The shape of cleaved tethered membranes.

A remarkable property of flexible self-avoiding elastic surfaces (membranes) is that they remain flat at all temperatures, even in the absence of a bending rigidity or in the presence of active fluctuations. Here, we report numerical results of these surfaces wherein we alter their topology by systematically cleaving internal bonds. While it is known that a random removal of membrane bonds does not disrupt the overall extended shape of the membrane, we find that cleaving an elastic surface with longitudinal parallel cuts leads to its systematic collapse into a number of complex morphologies that can be controlled by altering the number and length of the inserted cuts.

Spontaneous crumpling of active spherical shells.

The existence of a crumpled phase for self-avoiding elastic surfaces was postulated more than three decades ago using simple Flory-like scaling arguments. Despite much effort, its stability in a microscopic environment has been the subject of much debate. In this paper we show how a crumpled phase develops reliably and consistently upon subjecting a thin spherical shell to active fluctuations.

The crumpling transition of active tethered membranes.

We perform numerical simulations of active ideal and self-avoiding tethered membranes. Passive ideal membranes with bending interactions are known to exhibit a continuous crumpling transition between a low temperature flat phase and a high temperature crumpled phase. Conversely, self-avoiding membranes remain in an extended (flat) phase for all temperatures even in the absence of a bending energy.

Rectification of confined soft vesicles containing active particles.

One of the most promising features of active systems is that they can extract energy from their environment and convert it to mechanical work. Self propelled particles enable rectification when in contact with rigid boundaries. They can rectify their own motion when confined in asymmetric channels and that of microgears.

Effective forces between active polymers.

The characterization of the interactions between two fully flexible self-avoiding polymers is one of the classic and most important problems in polymer physics. In this paper we measure these interactions in the presence of active fluctuations. We introduce activity into the problem using two of the most popular models in this field, one where activity is effectively embedded into the monomers' dynamics, and the other where passive polymers fluctuate in an explicit bath of active particles.

Designing active colloidal folders.

Can active forces be exploited to drive the consistent collapse of an active polymer into a folded structure? In this paper, we introduce and perform numerical simulations of a simple model of active colloidal folders and show that a judicious inclusion of active forces into a stiff colloidal chain can generate designable and reconfigurable two-dimensional folded structures. The key feature is to organize the forces perpendicular to the chain backbone according to specific patterns (sequences). We characterize the physical properties of this model and perform, using a number of numerical techniques, an in-depth statistical analysis of structure and dynamics of the emerging conformations.

The coil-globule transition in self-avoiding active polymers.

We perform numerical simulations of an active fully flexible self-avoiding polymer as a function of the quality of the embedding solvent described in terms of an effective monomer-monomer interaction. Specifically, by extracting the Flory exponent of the active polymer under different conditions, we are able to pin down the location of the coil-globule transition for different strengths of the active forces. Remarkably, we find that a simple rescaling of the temperature is capable of qualitatively capturing the dependence of the Θ-point of the polymer on the amplitude of active fluctuations.

Universal reshaping of arrested colloidal gels via active doping.

Colloids that interact via a short-range attraction serve as the primary building blocks for a broad range of self-assembled materials. However, one of the well-known drawbacks to this strategy is that these building blocks rapidly and readily condense into a metastable colloidal gel. Using computer simulations, we illustrate how the addition of a small fraction of purely repulsive self-propelled colloids, a technique referred to as active doping, can prevent the formation of this metastable gel state and drive the system toward its thermodynamically favored crystalline target structure.

Dynamics of an active semi-flexible filament in a spherical cavity.

We perform numerical simulations of active semiflexible filaments inside a rigid spherical cavity. We study the problem as a function of the bending rigidity, degree of confinement, and strength of the active forces. For passive filaments, the multispool conformations already established in previous studies are recovered, yet even small amounts of activity, when aligned along the direction of the filament backbone, destabilize these passive conformations.

Colloidal swimmers near curved and structured walls.

We present systematic numerical simulations to understand the behavior of colloidal swimmers near a wall. We extend previous theoretical calculations based on lubrication theory to include walls with arbitrary curvature, and show how to extract from simulations a set of parameters crucial to accurately estimate the leading hydrodynamic contributions associated with the curvature of a wall. Our results show explicitly how introducing curvature to the wall not only affects the average incident angle the swimmer acquires when swimming near it, but it also leads to much broader angular distributions.

Deviations from Blob Scaling Theory for Active Brownian Filaments Confined Within Cavities.

Scaling arguments used to predict the radius of gyration of passive self-avoiding flexible polymers have been shown to hold for polymers under the influence of active fluctuations. In this Letter, we establish how the standard blob scaling theory representation of a polymer, capable of capturing the essential physics of passive polymers under a variety of settings, breaks down when dealing with active polymers under confinement. Using numerical simulations, we show how the predicted exponents associated to the forces applied by a polymer when restricted within cavities of different geometries hold only whenever the persistence length generated on the polymer by the active forces is much smaller than the size of the characteristic blob in the scaling theory.

Persistent Multiexcitons from Polymers with Pendent Pentacenes.

Singlet fission has emerged as a key mechanism of exciton multiplication in organic chromophores, generating two triplet excitons from a single photon. Singlet fission is typically studied in crystalline films or in isolated dimers. Here, we investigate an intermediate regime where through-space interactions mediate singlet fission and triplet pair recombination within isolated polymer chains.

Active sculpting of colloidal crystals.

