Ionic conductivity enhancement of PVA: carboxymethyl cellulose poly-blend electrolyte films through the doping of NaI salt

Cellulose - In this paper, we report the effect of doping sodium iodide (NaI) salt into a polymer blend matrix of sodium carboxymethyl cellulose (NaCMC) and poly(vinyl alcohol) (PVA). Solution...     

Numerical investigation of the effects of sluice spillway roof profiles on the hydraulic characteristics

There is a need for evolving hydraulically efficient roof profile of bellmouth for high head sluice spillways, as sluice roof is susceptible to cavitation damage. In this paper, formulation and development of a numerical model for simulating the spillway flow and its application to a sluice spillway are presented. The main focus of the simulation study is to apply the developed model to investigate the effects of sluice roof profile geometry on the pressure distribution, the discharge coefficient and the nature of flow regime within the sluice bellmouth. From the analysis of results for eight different roof profiles by varying the entry and exit angles of elliptic bellmouth transition, some important observations have been suggested, which are of practical relevance to hydraulic design engineers. The numerical model results are compared for one profile with physical model study. The simulated results are in close agreement with the measured values. Copyright © 2007 John Wiley & Sons, Ltd.     

Electron irradiation induced microstructural modifications in BaCl2 doped PVA: A positron annihilation study

Thin films of pure and 10 wt% BaCl₂ doped poly(vinyl alcohol) (PVA) were prepared by solution casting method. These films were subjected to electron irradiation for different doses ranging from 0 to 400 kGy in air at room temperature. The effect of electron irradiation on the optical and free volume related microstructures of these polymer films was studied using positron annihilation lifetime spectroscopy, FTIR and UV-vis techniques. The FTIR spectral studies indicate that the electron irradiation induces chemical modifications within the doped PVA, which results in chain scission as well as cross-linking of the polymer. The positron lifetime study on these irradiated polymers shows that the chain scissions and cross-linking within the polymer matrix affect the free volume content and hence the microstructure. The UV-vis optical absorption studies show that the induced microstructural change by electron irradiation also modifies the optical properties. Using UV-vis spectra, the optical energy band gap was estimated and it decreases with increase in electron dose. A correlation between positron results and optical results is obtained and electron irradiation induced microstructure modifications within the doped polymer are understood. The results highlight the usefulness of positron annihilation technique in the study of the microstructure of irradiated polymers.     

Effect of barium chloride doping on PVA microstructure: positron annihilation study

Microstructural studies on BaCl₂ doped polyvinyl alcohol (PVA) polymer films were carried out using density, PAL and dielectric measurements at room temperature. The positron annihilation studies on these samples shows considerable effect on the PVA microstructure due to doping and is understood by invoking the chemical reaction between Ba²⁺ ions of BaCl₂ with OH groups of PVA via intra/inter molecular hydrogen bonding, which forms the complex. This complex formation modifies the free volume content in the amorphous fraction, and results in an enhancement of the polymer crystallinity. At higher dopant concentrations, the number of such complexes increases, and ends up with the formation of dopant aggregates or agglomerates leading to certain phase separation into a polymer-rich phase and a dopant-rich phase. These phase separations are thought to be due to the existence of two or more crystalline phases within the polymer matrix. The XRD study also supports this enhancement of PVA crystallinity due to doping. The electrical studies on the doped PVA reflects that the complex formation due to doping affects the microstructure and hence the dielectric properties including the dc and ac conductivities of the polymer. All of these observed results were analyzed and understood based on the microstructural modification of PVA as a function of dopant concentrations. PACS 78.70.Bj; 73.61.Ph; 77.84.Jd     

Optical and microstructural studies on electron irradiated PMMA: A positron annihilation study

The effect of electron irradiation on the free volume related microstructural and optical properties of Poly(methyl methacrylate) have been studied using Positron Annihilation and other techniques. The FTIR spectral study on the irradiated films suggests the existence of CC group and is understood by invoking the carbonaceous clusters as a consequence of chain scission in PMMA. Using UV-Visible absorption spectra the optical parameters like optical energy bandgap and activation energy were determined and the variation of these parameters suggests the existence of defects within the irradiated sample. Following Robertson’s theory, the carbonaceous cluster size is estimated and it increases with increase in electron dose. The XRD study indicates the enhancement of amorphous nature of the film due to chain scission by irradiation. The Positron annihilation result shows that electron irradiation affects the free volume related microstructure and the carbonaceous clusters may act as positron scattering centers.