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The "isothermal" compressibility of active matter

Dulaney, Austin R. and Mallory, Stewart A. and Brady, John F. (2020) The "isothermal" compressibility of active matter. . (Unpublished)

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We demonstrate that the mechanically-defined "isothermal" compressibility behaves as a thermodynamic-like response function for suspensions of active Brownian particles. The compressibility computed from the active pressure - a combination of the collision and unique swim pressures - is capable of predicting the critical point for motility induced phase separation, as expected from the mechanical stability criterion. We relate this mechanical definition to the static structure factor via an active form of the thermodynamic compressibility equation and find the two to be equivalent, as would be the case for equilibrium systems. This equivalence indicates that compressibility behaves like a thermodynamic response function, even when activity is large. Finally, we discuss the importance of the phase interface when defining an active chemical potential. Previous definitions of the active chemical potential are shown to be accurate above the critical point but breakdown in the coexistence region. Inclusion of the swim pressure in the mechanical compressibility definition suggests that the interface is essential for determining phase behavior.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Mallory, Stewart A.0000-0003-1364-7252
Brady, John F.0000-0001-5817-9128
Additional Information:We gratefully acknowledge the support of NVIDIA Corporation with the donation of the Titan V GPU used for this research. S.A.M. acknowledges support by the Arnold and Mabel Beckman Foundation. J.F.B acknowledges support by the National Science Foundation under Grant No. CBET-1803662. Data Availability: The data that support the findings of this study are available from the corresponding author upon reasonable request.
Funding AgencyGrant Number
Arnold and Mabel Beckman FoundationUNSPECIFIED
Record Number:CaltechAUTHORS:20201019-100840969
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106141
Deposited By: Tony Diaz
Deposited On:20 Oct 2020 18:25
Last Modified:20 Oct 2020 18:25

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