Abstract
Electrospun nanowebs with pores ranging from nanometers to micrometers, constitute new materials with enhanced absorbency and ability to retain liquids in pores for a long period of time. These materials can be used as nanofluidic probes collecting minute amount of liquids. However, extraction of liquids from nanofibrous materials presents a problem: menisci in the interfiber pores create very high suction pressure which holds the liquid inside the material. This problem can be resolved if the probe is completely filled with the liquid: menisci at the probe edges become flat to establish a pressure equilibrium with the atmosphere. Therefore, one can take advantage of the nanoweb softness and extract liquid by mechanically deforming the nanowebs. We show that the liquid-saturated nanowebs follow the Voigt-type rheology upon loading. We theoretically explain this behavior and derive the relations between the Voigt phenomenological parameters, nanoweb permeability and compression modulus. We show that the limiting deformations follow the Hooke's law which assumes linear relation between the extracted volume of liquid and the applied load. Because of this predictable behavior, the nanoweb probes can be engineered to release minute liquid doses upon compression. The developed experimental methodology can be used for characterization of nanostructured materials which otherwise impossible to analyze by using the existing instruments.