A thermodynamic analysis of end-directed particle flocking in chemical systems

• Published in: Communications in nonlinear science & numerical simulation Vol. 106; p. 106107
• Main Authors: De Bari, B., Dixon, J., Pateras, J., Rusling, J., Satterwhite-Warden, J., Vaidya, A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.03.2022; Elsevier Science Ltd
• Subjects: Benzoquinone; Dissolution; Dynamic models; End-directedness; Flocking; Free energy; Liquid surfaces; Mass-action; Particle size; Self-organization; Surface tension; Thermodynamics; Flocking; Mass-action; Free energy; Self-organization; End-directedness
• ISSN: 1007-5704; 1878-7274
• DOI: 10.1016/j.cnsns.2021.106107

We discuss the thermodynamics behind self-organizing Benzoquinone (BQ) particles on air–water interface. Experiments (Satterwhite-Warden et al., 2015; Chen et al., 2019; Satterwhite-Warden et al., 2019) reveal that BQ particles undergo rapid transient flocking behavior as they move around on the liquid surface. Flocks are seen to vary in size and their formation and stability appears to be dependent upon their shape. It is hypothesized that self organization of particles is a result of surface tension gradients in the two dimensional liquid surface resulting from the slow dissolution of the BQ particles. The current paper uses a mass-action kinetic framework to study the flocking of particles. Two dynamical models, with and without a reservoir, are proposed and analyzed through the thermodynamic lens of free energy, which informs us about dominant and spontaneous ‘reactions’ or flock formations in the system. Results of the model are in good agreement with experiment, revealing that irregular shaped BQ particles do indeed show far greater propensity to form flocks compared with regularly shaped particles and validating the mass-action framework as an appropriate tool to investigate this system. •A new mass-action based approach to model the self-organization of BQ particles on a liquid surface.•A thermodynamic argument for stability of the observed states based on the Gibbs free energy of the system.•Ability to capture essential differences in the dynamics based on the shape of the BQ particles.•Addition of another system displaying end-directed behavior which can be explained using nonequilibrium thermodynamics.