Dose distribution in polyethylene irradiated with A 10-MeV electron beam

Radiation modification of the gel content and the complex modulus of plastics was used to determine the depth-dose distribution in a solid polyethylene block irradiated with a 10 MeV electron beam, under typical radiation processing conditions. The results indicate that the accumulated charge has no significant effect on the shape of the dose profile. This suggests that, under certain circumstances, intrinsic “dosimeters” could be more appropriate than conventional thin film dosimeters placed inside the material for dose measurements in electrically non-conducting materials.     

3–45 MeV/u ion beam dosimetry using thin film dosimeters

Four kinds of film dosimeters well-characterized for low linear energy transfer (LET) radiations were applied to 3–45 MeV/u ions. The dose–responses relative to those for low LET radiations are almost one at a stopping power of about 10 MeV/(mg/cm²) and gradually become smaller with an increase in the stopping power. The overall uncertainty in ion beam dosimetry using these characterized dosimeters is better than ±5% (1σ) including uncertainty in fluence measurement (±2%). Lateral- and depth-dose profile measurements were made using one of the dosimeters (Gafchromic) with a spatial resolution of better than 1 and 10 μm, respectively.     

Development and characterization of a DNA solar dosimeter

In this paper, we report the development and characterization of a solar ultraviolet (UV) dosimetry system that can be used as a film badge for radiation monitoring. DNA molecules are coated on a thin nylon membrane as a UV dosimeter. The membrane is sealed in a polyethylene filter envelope with silica gel to keep the humidity low. After exposure to UV or solar light, induced DNA damage is measured by an immunochemical reaction. The intensity of color developed during the immunological reaction can be correlated linearly with the irradiated UV dose delivered by an Oriel solar simulator within a limited dose range. We observe no effects of temperature on the level of damage induction. The membrane is proficient for measuring DNA damage for more than 21 days when stored at either 37 or 4°C. The induced damage remains stable on the membrane for at least 22 days at both 37 and 4°C. In addition to these indoor experiments, we report measurements of solar UV dose in outdoor experiments.     

Dosimetric properties of commercial grade plexiglas as a possible routine dosimeter for radiation processing

Dyed and undyed polymethylmethacrylate (PMMA) are commercially available for high dose dosimetry in radiation processing applications. In order to investigate the properties of the locally available clear perspex as a subsitute routine dosimeter, we have looked into the optical and dosimetric properties of clear perspex sheets with a thickness of 2 mm.

The selected wavelength used for read out was 314 nm. Absorption spectra obtained showed a sharp cutoff at 260 nm wavelength. Post-irradiation studies at different doses indicate that the optical density decrease with storage time. No significant dose rate dependence in the range of 1.1 to 11 kGy/hr has been observed. The temperature response of the said clear perspex in the range of 0–30°C during irradiation has also been determined.

Comparison of the optical density versus dose for the local clear perspex against that of red perspex from Harwell, at an absorbed dose of 25 kGy, as obtained in our gamma irradiator, IR-136, showed a difference of 3%. The reproducibility of the local clear PMMA has been observed to be also less than 3% in an absorbed dose range of 5 to 50 kGy.     

PVDF亲水复合膜的制备及表征

聚偏氟乙烯(PVDF)膜材料存在强疏水性的缺陷,亲水化改性是解决该问题的主要途径。以PVDF为基膜材料、聚乙烯醇(PVA)为共混材料、N,N-二甲基乙酰胺(DMAc)为溶剂,采用相转化法制备PVDF/PVA复合膜。考察了复合膜的PVDF/PVA共混比、固含量、低分子化合物添加剂、聚合物添加剂等非溶剂添加剂对复合膜接触角的影响。结果表明,当PVDF/PVA共混比为7/3,固含量为13%时,制备的复合膜接触角为22.92°;当添加剂为无水氯化锂、纳米二氧化硅、聚乙烯吡咯烷酮(PVP)时,复合膜接触角分别从53.12°、30.51°和41.89°都降低到了0°,亲水性提高,其中纳米二氧化硅作为添加剂时复合膜亲水性最好;当添加剂为丙三醇、PMMA、PEG时,复合膜接触角都增大,亲水性变差。     

Investigation of surface and shape changes accompanying the membrane alteration responsible for the heat-induced lysis of human erythrocytes

