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1. Self-Assembly in Mixtures of Charged Lobed Particles

   https://doi.org/10.3389/fphy.2022.936385  

   Srivastava, Arpita; Rocha, Brunno C.; Vashisth, Harish (July 2022, Frontiers in Physics)

   We report coarse-grained Langevin dynamics simulations of homogeneous mixtures of lobed colloidal particles with opposite charges. We show that dumbbell, trigonal planar, tetrahedral, square planar, trigonal bipyramidal, and octahedral shaped particles form distinct self-assemblies including chains, sheets, crystalline, and spherical structures. The dumbbell and square planar particles predominantly form chains and sheets while other particles form network-like self-assembled morphologies. At higher temperatures and lower charges, non-planar particles form three-dimensional aggregates. We further report on packing arrangements of particles which lead to differences in porosities within self-assembled morphologies. Our results show that the trigonal planar particles form larger porous structures. The self-assembled structures that we report are potentially useful in designing porous biomaterials for biomedical applications. 

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2. Self-assembly behavior of experimentally realizable lobed patchy particles

   https://doi.org/10.1039/D0SM00954G  

   Paul, Sanjib; Vashisth, Harish (January 2020, Soft Matter)

   We report simulation studies on the self-assembly behavior of five different types of lobed patchy particles of different shapes (snowman, dumbbell, trigonal planar, square planar, and tetrahedral). Inspired by an experimental method of synthesizing patchy particles (Wang et al., Nature, 2012, 491:51-55), we control the lobe size indirectly by gradually varying the seed diameter and study its effect on self-assembled structures at different temperatures. Snowman shaped particles self-assemble only at a lower temperature and form two-dimensional sheets, elongated micelles, and spherical micelles, depending on the seed diameter. Each of the four other lobed particles self-assemble into four distinct morphologies (random aggregates, spherical aggregates, liquid droplets, and crystalline structures) for a given lobe size and temperature. We observed temperature-dependent transitions between two morphologies depending on the type of the lobed particle. The self-assembled structures formed by these four types of particles are porous. We show that their porosities can be tuned by controlling the lobe size and temperature. 

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3. Co-ion Effects in the Self-Assembly of Macroions: From Co-ions to Co-macroions and to the Unique Feature of Self-Recognition

   https://doi.org/https://dx.doi.org/10.1021/acs.langmuir.0c01797  

   Jiahui Chen, Kun Qian (August 2020, Langmuir)

   Macroions, as soluble ions with a size on the nanometer scale, show unique solution behavior different from those of simple ions and large colloidal suspensions. In macroionic solutions, the counterions are known to be important and wellexplored. However, the role of co-ions (ions carrying the same type of charge as the macroions) is often ignored. Here, through experimental and simulation studies, we demonstrate the role of coions as a function of co-ion size on their interaction with the macroions (using {Mo72Fe30} and {SrPd12} as models) and the related self-assembly into blackberry-type structures in dilute solutions. Several regimes of unique co-ion effects are clearly identified: small ions (halides, oxoacid ions), subnanometer-scaled bulky ions (lacunary Keggin and dodecaborate ions), and those with sizes comparable to the macroions. Small co-ions have no observable effect on the self-assembly of fully hydrophilic {Mo72Fe30}, while due to hydrophobic interaction and intermolecular hydrogen bonds, the small co-ions show influences on the self-assembly of hydrophobic {SrPd12}. Subnanometer ions, a.k.a. “superchaotropic ions”, are still too small to assemble into a blackberry by themselves, but they can coassemble with the macroions, showing a strong interaction with the macroionic system. When the co-ion size is comparable to that of the macroions, they assemble independently instead of assembling with the macroions, leading to the previously reported unique self-recognition phenomenon for macroions. 

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4. Self-Assembly of Porous Structures From a Binary Mixture of Lobed Patchy Particles

   https://doi.org/10.3389/fphy.2021.767623  

   Paul, Sanjib; Vashisth, Harish (October 2021, Frontiers in Physics)

   null (Ed.)

   We report simulation studies on the self-assembly of a binary mixture of snowman and dumbbell shaped lobed particles. Depending on the lobe size and temperature, different types of self-assembled structures (random aggregates, spherical aggregates, liquid droplets, amorphous wire-like structures, amorphous ring structures, crystalline structures) are observed. At lower temperatures, heterogeneous structures are formed for lobed particles of both shapes. At higher temperatures, homogeneous self-assembled structures are formed mainly by the dumbbell shaped particles, while the snowman shaped particles remain in a dissociated state. We also investigated the porosities of self-assembled structures. The pore diameters in self-assemblies increased with an increase in temperature for a given lobe size. The particles having smaller lobes produced structures with larger pores than the particles having larger lobes. We further investigated the effect of σ , a parameter in the surface-shifted Lennard-Jones potential, on the self-assembled morphologies and their porosities. The self-assembled structures formed at a higher σ value are found to produce larger pores than those at a lower σ . 

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5. Design of Functionalized Lobed Particles for Porous Self-Assemblies

   https://doi.org/10.1007/s11837-021-04715-w  

   Gorai, Biswajit; Rocha, Brunno C.; Vashisth, Harish (June 2021, JOM)

   null (Ed.)

   Colloidal particles fabricated with anisotropic interactions have emerged as building blocks for designing materials with various nanotechnological applications. We used coarse-grained Langevin dynamics simulations to probe the morphologies of self-assembled structures formed by lobed particles decorated with functional groups. We tuned the interactions between the functional groups to investigate their effect on the porosity of self-assembled structures formed by lobed particles with different shapes (snowman, dumbbell, trigonal planar, tetrahedral, square planar, trigonal bipyramidal, and octahedral) at different temperatures. The dumbbell, trigonal planar, and square planar shaped particles, with planar geometries, form self-assembled structures including elongated chains, honeycomb sheets, and square sheets, respectively. The particles with non-planar geometries (tetrahedral, trigonal bipyramidal, and octahedral) self-assemble into random aggregate morphologies. The structures formed by trigonal bipyramidal and octahedral particles exhibit smaller and homogeneous pores compared to the structures formed by trigonal planar and square planar particles. The porosity in self-assembled structures is substantially enhanced by the functionalization of particles. 

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