Thermodynamics of imbibition in capillaries of double conical structures-Hourglass, diamond, and sawtooth shaped capillaries-

TL;DR

This paper presents a thermodynamic analysis of imbibition in double conical capillaries, revealing how spontaneous and forced imbibition behaviors depend on free energy landscapes, with implications for natural systems and fluidic device design.

Contribution

It extends classical capillary thermodynamics to double conical structures, elucidating the energy landscape and stability states during imbibition processes.

Findings

Spontaneous imbibition predicted by Laplace pressure.

Energy landscape shows barriers and traps affecting imbibition.

Multiple stable and metastable states identified.

Abstract

Thermodynamics of imbibition (intrusion and extrusion) in capillaries of double conical structures is theoretically studied using the classical capillary model. By extending the knowledge of the thermodynamics of a single conical capillary, not only the nature of spontaneous imbibition but that of forced imbibition under applied external pressure are clarified. Spontaneous imbibition in capillaries of double conical structure can be predicted from the Laplace pressure in a single conical capillary. To understand the forced imbibition process, the free energy landscape along the imbibition pathway is calculated. This landscape shows either a maximum or a minimum. The former acts as the energy barrier and the latter acts as the trap for the liquid-vapor meniscus so that the imbibition process can be either abrupt with a pressure hysteresis or gradual and continuous. The landscape also predicts a completely filled, a half-filled and a completely empty state as the thermodynamically stable state. Furthermore, it also predicts a completely filled and a half-filled state of metastable liquid which can be prepared by the combination of the intrusion and the extrusion process. Our study could be useful for understanding various natural fluidic systems and for designing functional fluidic devices such as a diode, a switch etc.