Heat induces several successive events in erythrocyte membrane; the denaturation of spectrin at about 50°C, thermoporation at 62°C and denaturation of the anion channel at 67°C. The heat denaturation of major membrane proteins, spectrin and the anion channel, is not needed for the thermoporation which is involved in thermohemolysis. This study reports about the surface and shape changes which are specific for thermoporated membranes with spectrin and anion channel preserved intact. Thermoporation was produced exposing human erythrocytes to 39.5°C for 3 min in isotonic medium containing 18% (v/v) ethanol as membrane fluidizer and sucrose as osmotic protectant which prevents hemolysis (Ivanov, J. Therm. Biol. 1996). The control cells were processed similarly except that they were incubated at 23°C, thus avoiding thermoporation. In control and porated membranes the overall structure of spectrin and the anion channel was retained inasmuch as their enthalpies and denaturation temperatures were microcalorimetrically found preserved. Nevertheless, irregular shape, grainy surface and asymmetric spicules were apparent in porated cells through scanning electron microscopy. A decrease in the number of binding sites for Alcian blue and an increased binding of eosine was established in the membranes of porated cells. After poration the hexane/aqueous partition coefficient K_d of cells increased from 5 to about 220 and the electrophoretic mobility of cells decreased by about 25% indicating marked increase in cell surface hydrophobicity and a decrease in surface charge, respectively. In addition, adhesivity to hydrophobic interfaces and aggregability in low ionic media strongly increased after poration. In contrast to intact and control cells, the porated ones (all prefixed with 0.2% glutaraldehyde) made molecular contacts with inclined hydrophobic interfaces at low (5 mM NaCl) but not at high (150 mM NaCl) ionic media. Thus, the microtopological shape changes and exposure of new hydrophobic and charge groups over the outer cell surface, without major thermal unfolding, possibly indicates an irreversible redistribution of membrane material and disturbed lipid–protein complementation during thermoporation.     

The effect of light on the electrical conduction of pure and doped poly(methyl methacrylate)

Thin films of pure and doped poly(methyl methacrylate) (PMMA) with thicknesses ranging from 0·1 to 0·2 mm were prepared by the casting method. The effect of light on the electrical conduction of these films was studied using a specially designed electrical cell. The results showed that the resistivity of PMMA decreases gradually with increasing exposure time and the effect was found to be reversible. The doped samples showed more stability against the light effect. The current-voltage (I–V) characteristics indicated that the mechanism of conduction of PMMA depends on the presence of localized states or trapping levels arising from lack of order. Some physical parameters such as fermi energy, E_f, trap energy, E_t, density of charge carriers, n₀, ion mobility, μ, as well as the electrical conductivity of the test samples were calculated.     

Preparation,Characterization and Thermal Energy Storage Properties of Micro/Nano Encapsulated Phase Change Material with Acrylic-Based Polymer

The eutectic mixture of octacosane (C28)–heptadecane (C17) as core material was successfully encapsulated with an acrylic-based polymer (polymethylmethacrylate; PMMA) as shell material through emulsion polymerization. The polymeric reaction occurred around the core material was characterized by FTIR spectroscopy analysis. The polarized optical microscopy, scanning electron microscopy and particle size distribution investigations showed that the most of the prepared capsules had almost spherical shape with non-unimodal size distribution in micro-nano range. The differential scanning calorimetry analysis results exhibited that the capsules including highest amount of the eutectic PCM had a melting temperature of about 21°C and a latent heat capacity of about 98 J/g. The high thermal durability of the prepared capsules was confirmed by thermogravimetric analysis. The thermal cycling test designated that the synthesized capsules had good long-term usage latent heat thermal energy storage (LHTES) performance and chemical stability. Furthermore; the fabricated capsules with (1: 2) shell/core ratio had a reasonable thermal conductivity. It can be drawn a conclusion from all results that the prepared capsules especially PMMA/(C28–C17) (1: 2) product is a hopeful PCM that can be evaluated for low-temperature LHTES applications.     

Analysis of operation mode of reflective twisted nematic liquid crystal display devices with rear film compensation

The rear film compensated reflective twisted nematic liquid crystal display device was studied in normally black and normally white operation conditions using a dynamic parameter space method. The electro-optical responses and reflectance spectra were also studied for different operation modes. A comparison was made between rear film and front film compensated reflective twisted nematic liquid crystal displays. We show that high quality normally white or normally black modes can be obtained by placing the fast axis of a quarter wave plate at 45° or 0° to the input director direction. The viewing angle characteristics of the optimum modes were also studied.     

A population distribution model for the alignment of nematic liquid crystals

In polymer aligned liquid crystal cells, a surface layer exists. In this surface layer the in-plane distribution of the mesogens, the shape of the mesogens, and their average angle with the surface determine the pretilt angle in the bulk of the sample. A model to incorporate those effects has been proposed. This model gives quantitative agreement with a number of experiments for thick cells, where the optical effects of the surface layer can be neglected. By introducing a linear variation of the optical axis through the surface layer we get qualitative agreement between the model and the pretilt found in thin cells. The thickness of the surface layer is of the order 0·1-1·0 μm.     

