1,721,322 research outputs found
Basic concepts in self-assembly
Full text linkIn this brief contribution we review the basic elements of self-assembly, calling attention on the competition between the energetic gain of forming a bond and the loss of translational entropy. We show how to calculate theoretically the distribution of cluster sizes, in the hypothesis of an ideal gas of cluster, and discuss how the cluster partition functions can be calculated numerically. Building on the thermodynamic formalism, we discuss some analytically soluble simple models of self-assembly: equilibrium and cooperative polymerization and micelle formation. Finally, we discuss the importance of directional interactions for self-assembly, its role in the bonding entropy reduction, in the suppression of the driving force for phase-separation and in the possibility of forming aggregates that do not expose attractive surfaces, thus minimizing inter-cluster attractive interactions
Entropy in self-assembly
No full textColloidal systems show beautiful examples of how entropy can lead to
self-assembly of ordered structures, challenging our perception of
disorder. In fact, dispersion of hard colloidal particles, systems in
which by default entropy is the only thermodynamic driving force,
displays both translational and orientational order on increasing
density. Entropy is also a fundamental concept for describing effective
interactions between colloidal particles. In several cases, entropy
maximization generates strong attractive forces, capable of inducing
condensation and sometimes crystallization. These entropic forces can
even be exploited to drive colloids in specific locations or to orient
them in the build-up of supracolloidal aggregates. Depletion
interactions and combinatorial contributions are two important
manifestations of these forces. Entropy also plays a leading role in
systems exploring the bottom of their potential energy surface. In
patchy colloids, particles interacting with highly anisotropic and
localized potentials, ground-state structures are often degenerate in
energy, leaving entropy to decide the thermodynamically stable
polymorph. A striking result is the possibility of generating colloidal
``liquids'' thermodynamically more stable than colloidal
``crystals'' even at vanishing temperature
Switching bonds in a DNA gel: An all-DNA vitrimer
No full textWe design an all-DNA system that behaves like vitrimers, innovative plastics with self-healing and stress-releasing properties. The DNA sequences are engineered to self-assemble first into tetra- and bifunctional units which, upon further cooling, bind to each other forming a fully bonded network gel. An innovative design of the binding regions of the DNA sequences, exploiting a double toehold-mediated strand displacement, generates a network gel which is able to reshuffle its bonds, retaining at all times full bonding. As in vitrimers, the rate of bond switching can be controlled via a thermally activated catalyst, which in the present design is very short DNA strands
PRIMITIVE MODELS OF PATCHY COLLOIDAL PARTICLES. A REVIEW
No full textIn this article I will review some recent studies of the phase behavior and of the self-assembly of patchy colloidal particles. These studies have been based on simple primitive models for colloid-colloid interactions, effectively extending to soft matter the seminal work of I. Nezbeda on associated fluids. I will discuss the possibilities offered by the study of the self-assembly of particles with limited valence in deepening our understanding of the onset of the liquid state, of the differences between gels and glasses and of the possible connection between physical and chemical gels. A review with 55 references
Gel-forming patchy colloids and network glass formers: thermodynamic and dynamic analogies
No full text82.70.Gg Gels and sols, 82.70.Dd Colloids, 61.20.Lc Time-dependent properties; relaxation,
Three-body potential for simulating bond swaps in molecular dynamics
No full textNovel soft matter materials join the resistance of a permanent mesh of strong inter-particle bonds with the self-healing and restructuring properties allowed by bond-swapping processes. Theoretical and numerical studies of the dynamics of coarse-grained models of covalent adaptable networks and vitrimers require effective algorithms for modelling the corresponding evolution of the network topology. Here I propose a simple trick for performing molecular dynamics simulations of bond-swapping network systems with particle-level description. The method is based on the addition of a computationally non-expensive three-body repulsive potential that encodes for the single-bond per particle condition and establishes a flat potential energy surface for the bond swap
Structural glasses: Flying to the bottom
No full textSingh, Ediger and de Pablo have introduced an algorithm which is a modified molecular dynamics simulation, progressively introducing small groups of particles into the system while locally minimizing the potential energy and slowly reducing the temperature of the added particles. The authors also investigated the mechanism behind the formation of these model low-energy glasses at the single particle level, unambiguously proving that a liquid layer does indeed exist on the surface of the deposited glass, and showed that particles in this layer are characterized by a mobility that is several orders of magnitude larger than that in the bulk. The presence of a free surface brings in a significant simplification to the complexity of the configuration space and a reduction of the intra-basin energy barriers
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