Time-Resolved Extensional Rheo-NMR Spectroscopy for Investigating Polymer Nanocomposites under Deformation

Abstract

Understanding the microstructure change of polymer nanocomposites (PNCs) under elongation deformation at the molecular level is the key to coupling structure−property relationships of PNCs. In this study, we developed our recently proposed in situ extensional rheology NMR device, Rheo-spin NMR, which can simultaneously obtain both the macroscopic stress−strain curves and the microscopic molecular information with the total sample weight of ∼6 mg. This enables us to conduct a detailed investigation of the evolution of the interfacial layer and polymer matrix in nonlinear elongational strain softening behaviors. A quantitative method is established for in situ analysis of (1) the fraction of the interfacial layer and (2) the network strand orientation distribution of the polymer matrix based on the molecular stress function model under active deformation. The results show that for the current highly filled silicone nanocomposite system, the influence of the interfacial layer fraction on mechanical property change during small amplitude deformation is quite minor, while the main role is reflected in rubber network strand reorientation. The Rheo-spin NMR device and the established analysis method are expected to facilitate the understanding of the reinforcement mechanism of PNC, which can be further applied to understand the deformation mechanism of other systems, i.e., glassy and semicrystalline polymers and the vascular tissues.

Elucidations of Structure and Molecular Dynamics of Complex Polymers by State-of-the-Art Solid-State NMR Spectroscopy

“…Under small-amplitude deformation, it was found that interfacial dynamics is invariant. However, orientation of the network chains was enhanced under deformation . The combination of in situ NMR measurement and mechanical tests indicates that the reduced chain orientation is responsible for stress softening during cyclic deformation, which further provides direct evidence for the nonlinear rheological properties at the molecular level.…”

“…However, orientation of the network chains was enhanced under deformation. 84 The combination of in situ NMR measurement and mechanical tests indicates that the reduced chain orientation is responsible for stress softening during cyclic deformation, which further provides direct evidence for the nonlinear rheological properties at the molecular level. It is anticipated that Rheo-NMR will further contribute to understanding the impacts of fillers on the mechanical property of polymer composite under active deformation, especially at a large-amplitude deformation region.…”

“…The in situ tensile experiments were conducted to investigate the chain orientation rearrangement in local constrained networks. Reproduced with permission from ref .…”

“…81,82 Very recently, Chen et al for the first time incorporated an in situ stretching module into a low-field NMR instrument and simultaneously obtained both macroscopic stress−strain curve and the microscopic structure and dynamics of polymer nanocomposite under active deformation, as shown in Figure 3. 83,84 The silicafilled silicone rubber ring was subjected to cyclic loading tests with a maximum stretching ratio of 1.6. The 1 H spin−spin relaxation time, T 2 , was used to in situ determine fractions of the interface and polymer matrix during stretching and the chain orientation under deformation.…”

“…The 1 H spin−spin relaxation time, T 2 , was used to in situ determine fractions of the interface and polymer matrix during stretching and the chain orientation under deformation. 84 Under small-amplitude deformation, it was found that interfacial dynamics is invariant. However, orientation of the network chains was enhanced under deformation.…”