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Efficiency of Various Lattices from Hard Ball to Soft Ball: Theoretical Study of Thermodynamic Properties of Dendrimer Liquid Crystal from Atomistic Simulation

Li, Youyong and Lin, Shiang-Tai and Goddard, William A., III (2004) Efficiency of Various Lattices from Hard Ball to Soft Ball: Theoretical Study of Thermodynamic Properties of Dendrimer Liquid Crystal from Atomistic Simulation. Journal of the American Chemical Society, 126 (6). pp. 1872-1885. ISSN 0002-7863. doi:10.1021/ja038617e.

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Self-assembled supramolecular organic liquid crystal structures at nanoscale have potential applications in molecular electronics, photonics, and porous nanomaterials. Most of these structures are formed by aggregation of soft spherical supramolecules, which have soft coronas and overlap each other in the packing process. Our main focus here is to study the possible packing mechanisms via molecular dynamics simulations at the atomistic level. We consider the relative stability of various lattices packed by the soft dendrimer balls, first synthesized and characterized by Percec et al. (J. Am. Chem. Soc. 1997, 119, 1539) with different packing methods. The dendrons, which form the soft dendrimer balls, have the character of a hard aromatic region from the point of the cone to the edge with C12 alkane “hair”. After the dendrons pack into a sphere, the core of the sphere has the hard aromatic groups, while the surface is covered with the C12 alkane “hair”. In our studies, we propose three ways to organize the hair on the balls, Smooth/Valentino balls, Sticky/Einstein balls, and Asymmetric/Punk balls, which lead to three different packing mechanisms, Slippery, Sticky, and Anisotropic, respectively. We carry out a series of molecular dynamics (MD) studies on three plausible crystal structures (A15, FCC, and BCC) as a function of density and analyze the MD based on the vibrational density of state (DoS) method to extract the enthalpy, entropy, and free energies of these systems. We find that anisotropic packed A15 is favored over FCC, BCC lattices. Our predicted X-ray intensities of the best structures are in excellent agreement with experiment. “Anisotropic ball packing” proposed here plays an intermediate role between the enthalpy-favored “disk packing” and entropy-favored “isotropic ball packing”, which explains the phase transitions at different temperatures. Free energies of various lattices at different densities are essentially the same, indicating that the preferred lattice is not determined during the packing process. Both enthalpy and entropy decrease as the density increases. Free energy change with volume shows two stable phases:  the condensed phase and the isolated micelle phase. The interactions between the soft dendrimer balls are found to be lattice dependent when described by a two-body potential because the soft ball self-adjusts its shape and interaction in different lattices. The shape of the free energy potential is similar to that of the “square shoulder potential”. A model explaining the packing efficiency of ideal soft balls in various lattices is proposed in terms of geometrical consideration.

Item Type:Article
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URLURL TypeDescription
Li, Youyong0000-0002-5248-2756
Lin, Shiang-Tai0000-0001-8513-8196
Goddard, William A., III0000-0003-0097-5716
Additional Information:© 2004 American Chemical Society. Received 19 September 2003. Published online 24 January 2004. Published in print 1 February 2004. This paper is dedicated to the late Paul Miklis, who initiated the study of these Percec systems shortly after the first publication. In addition to the early stimulation by Paul, we also thank Dr. Tahir Cagin and Virgil Percec for many helpful discussions about these dendrimers, and we thank Dr. Mario Blanco with help using Lammps. This research is based in part on work supported by the U.S. Army Research Laboratory and the U.S. Army Research Office under grant number DAAG55-97-1-0126 (MURI-program officer Doug Kiserow). The facilities of the MSC used in this research have been supported by grants from the ARO (DURIP), ONR (DURIP), NSF (MRI), and IBM (SUR). Other support to the MSC is provided by the NIH, NSF, DOE, Chevron-Texaco, General Motors, Seiko Epson, Asahi Kasei, Beckman Institute, and Toray Corp.
Funding AgencyGrant Number
Army Research LaboratoryUNSPECIFIED
Army Research Office (ARO)DAAG55-97-1-0126
Office of Naval Research (ONR)UNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Caltech Beckman InstituteUNSPECIFIED
Issue or Number:6
Record Number:CaltechAUTHORS:20170419-145524618
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Official Citation:Efficiency of Various Lattices from Hard Ball to Soft Ball:  Theoretical Study of Thermodynamic Properties of Dendrimer Liquid Crystal from Atomistic Simulation Youyong Li, Shiang-Tai Lin, and William A. Goddard III Journal of the American Chemical Society 2004 126 (6), 1872-1885 DOI: 10.1021/ja038617e
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:76711
Deposited By: Ruth Sustaita
Deposited On:19 Apr 2017 22:42
Last Modified:15 Nov 2021 17:02

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