Irradiated PMMA Research Articles

Heterogeneous Models for UV Induced Precursor-Mediated Growth of CdS Nanoparticles in PMMA Films: Fitting Experimental Curves and Core-Shell Growth.

Experimental data on the absorbance evolution of an UV irradiated PMMA film containing the TEDBCd CdS precursor published earlier are fitted by the authors' recently published model of precursor-mediated heterogeneous nucleation and growth of nanoparticles in polymer films. Two types of nucleation centers are considered. The centers of the first type are nanoparticles initially existing in the material. The centers of the second type belong to polymer chains. The study shows that the experimental data indicate a wide size distribution of the obtained CdS nanoparticles. For the estimated parameter values, the problem of core-shell nanoparticle growth where the nucleation centers of the first type are nanoparticles of a different nature is considered.

Effects of unmagnetized and magnetically confined laser induced copper plasma ions on the surface, optical, wetting, electrical and mechanical properties of PMMA

Effects of unmagnetized and Magnetically Confined Laser-Induced Cu plasma Ions (MCLICPI) on surface, optical, wetting, electrical and mechanical properties of PMMA have been explored by SEM, UV–visible spectroscopy, contact angle measurements, four probe method and hardness tester respectively. The enhancement in maximum fluence from 3.7 × 1016 to 3. 8 × 1017 ions/cm2 and energy from 5.1 keV to 6.7 keV of MCLICPI are attributed to magnetic confinement and Joule’s heating effect. SEM analysis reveals the formation of beaded structures, pits, dendrites and flakes on PMMA. Growth of CuO and Cu2O phases and variations in hydrophilicity of PMMA are observed after ion irradiation. Significant increase in electrical conductivity and hardness of MCLICPI irradiated PMMA is observed. The ions range, electronic and nuclear stopping are 122 Å, 2.7 eV/Å, 57.5 eV/Å for unmagnetized and 146 Å, 3.1 eV/Å, 61.7 eV/Å for MCLICPI respectively.

One-step 3D microstructuring of PMMA using MeV light ions

The conventional procedure for creating 3D microstructures in resists by ion beam lithography consists of two stages – exposure and developing. However, single stage of manufacturing 3D structures in resist is also possible. Irradiation of PMMA can cause it to shrink. This feature of the polymer can be used for one-step three-dimensional microstructuring, which simplifies the manufacturing process. The shrinkage of PMMA film on a substrate has been extensively studied, while research on free-standing film is not comprehensive. The use of free-standing PMMA film allows the creation of a flexible material with 3D microstructures, which can be used in medicine, optics, and electronics. The question here is whether the results obtained for the PMMA film on the substrate are applicable to the freestanding film. Since the nature of shrinking is outgassing of volatile products, the film on the substrate has only one surface for the release of gases, while in the free-standing film, gases can be released from the sample from both sides. Therefore, the shrinking in the free-standing film occurs on both sides. The aim of this work is to study the shrinkage of the free-standing film and compare it with that of the film of the same thickness coated on the substrate.

Hardness and tribological properties of laser irradiated PMMA based nano-microcomposites

In this work, new composite material is manufactured from poly(methyl methacrylate) PMMA matrix reinforced by glass fibre type E-glass. The effect of volume fraction of fibre and length to diameter ratio is studied, and friction and wear characteristics were determined at different volume fractions and fibre sizes. The hardness and wear resistance of randomly distributed PMMA matrix composite were significantly enhanced, and the maximum conditions for reinforcement of PMMA matrix composite to improve tribology characteristics were evaluated. The effect of laser irradiation on the mechanical properties was evaluated by irradiation of composite material after manufacturing, with different kinds of lasers. The continuous wave (CW) argon-ion laser and pulsed Nd:YAG laser were used to irradiate composite material. Hardness, wear rate, and coefficient of friction were evaluated at the same test condition of the unirradiated composite. The significant improvement in improvement in the mechanical properties at certain irradiation conditions was evaluated. Keywords: structure, hardness, wear, PMMA, random distribution.