Adsorption of bovine serum albumin at solid/aqueous interfaces

Adsorption of soluble serum proteins on hydrophilic and hydrophobic solid surfaces is important for biomaterials and chromatographic separations of proteins. The adsorption of bovine serum albumin (BSA) from aqueous solutions was studied with in situ ATR-IR spectroscopy, and with ex situ ATR-IR, ellipsometry, and water wettablity measurements. The results were used to quantitatively determine the adsorbed film thickness and surface density of BSA on hydrophilic silicon oxide/silicon surfaces, and on these surfaces covered with a hydrophobic lipid monolayer of dipalmitoylphosphatidylcholine (DPPC). The water contact angles were 5° for silicon oxide, 47° ± 1° for the DDPC monolayer, and 53° ± 1° for the BSA monolayers. At 25 °C, and with 0.01–1 wt% BSA in water, the surface densities range from Γ = 2.6–5.0 mg/m², and the film thicknesses range from d = 2.0–3.8 nm, on the assumption that the film is as dense as bulk protein. These results, and certain changes in the IR amide I and II bands of the protein, indicate that the protein adsorbs as a side-on monolayer, with some flattening due to unfolding or denaturation. The estimated -helical content for protein in buffer solutions is 15% higher than for solutions in water. The adsorption density reaches a steady-state value within 10 min for the lowest concentration, but does not appear to reach a steady-state value after 3 h f‘or the higher concentrations. Adsorption of BSA on a silicon oxide surface covered with a monolayer of DPPC leads to an adsorbed protein film of about half the thickness and surface density than on silicon oxide, but the same contact angle, indicating more protein unfolding on the hydrophobic than on the hydrophilic surface.     

Photoinduced liquid crystal alignment by layer-by-layer ultrathin films with dual photoreaction moieties

A novel layer-by-layer (LBL) film containing dual photoreaction groups, cinnamoyl and azobenzene, was prepared from poly(diallyldimethylammonium chloride) (PDDA) and a photosensitive polyanion, PCAzo, in aqueous solution via electrostatic attraction. The film was able to induce uniform alignment of liquid crystals (LCs) with good stability and 2.3° pretilt angle by oblique irradiation with linearly polarised ultraviolet light (LPUVL). UV absorption and FTIR spectroscopic results indicate that the photoreactions of the two photoreactive groups jointly participate in generating the anisotropy of the film. The dichroic ratio of the film was found to depend on the number of adsorbed layers. The thicker film has the larger dichroic ratio after the LPUVL irradiation. The reorientation behaviour of the LC molecules was found to be associated with the LBL film thickness. Experiment results revealed that the photo-crosslinking of the cinnamoyl groups was responsible for the stability of the anisotropic orientation, and the isomerisation of the azobenzene chromophores led primarily to the appropriate pretilt angle.     

Phenolic compounds and the colour of oranges subjected to a combination treatment of waxing and irradiation

The effects of waxing, irradiation dose and storage on phenolics and colour of irradiated oranges were investigated. Mature oranges (Maroc late) waxed or unwaxed were treated with 0, 1 or 2 kGy radiation and stored up to 9 weeks at 20°C and 40–50% r.h. Colour of the oranges, total phenols and flavones in the peel were measured. Phenolic compounds increased with irradiation dose and storage time. Hue angle, value and chroma of the orange colour were more affected by waxing and storage time than the irradiation treatment. Changes in the phenolic compounds were linked with changes in the redness and saturation of the orange colour. Irradiation stimulated synthesis of flavones; waxing controlled changes induced by irradiation.     

Analysis of the operation mode of reflective liquid crystal display devices with front film compensation

The front film compensated reflective liquid crystal display device was studied in normally black and normally white operation conditions using a dynamic parameter space method. The electro-optical response and reflectance spectra were also studied for different operation modes. We show that high quality normally white or normally black modes can be obtained by placing the fast axis of a quarter wave plate at 45° or 0° to the input director direction. The viewing angle characteristics of the optimum modes are wide and symmetrical.     

Polypyrrole/poly(methylmethacrylate) blend as selective sensor for acetone in lacquer

A film of α-naphthalene sulfonate-doped polypyrrole/poly(methylmethacrylate), PPy/α-NS⁻/PMMA, obtained from solution mixing was successfully used as sensing material for acetone vapor in lacquer with a high degree of selectivity based on electrical conductivity over acetic acid and a high degree of stability over the humidity change. Compared with pure PPy/α-NS⁻, the selectivity ratio of acetone/acetic acid response of PPy/α-NS⁻/PMMA blend with a PMMA/PPy weight ratio of 3.0 was ca. 3.9 times higher. The film was found to be insensitive to moisture unless the relative humidity (RH) was lower than 20% RH in which the selectivity ratio of acetone/acetic acid response was enhanced. The time required to reach the equilibrium for acetone exposure was found to increase slightly with increasing humidity.     

