scale attachment rate coefficients (k(f)) were determined from the experimental colloid retention and were then utilized to predict the distribution of retained colloids from source in target porous media at field scales. These experiments and simulations demonstrate the viability of size-tuning colloids to the n-mu transition range in order to facilitate their transport through non-target porous media. Disaggregation triggered by, for example, reduced ionic strength achieved by preferential advection of colloids, was demonstrated to greatly increase retention in target porous media, with an expectation of increased surface area and enhanced reactivity.