Positron gamma ray spectroscopy coupled with an energy-tunable positron beam was utilized to the study of the microstructure in polyethylene (PE) modified by the radio-frequency (RF) plasma. The energy dependence of the line-shape S parameter, a measure of the Doppler broadening of the positron radiation, confirmed that the change in the hydrophilic state of the PE surface after plasma modification was due to the altered chemical structure in the near-surface region. Moreover, only a region at a depth shallower than 700 nm was influenced by the plasma modification. The recovery in the surface hydrophobicity after plasma modification was observed through contact angle measurements. The variation of the contact angle of water can be fitted by a two-factor decay model, suggesting that the surface recovery is caused by the diffusion of two different groups.

Pore interconnectivities of mesoporous silica prepared with precursor sols aged for various times were investigated by N 2 adsorption-desorption measurement and cyclic voltammetry. With increasing aging time of the precursor sol to 4 days, an abnormal decrease in both total open volumes and specific surface areas was found. However, with further increasing the aging time to 15 days, the total open volumes and specific surface areas dramatically increased, indicative of the formation of highly interconnected pores and a remarkable increase in the silica porosity. This was further confirmed by cyclic voltammetry measurements using aqueous potassium iodide solutions on the corresponding silica films, which showed a significant rise in redox current and total charge Q across the films prepared after a longer time aging of precursor sols. This rise can be attributed to the diffusion of I − across the silica films with enhanced pore interconnectivity, despite of the decline in total porosity for some silica samples.

Undoped and Sb doped tin oxide thin films were fabricated by the dip-coating technique through a propylene oxide assisted sol-gel method. Atomic force microscope measurements reveal that the grain size increased after being calcined at higher temperature; while increasing the dopant content leads to a reduction in grain size and a corresponding increase in the concentration of grain boundaries. Positron annihilation spectroscopy analysis shows the defects are reduced with increasing Sb content to 5 %; however, further increasing the doping level to 10 % introduces more defects to the films. At all doping levels, the defects in Sb doped tin oxide films decreases significantly upon elevating the calcination temperature.

The photodegradation progress of epoxy cured with polyamide and the effect of the curing agent content under UV-A irradiation have been investigated using positron annihilation spectroscopy with an energy tunable positron beam. After 88 h of irradiation, a post-cure process and the generation of carbonyl groups reduce the value of the S parameter, compared with the virgin samples. As the irradiation time increases from 208 h to 399 h, the S parameter decreases, which may be due to the growth of carbonyl groups and the generation of free radicals. After 543 h of irradiation, a dead layer with very low S value appears near the sample surface probably induced by a dramatic decrease in the Ps formation probability. The positron results also reveal that epoxy cured with an appropriate amount of polyamide has a smaller dead layer suggesting that the amount of curing agent is a key factor affecting the photodegradation of epoxy resin.

Variable-energy positron annihilation spectroscopy was applied to the investigation of nanopore formation in hydrocarbon-siliconoxide hybrid films fabricated through plasma enhanced chemical vapor deposition. Positron lifetime and Fourier transform infrared absorption measurements revealed that the pore size increases from 0.4 nm to 0.8 nm in radius with increasing annealing temperature, illustrating that the formed pores are in the micropore range. Based on a one-dimensional diffusion model, the ortho-positronium diffusion length was estimated from the variation of the positron 3γ decay probability for the films annealed with various temperatures as a function of positron incident energy. The result suggested that the pore interconnectivity during the pore formation by annealing depends on the gradual decomposition of the carbonaceous component.