Improving photoluminescence, optical and electrical characteristics of PMMA films with gamma irradiation

Polymeric materials are macromolecules, essentially a combination of numerous repeated subunits. Polymers are innovative and advanced materials that currently have a strong impact on our daily lives. In recent years, polymer use has been prominent due to the materials’ distinctive properties; thus, they entered different fields of science, technology and industrial-biomedical applications.The improvement of photoluminescence, optical and electrical characteristics of non-conducting Poly(methyl methacrylate) (PMMA) films was studied. Upon gamma irradiation of various doses, the photophysical and electrical properties of PMMA films were investigated using photoluminescence spectroscopy, ultraviolet–visible (UV–vis) spectroscopy and the LCR Meter Bridge Circuit technique. The fluorescent response improved the photoluminescence (PL) spectral emission peaks according to gamma values. Strong fluorescence peaks appeared with the highest gamma dose. The UV–Vis results revealed a significant red-shift in the absorption edge as gamma doses increased. This shift exhibits a continuous decrease in the energy band gap values (from 3.50 to 2.60 eV for direct transition and from 3.05 to 1.55 eV for indirect transition). This was due to the formation of carbon clusters, which led to an increase in the electrical conductivity and improved the dielectric parameters of the irradiated PMMA films. Among a variety of measurements presented and discussed in the present study, the electrical measurements showed improved electrical characteristics of gamma-irradiated PMMA films.

Range verification of radioactive ion beams of 11C and 15O using in-beam PET imaging

In advanced ion therapy, the visualization of the range of incident ions in a patient’s body is important for exploiting the advantages of this type of therapy. It is ideal to use radioactive ion beams for in-beam positron emission tomography (PET) imaging in particle therapy due to the high quality of PET images caused by the high signal-to-noise ratio. We have shown the feasibility of this idea through an in-beam PET study for 11C and 15O ion beams using the dedicated OpenPET system. In this work, we investigate the potential difference between the Bragg peak position and the position of the maximum detected positron-emitting fragments by a PET system for the radioactive beams of 11C and 15O. For this purpose, we measured the depth dose in a water phantom and performed PET scans of an irradiated PMMA phantom for the available beams of 11C and 15O at the Heavy Ion Medical Accelerator in Chiba (HIMAC). Then, we simulated the depth dose profiles in the water phantom and the yield of the positron-emitting fragments in a PMMA phantom for both available beams using the Monte Carlo code PHITS. The positions of the Bragg peak and maximum positron-emitting fragments from the measurements were well reproduced by simulation. The effect of beam energy broadening on the positional differences between two peaks was studied by simulating an irradiated PMMA phantom. The differences in position between the Bragg peak and the maximum positron-emitting fragments increased when the beam energy spread was broadened, although the differences were zero for the ideal mono-energetic beams. Greater differences were observed for 11C ion beams compared to 15O ion beams, although both beams had the same range in water, and the higher energy corresponded to a larger difference. For the known energy spread of the beams, the predicted differences between two peaks from the simulation were consistent with the measured data within submillimetre agreement.

Effect of neutron irradiation on the optical properties of PMMA/RhB used in optical fiber amplification

The structural and optical properties of the neutron irradiated PMMA doped by 5 wt% RhB have been investigated. Fourier transform infrared analysis showed a significant variation in the polymer’s main chain. Moreover, the linear and nonlinear optical properties of the doped samples, both pre and post irradiation were studied. The results showed that the refractive indices and energy gaps of the examined samples were increased at a neutron dose of 1.5 kGy by about 8% and 7%, respectively. The results gave a good indication in predicting the gain degradation of the polymer optical amplifier when exposed to a low dose irradiation.

Physicochemical and Structural Characterization of Surface Modified Electrospun PMMA Nanofibre

