Probing the surfaces of core‐shell and hollow nanoparticles by solvent relaxation NMR

Abstract

Measurement of the spin-spin NMR relaxation time (or its inverse, the rate) of water molecules in aqueous nanoparticle dispersions has become a popular approach to probe of the nature and structure of the particle surface and any adsorbed species. Here, we report on the characterisation of aqueous dispersions of hollow amorphous nanoparticles that have two liquid accessible surfaces (inner cavity surface and outer shell surface) plus the solid (silica) and core-shell (titania-silica) nanoparticle precursors from which the hollow particles have been prepared. In all cases, the observed water relaxation rates scale linearly with particle surface area, with the effect being more pronounced with increasing levels of titania present at the particle surface. Two distinct behaviours were observed for the hollow nanoparticles at very low volume fractions, which appear to merge with increasing surface area (particle concentration). Herewith, we further show the versatility of solvent NMR spectroscopy as a probe of surface character.

Probing Selective Adsorption in Cationic-Polymer Induced Aggregation of Binary Anionic Particulate Dispersions Using Solvent Relaxation NMR

“…The effect of a given surface area on the measured property R enh (silica) 2sp = 0.24 mL g −1 , R enh (latex) 2sp = 0.48 mL g −1 , R enh (laponite) 2sp = 4.0 mL g −1 and R enh (TiO2) 2sp = 14 mL g −1 . The polymer and particles bear opposite charges, so changes in the surface area are expected to be induced through macroscopic phase separation, as per our previous study [19] i.e., polymer-coated particles aggregate leaving a coexisting polymer-free bare particle dispersion. It is worth highlighting at this stage, that all the particles bear an anionic charge, and have comparable ζ-potentials.…”

Solvent Relaxation NMR as a Tool to Study Particle Dispersions in Non-Aqueous Systems

“…NMR presents a family of experimental methodologies that can probe concentrated, opaque systems such as particulate dispersions, yielding a variety of dynamic characterisations-diffusion rates [5,6] and relaxation times [7,8]-as well as structural information, e.g., solid-state spectra [9,10], which can be used to investigate the molecular environment of near-surface species. Over the past few years, the solvent relaxation NMR approach has been particularly insightful in characterising aqueous dispersions, both theoretically and experimentally [11][12][13][14][15][16][17][18]. The present work focuses on assessing whether the measurement of solvent relaxation times (rates) in binary aqueous-nonaqueous solvent blends or, indeed, non-aqueous dispersions offer the same experimental potential as aqueous dispersions.…”

Green earth pigments dispersions: Water dynamics at the interfaces

“…aqueous suspensions of various green earth materials in the absence of any organic binder and try to better assess the links between green earth nature and the interaction of water with pigment surfaces. For reaching such an aim, we use NMR relaxometry that has proven to be an efficient tool to evaluate particle dispersions [15], [16], [17], their stability [18], [19], [20], [21], [22] and especially the interaction of the solvent with the colloidal surfaces [19], [23], [24], [25]. The sensitivity of NMR relaxation rates of the solvent to the interaction with interfaces makes it even possible to evidence the counterion specific effect with charged surfaces [26], [27].…”