The development of colloidal particles that can become self-propelled when exposed to a source of light of a given frequency represents one of the most exciting new developments in the field of active matter. In this paper, we perform numerical simulations to explore several properties of crystalline colloidal aggregates in the presence of such external light fields. We show how permanent gaps of tunable size can be carved into these crystals as a result of a solid-gas transition that occurs above a threshold light intensity.

Activity-Enhanced Self-Assembly of a Colloidal Kagome Lattice.

Here, we describe a method for the enhanced self-assembly of triblock Janus colloids targeted to form a kagome lattice. Using computer simulations, we demonstrate that the formation of this elusive structure can be significantly improved by self-propelling or activating the colloids along the axis connecting their hydrophobic hemispheres. The process by which metastable aggregates are destabilized and transformed into the favored kagome lattice is quite general, and we argue this active approach provides a systematic pathway to improving the self-assembly of a large number of colloidal structures.

Surface Fluctuations Dominate the Slow Glassy Dynamics of Polymer-Grafted Colloid Assemblies.

Colloids grafted with a corona layer of polymers show glassy behavior that covers a wide range of fragilities, with this behavior being tunable through variations in grafting density and grafting chain length. We find that the corona roughness, which is maximized for long chain lengths and sparse grafting, is directly correlated to the concentration-dependence of the system relaxation time (fragility). Relatively rougher colloids result in stronger liquids because their rotational motions become orientationally correlated across the whole system even at low particle loadings leading to an essentially Arrhenius-like concentration-dependence of the relaxation times near the glass transition.

Hierarchical collective motion of a mixture of active dipolar Janus particles and passive charged colloids in two dimensions.

We use computer simulations to study the behavior of a mixture of large passive charged colloids in a suspension of smaller active dipolar Janus particles. We find that when a single charged colloid is present in solution, it acquires a rotational or translational motion depending on how the active dipoles self-assemble on its surface to form active complexes. The collective behavior of these complexes is quite remarkable, and includes swarming behavior and coherent macroscopic motion.

An Active Approach to Colloidal Self-Assembly.

In this review, we discuss recent advances in the self-assembly of self-propelled colloidal particles and highlight some of the most exciting results in this field, with a specific focus on dry active matter. We explore this phenomenology through the lens of the complexity of the colloidal building blocks. We begin by considering the behavior of isotropic spherical particles.

Influence of Nanostructure on the Exciton Dynamics of Multichromophore Donor-Acceptor Block Copolymers.

We explore the synthesis and photophysics of nanostructured block copolymers that mimic light-harvesting complexes. We find that the combination of a polar and electron-rich boron dipyrromethene (BODIPY) block with a nonpolar electron-poor perylene diimide (PDI) block yields a polymer that self-assembles into ordered "nanoworms". Numerical simulations are used to determine optimal compositions to achieve robust self-assembly.

Lipid membrane-assisted condensation and assembly of amphiphilic Janus particles.

Amphiphilic Janus particles self-assemble into complex metastructures, but little is known about how their assembly might be modified by weak interactions with a nearby biological membrane surface. Here, we report an integrated experimental and molecular dynamics simulation study to investigate the self-assembly of amphiphilic Janus particles on a lipid membrane. We created an experimental system in which Janus particles are allowed to self-assemble in the same medium where zwitterionic lipids form giant unilamellar vesicles (GUVs).

Activity-assisted self-assembly of colloidal particles.

We outline a basic strategy of how self-propulsion can be used to improve the yield of a typical colloidal self-assembly process. The success of this approach is predicated on the thoughtful design of the colloidal building block as well as how self-propulsion is endowed to the particle. As long as a set of criteria are satisfied, it is possible to significantly increase the rate of self-assembly, and greatly expand the window in parameter space where self-assembly can occur.

Micro-phase separation in two dimensional suspensions of self-propelled spheres and dumbbells.

We use numerical simulations to study the phase behavior of self-propelled spherical and dumbbellar particles interacting via micro-phase separation inducing potentials. Our results indicate that under the appropriate conditions, it is possible to drive the formation of two new active states; a spinning cluster crystal, i.e.

Anomalous dynamics of an elastic membrane in an active fluid.

Using numerical simulations, we characterized the behavior of an elastic membrane immersed in an active fluid. Our findings reveal a nontrivial folding and re-expansion of the membrane that is controlled by the interplay of its resistance to bending and the self-propulsion strength of the active components in solution. We show how flexible membranes tend to collapse into multifolded states, whereas stiff membranes fluctuate between an extended configuration and a singly folded state.

Activity-induced collapse and reexpansion of rigid polymers.

We study the elastic properties of a rigid filament in a bath of self-propelled particles. We find that while fully flexible filaments swell monotonically upon increasing the strength of the propelling force, rigid filaments soften for moderate activities, collapse into metastable hairpins for intermediate strengths, and eventually reexpand when the strength of the activity of the surrounding fluid is large. This collapse and reexpansion of the filament with the bath activity is reminiscent of the behavior observed in polyelectrolytes in the presence of different concentrations of multivalent salt.

Quantitative analogy between polymer-grafted nanoparticles and patchy particles.

We establish a quantitative analogy between polymer grafted nanoparticles (PGNPs) and patchy nanoparticles (NPs). Over much of the experimentally relevant parameter space, we show that PGNPs behave quantitatively like Janus NPs, with the patch size having a universal dependence on the number of grafts and the ratio of the size of the NPs to the grafted chain size. The widely observed anisotropic self-assembly of PGNP into superstructures can thus be understood through simple geometric considerations of single patch models, in the same spirit as the geometry-based surfactant models of Israelachvili.