Although electrospun poly(methyl methacrylate) (PMMA) may mimic structural features of extracellular matrix, its highly hydrophobic nature causes reduced cell attachment. This study analysed the physicochemical and structural changes of the surface modified PMMA nanofiber. The electrospun PMMA nanofibers (PM) were surface-treated as follows: PM alone, collagen coated-PM (PM-C), UV-irradiated PM (PM-UV), collagen coated UV-irradiated PM (PM-C-UV) and collagen coated-PM crosslinked with genipin (PM-C-GEN). They were subjected to scanning electron microscopy, Fourier transform infrared (FTIR), cell attachment analysis, X-ray photoelectron spectroscopy (XPS), atomic force microscopy and X-ray powder diffraction (XRD). The surface roughness was lower in PM-C-UV group compared to others. Based on FTIR results, all expected functional group were present in all groups. XPS result showed that there are changes in the mass concentration of UV-treated surfaces and in the collagen coated surfaces. All PM groups showed amorphous nature through XRD. UV irradiation and collagen coating were shown to increase PM’s functional groups and modify its surface, which contributed to the increased attachment of cells onto the inert PM scaffold. As conclusion, collagen coated UV irradiated PMMA provided a better surface for cell to attach hence are suitable to be used further as scaffold for in vitro model.

Prompt gamma spectroscopy for range control with CeBr3

Abstract The ultimate goal of radiotherapy using external beams is to maximize the dose delivered to the tumor while minimizing the radiation given to surrounding healthy critical organs. Prompt Gamma Spectroscopy (PGS) has been proposed for range control of particle beams along with the determination of the elemental composition of irradiated tissues. We aim at developing a PGS system for the German Cancer Research Center – DKFZ that takes advantage of the superior selectivity of Helium and Carbon beams accelerated at the Heidelberg Ion-Beam Therapy Center. Preliminary tests with protons accelerated with an IBA C230 cyclotron located at the Universitäts Protonen Therapie Dresden were performed at OncoRay – National Center for Radiation Re-search in Oncology. We present results obtained with a PGS system composed of CeBr3 detectors (Ø 2’’ × 2’’) and (Ø 1.5’’ × 3’’) coupled to a Hamamatsu R13089 photomulti-plier tube and plugged to a Target U100 Spectrometer. Such system provides accurate time-of-flight measurements to increase the signal-to-noise ratio relative to neutron-induced background. First measurements resulted from the irradiation of PMMA and water phantoms, and graphite and aluminum bricks. Several PG energy lines ranging from 0.511 MeV up to 8 MeV were identified and compared with reference re-sults. Two further experiments consisted in irradiating PMMA phantoms in a slit- and semi-collimated configuration with mono-energetic proton beams of 165 MeV and 224 MeV, respectively. Results acquired by means of trans-versal PGS at different phantom depths, ranging from 6 cm before the Bragg peak (BP) to 3.5 cm beyond the BP in 5 mm steps with a 1 cm slit collimation (tungsten) showed a slight decrease of PG yields after the BP. Similar measurements with a semi-opened collimation configuration demonstrated a steeper decrease of PG yields after the BP.

Surface, electrical and mechanical modifications of PMMA after implantation with laser produced iron plasma ions

Laser Produced Plasma (LPP) was employed as an ion source for the modifications in surface, electrical and mechanical properties of poly methyl (methacrylate) PMMA. For this purpose Nd:YAG laser (532nm, 6ns, 10Hz) at a fluence of 12.7J/cm2 was employed to generate Fe plasma. The fluence and energy measurements of laser produced Fe plasma ions were carried out by employing Thomson Parabola Technique in the presence of magnetic field strength of 0.5T, using CR-39 as Solid State Nuclear Track Detector (SSNTD). It has been observed that ion fluence ejecting from ablated plasma was maximum at an angle of 5° with respect to the normal to the Fe target surface. PMMA substrates were irradiated with Fe ions of constant energy of 0.85MeV at various ion fluences ranging from 3.8×106ions/cm2 to 1.8×108ions/cm2 controlled by varying laser pulses from 3000 to 7000. Optical microscope and Scanning Electron Microscope (SEM) were utilized for the analysis of surface features of irradiated PMMA. Results depicted the formation of chain scission, crosslinking, dendrites and star like structures. To explore the electrical behavior, four probe method was employed. The electrical conductivity of ion irradiated PMMA was increased with increasing ion fluence. The surface hardness was measured by shore D hardness tester and results showed the monotonous increment in surface hardness with increasing ion fluence. The increasing trend of surface hardness and electrical conductivity with increasing Fe ion fluence has been well correlated with the surface morphology of ion implanted PMMA. The temperature rise of PMMA surface due to Fe ion irradiation is evaluated analytically and comes out to be in the range of 1.72×104 to 1.82×104K. The values of total Linear Energy Transfer (LET) or stopping power of 0.8MeV Fe ions in PMMA is 61.8eV/Å and their range is 1.34μm evaluated by SRIM simulation.

