Intermolecular forces for self-assembly identified through simulations
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rmolecular forces for selfassembly identified through simulations
T
he patterns that form upon molecular self-assembly are a direct consequence of interaction forces among the entities constituting the structure. Thus, the study of different intermolecular forces and the resulting self-assembled pattern is of extreme importance. Corresponding mathematical modeling has its roots in statistical mechanics. The usual practice is to modify the interparticle interaction and simulate the resulting self-assembly. A recent study led by Thomas Truskett and co-workers at The University of Texas at Austin asks an
inverse question: “Can one know what sort of intermolecular forces are required to produce a desired structure upon selfassembly?” The findings were published recently in the Journal of Chemical Physics (doi:10.1063/1.4981796). The simulations begin with an initial estimate of the interaction potential and a target structure. Other inputs such as number of particles (N), volume of the ensemble (V), and temperature (T) are specified and kept constant (for an NVT ensemble). First, molecular dynamics simulations are used to compute the equilibrium structure from the initial guess for intermolecular forces. Then based upon the difference between the current and target structures, optimization calculations are used to iteratively improve the interaction potentials
(“difference of two self-assembled structures” is defined by the Kullback–Leibler measure in the present calculations). At every iteration, the researchers find a new equilibrium structure based on the most recent estimate for interaction potential. Calculations are terminated once a prescribed accuracy is achieved; in other words, when the structure based on the force field is close to the target structure. The research team also demonstrated the applicability of the formulation by applying it to three distinct system types: cluster fluids (fluid-like particle aggregates that are roughly spherical in shape and monodisperse in size); porous mesophases (self-assembly of the conjugate inverse cluster phase); and crystals, with multiple examples of each.
• VOLUME 42 • JULY 2017IP • address: www.mrs.org/bulletin Downloaded MRS fromBULLETIN https://www.cambridge.org/core. 80.82.77.83, on 31 Jul 2017 at 10:32:35, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/mrs.2017.151
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NEWS & ANALYSIS MATERIALS NEWS The beauty of the a c b procedure lies in its generality. It can be easily extended to study systems with more complex molecules such as polymer chains having additional rotational and stretching degrees of freedom. Similarly, additional Representative structures obtained with particles interacting through the inverse designed pair potentials: (a) cluster fluid, (b) porous mesophase, and (c) truncated hexagonal lattice. Credit: Thomas Truskett. effects such as solvent interaction, boundary and interfacial contributions, and field effects can particles into a variety of complex microinteracti
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