Nanoparticle Adsorption at ITIES

In 2004, Sn et al. reported the voltage-indnced assembly of mercaptosnccinic-acid-stabilized An nanoparticles of abont 1.5 nm diameter at the H2O-DCE interface. Admittance measnrements and qnasi-elastic laser scattering (QELS) were nsed to show that the snrface concentration of the nanoparticle is reversibly controlled by the interfacial polarization. No evidence of irreversible aggregation of the particles at the interface was observed, and the electrocapillary cnrves provide an estimate of the maximnm particle snrface density corresponding to 67% of a sqnare closed-pack arrangement [348]. Similarly, Sn et al. stndied the voltage-indnced assembly and photoreactivity of cadminm selenide (CdSe) 

FIGURE 1.38 Different contributions to the nanoparticle energy profile at ITIES, compared to the total profile. Parameters—potential drop across the interface is -250 mV. (Flatte, M. E., A. A. Kornyshev, and M. Urbakh, 2008, J Phys-Condens Mat, Vol. 20, p. 073102. Used with permission.) 

The main conclusions are that classically charged nanoparticles cannot be spontaneously adsorbed at the H20-1,2-DCE interface without applying an external electric field, but small potential difference of 0.1 V are sufficient. Also, the variation of surface coverage with applied electric field can be extremely strong for highly charged particles. 

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The theoretical aspects of nanoparticle adsorption at ITIES was recently reviewed by Flatte et al. [355]. In particular, they discuss the effects that drive or hamper the localization at the interface, namely, competitive wetting, solvation of the charged nanoparticles, shift in the external electric field, polarizability drive, and line tension. A simple model is presented to account for these different contributions, and the results are shown in Figure 1.38. 

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