Time domain NMR evaluation of poly(vinyl alcohol) xerogels

Abstract

SbstractPoly(vinyl alcohol) (PVA)-based chemically cross-linked xerogels, both neat and loaded with nanoparticulate hydrophilic silica (SiO 2 ), were obtained and characterized mainly through time domain NMR experiments (TD-NMR). Fourier-transform infrared (FT-IR) and wide angle X-ray diffraction (WAXD) analyses were employed as secondary methods. TD-NMR, through the interpretation of the spin-lattice relaxation constant values and related information, showed both cross-linking and nanoparticle influences on PVA matrix. SiO 2 does not interact chemically with the PVA chains, but has effect on its molecular mobility, as investigated via TD-NMR. Apparent energy of activation, spin-lattice time constant and size of spin domains in the sample have almost linear dependence with the degree of cross-linking of the PVA and are affected by the addition of SiO 2 . These three parameters were derived from a single set of TD-NMR experiments, which demonstrates the versatility of the technique for characterization of inorganic-organic hybrid xerogels, an important class of materials.

Effect of modified microcrystalline cellulose on poly(3-hydroxybutyrate) molecular dynamics by proton relaxometry

“…This increase in the molecular mobility also indicates weak interactions between the polymer chains and cellulose, since the separation between chains allowed them to move with more freedom. 32…”

“…This increase in the molecular mobility also indicates weak interactions between the polymer chains and cellulose, since the separation between chains allowed them to move with more freedom. 32 The material containing 0.50% cellulose showed higher T 1 H value, showing that this cellulose content caused greater rigidity. This was probably due to the formation of strong intermolecular interactions that restricted the molecular mobility of hydrogen groups.…”

Cristallinity Evaluation of Oriented Nanocomposites Based on Polypropylene and Silica by Time Domain NMR

“…Due to the abundant presence of these hydrogen nuclei in the polymer, it is possible to differentiate the relaxation times after being excited by an electromagnetic pulse sequence, since different chemical environments influence the relaxation process of the hydrogen nuclei. [13,15] The domain curves of pure PP and nanocomposites oriented at different rotation speeds are shown in Figure 4. The domain curves reflect the homogeneity of polymer chains, i.e., narrow domains are related to larger organization.…”

“…[12] Time domain nuclear magnetic resonance (TD-NMR) allows the identification of different regions of polymer mobility through the proton spin-lattice relaxation time (T 1 H). [13] The NMR relaxometry allows to evaluate the molecular dynamics of the polymeric compounds, as in the studies that evaluated the mobility levels of amorphous and crystalline regions, [7,14] in the presence of crosslinkings, [15] in polymeric mixtures. [16] Several literature reports focused on modifying the crystalline structure of PP by adding particles or through orientation.…”

Synthesis and Characterization of Novel Ion‐Conducting Membranes Based on Poly(ether sulfone) and Protic Ionic Liquid

“…The dynamics of the confined PIL in the polymer matrix was probed through the interpretation of the transversal relaxation time (T 2 H). The transverse relaxation time distributions, from ILT, represent different relaxation environments, or domains, of the protons present in PIL ions inside polymer matrix …”