Giant enhancement of the NMR resolution and sensitivity of the critical solutions of hyperpolarized fluids within closed carbon nanotubes

TL;DR

This paper predicts a giant enhancement in NMR resolution and sensitivity for critical solutions of hyperpolarized fluids within closed carbon nanotubes, driven by density fluctuations near the critical temperature.

Contribution

It introduces a theoretical framework for understanding how density fluctuations in nanoconfined hyperpolarized fluids dramatically improve NMR signals and resolution.

Findings

g_1 coupling remains finite for long CNTs near criticality

NMR signals exhibit splitting and large shifts at critical temperature

Superradiance bursts scale with N^3 at critical point

Abstract

We predict the effect of the nuclear spin density fluctuations on NMR spectra of critical solutions of spin-carrying atoms in closed carbon nanotubes (CNTs). The total effective dipolar coupling of nuclear spin-carrying of 129^Xe atoms is the sum of 2 terms i.e. g_0 of non-correlated 129^Xe atoms and g_1 depending on density fluctuations of Xe atoms. The coupling g_0 falls off to 0 as 1/V with increasing the volume V of CNTs, while the g_1 remains finite for long CNTs containing critical solution of Xe atoms. The g_1 is derived within the Landau-Ginzburg framework. When temperature T goes to critical temperature T_c, the g_1 is about 10 Hz for 129^Xe fluid in closed long tubes. To achieve the g_1>> g_0, 3 conditions should be met: (1) the large mobility of 129^Xe atoms, (2) the maximal isothermal compressibility of Xe nanofluid within CNTs that have to be (3) long and closed. We discuss 3 applications of such a behavior. First, when T goes to T_c, the FID from N magnetically equivalent 129^Xe atoms is broadened so wide that the FID splits into lattice of N equidistant resonances with finite spacing G=3g_1. Second, the absorption line shape of 129^Xe atoms in spin state I=N/2, m=N/2 has a single delta peak at frequency with the large shift N*G/2 from Larmor frequency W for N>>1. The dipolar field of nanofluid in the spin state I=N/2, m=-N/2 inverts the total magnetic field if N>1+2W/G. Third, we discuss the spontaneous superradiation of the nanofluid in course of depolarization I_x(t) in low-field resonator. At CP of the nanofluid, the I_x(t) causes the bursts of dissipated power ~(g_1)^2*N^3. In the opposite limiting case of the strong field resonator, the depolarization I_x(t) has the Dicke's power ~(W*N)^2. Far from the CP of Xe nanofluid, the dissipated power scales linear with N for fixed density of 129^Xe atoms.