Engineered nanoparticles
(NPs) will obtain macromolecular coatings in environmental systems,
changing their subsequent interactions. The matrix complexity inherent
in natural waters and wastewaters greatly complicates prediction of
the corona formation. Here, we investigate corona formation on titanium
dioxide (TiO2) NPs from mixtures of natural organic matter
(NOM) and a protein, bovine serum albumin (BSA), to thoroughly probe
the role of mixture interactions in the adsorption process. Fundamentally
different coronas were observed under different NP exposure conditions
and time scales. In mixtures of NOM and protein, the corona composition
was kinetically determined, and the species initially coadsorbed but
were ultimately limited to monolayers. On the contrary, sequential
exposure of the NPs to pure solutions of NOM and protein resulted
in extensive multilayer formation. The intermolecular complexation
between NOM and BSA in solution and at the NP surface was the key
mechanism controlling these distinctive adsorption behaviors, as determined
by size exclusion chromatography (SEC) and in situ attenuated total
reflectance–Fourier transform infrared (ATR–FTIR) spectroscopy.
Overall, this study demonstrates that dynamic intermolecular interactions
and the history of the NP surface must be considered together to predict
corona formation on NPs in complex environmental media.
Water-ice transformation of few nm nanodroplets plays a critical role in nature including climate change, microphysics of clouds, survival mechanism of animals in cold environments, and a broad spectrum of technologies. In most of these scenarios, water-ice transformation occurs in a heterogenous mode where nanodroplets are in contact with another medium. Despite computational efforts, experimental probing of this transformation at few nm scales remains unresolved. Here, we report direct probing of water-ice transformation down to 2 nm scale and the length-scale dependence of transformation temperature through two independent metrologies. The transformation temperature shows a sharp length dependence in nanodroplets smaller than 10 nm and for 2 nm droplet, this temperature falls below the homogenous bulk nucleation limit. Contrary to nucleation on curved rigid solid surfaces, ice formation on soft interfaces (omnipresent in nature) can deform the interface leading to suppression of ice nucleation. For soft interfaces, ice nucleation temperature depends on surface modulus. Considering the interfacial deformation, the findings are in good agreement with predictions of classical nucleation theory. This understanding contributes to a greater knowledge of natural phenomena and rational design of anti-icing systems for aviation, wind energy and infrastructures and even cryopreservation systems.
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