Revealing the Nano‐Level Molecular Packing in Chitosan–NiO Nanocomposite by Using Positron Annihilation Spectroscopy and Small‐Angle X‐ray Scattering

Abstract

Chitosan-NiO nanocomposite (CNC) is shown to be a potential dielectric material with promising properties. CNCs containing NiO nanoparticles (0.2, 0.6, 1, 2, 5 wt %) are prepared through chemical methods. The inclusion of NiO nanoparticles in the chitosan matrix is confirmed by scanning electron microscopy (SEM) and X-ray diffraction. The morphology of the NiO nanoparticles and the nanocomposites is investigated by transmission electron microscopy and SEM, respectively. Positron annihilation lifetime spectroscopy (PALS) and the coincidence Doppler broadening (CDB) technique are used to quantify the free volume and molecular packing in the nanocomposites. The triplet-state positronium lifetime and the corresponding intensity show the changes in nanohole size, density, and size distribution as a function of NiO loading. Small-angle X-ray scattering indicates that the NiO aggregates are identical in all the CNCs. The momentum density distribution obtained from CDB measurements excludes the possibility of a contribution of vacant spaces (pores) available in NiO aggregates to the free volume of nanocomposites upon determination by using PALS. The results show systematic variation in free-volume properties and nano-level molecular packing as a function of NiO loading, which is presumed to play a vital role in determining the various properties of the nanocomposites.

Chemical Information of Chitosan-Based Complex Extracted from Coincidence Doppler Broadening Spectra

“…However, the reverse on the dropping trend is observed, implying that such a variation is mainly caused by the change of chemical environment for positron annihiltion. A similar type of change in the CDB ratio curve on incorporation of NiO as dopant in chitosan has also been reported [12]. This clearly indicates that most probable free positron annihilation site in CS-Fe 3 O 4 is the bulk of chitosan matrix or it is the interphase region where free positrons mostly annihilate with H and C atoms having high contribution in the lower momentum region, and the decrease in the area under the ratio curves is the result of the reduction in contribution from N and O element in polar -NH 2 and -OH groups of chitosan molecules.…”

“…The data were analyzed in the form of ratio curve; each CDB spectrum was normalized to unit area and then re-normalized to the numeral data obtained for the reference sample to get the ratio curve. • are observed [12]. On incorporation of Fe 3 O 4 , these peaks become broader indicating the disruption in the original structure of pure CS due to a reduction in intermolecular hydrogen bonding.…”

Free volume and lamellar structure of poly vinyl alcohol-nanosized BaTiO3 composite: Positron annihilation and small angle X-ray scattering study

“…PALS has been shown to be an efficient technique for the investigation of the changes in free volume structure of polymer matrix through annihilation parameters of o-Ps probe [14,15,[19][20][21]26,27]. In order to elucidate the changes in the free volume structure of PVA matrix, the PALS spectra were analysed using a computer program PALSFIT [28].…”

“…In last few years, we have used positron annihilation lifetime spectroscopy (PALS) for the characterization of molecular packing (free volume structure) of polymer nanocomposites [14,15,[19][20][21]. It has been shown through these studies that like pure polymers, the molecular packing of amorphous phase of a semicrystalline polymer in its nanocomposites can be efficiently characterized through the ortho-positronium probe.…”

Molecular packing of polyvinyl alcohol in PVA‐gold nanoparticles composites and its role on thermo‐mechanical properties

“…To invoke the structure‐property relationship in polymer nanocomposites, conventional techniques like X‐ray diffraction (XRD), Fourier transform infra‐red (FTIR), dynamical mechanical analysis, and electron microscopy techniques are used to infer changes in the polymer structure. Recently, we have used triplet state of positronium i.e., ortho ‐positronium ( o ‐Ps) as probe through positron annihilation lifetime spectroscopy (PALS) technique to investigate the molecular packing of polymer matrix in polymer nanocomposites . PALS is an established technique to measure the free volume hole size, density, and their size distribution in polymers.…”