Presence Of Excluded Volume Interactions Research Articles

Emergent collective behavior of active Brownian particles with visual perception.

Systems comprised of self-steering active Brownian particles are studied via simulations for a minimal cognitive flocking model. The dynamics of the active Brownian particles is extended by an orientational response with limited maneuverability to an instantaneous visual input of the positions of neighbors within a vision cone and a cut-off radius. The system exhibits large-scale self-organized structures, which depend on selected parameter values, and, in particular, the presence of excluded-volume interactions. The emergent structures in two dimensions, such as worms, worm-aggregate coexistence, and hexagonally close-packed structures, are analysed and phase diagrams are constructed. The analysis of the particle's mean-square displacement shows ABP-like dynamics for dilute systems and the worm phase. In the limit of densely packed structures, the active diffusion coefficient is significantly smaller and depends on the number of particles in the cluster. Our analysis of the cluster-growth dynamics shows distinct differences to processes in systems of short-range attractive colloids in equilibrium. Specifically, the characteristic time for the growth and decay of clusters of a particular size is longer than that of isotropically attractive colloids, which we attribute to the non-reciprocal nature of the directed visual perception. Our simulations reveal a strong interplay between ABP-characteristic interactions, such as volume exclusion and rotational diffusion, and cognitive-based interactions and navigation.

Influence of excluded volume interactions on the dynamics of dendrimer and star polymers in layered random flow

The influence of excluded volume interactions (EVIs) governs the dynamics of branched polymeric structures. Therefore, we developed a theory with the inclusion of ubiquitous EVIs on average square displacement (ASD) of the centre of mass in layered random flow (LRF). The mean-field approach is used to account for effective EVIs between non-bonded monomers of generalised Gaussian structures. The effect of polymer topology is analysed under the influence of $$\delta $$ - and power-law correlated LRF. Qualitatively, the theory predicts two anomalous power-law regimes: (i) the intermediate time subdiffusive behaviour with enhanced ASD, due to EVIs, shows the internal motion of the chain and (ii) the long-time superdiffusive behaviour with slightly suppressed ASD represents the overall diffusion of the polymer. The time dependence of ASD in the presence of EVIs reveals the anomalous long-time dynamics governed by a power-law, $$t^{2-\alpha /2}$$ . The model with EVIs predicts enhanced swelling of the polymeric structure and the stretching regime in the magnitude of the ASD. The influence of EVIs in star polymer causes enhanced delay in cross-over time which is further increased with increase in functionality. Dendrimer structure with EVI delays the cross-over time with spacer length. Finally, the increase in EVIs in all topologies causes the enhancement in ASD and delay in cross-over time from subdiffusive to superdiffusive regime.

Swelling of ionic microgel particles in the presence of excluded-volume interactions: a density functional approach.

In this work a new density functional theory framework is developed to predict the salt-concentration dependent swelling state of charged microgels and the local concentration of monovalent ions inside and outside the microgel. For this purpose, elastic, solvent-induced and electrostatic contributions to the microgel free energy are considered together with the free energy of the ions. In addition to the electrostatic interaction, the model explicitly considers both the microgel-ion excluded-volume (steric) repulsion and the ionic correlations, in such a way that the formalism is consistent with the Hypernetted-Chain Closure approximation (HNC). We explore the role that the solvent quality, chain elasticity, salt concentration and microgel bare charge play on the swelling state, the effective charge and on the ionic density profiles. Our results show that the microgel-ion steric exclusion foments the increase of the particle size up to 10%. The role that the steric effect plays on the counterion distribution becomes more important when the microgel approaches the shrunken configuration, developing an accumulation peak at the microgel interface and a reduction in the inner core of the microgel that induce a significant increase of the microgel effective charge. We further find that deep inside the particle charge electroneutrality is achieved and a Donnan potential corrected by the steric exclusion is established.