Efficient Molecular Approach to Quantifying Solvent-Mediated Interactions

Engulfing Behavior of Nanoparticles into Thermoresponsive Microgels: A Mesoscopic Simulation Study

The engulfing of nanoparticles into microgels provides a versatile platform to design nano- and microstructured materials with various shape anisotropies and multifunctional properties. Manipulating the spontaneous engulfment process remains elusive. Herein, we report a mesoscopic simulation study on the engulfing behavior of nanoparticles into thermoresponsive microgels. The effects of the multiple parameters, including binding strength, temperature, and nanoparticle size, are examined systematically. Our simulation results disclose three engulfing states at different temperatures, namely full-engulfing, half-engulfing, and surface contact. The engulfing depth is determined by the complementary balance of interfacial elastocapillarity. Specifically, the van der Waals interaction of hybrid microgel-nanoparticle offers the capillary force while the internally networked structure of microgel reinforces the elasticity repulsion. Our study, validated by relevant experimental results, provides a mechanistic understanding of the interfacial elastocapillarity for nanoparticle-microgels.

Thermodynamic Barrier for Nanoparticle Penetration into Nanotubes

It is promising yet challenging to develop efficient methods to separate nanoparticles (NPs) with nanochannel devices. Herein, in order to guide and develop the separation method, the thermodynamic mechanism of NP penetration into solvent-filled nanotubes is investigated by using classical density functional theory. The potential of mean force (PMF) is calculated to evaluate the thermodynamic energy barrier for NP penetration into nanotubes. The accuracy of the theory is validated by comparing it with parallel molecular dynamics simulation. By examining the effects of nanotube size, solvent density, and substrate wettability on the PMF, we find that a large tube, a low bulk solvent density, and a solvophilic substrate can boost the NP penetration into nanotubes. In addition, it is found that an hourglass-shaped entrance can effectively improve the NP penetration efficiency compared with a square-shaped entrance. Furthermore, the minimum separation density of NPs in solution is identified, below which the NP penetration into nanotubes requires an additional driving force. Our findings provide fundamental insights into the thermodynamic barrier for NP penetration into nanotubes, which may provide theoretical guidance for separating two components using microfluidics.

Wetting Transition of Ionic Substrate by Modulating Surface Charge Distribution

Surface wettability regulation plays a crucial role in antifouling and related applications. For regulating surface wettability, one of the effective approaches is to modulate the surface charge distribution. Herein, we report a theoretical study for unraveling the mechanistic relation between surface charge distribution and ionic substrate wettability. Specifically, acetonitrile liquids at ambient condition in contact with various ionic substrates are considered. At different surface charge distributions, the interfacial thermodynamic properties are investigated by means of molecular density functional theory. We find that the variation of the spatial interval among the discrete charges strongly alters the substrate-acetonitrile interaction and leads to an oscillation in the interfacial tension, indicating that the substrate can be tuned from a solvophobic one to a solvophilic one. This trend can be further enhanced by increasing the charge quantity. The underlying mechanisms are extensively discussed and expatiated. Our work provides theoretical guidance to engineer and regulate surface wettability.

A reaction density functional theory study of the solvent effect in prototype SN2 reactions in aqueous solution

Reaction density functional theory (RxDFT), combining quantum DFT with classical DFT, has been employed to investigate the solvent effect and free energy profiles of S_N2 reactions in aqueous solution.

The size-selective interaction of key and lock nanocrystals driven by depletion attraction at the nanoscale

In this article, we study the size-dependent interactions of quasi-spherical nanocrystals with voids of concave nanoparticles of complementary sizes and shapes. Experimental insights into a system with key and lock particles with smaller dimensions than 15 nm are presented, which provide evidence for key-lock specific interaction on this length scale. Using depletion attraction as a driving force, the key-lock interaction is shown to be reversible and independent of the material composition of the key particles. Poly(ethylene glycol) methacrylate was utilized as a depletion agent in toluene, the solvent of the studied key-lock system. For this work, a model system of specifically developed concave manganese oxide nanocrystals, synthesized via a cast-mold approach, in combination with highly monodisperse quasi-spherical gold nanocrystals, was investigated with transmission electron microscopy, optical UV/vis/NIR spectroscopy and powder X-ray diffraction. Size-dependent key-lock interactions are clearly identified to occur. For geometrical reasons, only key particles with smaller particle diameters than the voids of the complementary lock particles are able to enter the void. So the void diameter of the lock particles sets a diameter threshold for the key-lock interaction. Additionally, other key particles like silver, iron oxide and even core-shell structured gold-nickel sulfide nanocrystals show key-in-lock assemblies with concave manganese oxide nanocrystals. This behaviour might open up new routes for size-selective particle sensing.