Nanohole structure prepared by a polystyrene-block-poly(methyl methacrylate)/poly(methyl methacrylate) mixture film

Cylindrical nanoporous structures were prepared by using a mixture film of polystyrene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) and PMMA homopolymer (hPMMA), and they were analyzed by transmission electron microtomography (TEMT), X-ray reflectivity (XR), and grazing incidence small-angle X-ray scattering. For this purpose, the mixture film was spin-coated onto a silicon wafer modified by a neutral brush for PS and PMMA blocks, which generates PMMA cylindrical microdomains oriented normal to the substrate. Two methods were employed to prepare nanoporous structures: (1) all of the PMMA phase (PMMA block and PMMA homopolymer) in the film was removed by UV irradiation, followed by rinsing with a selective solvent (acetic acid) to PMMA and (2) only PMMA homopolymer was removed by selective solvent etching without UV irradiation. We found via TEMT and XR that the nanoporous structure in the film prepared by UV irradiation exhibited almost perfect cylindrical shape throughout the entire film thickness. However, when the film was rinsed with a selective solvent, nanoporous structures were not straight cylinders but had a funnel shape in which the diameter of nanopores located near the top of the film was larger than that located near the bottom of the film.     

Optical activity of chiral thin film and liquid crystal hybrids

Using the glancing angle deposition (GLAD) technique, we have fabricated porous, chiral thin films with optically anisotropic helical microstructures that exhibit optical phenomena such as wavelength specific rotation of linearly polarized light. Initial research has shown that the porosity of the films allows for the addition of nematic liquid crystals (NLCs) to the films for promising applications in dynamically switchable devices, while simultaneously enhancing the optical properties of the film. This study describes the fundamental optical behaviour of LC-filled chiral thin films in relation to material, porosity, structure and thickness. It was found that for SiO₂ films, the addition of NLCs increased the effective rotatory power by two-fold when compared with results from the film without added LCs. The rotatory power of Al₂O₃ and MgF₂ films, while being similarly increased by the addition of LCs, exhibited a reversal in sign, or direction of rotation, for the visible wavelength spectrum investigated. The effects of film porosity and structure were studied by varying the angle of incidence from 83° to 86°; it was found that the greater porosity of the films deposited at larger angles allowed for more filling by the LCs and thus a larger increase in rotatory power. Finally, the addition of LCs was observed to shift the wavelength of peak rotation towards smaller values.     

Effects of temperature and humidity during irradiation on the response of radiachromic film dosimeters

The effects of temperature and humidity during γ irradiation on the response of two types of film dosimeters (Far Wesr radiachromic and GafChromic films) were studied in the dose range of 0.3–3 kGy. Both films show a significant effect of temperature and humidity and a simple correction function is proposed. This correction is usually between 5 and 10% for the range studied.

For the GafChromic film, a colour change at temperatures above 50°C was observed and, consequently, this system cannot be used at these temperatures. At lower temperatures down to - 70°C the sensitivity of both films is reduced and a simple correction is possible. In this study and for the dose ranges used, only a slight dependence on humidity was observed for both films from 0 to 60% r.h. Whereas the GafChromic film at humidities up to 90% r.h. shows only a moderate effect, the Far West films shows a considerable inconsistency for the dose range studied. A simple correction function may be applied for humidity effects, except for the Far West film above 60% r.h. where the effect of humidity is also dose dependent.     

Optical and electrical analysis of blue polymethyl methacrylate for high-dose dosimetry

The response to gamma radiation of polymethyl methacrylate (“blue PMMA”) containing a blue dye was investigated, with the aim of providing a high-dose dosimeter based on either spectrophotometry or electrical-conductivity measurements. It is found that the 3-mm thick pieces of blue PMMA can be used for dosimetry in a range of absorbed doses from about 5-50 kGy, for which the changes in optical transmission density (absorbance) at different wavelengths in the visible region (402, 596, 612, and 643 nm) are linear functions of dose. Results also show that irradiation of thin 0.1 mm films of blue PMMA produces two components of radiation-induced conductivity: a transient component which can be used to determine the absorbed dose rate and a steady-state component which registers the total absorbed dose in the range 20–80 kGy as based on a suitable calibration. The effects of post-irradiation storage time, day light, and storage temperature on the radiation-induced visible spectrum were investigated. The storage-temperature effect on post-irradiation conductivity measurement was also evaluated.