Positron Annihilation Spectroscopy of Polystyrene Filled with Carbon Nanomaterials

Abstract

Positron annihilation lifetime spectroscopy (PALS) was employed to study the free volume properties of polystyrene (PS) containing three different types of carbon nanoparticles: polystyrenegrafted single wall carbon nanotubes (SWCNTs-g-PS), single wall carbon nanotubes (SWCNTs), and carbon nanofibers (CNFs). The glass transition temperature measured via PALS was significantly lower than that from differential scanning calorimetry (DSC), although qualitatively the two methods agreed in that the T g measured increased as nanotubes were added to the material. There were some specific differences between the two measurements which may have been related to the fact that DSC does not measure T g of a portion of the material which is immobilized on the surface of the particle, while PALS measures all polymer, whether immobilized or not. PALS was also used to measure the thermal expansion coefficient and distributions of the free volume of the polystyrene.

Gas permeation parameters of mixed matrix membranes based on the polymer of intrinsic microporosity PIM-1 and the zeolitic imidazolate framework ZIF-8

“…There are examples of independence of lifetimes on the content of nano-additives (the systems PS/CNT [97] and PMMA/TiO 2 [98]) and even reduction of lifetimes with the loading of nano-particles [99]. In interpreting such results one should take into account that diffusivity and permeability depend not only on the size of FVEs but also on the connectivity of free volume.…”

Characterization, optical, and nanoscale free volume properties of Na‐CMC/PAM/CNT nanocomposites

“…The data of τ 3 was fitted into two straight lines intersecting at the onset temperature known to be the glass transition temperature of our blend. As shown, τ 3 data does not show any hysteresis, which indicates the absence of physical or chemical aging of the blend, at the used temperature range during a period of 2 months of PALS experiments. Therefore, the increase in τ 3 or V h is assigned the thermal expansion of free volume.…”

Light-cured dimethacrylate dental restorative composites under a prism of annihilating positrons

“…[14][15][16][17][18][19][20][21] Under such analysis (arranged as constraint-free decomposition [14][15][16][17][18][19][20] or partially-constrained decomposition fixing the shortest τ 1 lifetime 14,15,21 ), the 3 rd component with a long-lived lifetime τ 3 is ascribed to o-Ps annihilation in free-volume holes (voids), the 2 nd component with an intermediate lifetime τ 2 is due to free positron annihilation in interfacial free volumes or other defect states mainly in a solid phase, and the 1 st component with the shortest lifetime τ 1 is attributed to p-Ps self-annihilation conjugated with reduced e + annihilation from defect-free bulk state. [4][5][6] The lifetime-fixing fitting is preferred to overcome inadequacy in the resolving of the shortest component due to mixing different annihilation events (especially, when I 1 intensity occurs to be substantially greater than I 3 ).…”

“…In case of stronger input from Ps decaying in the x3-term decomposed PAL spectrum (as for many nanocomposites 5,9,[14][15][16][17][18][19][20][21] ), the e + -trapping can be defined in terms of a simple trapping model assuming 2 additive inputs arise from trapped e + and decayed o-Ps states. 22 This model with 2 additive e + -trapping defects with κ d1 and κ d2 annihilation rates defined as …”

“…[24][25][26] Within a x4-fitting route assuming fixed τ 1 value, the 4 th component was ascribed to o-Ps annihilation in the main part of the polymer matrix, while the 3 rd was explained as arising from o-Ps annihilation in the filler-matrix interphase. With re- [16][17][18][19] Recently, some current authors have shown that x4-fitting assuming fixed shortest lifetime (τ 1 = 0.125 ns) was also favorable for dimethacrylate DRC subjected to long-term aging, which were initially characterized by x3-decomposed best-fitted PAL spectra. 20,27 The origin of the additional component in o-Ps decaying in these polymer/filler DRC was not clarified unambiguously, while a version on stress-inducing destruction through growing inner and surface cracks seems quite plausible.…”