Water Dynamics at the Solid–Liquid Interface to Unveil the Textural Features of Synthetic Nanosponges

Abstract

A fast-field-cycling NMR investigation was carried out on a set of polyurethane cyclodextrin nanosponges, in order to gain information on their textural properties, which have been proven to be quite difficult to assess by means of ordinary porosimetric techniques. Experiments were performed on both dry and wet samples, in order to evaluate the behavior of the “nonexchangeable” C-bound 1 H nuclei, as well as the one of the mobile protons belonging to the skeletal hydroxyl groups and the water molecules. The results acquired for the wet samples accounted for the molecular mobility of water molecules within the channels of the nanosponge network, leading back to the possible pore size distribution. Owing to the intrinsic difficulties involved in a quantitative assessment of the textural properties, in the present study we alternatively propose an extension to nanosponges of the concept of “connectivity”, which has been already employed to discuss the properties of soils.

Nuclear Magnetic Resonance with Fast Field-Cycling Setup: A Valid Tool for Soil Quality Investigation

“…It is clear, now, that water dynamics in the quartz sand is more complex than the simple data interpretation based on the biexponential form of Equations 2 Figure 3. It is clear, now, that water dynamics in the quartz sand is more complex than the simple data interpretation based on the biexponential form of Equations 2 Figure 5 do not show any band at around 2.5 s, which is the typical longitudinal relaxation time of free water [38]. This finding can only mean that all the water is trapped inside the quartz sand.…”

“…Agronomy 2020, 10, x FOR PEER REVIEW 9 of 33 2.5 s, which is the typical longitudinal relaxation time of free water [38]. This finding can only mean that all the water is trapped inside the quartz sand.…”

“…The first explanation of the relationship between porosity of a porous medium and longitudinal relaxation was given by Brownstein and Tarr [140]. In particular, for wet micro-or nano-porous materials the relaxation rates R 1 can be related to the fraction of water molecules interacting with the pore surface ( f s ) by the equation [38]:…”

“…FFC NMR relaxometry versatility makes the technique quite useful in many fields. As an example, it has been applied to monitor food quality [25,26], traceability [27][28][29], conservation [30], and transformation [31][32][33][34][35][36][37]; to evaluate the physical chemical characteristics of systems useful for drug delivery [38]; to design new contrast agents to be used in diagnostic imaging techniques [39][40][41]; to explore tumor development [42]; to monitor environmental quality [18,43,44], and many other different applications that can be found elsewhere [45,46]. The present review paper is intended to explore the suitability in soil science of FFC NMR relaxometry.…”

Recent Developments in Understanding Biochar’s Physical–Chemistry

“…It is widely recognized that the molecular dynamics investigated by the T 1 value measurements of liquid systems, such as water, in biochar pores is affected by the interactions with the porous boundaries [163,164,[191][192][193][194][195][196]. Namely, the smaller the pore size, the more constrained water molecules are.…”