title: Mechanical Behavior of Polymer Gels for RDCs and RCSAs Collection: NMR Imaging Study of Buckling Phenomena.
abstract: Anisotropic NMR parameters, such as residual dipolar couplings (RDCs), residual chemical shift anisotropies (RCSAs) and residual quadrupolar couplings (RQCs or ΔνQ), 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.
authors.affiliation: Department of Chemistry, Carnegie Mellon University, 4400 Fifth Ave., Pittsburgh, PA, 15213, USA.
authors.forename: Erich
authors.initials: E
authors.lastname: Hellemann
authors.affiliation: Departamento de Química Fundamental, Universidade Federal de Pernambuco, Cidade Universitária, CEP,50.740-540, Recife, PE, Brazil.
authors.forename: Rubens R
authors.initials: RR
authors.lastname: Teles
authors.affiliation: Departamento de Química Fundamental, Universidade Federal de Pernambuco, Cidade Universitária, CEP,50.740-540, Recife, PE, Brazil.
authors.forename: Fernando
authors.initials: F
authors.lastname: Hallwass
authors.affiliation: Departamento de Física, Universidade Federal de Pernambuco, Cidade Universitária, CEP,50.740-540, Recife, PE, Brazil.
authors.forename: W
authors.initials: W
authors.lastname: Barros
authors.affiliation: Departamento de Química Fundamental, Universidade Federal de Pernambuco, Cidade Universitária, CEP,50.740-540, Recife, PE, Brazil. armando.navarro@ufpe.br.
authors.forename: Armando
authors.identifier: http://orcid.org/0000-0003-4364-516X
authors.initials: A
authors.lastname: Navarro-Vázquez
authors.affiliation: Department of Chemistry, Carnegie Mellon University, 4400 Fifth Ave., Pittsburgh, PA, 15213, USA. rgil@andrew.cmu.edu.
authors.forename: Roberto R
authors.identifier: http://orcid.org/0000-0002-8810-5047
authors.initials: RR
authors.lastname: Gil
keywords: NMR spectroscopy; anisotropy; compression/relaxation method; gels