Abstract
Surface energy with its polar and disperse components describes the physicochemical state of nanoparticles’ (NPs) surfaces, and can be a valuable parameter for predicting their bulk behavior in powders. Here, we introduce a new method, namely, Nanoparticles Trapped on Polymerized Pickering Emulsion Droplets (NanoTraPPED), for measuring the surface energy of a series of silica NPs bearing various surface functional groups. The method consists in creating Pickering emulsions from vinyl bearing monomers, immiscible with water, whereas NPs of interest have a stabilizing role, and in the process, become trapped at the monomer/water interface of emulsion droplets. The Pickering emulsion is polymerized, and polymer microspheres (colloidosomes) decorated with NPs are obtained. NanoTraPPED relies on measuring contact angles from the immersion depth of nanoparticles at the interface of various polymer colloidosomes with the electron microscope. The contact angle values are used as input for the Owens-Wendt-Rabel-Kaelble (OWRK) model, to quantitatively determine the total surface energy with water γNP/water, air γNP, and the corresponding polar and dispersive interaction components of NPs carrying -NH2, -SH, -OH, -CN and -C8 surface functional groups, ranking these according to their polarity. Our findings were confirmed independently by calculating the interfacial desorption energies of NPs from contact angles.
Highlights
Nanoparticles’ (NPs) surface functional groups that control their surface reactivity may at least in part control their behavior, such as their ability to aggregate, disperse, attach on surfaces, flow, etc
We have developed a new method, namely, Nanoparticles Trapped on Polymerized Pickering Emulsion Droplets (NanoTraPPED), for determining the surface energy of nanoparticles by employing a new strategy to measure the contact angle, based on trapping
NanoTraPPED is a new method we have developed to visualize interfacial immersion depth of the NPs trapped at the interface, by polymerizing the emulsion droplets and creating a solid system, i.e., colloidosomes, that can be studied with electron microscopy techniques
Summary
Nanoparticles’ (NPs) surface functional groups that control their surface reactivity may at least in part control their behavior, such as their ability to aggregate, disperse, attach on surfaces, flow, etc. While, establishing causal relationships between various components of the surface energy and the bulk behavior of NPs in powders represents an ongoing challenge for fundamental science, it has great technological importance for the design of drug formulations with enhanced bioavailability [6,7], flowing ability [8], dispersing of pigments in paints or fillers in polymer matrices [9], heterogeneous catalysis [10,11] and reactor design [12], stabilization of reactive nanopowders [13], powder cohesion [14], flotation of ore minerals [15,16,17], emulsification [18], gauging the amphiphilicity of colloids [19], etc. The surface energy models [1,2,3,4,5]
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