Short-lived positron emitters in beam-on PET imaging during proton therapy

The only method for in vivo dose delivery verification in proton beam radiotherapy in clinical use today is positron emission tomography (PET) of the positron emitters produced in the patient during irradiation. PET imaging while the beam is on (so called beam-on PET) is an attractive option, providing the largest number of counts, the least biological washout and the fastest feedback. In this implementation, all nuclides, independent of their half-life, will contribute. As a first step towards assessing the relevance of short-lived nuclides (half-life shorter than that of 10C, T1/2 = 19 s) for in vivo dose delivery verification using beam-on PET, we measured their production in the stopping of 55 MeV protons in water, carbon, phosphorus and calcium The most copiously produced short-lived nuclides and their production rates relative to the relevant long-lived nuclides are: 12N (T1/2 = 11 ms) on carbon (9% of 11C), 29P (T1/2 = 4.1 s) on phosphorus (20% of 30P) and 38mK (T1/2 = 0.92 s) on calcium (113% of 38gK). No short-lived nuclides are produced on oxygen. The number of decays integrated from the start of an irradiation as a function of time during the irradiation of PMMA and 4 tissue materials has been determined. For (carbon-rich) adipose tissue, 12N dominates up to 70 s. On bone tissue, 12N dominates over 15O during the first 8–15 s (depending on carbon-to-oxygen ratio). The short-lived nuclides created on phosphorus and calcium provide 2.5 times more beam-on PET counts than the long-lived ones produced on these elements during a 70 s irradiation. From the estimated number of 12N PET counts, we conclude that, for any tissue, 12N PET imaging potentially provides equal to superior proton range information compared to prompt gamma imaging with an optimized knife-edge slit camera. The practical implementation of 12N PET imaging is discussed.

Spectrophotometric Analysis UV-VIS Irradiated Ternary Hybrid PMMA Composite

Ternary hybrid composite PMMA matrix with TiO2-Al2O3- ZrO2 as additives were prepared carried out casting method. Range of weight fractions (92-84 wt %) of PMMA, fixed percentage (4%) of TiO2 and range of weight fractions (4-12 wt %) of Al2O3 and ZrO2 were used as started materials. Optical constants were obtained of the prepared samples using spectrometer (UV- VIS). Absorption coefficient, extinction coefficient, refractive index and optical energy gap were calculated. It was noticing of absorption coefficient and extinction coefficient and refractive index values for (PMMA - TiO2- Al2O3) higher than that of (PMMA - TiO2- ZrO2), also, more decreasing optical energy gap values in the first composites than other samples.

Thermal degradation of Poly(methyl methacrylate) with a 1.064 μm Nd:YAG laser in a buoyant flow

The laser radiative oxidative decomposition of poly(methyl methacrylate) (PMMA) and the evolved decomposition products in the gas-phase are investigated using imaging Fourier transform infrared spectroscopy (IFTS). The spatial and temporal evolution of the gas plume in air was investigated with adequate spatial (0.81 mm2 per pixel) and spectral resolutions (2 cm−1). Surfaces of black PMMA samples were irradiated from 4 to 22 W/cm2 with a cw 1.064 μm Nd:YAG laser. Strong spectral emission of methyl methacrylate (MMA) was observed in the infrared. Spatial maps of plume temperature and MMA column density were obtained from modeling the observed spectra by assuming a homogeneous single-plume radiative transfer model (RTM). A spectral model was used to compute the gas emissivity from an experimentally measured, interpolated and extrapolated MMA absorption coefficient database. In addition, the spectral radiance from the irradiated PMMA surface was fitted with Planck's distribution to obtain temporal and spatial surface temperature profiles. The peak signal-to-noise exceeded 50:1, allowing plume temperature and MMA column density determinations with low statistical errors. Laser irradiated PMMA reached a steady surface temperature of 613.9 ± 0.8 K and a peak gas-phase temperature of 700 ± 19 K at 22 W/cm2. The reported statistical uncertainties for all the results are defined as the half-width of the 95% confidence interval and do not include systematic errors associated with the assumption of a homogeneous plume or the effects of turbulence. As laser intensity increased, gas temperature decreased at the surface-boundary layer. A simplified thermal analysis was developed to understand the wavelength dependent surface heating rates from using both CO2 and Nd:YAG lasers. An Arrhenius plot of MMA formation at the surface for a single pixel was compared with established kinetics models. At surface temperatures of 450–600 K, an effective activation energy of 30.83 ± 8.29 kJ/mol was obtained, consistent with surface desorption of the monomer.

