Carbon-ion-induced modifications of the diffusion kinetics in poly (ethylene terephthalate):a free volume study

The free volume modifications in carbon-ion irradiated poly (ethylene terephthalate) (PET) have been investigated using positron lifetime method and sorption kinetics by the gravimetric method. The positron results indicate the formation of linear tracks and free radicals. Iodine sorption suggests Longmuir type of filling of the free volume sites by iodine in the initial stages of sorption, and in the later stages, swelling and conformational changes dominate. Using dual sorption model, diffusion- and relaxation-controlled sorption have been separated. Further, it has been found that the diffusion process deviates from Fick's law and hence from Fujita's free volume theory for both virgin and C-ion irradiated PET

Water sorption studies in a RGP contact lens polymer paraperm by positron lifetime technique

The kinetics of moisture uptake in a rigid gas permeable contact lens material Paraperm has been investigated. The free volume changes accompanied by the sorption of water have been monitored using Positron Lifetime Spectroscopy (PLS) technique. The positron results indicate the swelling in the initial stages of sorption which seems to be balanced by the rearrangement of chains in the presence of water molecules and filling of vacant free volume sites with water at the later stages of sorption. The sorption curve suggests that diffusion process in this polymer follows dual‐mode sorption model. Using this model we have been able to separate the Fickian controlled diffusion and relaxation controlled diffusion. Further, the positron results combined with sorption results indicate that Fujita's free volume theory seems to be not valid for the diffusion process in the present sample under study. The variation of permeability as a function of free volume suggests the amount of water in a contact lens is a measure of its permeability

A positron lifetime study of structural relaxation in UV irradiated poly (ethylene terephthalate)

Structural relaxation in UV irradiated poly (ethylene terephthalate) (PET-UV) has been investigated using positron lifetime techniques. Positron lifetime results show that the structural relaxation processes in PET-UV encompass three different time regimes, unlike the unirradiated poly (ethylene terephthalate) (PET) where only two relaxation times were observed. The relaxation functions constructed from the measured ortho positronium intensity, I3, exhibit non-exponential character that can be best fitted with two additive exponentials. To determine the extent of deviation from exponential relaxation, we have used the Narayanaswamy model (KWW function) and evaluated the stretching parameter β. From the relaxation times derived from the exponential decay curves, the activation energies have been calculated and from these activation energies it seems possible to label the different kinetic units of the UV irradiated poly (ethylene terephthalate) structure participating in the relaxation processes

A free volume microprobe study of water sorption in a contact lens polymer

The kinetics of moisture uptake in a rigid gas-permeable contact lens material, Fluoroperm60, has been investigated. The free volume changes accompanied by the sorption of water were monitored using the positron lifetime spectroscopy (PLS) technique. The positron results indicated swelling in the initial stages of sorption and the filling of vacant free volume sites with water in the later stages of sorption. The sorption curve suggests that the diffusion process in this polymer follows the dual-mode sorption model. Using this model, it was possible to separate Fickian-controlled diffusion and relaxation-controlled diffusion. Furthermore, the positron results combined with the sorption results indicated that Fujita's free volume theory does not seem to be valid for the diffusion process in the present sample under study. The variation of the permeability as a function of the free volume suggests that the amount of water in a contact lens is a measure of its permeability

Positron lifetime study of diffusion kinetics in electron irradiated polycarbonate

Positron lifetime and gravimetric measurements of iodine sorption and diffusion behaviour in electron-irradiated polycarbonate and un-irradiated polycarbonate are investigated. The increase in ortho-positronium lifetime on electron-irradiation shows that scission of carbonate groups in the main-chain and formation of free radicals is the predominant process. The UV absorption measurement supports this. The free volume in polycarbonate after electron-irradiation seems to be not composed of independent pores but of interconnected channels. The positron results on iodine diffusion in un-irradiated polycarbonate shows a slower diffusion rate, whereas in electron-irradiated polycarbonate faster diffusion is observed. The gravimetric measurement of iodine diffusion attains an early saturation in electron-irradiated polycarbonate as compared to un-irradiated polycarbonate although in both cases the diffusion is nearly Fickian. An exponential type of correlation has been observed between fractional free volume and diffusion coefficient validating Fujita's free volume theory for un-irradiated and electron-irradiated polycarbonate

Biosynthesized gold nanoparticles-doped hydroxyapatite as antibacterial and antioxidant nanocomposite

A composite of hydroxyapatite (HA) doped with green synthesized gold nanoparticles (Au NPs) was prepared. Au NPs were produced via the bioreduction of HAuCl _4 with Clitoria ternatea flower extract and utilized in HA synthesis, using Ca(OH) _2 and ammonium diphosphate as precursors. The aim of this research was to analyze the structure of the composite and conduct an antibacterial activity test involving Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae , and Streptococcus pyogenes . In addition, antioxidant activity was evaluated by 2,2-diphenyl-1-picrylhydrazyl radical scavenging. Au NP formation monitoring was conducted by UV–visible spectroscopy and particle size analysis, and the synthesized composite was studied using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results revealed homogeneously dispersed Au NPs (particle size ranging from 5 to 80 nm) in the HA structure. The nanocomposite demonstrated enhanced antibacterial activity against the tested bacteria compared to HA, with minimum inhibition concentrations of 3 μ g ml ^−1 for E.coli and S.aureus and 10 μ g ml ^−1 for K. pneumoniae and S. pyogenes . The nanocomposite expressed antioxidant activity, as shown by 2,2-diphenyl-1-picrylhydrazyl scavenging activities of 66% and 58% at concentrations of 100 μ g ml ^−1 and 50 μ g ml ^−1 , respectively