Correlating Surface Chemistry to Surface Relaxivity via TD-NMR Studies of Polymer Particle Suspensions

Abstract

This study elucidates the impact of surface chemistry on solvent spin relaxation rates via time-domain nuclear magnetic resonance (TD-NMR). Suspensions of polymer particles of known surface chemistry were prepared in water and n-decane. Trends in solvent transverse relaxation rates demonstrated that surface polar functional groups induce stronger interactions with water with the opposite effect for n-decane. NMR surface relaxivities (ρ 2 ) calculated for the solid−fluid pairs ranged from 0.4 to 8.0 μm s −1 and 0.3 to 5.4 μm s −1 for water and n-decane, respectively. The values of ρ 2 for water displayed an inverse relationship to contact angle measurements on surfaces of similar composition, supporting the correlation of the TD-NMR output with polymer wettability. Surface composition, i.e., H/C ratios and heteroatom content, mainly contributed to the observed surface relaxivities compared to polymer % crystallinity and mean particle sizes via multiple linear regression. Ultimately, these findings emphasize the significance of surface chemistry in TD-NMR measurements and provide a quantitative foundation for future research involving TD-NMR investigations of wetted surface area and fluid-surface interactions. A comprehensive understanding of the factors influencing solvent relaxation in porous media can aid the optimization of industrial processes and the design of materials with enhanced performance.

Characterization of Functionalized Chromatographic Nanoporous Silica Materials by Coupling Water Adsorption and Intrusion with Nuclear Magnetic Resonance Relaxometry

“…However, the relaxation time is affected by surface chemistry as well as surface area and confinement effects, and the relaxation time can therefore not be interpreted in a straightforward way for the quantification of the surface chemistry of different nanoporous materials. In this context, Suekuni et al recently showed a correlation between the spin–spin surface relaxivity and the surface chemistry of polymer particles . D’Agostino et al suggested to use the ratio of spin–lattice to spin–spin relaxation time as a measure for the effective interaction strength between liquids and porous materials surfaces. − They found a linear correlation between the inverse relaxation time ratio (− T 2 / T 1 ) and the desorption enthalpy determined from TPD measurements for water-saturated samples. − Our previous experiments confirmed that the T 1 / T 2 ratio can be coupled with the interaction strength of adsorbates on surfaces .…”

“…In this context, Suekuni et al recently showed a correlation between the spin−spin surface relaxivity and the surface chemistry of polymer particles. 71 D'Agostino et al suggested to use the ratio of spin−lattice to spin−spin relaxation time as a measure for the effective interaction strength between liquids and porous materials surfaces. 25−27 They found a linear correlation between the inverse relaxation time ratio (−T 2 /T 1 ) and the desorption enthalpy determined from TPD measurements for water-saturated samples.…”

Towards Quantifying the Chemical Sensitivity of Nuclear Spin Surface Relaxivity in Mesoporous Media

“…PFG NMR diffusion measurements are employed to investigate the mass transport of fluids in porous media [25][26][27], and to quantify the tortuosity of the attendant pore networks [28][29][30][31][32]. NMR relaxation measurements quantify the longitudinal (T1) and transverse (T2) relaxation time constants associated with confined fluids; these time constants are directly related to molecular dynamics and can provide valuable information on pore structure characteristics [33][34][35][36] and solid-liquid interactions [37][38][39][40], especially when screening adsorption processes in sorbents and in catalytically active systems [41][42][43]. Two-dimensional (2D) 𝑇1 − 𝑇2 relaxation time correlation measurements are now employed widely to provide comprehensive information on nuclear spin relaxation processes in porous materials [44][45][46][47][48][49][50][51].…”

Toward Quantifying the Chemical Sensitivity of Nuclear Spin Surface Relaxivity in Mesoporous Media

“…Nuclear magnetic resonance (NMR) is a non-invasive and chemically selective technique for characterizing porous materials. − Traditional NMR spectroscopy approaches provide structural information via chemical shift analysis, and are regularly applied to inform the solid state structures of porous materials, including oxides, , zeolites, , and porous coordination frameworks and polymers (such as metal–organic and covalent–organic frameworks). − However, for liquids confined within the pore structures of such materials, chemical shift resolution is usually significantly limited by line-broadening effects (especially for standard 1 H NMR spectra, which typically exhibit narrow chemical shift ranges), which occur due to local magnetic field distortions caused by magnetic susceptibility differences at the solid–liquid interface. , Dynamic NMR measurements are comparatively unaffected by this problem, and instead provide information on the molecular translational and rotational motion of confined species by assessing the decay of NMR signals over time, with typical means including pulsed field gradient (PFG) NMR diffusion and NMR relaxation time measurements . PFG NMR diffusion measurements are employed to investigate the mass transport of fluids in porous media, − and to quantify the tortuosity of the attendant pore networks. − NMR relaxation measurements quantify the longitudinal ( T 1 ) and transverse ( T 2 ) relaxation time constants associated with confined fluids; these time constants are directly related to molecular dynamics and can provide valuable information on pore structure characteristics − and solid–fluid interactions, − especially when screening adsorption processes in sorbents and in catalytically active systems. − …”