Large pulsed electron beam surface treatment of translucent PMMA

Abstract A large pulsed electron beam (LPEB) was used to modify the surface properties of a poly(methyl methacrylate) (PMMA) sample. Translucent PMMA samples were fabricated using a conventional milling process. Then, the surface was irradiated with an energy density of 2 to 4 J/cm 2 by a large electron beam, 60 mm in size. Surface property characterization of the irradiated PMMA samples was performed using an ultraviolet–visible–near infrared (UV–vis–NIR) spectrophotometer, atomic force microscopy, a form tracer, and drop-shape analysis and compared with the non-irradiated surface. It was observed that the visible light transmission of the prepared PMMA sample was enhanced by 40%. The surface roughness of the PMMA sample after irradiation was also reduced by 30%, compared with the baseline case with no irradiation. Additionally, the water contact angle increased as the number of LPEB shots increased.

First full-beam PET acquisitions in proton therapy with a modular dual-head dedicated system

During particle therapy irradiation, positron emitters with half-lives ranging from 2 to 20 min are generated from nuclear processes. The half-lives are such that it is possible either to detect the positron signal in the treatment room using an in-beam positron emission tomography (PET) system, right after the irradiation, or to quickly transfer the patient to a close PET/CT scanner. Since the activity distribution is spatially correlated with the dose, it is possible to use PET imaging as an indirect method to assure the quality of the dose delivery. In this work, we present a new dedicated PET system able to operate in-beam. The PET apparatus consists in two 10 cm × 10 cm detector heads. Each detector is composed of four scintillating matrices of 23 × 23 LYSO crystals. The crystal size is 1.9 mm × 1.9 mm × 16 mm. Each scintillation matrix is read out independently with a modularized acquisition system. The distance between the two opposing detector heads was set to 20 cm. The system has very low dead time per detector area and a 3 ns coincidence window, which is capable to sustain high single count rates and to keep the random counts relatively low. This allows a new full-beam monitoring modality that includes data acquisition also while the beam is on. The PET system was tested during the irradiation at the CATANA (INFN, Catania, Italy) cyclotron-based proton therapy facility. Four acquisitions with different doses and dose rates were analysed. In all cases the random to total coincidences ratio was equal or less than 25%. For each measurement we estimated the accuracy and precision of the activity range on a set of voxel lines within an irradiated PMMA phantom. Results show that the inclusion of data acquired during the irradiation, referred to as beam-on data, improves both the precision and accuracy of the range measurement with respect to data acquired only after irradiation. Beam-on data alone are enough to give precisions better than 1 mm when at least 5 Gy are delivered.

Ultrafast electron and material dynamics following femtosecond filamentation induced excitation of transparent solids

We examine the spatiotemporal dynamics of filamentation and subsequent material changes in two transparent media, fused silica and poly(methyl methacrylate) (PMMA), using inline holographic microscopy. We are able to dynamically observe the nonlinear propagation of femtosecond laser pulses and the consequent evolution of the electronic excitatio n and trapping inside the bulk of both materials. In the case of fused silica we reveal the physical conditions for the formation of nanogratings, measuring excited electron densities well below the critical density while for PMMA we show that excited electrons with densities exceeding 1018 cm−3, exhibit complex trapping dynamics in a 200 fs time scale. The clear demonstration of ultrafast sub-ps photochemical processes that take place during the irradiation of PMMA with femtosecond pulses will have a strong impact on the laser microprocessing of polymers and nanosurgery applications of bio-related materials.

