Molecular Dynamics in the Lyophases of Copolymer P123 Investigated with FFC NMR Relaxometry

Abstract

Associative block copolymers of the type (EO) x (PO) y (EO) x (where EO and PO represent ethylene and propylene oxides, respectively) in aqueous solution have far reaching commercial applications such as solubilization, controlled-drug delivery, etc. The molecular dynamics of a self-associating triblock copolymer (EO) 20 (PO) 70 (EO) 20 (known as P123 with a molecular weight of ∼5800), in aqueous solution (D 2 O), consisting of various lyotropic liquid crystalline phases such as isotropic micellar, cubic, hexagonal, and lamellar phases, is investigated using the fast field cycling nuclear magnetic resonance (FFC NMR) relaxometry technique in the Larmor frequency range from 5 kHz to 30 MHz. A nuclear spin-relaxation model consisting of chain modes (Rouse modes) and order fluctuation (OF) modes typical for polymers and liquid crystals, respectively, is considered to explain the observed proton magnetic relaxation dispersion (PMRD) data in the lyophases under investigation. The PMRD analysis in both isotropic micellar and cubic phases revealed a Rouse frequency dependence of spin−lattice relaxation rate (R 1 ), i.e., R 1 ∝ −τ s ln(ωτ s ), in the entire frequency range of study. Hexagonal and lamellar phase data show Rouse modes as well as OF modes, leaving the signature of the latter as R 1 ∝ ω −p , where p ∼ 0.5 is typical for nematic mesogens. The activation energies were also determined from segmental correlation times in the lyophases of study. To the best of our knowledge, the present FFC NMR relaxometry study is unique and quantitative in unraveling molecular dynamics of the associative copolymer P123 in aqueous solution.

Exploring Crystal-Phase Molecular Dynamics of the Low-Viscous Mesogen 6CHBT: A Combined FFC and High-Field NMR Relaxometry Investigation

“…Rich polymorphism exhibited by thermotropic liquid crystals provides a challenge to probe complex motions in isotropic, nematic, smectic, and crystal phases. ,, Molecular dynamical processes in thermotropic liquid crystals encompass a frequency range from ultraslow (kHz) to ultrafast motions (MHz). , The ultraslow motions are in general collective motions that contribute to nuclear spin relaxation due to the orientation fluctuations of the local nematic order above the nematic–isotropic transition temperature ( T NI ), long-range order parameter fluctuations just below T NI , order director fluctuations (ODF) in the midnematic phase, local smectic organizations in the nematic phase, i.e., cybotactic clusters ( T > T AN ), layer undulations in the smectic-A phase, and slow molecular reorientations in solid phases, − while ultrafast motions cover noncollective motions such as translational self-diffusion and molecular reorientations about their short and long axes, including end chain rotations. − The cumulative effect of all these dynamical processes has a bearing influence on a nuclear spin probe, leading to specific frequency and thermal signatures on nuclear spin–lattice relaxation rates. − The molecular motions covering the kHz to MHz regime are in general amenable to the NMR relaxometry window tasked by fast field cycling (FFC) NMR (10 kHz–30 MHz) and high-field NMR (∼1 GHz). − Sizable work on molecular dynamics of isotropic, nematic, and smectic phases by employing NMR relaxometry is available elsewhere. − …”

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

“…Since the seminal work by Brownstein and Tarr, − fast-field-cycling (FFC) NMR relaxometry has been used as a valuable tool to assess water mobility at the liquid–solid interface (and also to study the microscopic dynamics of polymers − and proteins − ). Data interpretation can be related to the textural features of solid systems such as clays and microporous materials in general. − Very briefly (the bases of FFC-NMR relaxometry are summarized in the Supporting Information), this technique relies on the simple though counterintuitive idea that the tighter a water molecule is bound to the surface of a porous wet system (that is the more restricted its motion is), the faster the longitudinal relaxation rate ( R 1 ) is that the water 1 H nuclei will experience (the same is true, indeed, also for transverse relaxation, which we do not consider here).…”