124 research outputs found
Mechanism of membrane tube formation induced by adhesive nanocomponents
We report numerical simulations of membrane tubulation driven by large
colloidal particles. Using Monte Carlo simulations we study how the process
depends on particle size, concentration and binding strength, and present
accurate free energy calculations to sort out how tube formation compares with
the competing budding process. We find that tube formation is a result of the
collective behavior of the particles adhering on the surface, and it occurs for
binding strengths that are smaller than those required for budding. We also
find that long linear aggregates of particles forming on the membrane surface
act as nucleation seeds for tubulation by lowering the free energy barrier
associated to the process
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. In this paper, we study the shape fluctuations of two dimensional
flexible vesicles containing active Brownian particles. We show how these
fluctuations not only are capable of easily squeezing a vesicle through narrow
openings, but are also responsible for its rectification when placed within
asymmetric confining channels (ratchetaxis). We detail the conditions under
which this process can be optimized, and sort out the complex interplay between
elastic and active forces responsible for the directed motion of the vesicle
across these channels.Comment: 8 pages, 8 figure
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. We find that the introduction of active fluctuations into the
system produces a phase behavior that is overall consistent with that observed
for passive membranes. The phases and the nature of the transition for ideal
membranes is unchanged and active fluctuations can be remarkably accounted for
by a simple rescaling of the temperature. For the self-avoiding membrane, we
find that the extended phase is preserved even in the presence of very large
active fluctuations.Comment: 9 pages, 7 figure
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. The
simplicity and robust nature of this strategy offers a systematic and generic
pathway to improving the self-assembly of a large number of complex colloidal
structures. We discuss in detail the process by which this feat is accomplished
and provide quantitative metrics for exploiting it to modulate self-assembly.
We provide evidence for the generic nature of this approach by demonstrating
that it remains robust under a number of different anisotropic short-ranged
pair interactions in both two and three dimensions. In addition, we report on a
novel microphase in mixtures of passive and active colloids. For a broad range
of self-propelling velocities, it is possible to stabilize a suspension of
fairly monodisperse finite-size crystallites. Surprisingly, this microphase is
also insensitive to the underlying pair interaction between building blocks.
The active stabilization of these moderately-sized monodisperse clusters is
quite remarkable and should be of great utility in the design of hierarchical
self-assembly strategies. This work further bolsters the notion that active
forces can play a pivotal role in directing colloidal self-assembly.Comment: Supplemental Material available here:
https://aip.scitation.org/doi/suppl/10.1063/5.001651
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 Letter we show how a crumpled phase
develops reliably and consistently upon subjecting a thin spherical shell to
active fluctuations. We find a master curve describing how the relative volume
of a shell changes with the strength of the active forces, that applies for
every shell independent of size and elastic constants. Furthermore, we extract
a general expression for the onset active force beyond which a shell begins to
crumple. Finally, we calculate how the size exponent varies along the crumpling
curve.Comment: 6 pages and 6 figures including the appendi
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