Poly Methyl Methacrylate Matrix Research Articles

Magnetically Induced Circular Polarization of Emission: Application to Inorganic Complexes

A sensitive spectrometer for the measurement of circular polarization of emission, utilizing a photoelastic modulator, is presented. This spectrometer, when augmented by a superconducting magnet and dewar assembly, provides an excellent system for studying magnetically induced circular polarization of emission (MICE). In order to exemplify both the system and the usefulness of MICE, a partial analysis of the MICE observed from Ru-(4,7-dipheny1-1,10-phenanthroline)3C12 dispersed in a polymethylmethacrylate (PMM) matrix in the 2 to 100 K temperature range is reported. Also presented is a discussion of the effects of photoselection on the observed MICE for these D3 symmetry complexes. It is found that MICE is more sensitive to the detailed nature of the levels involved in emission than a combination of zero field techniques. MICE should prove to be an exceptionally useful tool for probing excited states of inorganic complexes.

Magnetic Circular Dichroism of the Iron(III) Porphins

Abstract Magnetic circular dichroism (MCD) spectra were measured of some low-spin and high-spin Fe(III) porphins in a rigid matrix of polymethyl methacrylate(PMMA) for a variety of temperature. Some of the most prominent MCD, extrema of the low-spin Fe(III) porphins showed a remarkable enhancement of the intensity at reduced temperatures, while no appreciable increase was observed in the absorption intensity. The temperature dependence of the MCD dispersion of the low-spin Fe(III) porphins arises, in principle, from a change in the Boltzmann distribution between the ground Kramers doublet splitting in a magnetic field, however, the MCD enhancement observed in the Soret region can correctly be interpreted only when the excited states described by a product wave function of the porphin B state and the spin-orbit coupling substates of low-spin iron(III) d5 system are split by a configuration interaction with the “porphin to iron(III)” charge-transfer excited states.

Ultrasonic attenuation and velocity in two-phase microstructures

The scattering attenuation and velocity of elastic waves propagating in two-phase microstructures are computed by an extension of multiple scattering analysis. The computation is based on a model of an array of isotropic spherical scatterers embedded in an isotropic matrix. Attenuation α is predicted to increase with volume fraction and number density of scatterers and to approach a plateau with frequency. Group velocity vg is predicted to decrease with volume fraction and frequency. Ultrasonic measurements of α and vg are made on model microstructures consisting of Cu spheres embedded in a polymethylmethacrylate matrix. The measured values agree qualitatively with the predicted ones, and physical reasons are proposed to account for the agreement. The inability of the theory to provide accurate quantitative predictions of these quantities is discussed. Subject Classification: 35.26; 20.30, 20.35.

Increased Resistance to Photodegradation of Rhodamine 6G in Cooled Solid Matrices

Improved resistance to photodegradation for Rhodamine 6G was observed when the dye was held in a cooled solid matrix of polymethylmethacrylate. The fraction of dye bleached decreased with decreasing temperature as did the rate of bleaching. The minimum detectable quantum efficiency for photodegradation was φ ≅ 10−7.

Laser-Heating Studies of Composite Materials

Experiments on laser heating of carbon-methacrylate composite materials are described and compared to a theoretical model. The model assumes hydrodynamic response and uses the Mie-Grüneisen equation of state. The laser experiments are carried out on samples with carbon fibers (10-μ diam and 250 μ long) uniformly dispersed in a polymethylmethacrylate (PMMA) matrix. The samples irradiated had a carbon to PMMA mass ratio of 1:1000. The fluence range was from 0.12 to 2.0 J/cm2 and the resulting pressure ranged from 0.3 to 30 bar. By assuming that rapid energy transfer is accomplished by vaporized carbon penetrating cracks in the matrix, the results are in accord with the theory.

Radiation-Induced Trapped Charge Carriers in Organic Polymers. A Model of Thermoelectric Current Generation

Trapping and detrapping of radiation-induced charge carriers in polymethylmethacrylate (PMMA), polyvinyl chloride (PVC), and several other polymers were investigated. Thermoelectric currents were generated in the polymers after irradiation by thermally stimulating the release of the trapped charges and subjecting them to a temperature gradient. Heating similarly irradiated samples in the absence of a temperature gradient produced a tenfold reduction in the observed current. The charge carriers were determined to be positive from the polarity of the colder electrode. To observe thermoelectric currents, electrons liberated during irradiation had to be trapped to prevent recombination with trapped positive charges. This trapping is not done by the polymer matrix of PMMA at 25°C but by added impurities. PVC contains a built-in trap in the polymer chain at the C-C1 group. The electron trap in commercial PMMA (Lucite) is benzoyl peroxide or another chemical initiator. Electron traps were also internally generat...

Additional Observations of Probable Stimulated Emission of a Terbium Ion Chelate in a Vinylic Resin Matrix

THE experimental results presented here were to have been included as an addition to my first communication1. However, the results were not submitted in time to be included in it. I should like at this time to present these additional results, as they provide a more definite indication of probable stimulated emission of terbium thenoyltrifluoroacetonate Tb(TTA) in a polymethyl-methacrylate (PMMA) matrix than the results presented in the previous communication1.

Anchorage of the femoral head prosthesis to the shaft of the femur.

Anchorage of the femoral head prosthesis to the shaft of the femur.