Ionizing Radiation Effect on PMMA Measured by Microhardness

The experimental study deals with the effect of modification of the surface layer by irradiation cross-linking on the mechanical properties of the Poly (methyl methacrylate) - PMMA tested using the instrumented microhardness test. The surface layer of PMMA specimen made by injection technology was modified by irradiation cross-linking using beta irradiation, which significantly influences mechanical properties of the surface layer. Compared to the heat and chemical-heat treatment of metal materials (e.g. hardening, nitridation, case hardening), cross-linking in polymers affects the surfaces in micro layers. These mechanical changes of the surface layer are observed in the instrumented microhardness test. Our research confirms the comparable properties of surface layer of irradiated PMMA with highly efficient polymers. The subject of this research is the influence of irradiation dosage on the changes of mechanical properties of PMMA.

The influence of low‐ and high‐linear energy transfers on some physical properties of poly(methyl‐methacrylate) samples

AbstractClear poly(methyl‐methacrylate)—PMMA—dosimeter is widely used in food irradiations. Positron annihilation lifetime spectroscopy (PALS) is one of the unique tools used for studying free‐volumes and open‐volume type defects in solid media. The Vicker's microhardness measurements offer a simple and nondestructive tool for investigating the mechanical behavior of polymer materials. PALS as well as microhardness measurements were carried out for PMMA samples, irradiated with low‐ and high‐linear energy transfers (LET). The low‐LET irradiations were provided at lethal doses of gamma radiations for vegetative bacteria. Such irradiations showed a chain scission in the PMMA samples. High‐LET irradiations showed behavior different from the low‐LET ones. The observed behavior depends on the alpha particle fluence. The microhardness testing was carried out for virgin and irradiated PMMA samples at high‐LET. A negative correlation was found between PALS measurements and microhardness results. The optical characteristics and structural studies for the virgin and irradiated PMMA samples were in agreement with the PALS and microhardness measurements. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

A study of the effect of synchrotron radiation exposure on the thermophysical parameters of the PMMA X-ray resist

Differential scanning calorimetry and thermogravimetric analysis results for polymethyl methacrylate (PMMA, monomer with the atomic formula C5H8O2) samples, extensively used as an X-ray resist, are presented. The size distribution of aerosol particles formed by PMMA sample ablation under terrahertz radiation is obtained. The size dependence of the coil-like macromolecules of irradiated PMMA on the exposure dose is found experimentally, and a descriptive model is proposed that is well consistent with the characteristic curve. The processes occurring during irradiation of PMMA are explained (at the qualitative level), and recommendations on intensive SR irradiation of PMMA are given.

EPR study of radical annihilation kinetics of γ-ray-irradiated acrylic (PMMA) at elevated temperatures

High-energy irradiations of polymers may cause bond cleavage or crosslinking and change the structures and physical properties of the polymers, which may offer various applications. Despite wide investigation, relationship between the kinetics and mechanism of annihilation after irradiations and the structure and some physical properties of irradiated polymers is still poorly established. We have been exploring such possible relationship and report herein investigation of the kinetics of radical annihilation of γ-ray irradiated acrylic, i.e., poly(methylmethacrylate) or PMMA, at elevated temperatures with EPR spectroscopy. The EPR spectra consist of three components, a quintet Ra, a quartet Rb, and a broad singlet Rc. Ra and Rb follow second-order annihilation kinetics, while the decay of the radical Rc is comprised of at least two parallel kinetic processes, a slow second-order pathway and a fast pathway which can be equally well fitted to first- or second-order kinetics. The kinetics is analogous to that for the radical decays in irradiated 2-hydroxyethyl methacrylate copolymer. On the basis of the large hyperfine coupling constant of 2.3 mT, Ra may be assigned to a radical adjacent to two groups of protons, such as a doublet of quartet with similar coupling constants due to an anti-methylene proton and a methyl group; the Rb signal, possibly a methyl radical; and the broad singlet Rc, a magnetically coupled combination species. Alternative assignments of the radicals have also been suggested. The rate constant increases with increasing dose for each radical at a given temperature, possibly due to increase in radical concentrations at higher doses. The rate constants satisfy the Arrhenius equation, suggesting a single mechanistic pathway for the annihilation process in the temperature range; wherein the activation energy decreases with increasing dose for all radicals, possibly due to higher concentrations of free radicals in close proximity produced at higher doses.