@article{rutkowski_marcoux_socolar_hall_2017, title={Formation of limit-periodic structures by quadrupole particles confined to a triangular lattice}, volume={95}, ISSN={["2470-0053"]}, DOI={10.1103/physreve.95.012604}, abstractNote={We have performed Monte Carlo (MC) simulations on two-dimensional systems of quadrupole particles confined to a triangular lattice in order to determine the conditions that permit the formation of a limit-periodic phase. We have found that limit-periodic structures form only when the rotations of the particles are confined to a set of six orientations aligned with the lattice directions. Related structures including striped and unidirectional rattler phases form when π/π66 rotations or continuous rotations are allowed. Order parameters signaling the formation of the limit-periodic structure and related structures are measured as a function of temperature. Our findings on the formation of the limit-periodic structure elucidate features relevant to the experimental creation of such a structure, which is expected to have interesting vibrational and electromagnetic modes.}, number={1}, journal={PHYSICAL REVIEW E}, author={Rutkowski, David M. and Marcoux, Catherine and Socolar, Joshua E. S. and Hall, Carol K.}, year={2017}, month={Jan} }
 @article{rutkowski_velev_klapp_hall_2017, title={Simulation study on the structural properties of colloidal particles with offset dipoles}, volume={13}, ISSN={["1744-6848"]}, DOI={10.1039/c7sm00226b}, abstractNote={A major research theme in materials science is determining how the self-assembly of new generations of colloidal particles of complex shape and surface charge is guided by their interparticle interactions. In this paper, we describe results from quasi-2D Monte Carlo simulations of systems of colloidal particles with offset transversely-oriented extended dipole-like charge distributions interacting via an intermediate-ranged Yukawa potential. The systems are cooled slowly through an annealing procedure during which the temperature is lowered in discrete steps, allowing the system to equilibrate. We perform ground state calculations for two, three and four particles at several shifts of the dipole vector from the particle center. We create state diagrams in the plane spanned by the temperature and the area fraction outlining the boundaries between fluid, string-fluid and percolated states at various values of the shift. Remarkably we find that the effective cooling rate in our simulations has an impact on the structures formed, with chains being more prevalent if the system is cooled quickly and cyclic structures more prevalent if the system is cooled slowly. As the dipole is further shifted from the center, there is an increased tendency to assemble into small cyclic structures at intermediate temperatures. These systems further self-assemble into open lattice-like arrangements at very low temperatures. The novel structures identified might be useful for photonic applications, new types of porous media for filtration and catalysis, and gel matrices with unusual properties.}, number={17}, journal={SOFT MATTER}, author={Rutkowski, David M. and Velev, Orlin D. and Klapp, Sabine H. L. and Hall, Carol K.}, year={2017}, month={May}, pages={3134–3146} }
 @article{bharti_rutkowski_han_kumar_hall_velev_2016, title={Capillary Bridging as a Tool for Assembling Discrete Clusters of Patchy Particles}, volume={138}, ISSN={["0002-7863"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84996490588&partnerID=MN8TOARS}, DOI={10.1021/jacs.6b08017}, abstractNote={Janus and patchy particles are emerging as models for studying complex directed assembly patterns and as precursors of new structured materials and composites. Here we show how lipid-induced capillary bridging could serve as a new and nonconventional method of assembling patchy particles into ordered structures. Iron oxide surface patches on latex microspheres were selectively wetted with liquid lipid, driving the particle assembly into two- and three-dimensional clusters via interparticle capillary bridge formation. The liquid phase of the bridges allows local reorganization of the particles within the clusters and assists in forming true equilibrium configurations. The temperature-driven fluid-to-gel and gel-to-fluid phase transitions of the fatty acids within the bridge act as a thermal switch for cluster assembly and disassembly. By complementing the experiments with Monte Carlo simulations, we show that the equilibrium cluster morphology is determined by the patch characteristics, namely, their size, number, and shape. This study demonstrates the ability of capillary bridging as a versatile tool to assemble thermoresponsive clusters and aggregates. This method of binding particles is simple, robust, and generic and can be extended further to assemble particles with nonspherical shapes and complex surface chemistries enabling the formation of sophisticated colloidal molecules.}, number={45}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Bharti, Bhuvnesh and Rutkowski, David and Han, Koohee and Kumar, Aakash Umesh and Hall, Carol K. and Velev, Orlin D.}, year={2016}, month={Nov}, pages={14948–14953} }
 @article{rutkowski_velev_klapp_hall_2016, title={The effect of charge separation on the phase behavior of dipolar colloidal rods}, volume={12}, ISSN={["1744-6848"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84973369454&partnerID=MN8TOARS}, DOI={10.1039/c6sm00317f}, abstractNote={Colloids with anisotropic shape and charge distribution can assemble into a variety of structures that could find use as novel materials for optical, photonic, electronic and structural applications. Because experimental characterization of the many possible types of multi-shape and multipolar colloidal particles that could form useful structures is difficult, the search for novel colloidal materials can be enhanced by simulations of colloidal particle assembly. We have simulated a system of dipolar colloidal rods at fixed aspect ratio using discontinuous molecular dynamics (DMD) to investigate how the charge separation of an embedded dipole affects the types of assemblies that occur. Each dipolar rod is modeled as several overlapping spheres fixed in an elongated shape to represent excluded volume and two smaller, embedded spheres to represent the charges that make up the extended dipole. Large charge separations predominately form structures where the rods link head-to-tail while small charge separations predominately form structures where the rods stack side-by-side. Rods with small charge separations tend to form dense aggregates while rods with large charge separations tend to form coarse gel-like structures. Structural phase boundaries between fluid, string-fluid, and "gel" (networked) phases are mapped out and characterized as to whether they have global head-to-tail or global side-by-side order. A structural coarsening transition is observed for particles with large charge separations in which the head-tail networks thicken as temperature is lowered due to an increased tendency to form side-by-side structures. Triangularly connected networks form at small charge separations; these may be useful for encapsulating smaller particles.}, number={22}, journal={SOFT MATTER}, author={Rutkowski, David M. and Velev, Orlin D. and Klapp, Sabine H. L. and Hall, Carol K.}, year={2016}, pages={4932–4943} }