Solvent-induced interactions for controlling nanoparticle adhesion at nanostructured liquid-solid interfaces

This project will produce new fundamental knowledge to understand and control the physical adhesion and aggregation of nanomaterials in liquid by considering the effects of so-called solvent-induced interactions between nanoparticles and surfaces with nanoscale topography. Solvent-induced interactions are a class of nanoscale interactions that occur because liquid molecules rearrange themselves when confined in nanoscopic spaces between solid surfaces. These interactions significantly influence how nanomaterials cluster together and adhere to surfaces. This research will improve our ability to predict and control these behaviors, which is crucial for creating accurate models for the toxicity and environmental fate of engineered nanomaterials. The sought knowledge is also vital for advancing technologies of strategic importance such as environmental remediation, colloidal filtration and water treatment, nanomaterial self-assembly, and energy storage. A new educational initiative named “The Green Nanotechnology Forum” will be created for this project as a hybrid (in-person/virtual) workshop and a forum with an online open-access repository to inform the public and research community on the potential toxicity and environmental fate of nanomaterials commonly employed by different industries, and emerging green nanotechnologies for environmental sustainability. The research and educational activities in this project are tightly integrated and have a strong focus on broadening the participation of underrepresented groups and workforce development in STEM. Although solvent-induced interactions are known to dominate at nanoscale separations, current standard approaches for adhesion and aggregation solely consider classical Derjaguin-Landau-Verwey-Overbeek interactions (i.e., van der Waals and electrostatic forces) in a perfectly uniform liquid and between sharp and smooth interfaces. The primary goal of this project is to address this significant limitation by formulating and validating a material-agnostic approach to predict and control the physical adhesion of general nanoparticles smaller than 100 nm dispersed in liquid by considering the role of solvent-induced interactions such as the oscillatory structural and hydration force. A secondary objective is to test the mechanistic hypothesis that surface features such as the nanoparticle facet/crystallite size and nanostructure contact area control the magnitude of solvent-induced interactions and thus can prevent (or promote) adhesion and aggregation by inducing (or suppressing) kinetic trapping at secondary energy minima for which the nanomaterial mobility is retained. These objectives are pursued through two interconnected aims: (1) Theoretical formulation of a mean-field model for nanoparticle adhesion/aggregation, and (2) Experimental characterization of nanoparticle adhesion on surfaces with a well-characterized interfacial energy and physical nanostructure. The research plan combines theoretical work, molecular dynamics simulations, and hypothesis-driven experimental analyses, to characterize and rationalize solvent-induced interactions and adhesion rates in aqueous media, primarily for metal oxide nanoparticles and nanoplastics on hydrophilic/hydrophobic surfaces with natural or synthetic nanostructures with controlled geometry and dimensions ranging from 10 to 100 nm. Metal oxide nanoparticles and nanoplastics are of primary interest because they are among the most common nanomaterials employed in industrial applications and released into the environment, although their fate in aqueous media remains poorly understood. Undergraduate and graduate students supported by this project will create research reports and video presentations for The Green Nanotechnology Forum that will be created for this project to inform the general public on the environmental faith of common nanomaterials and support the selection of specific nanomaterials to be studied for this project. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.