Effect of annealing temperature on interrelation between the microstructural evolution and plastic deformation in polymers

Abstract

The mechanical loading induced flow of glassy polymers is triggered by the nucleation of shear transformation units, and strongly depends on the initial microstructural state of the material. Therefore, investigation of the possible relationship between the microstructural state variables and plastic deformation is required for a better understanding of the macroscopic response of this class of materials during large deformation. In this study, free volume content is considered as a state variable and thermal treatment is selected as a process through which the accelerated and forced evolution of the free volume can be imposed. For two well-known glassy polymers, poly(methyl methacrylate) and polycarbonate, the free volume content alteration upon annealing is monitored via positron annihilation spectroscopy, and the changes of the micro-and macromechanical properties are also obtained by utilizing nanoindentation technique and employing the homogeneous amorphous flow theory. The correlation between the microstructural state variable, that is, free volume, and the micromechanical state variable, that is, shear activation volume, is then investigated. The results reveal opposite direction of alterations of free volume and shear activation volume with annealing temperature. Accordingly, the possibility of the existence of an interrelation between these two state variables is critically discussed.

Nano-Indentation Response of Ultrahigh Molecular Weight Polyethylene (UHMWPE): A Detailed Analysis

“…The rate dependency of hardness is realistic for polymers (i.e., visco-elastic-plastic materials) due to the direct relation between the hardness and the yield stress of the material. Conversely, the modulus is mainly linked with the Van der Waals interactions, which are not dependent on the strain or loading rate [37][38][39]. All the results presented above confirmed the existence of an indentation size effect in the investigated polymeric sample, as has also been reported in the literature for other polymeric materials [40,41].…”

“…The rate dependency of hardness is realistic for polymers (i.e., visco-elastic-plastic materials) due to the direct relation between the hardness and the yield stress of the material. Conversely, the modulus is mainly linked with the Van der Waals interactions, which are not dependent on the strain or loading rate [37][38][39]. The nano-mechanical properties, including hardness and modulus, can also be measured for each strain rate and are depicted in Figures 11 and 12 as a function of indentation displacement.…”

Aligned P(VDF-TrFE) Nanofibers for Enhanced Piezoelectric Directional Strain Sensing

“…The highest piezoelectric charge constant of P(VDF-TrFE) nanofibers reported in previous studies was 35.5 pm/V, which were fabricated by the electrospinning process and followed by annealing at 135 °C [ 33 ]. The annealing process is a crucial processing factor to improve the crystallinity and the performances of polymers for sensing applications [ 34 , 35 , 36 , 37 , 38 ]. The piezoelectricity of P(VDF-TrFE) is determined not only by the crystallinity and fraction of the β-phase, but also the orientations of the dipoles in the β-phase.…”

Small molecule self‐assembly in polymer matrices

“…Annealing at temperatures in the vicinity of the T g is one of the means to assess the accelerated aging. For example, in a recent publication, Malekmotiei et al used annealing below and above the T g of PMMA and polycarbonate for this purpose, to measure the free volume changes and the effect on the plastic deformation of these polymers. To simulate an accelerated aging test, Tuteja et al annealed the solvent cast films at 120–140 °C, the temperatures just below the original T g of the BPAPC.…”

“…With TTA, which is a smaller molecule, the T g would reduce even more, from 150 to 41 °C. To simulate accelerated aging, when these films are annealed at a temperature close to the original T g of the polycarbonate, the charge transport molecule would diffuse to the surface of the film and crystallize leading to a recovery of the T g of the polymer. Figure shows the optical micrographs of the crystals of phase separated TPD from the polycarbonate matrix upon annealing the film at various temperatures for 1 and 2 h. The extent of phase separation and crystallization would depend on the temperature of annealing and the type of small molecule.…”