Adsorption-driven self-assembly of nanoparticles at fluid interfaces is a promising bottom-up approach for the preparation of advanced functional materials and devices. Full realization of its potential requires quantitative understanding of the parameters controlling the self-assembly, the structure of nanoparticles at the interface, the barrier properties of the assembly, and the rate of particle attachment. We argue that models of dynamic surface or interfacial tension (DST) appropriate for molecular species break down when the adsorption energy greatly exceeds the mean energy of thermal fluctuations and validate alternative models extending the application of generalized random sequential adsorption theory to nanoparticle adsorption at fluid interfaces. Using a model colloidal system of hydrophobic, charge-stabilized ethyl cellulose nanoparticles at neutral pH, we demonstrate the potential of DST measurements to reveal information on the energy of adsorption, the adsorption rate constant, and the energy of particle-interface interaction at different degrees of nanoparticle coverage of the interface. These findings have significant implications for the quantitative description of nanoparticle adsorption at fluid interfaces.

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The effect of CuO nanoparticles on the thermal conductivities of paraffin and monoethylene glycol (MEG) was investigated. An enhancement in the effective thermal conductivity was found for both fluids. This enhancement was studied with regard to various factors: nanoparticle concentration, nanoparticle size, and base-fluid type. For both base fluids, an improvement in thermal conductivity was found as nanoparticle concentration increased; this was attributed to an increase in particle-to-particle interactions. It was also found that, as the particle size was reduced, there was also an improvement in the thermal conductivities of the fluids. A reduction in nanoparticle size leads to an increase in the Brownian motion of the particles, which also causes more particle-to-particle interactions. The role that the base fluid plays in the observed enhancement is complex. Lower fluid viscosities are believed to contribute to greater enhancement, but a second effect, the interaction of the fluid with the nanoparticle surface, can be even more important. Nanoparticle−liquid suspensions generate a shell of organized liquid molecules on the particle surface. These organized molecules more efficiently transmit energy, via phonons, to the bulk of the fluid. The efficient energy transmission results in enhanced thermal conductivity. The experimentally measured thermal conductivities of the suspensions were compared to a variety of models. None of the models were found to adequately predict the thermal conductivities of the nanoparticle suspensions.