Abstract
In simple colloidal suspensions, clusters are various multimers that result from colloid self-association and exist in equilibrium with monomers.There are two types of potentials that are known to produce clusters: a) potentials that result from the competition between short-range attraction and long-range repulsion and are characterized by a global minimum and a repulsive tail and b) purely repulsive potentials which have a soft shoulder. Using computer simulations, we demonstrate in this work that potentials with a local minimum and a repulsive tail, not belonging to either of the known types, are also capable of generating clusters. A detailed comparative analysis shows that the new type of cluster-forming potential serves as a bridge between the other two. The new clusters are expanded in shape and their assembly is driven by entropy, like in the purely repulsive systems but only at low density. At high density, clusters are collapsed and stabilized by energy, in common with the systems with competing attractive and repulsive interactions.
Highlights
The term “clusters” refers to a large variety of objects that range in size from small multimers to mesoscopic domains [1] and arise as a consequence of monomer self-association in a large variety of soft materials [2]
Clusters are discussed in reference to colloidal suspensions [3], where they exist in equilibrium with monomers, but they were reported for proteins [4], synthetic clays [5] and metal nanoparticles [6]
In this work we demonstrate by computer simulations that potentials that do not belong to either of the classes mentioned above are capable of forming equilibrium clusters
Summary
The term “clusters” refers to a large variety of objects that range in size from small multimers to mesoscopic domains [1] and arise as a consequence of monomer self-association in a large variety of soft materials [2]. Equilibrium clusters become the dominant species in the solution at appropriate thermodynamic conditions They may arise transiently, as a consequence of arrested phase transition [7]. As a particular case of the self-assembly process, cluster formation is of key interest to basic research, in particular condensed matter physics. It has appreciable practical applications, for instance as a drug-delivery vehicle [8]. Clusters are capable of significantly altering the mechanical properties of aqueous solutions in which they assemble This is the case, for instance, of solutions containing monoclonal antibodies, a known biopharmaceutical, which experience a considerable viscosity increase if clusters are present [9]. To develop a basic understanding of the principles underlying the formation of clusters, in order to use these systems successfully for therapeutic purposes
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