A monomolecular layer model of the surface phase of microdroplets was proposed, and the exact expression for Tolman length was derived in this paper. The Tolman lengths of water, n-pentane, and n-heptane were calculated by the expression, and the values are quite in agreement with the experimental values. By use of the Gibbs-Tolman-Kening-Buff equation, the exact relationship between the microdroplet surface tension and the radius is obtained, and the predicted values agree well with the simulated values. The results show that there is an obvious effect of the size of microdroplets (or nanoparticles) on the surface tension, and the surface tension decreases with decreasing droplet size. For the microdroplets of general liquid, only if their radius approaches or reaches 10(-9) m does the effect become significant.
An equation for a phase transition in a dispersed system has been proposed, and the applications of the equation in various kinds of phase transitions have been discussed. The determinate relation between the interfacial tension and the radius of a droplet has been derived by the monolayer model. Applying the fusion transition equation and the interfacial tension relation, the melting temperatures of Au and Sn nanoparticles have been calculated, and the predicted melting temperatures are in good agreement with the available experimental data. The research results show that the phase transition equations can be applied to predict the temperatures of phase transitions of dispersed systems and to explain the phenomenon of metastable states; that the size of a dispersed phase has a remarkable effect on the phase transition temperatures, and the phase transition temperatures decrease with the radius of the dispersed phase decreasing; and that the depression of the melting temperature for a nanowire is half of that for a spherical nanoparticle with identical radius.
Reasonable modifications to the attachment energy model were made for accurately predicting the crystal growth morphology of energetic materials in solution.
Molecular
shape is observed to greatly determine the properties
of energetic materials (EMs); that is, the spherical molecules generally
have high energy while the planar molecules have low sensitivity in
common. Nevertheless, how the molecular shapes along with their packing
modes affect the crystal packing features, such as crystal density
and packing coefficient (PC), that are crucial factors describing
the energy and sensitivity properties of EMs, is still unclear. Herein,
this issue was addressed via a statistical analysis of more than 103 available energetic crystals. Despite crystal density having
an overall increasing trend with PC, high crystal density and high
PC are dominated by spherical and planar molecules, respectively.
Intra- and intermolecular hydrogen bonds are important factors that
affect molecular shapes and packing features of EMs, respectively.
Hopefully, the results reported here can deepen the understanding
of the structure–property relationship to rationally design
novel EMs with outstanding properties. Moreover, the present study
provides a route to quantitatively identify the molecular shapes and
packing modes based on simple structural parameters, which can be
further applied to the detailed identification and analysis of energetic
crystals with specific packing modes.
The solvent effect on the growth morphology of an explosive crystal was explored by deciphering the molecular interactions at the crystal–solvent interface.
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