Spatially Resolved Monitoring of Drying of Hierarchical Porous Organic Networks

Abstract

Evaporation kinetics of water confined in hierarchal polymeric porous media is studied by low field nuclear magnetic resonance (NMR). Systems synthesized with various degrees of cross-linker density render networks with similar pore sizes but different response when soaked with water. Polymeric networks with low percentage of cross-linker can undergo swelling, which affects the porosity as well as the drying kinetics. The drying process is monitored macroscopically by single-sided NMR, with spatial resolution of 100 μm, while microscopic information is obtained by measurements of spin-spin relaxation times (T2). Transition from a funicular to a pendular regime, where hydraulic connectivity is lost and the capillary flow cannot compensate for the surface evaporation, can be observed from inspection of the water content in different sample layers. Relaxation measurements indicate that even when the larger pore structures are depleted of water, capillary flow occurs through smaller voids.

Enhanced Surface Interaction of Water Confined in Hierarchical Porous Polymers Induced by Hydrogen Bonding

“…This leads to a change in the size distribution of the polymer beads, which affects the overall PSD. The change in the overall porosity of the system was reported by means of gravimetric experiments as well as the changes in the individual T 2 values of water contained in each pore. , A maximum in the diameter of P 2 is observed for 17 mol % EGDMA. For a lower cross-linker content, the primary particles suffer deformations, rendering a collapse in the pore structure.…”

Quantification of Imbibed Heptane in Shale Rocks Determined by Edited T1–T2 Nuclear Magnetic Resonance Relaxation Experiments at High Magnetic Field

“…Once the signal in region 4 decreases significantly, the amount of heptane in region 2 starts to decay. At this time, the connectivity of the main heptane cluster is lost, and the pendular regime is reached. , This phenomenon also evidences the interconnection between the kerogen porous matrix and the inorganic pores developed in the shale. From this stage on, the only source of evaporation is the heptane located in the smaller kerogen pores, and the evaporation proceeds through the vapor phase developed in the inorganic pores.…”

Surface Area Determination of Kevlar Particles in Suspensions Containing Iron Impurities Using Low-Field Nuclear Magnetic Resonance Relaxometry

“…It is worth noting that NMR studies can also be used to characterize porous media with unique subpopulations of water molecules differentiated by confinement. The inverse Laplace transform of the decay signal is a well-known technique for studies of porous media. ,,,− ,,,, The presence of unique subpopulations was not detected at the weight ratios utilized in this study; however, future investigation of the effects of higher polymer concentrations in water or in polymer matrices could explore this topic.…”

“…The inverse Laplace transform of the decay signal is a well-known technique for studies of porous media. 19,22,25,[27][28][29]35,47,50,51 The presence of unique subpopulations was not detected at the weight ratios utilized in this study; however, future investigation of the effects of higher polymer concentrations in water or in polymer matrices could explore this topic.…”

“…Two time constants describe this relaxation, the spin-lattice or longitudinal time constant, T 1 , describes relaxation in the z -axis, aligned with the magnetic field and the spin–spin or transverse time constant, T 2 , describes the loss of phase coherence in the x- , y -plane as individual spins precess about the magnetic field vector. Interpretation of the NMR relaxation rates provides valuable information about the physical state, morphology, and bulk behavior of particle suspensions and fluid-filled porous media. − …”