We map out the solid-state morphologies formed by model soft-pearl-necklace polymers as a function of chain stiffness, spanning the range from fully flexible to rodlike chains. The ratio of Kuhn length to bead diameter (lK/r0) increases monotonically with increasing bending stiffness kb and yields a one-parameter model that relates chain shape to bulk morphology. In the flexible limit, monomers occupy the sites of close-packed crystallites while chains retain random-walk-like order. In the rodlike limit, nematic chain ordering typical of lamellar precursors coexists with close-packing. At intermediate values of bending stiffness, the competition between random-walk-like and nematic chain ordering produces glass-formation; the range of kb over which this occurs increases with the thermal cooling rate |Ṫ| implemented in our molecular dynamics simulations. Finally, values of kb between the glass-forming and rodlike ranges produce complex ordered phases such as close-packed spirals. Our results should provide a useful initial step in a coarse-grained modeling approach to systematically determining the effect of chain stiffness on the crystallization-vs-glass-formation competition in both synthetic and colloidal polymers.

We numerically examine clogging transitions for bidisperse disks flowing through a two dimensional periodic obstacle array. We show that clogging is a probabilistic event that occurs through a transition from a homogeneous flowing state to a heterogeneous or phase separated jammed state where the disks form dense connected clusters. The probability for clogging to occur during a fixed time increases with increasing particle packing and obstacle number. For driving at different angles with respect to the symmetry direction of the obstacle array, we show that certain directions have a higher clogging susceptibility. It is also possible to have a size-specific clogging transition in which one disk size becomes completely immobile while the other disk size continues to flow.A loose collection of particles such as grains or bubbles can exhibit a transition from a flowing liquidlike state to a non-flowing or jammed state as a function of increasing density, where the density φ j at which the system jams is referred to as Point J 1-3 . One system in which jamming has been extensively studied is a bidisperse twodimensional (2D) packing of frictionless disks, where the area faction covered by the disks at Point J is approximately φ = 0.84, and where the system density is uniform at the jamming transition 1,2,4 . Related to jamming is the phenomenon of clogging, as observed in the flow of grains 5-8 or bubbles 9 through an aperture at the tip of a hopper. The clogging transition is a probabilistic process in which, for a fixed grain size, the probability of a clogging event occurring during a fixed time interval increases with decreasing aperture size. A general question is whether there are systems that can exhibit features of both jamming and clogging. For example, such combined effects could appear in a system containing quenched disorder such as pinning or obstacles where jammed or clogged configurations can be created by a combination of particles that are directly immobilized in a pinning site as well as other particles that are indirectly immobilized through contact with obstacles or pinned particles. In many systems where pinning effects arise, such as for superconducting vortices or charged particles, the particle-particle interactions are long range, meaning that there is no well defined areal coverage density 10 at which the system can be said to jam, so a more ideal system to study is an assembly of hard disks with strictly short range particle-particle interactions. Previous studies have considered the effect of a random pinning landscape on transport in a 2D sample of bidisperse hard disks 11 , while in other work on the effect of obstacles, the density at which jamming occurs decreases when the number of pinning sites or obstacles increases 12,13 .Here we examine a 2D system of bidisperse frictionless disks flowing through a square periodic obstacle array composed of immobile disks with an obstacle lattice constant of a. The total disk density, defined as the area coverage of the mobile disks and the obstacl...

The effects of particle roughness and short-ranged non-central forces on colloidal gels are studied using computer simulations in which particles experience a sinusoidal variation in energy as they rotate. The number of minima n and energy scale K are the key parameters; for large K and n, particle rotation is strongly hindered, but for small K and n particle rotation is nearly free.A series of systems are simulated and characterized using fractal dimensions, structure factors, coordination number distributions, bond-angle distributions and linear rheology. When particles rotate easily, clusters restructure to favor dense packings. This leads to longer gelation times and gels with strand-like morphology. The elastic moduli of such gels scale as G ∝ ω 0.5 at high shear frequencies ω. In contrast, hindered particle rotation inhibits restructuring and leads to rapid gelation and diffuse morphology. Such gels are stiffer, with G ∝ ω 0.35 . The viscous moduli G in the low-barrier and high-barrier regimes scale according to exponents 0.53 and 0.5, respectively.The crossover frequency between elastic and viscous behaviors generally increases with the barrier to rotation. These findings agree qualitatively with some recent experiments on heterogeneouslysurface particles and with studies of DLCA-type gels and gels of smooth spheres. arXiv:1909.01491v1 [cond-mat.soft] 3 Sep 2019Key simulation parameters are summarized in Table I. Because the particles are monodisperse, they all have the same mass m. All quantities are reported in reduced units, with temperature scaled by , distance scaled by the particle diameter σ. The reduced unit for