Effect of Buffer on the Optical Properties of Irradiated Hydroxyethyl Methacrylate Copolymer
- PDF / 1,445,803 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 107 Downloads / 192 Views
C.C. Han Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
Sanboh Lee Department of Materials Science, National Tsing Hua University, Hsinchu, Taiwan 30043, Republic of China (Received 10 July 2001; accepted 1 March 2002)
The effect of buffer and ␥ irradiation on the optical properties of hydroxyethyl methacrylate (HEMA) copolymer was investigated. The transmission of HEMA copolymer decreased with the increase of irradiation dose and/or pH value of the buffer. The cutoff wavelength of HEMA copolymer exhibits a bathochromic shift as the ␥-ray dose and/or pH value of buffer increases. The influence of atmosphere during ␥-ray irradiation on the optical properties of HEMA copolymer was investigated. The change of optical properties of HEMA copolymer irradiated in air was more pronounced than that irradiated in vacuum. Light was scattered by holes in the polymer. The relationship between scattering intensity (Is) and incident wavelength () can be described by the formula Is ⬀ −n. The span of holes increases with the irradiation dose regardless of radiation atmosphere and pH value in the range of 4.1–6.5. A boundary between the inner and outer layers of HEMA copolymer irradiated in air was observed, separating two differential morphologies of holes.
I. INTRODUCTION
When polymeric materials are irradiated by ␥-rays, their chemical structure is changed. A series of reactions results in crosslinking or scission of polymer chains and the creation of color centers, e.g., free radicals and conjugated structures.1 The color centers adsorb the light of certain wavelengths. The atmosphere of irradiation affects the type and number of color centers. Harmon et al. showed that the presence of O2 during irradiation raises the concentration of color centers.2 According to Wallace et al., the color centers are classified as two types: one type is a color center that can be eliminated by annealing, and the other is a color center that persists upon annealing.3 Clough et al. found the annihilation rate of color centers depends on the atmsophere of annealing.4 Swelling induced by solvent enlarges holes in the polymer, and the holes scatter light. The crosslinking and scission of polymer chains are also related to the atmosphere of irradiation. Sometimes oxygen reacts with free radicals and produces peroxides or hydroperoxides, so that the crosslinking induced by recombination of free J. Mater. Res., Vol. 17, No. 5, May 2002
http://journals.cambridge.org
Downloaded: 18 Mar 2015
radicals is reduced.5,6 On the other hand, oxygen can promote the degradation of chains for some linear polymers.6–8 The crosslinking induced by irradiation and ionizing reactions19 changes the equilibrium swelling ratio and therefore the optical properties of polymer are influenced. According to Rayleigh, the scattering intensity of particles is dependent on the wavelength of incident light.10 For surface scattering, the scattering intensity is proportional to −4, where is the wavelength of incident light. I
Data Loading...
