Mechanical Behavior of Polymer Gels for RDCs and RCSAs Collection: NMR Imaging Study of Buckling Phenomena

Erich Hellemann; Rubens R Teles; Fernando Hallwass; W Barros Jr; Armando Navarro-Vázquez; Roberto R Gil

doi:10.1002/chem.201603333

Mechanical Behavior of Polymer Gels for RDCs and RCSAs Collection: NMR Imaging Study of Buckling Phenomena

Chemistry. 2016 Nov 7;22(46):16632-16635. doi: 10.1002/chem.201603333. Epub 2016 Oct 14.

Authors

Erich Hellemann¹, Rubens R Teles², Fernando Hallwass², W Barros Jr³, Armando Navarro-Vázquez⁴, Roberto R Gil⁵

Affiliations

¹ Department of Chemistry, Carnegie Mellon University, 4400 Fifth Ave., Pittsburgh, PA, 15213, USA.
² Departamento de Química Fundamental, Universidade Federal de Pernambuco, Cidade Universitária, CEP,50.740-540, Recife, PE, Brazil.
³ Departamento de Física, Universidade Federal de Pernambuco, Cidade Universitária, CEP,50.740-540, Recife, PE, Brazil.
⁴ Departamento de Química Fundamental, Universidade Federal de Pernambuco, Cidade Universitária, CEP,50.740-540, Recife, PE, Brazil. armando.navarro@ufpe.br.
⁵ Department of Chemistry, Carnegie Mellon University, 4400 Fifth Ave., Pittsburgh, PA, 15213, USA. rgil@andrew.cmu.edu.

PMID: 27739109
DOI: 10.1002/chem.201603333

Abstract

Anisotropic NMR parameters, such as residual dipolar couplings (RDCs), residual chemical shift anisotropies (RCSAs) and residual quadrupolar couplings (RQCs or Δν_Q ), appear in solution-state NMR when the molecules under study are subjected to a degree of order. The tunable alignment by reversible compression/relaxation of gels (PMMA and p-HEMA) is an easy, user-friendly, and very affordable method to measure them. When using this method, a fraction of isotropic NMR signals is observed in the NMR spectra, even at a maximum degree of compression. To explain the origin of these isotropic signals we decided to investigate their physical location inside the NMR tube using deuterium 1D imaging and MRI micro-imaging experiments. It was observed that after a certain degree of compression the gels start to buckle and they generate pockets of isotropic solvent, which are never eliminated. The amount of buckling depends on the amount of cross-linker and the length of the gel.

Keywords: NMR spectroscopy; anisotropy; compression/relaxation method; gels.