Search results for "PMMA"
showing 10 items of 36 documents
Stability improvement of PMMA and Lumogen® coatings for hybrid white LEDs
2014
Hybrid white LEDs employing perylene-based dyes for the frequency down-conversion of blue light, generated by a standard inorganic source, suffer from colour rendering variations due to the degradation of the organic molecule under prolonged irradiation. To avoid such inconvenient, proper encapsulation of the dyes in resins or other polymer matrices can prevent their accelerated ageing; nevertheless, embedding polymers can also exhibit significant bleaching caused by chemico-physical agents. Among all, polymethyl methacrilate (PMMA) is one of the most used materials for the fabrication of hybrid LEDs' colour conversion coatings, therefore its stability needs to be investigated.
Preparation and characterization of Ce:YAG-PMMA and Ce:YAG-PC composites for white LED
2015
Polymeric composites of lanthanide-doped materials were considered as potential candidates for the development of white LED. Ce:YAG-PMMA and Ce:YAG-PC composites were prepared by melt compounding. The characterization was performed using transmission electron microscopy, X-ray diffractometry, thermogravimetry and photoluminescence spectroscopy. The effect of filler quantity, in the range 0.1-5 wt.%, on the morphology, optical and thermal properties was investigated.
Valence bands of poly(methylmethacrylate) and photoion emission in vacuum ultraviolet region
1992
Photoion and photoelectron yields were measured for poly(methylmethacrylate) in the photon energy region of 8–40 eV using synchrotron radiation. Further, the valence‐band structure was investigated with ultraviolet photoelectron spectra and valence effective Hamiltonian calculations. A significant difference was observed between the photon energy dependencies of photoion and photoelectron yields. The threshold energy for photoion emission was found to be 10.5 eV, while that for photoelectron emission was 8.5 eV, indicating holes created near the valence‐band top do not contribute to the ion emission. At the higher‐energy region, the ion emission efficiency was found to be enhanced in the ph…
Management of Spinal Bone Metastases With Radiofrequency Ablation, Vertebral Reinforcement and Transpedicular Fixation: A Retrospective Single-Center…
2022
Spine is a frequent site of bone metastases, with a 8.5 months median survival time after diagnosis. In most cases treatment is only palliative. Several advanced techniques can ensure a better Quality of Life (QoL) and increase life expectancy. Radiofrequency ablation (RFA) uses alternating current to produce local heating and necrosis of the spinal lesion, preserving the healthy bone. RFA is supported by vertebral reinforcement through kyphoplasty and vertebroplasty in order to stabilize the fracture with polymethylmethacrylate (PMMA) injection, restoring vertebral body height and reducing the weakness of healthy bone. The aim of this study is to demonstrate the efficacy and advantages of …
Rapid prototyping for micro-engineering and microfluidic applications: Recycled pmma, a sustainable substrate material
2018
Poly(methylmethacrylate), PMMA, is one of the most commonly used thermoplastics for the manufacture of micromechanical and microfluidic devices, due to its optical transparency, rigid mechanical properties, low cost and good workability in conjunction with its rapid prototyping and mass manufacturing. Recent advances in the rapid-prototyping fields have allowed the production of precise features compatible with microfluidic structures and accelerated the conversion process from bench-side to mass market. For example, to address the need for fast design cycles using material compatible with mass manufacturing, we have developed an ultrafast prototyping technique for the manufacture of multil…
PMMA-titania nanocomposites: Properties and thermal degradation behavior
2012
Titania nanoparticles were prepared using a solegel method and calcination at 200 and 600 � C in order to obtain anatase and rutile phases, respectively. The obtained powders were used to prepare PMMAe titania nanocomposites by a melt compounding method. The effect of the crystalline phase and the amount of titania, in the range 1e5 wt.%, on the morphology, mechanical properties and thermal degradation kinetics of PMMA was investigated by means of X-ray diffractometry (XRD), transmission electron microscopy (TEM), 13 C cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy ( 13 C{ 1 H}CP-MAS NMR), including the measurement of proton spinelattice relaxation time in t…
Evaluación de la liberación de antibióticos incorporados en cementos utilizados en artroplastia
2017
Una de las complicaciones más serias de la artroplastia se encuentra asociada con el desarrollo de una infección, que, aunque la prevalencia de sitúa entre un 0,5 y un 3%, en algunos casos tiene consecuencias devastadoras. Por ello, uno de los mayores retos en la actualidad es la prevención de infecciones cuando un paciente es sometido a una artroplastia. El uso de antibióticos cargados en cementos óseos destinados a la artroplastia podría ser una herramienta eficaz debida a sus numerosas ventajas, la mayor ventaja de este sistema de liberación deriva de que la liberación del antibiótico se realiza en biofase y por ello permite alcanzar altas concentraciones con una baja o nula toxicidad si…
Influence of MeV H+ ion beam flux on cross-linking and blister formation in PMMA resist
2012
In soft lithography, a pattern is produced in poly(dimethylsiloxane) (PDMS) elastomer by casting from a master mould. The mould can be made of poly(methylmethacrylate) (PMMA) resist by utilising either its positive or negative tone induced by an ion beam. Here we have investigated the irradiation conditions for achieving complete cross-linking and absence of blister formation in PMMA so that its negative characteristic can be used in making master moulds. PMMA thin films approximately 9 µm thick on Si were deposited by spin coating. The 2-MeV H+ ion beam was generated using a 1.7-MV tandem Tandetron accelerator. The beam was collimated to a 500×500 µm2 cross section using programmable proxi…
Properties and morphology of PMMA/ABN blends obtained via MMA in situ polymerisation through γ-rays
2001
Abstract Methylmethacrylate polymerisation in the presence of 4 wt% butadiene-acrylonitrile rubber was carried out at fixed dose-rate and temperature. The effect of irradiation was investigated with respect to the mechanical and dynamic-mechanical properties in the solid state. A general increase of the “compatibilisation” on irradiation is obtained. In fact both rubber and polymethylmethacrylate glass transition temperatures, determined through dynamic-mechanical analysis, reveal the presence of strong interactions between the components. Furthermore an improvement of the mechanical tensile properties of the blends is observed when irradiation is continued after polymerisation, at least un…
Measurement of the strain-optic coefficients of PMMA from 800 to 2000 nm
2020
The strain-optic coefficients of PMMA are measured in a broad wavelength range from 800 to 2000 nm. The sensitivity of the azimuthal whispering gallery mode resonances to the strain is exploited to measure the strain-optic coefficients of PMMA micro-rods. The technique is based on measuring the wavelength shift of the resonances of both polarizations states, the TE and TM, when an axial strain is applied to the polymer rods. This method enables the determination of the strain-optic coefficients of the material in a broad wavelength range. In particular, in the near-infrared range, the PMMA exhibits negligible dispersion and anisotropy, and the strain-optic coefficients show constant values …