Browsing by Subject "PMMA"
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Item Open Access Assessment of PMMA and polystyrene based microfluidic chips fabricated using CO2 laser machining(Elsevier, 2020-08-19) Bilican, İsmail; Güler, Mustafa TahsinLaser machining could be an alternative way for the fabrication of microchannels. In this study, laser machining of polymethylmethacrylate (PMMA) and polystyrene (PS) substrates were characterized in detail. A fabrication method preventing leakage at PS microchannel inlets was developed. The effect of laser parameters (power, speed and frequency) on engraving was analyzed by scanning electron microscopy. Laser ablation mechanism of both materials was explained through thermal analysis and material properties. Defocusing the laser beam was also analyzed as an additional parameter affecting the channel profile. Two parameters affecting the resolution were analyzed which are the minimum channel size that can be achieved by the laser beam and x-y stage of the laser engraver for straight and complex microchannel geometries. The hydrophilicity of the surface before and after laser machining was tested with contact angle measurements. The capabilities/limitations of machining were revealed through some complex channel structures. Finally, a passive micromixer and a droplet generator microfluidic devices were manufactured and tested, and promising results were obtained.Item Open Access Characterization of denture acrylic resin surfaces modified by glow discharges(Sage Publications, Inc., 1997) Süzer, Ş.; Özden, N.; Akaltan, F.; Akovali, G.Resin samples prepared by compression molding using a poly (methyl methacrylate) (PMMA) denture base material were exposed to radio-frequency (rf) glow discharges to improve the wettability of the material. Fourier transform infrared (FT-IR) reflectance, X-ray photoelectron spectroscopy (XPS), and contact-angle measurements have been employed to characterize the changes introduced by the glow discharge plasma. FT-IR measurements cannot detect any modification. XPS reveals an increase in the O/C atomic ratio. Contact angles of the plasma-treated samples are always lower when compared with untreated ones. The increased O atomic concentration is attributed to formation of -COH groups on the surface during plasma treatment. The O/C atomic ratio decreases upon heating the samples in vacuum to 100 °C for 1-2 min and exposing the samples to liquid CH2Cl2 for 1-2 min. Exposure to distilled water for prolonged periods causes a slight decrease during the initial 1-20 days but levels off to a constant value up to a period of 60 days. Plasma treatment seems to offer a durable increase in the wettability for these materials left in air or distilled water.Item Open Access Preparation and characterization of polymer composites containing gold nanoparticles(Bilkent University, 2011) Yılmaz, EdaIn this study, light-assisted synthesis of gold nanoparticles in polymer films is demonstrated and characterization of gold nanoparticle-polymer composites using various techniques is shown. There are various methods introduced for the synthesis of gold nanoparticles in solution and their integration to the polymer films afterwards. However, synthesizing gold nanoparticles directly inside the polymer matrix is more advantageous for the production of polymer-nanoparticle composites. An advantage of synthesizing gold nanoparticles within polymer films is the opportunity of photo-patterning. Films having patterns made of regions with and without gold nanoparticles can be produced, using masks designed to cut off the radiation at desired places. Such patterned films were investigated with scanning electron microscope (SEM) and dark regions between irradiated regions and masked regions were observed. These dark regions are shown to be “ion depleted regions”, where gold ions diffuse through irradiated regions during the irradiation. These regions of about 10 m width, suggests a very large distance for gold ions to diffuse through a rigid matrix like Poly(methyl methacrylate)(PMMA), which is very interesting. Supporting evidence for the existence of these regions was obtained from fluorescence studies with Rhodamine 6G molecule and x-ray electron spectroscopy (XPS). The observations made through the formation of ion depleted regions can be used to estimate the diffusion constant of gold ions inside the PMMA matrix. Also the presence of ion depleted regions indicate the stability of photo-patterns created on the polymer film against smearing during light exposure after the production, by setting an upper limit to the critical feature size. During the characterization of gold nanoparticle-polymer composites, the electrical properties of PMMA with and without gold nanoparticles were investigated using charge resolved XPS, while applying external bias to the films with and without gold nanoparticles to probe the charging properties of the films. An enhancement of conductivity of PMMA films containing gold nanoparticles was observed using this technique. Additionally charge resolved XPS technique was also used to determine the charge storage characteristics of the polymer surfaces, which is important for the identification of charging mechanisms during contact and other electrification processes. It was shown that the PMMA surface is very susceptible to negative charging and even native negative charges on the PMMA surface can be observed prior to any treatment. Also when the surface is charged carbon and oxygen atoms of the carbonyl and methoxy groups of PMMA were observed to behave differently from the backbone of the polymer, which shows the chemical specificity of the charge accumulating spots on the surface.Item Open Access Sterilization of PMMA microfluidic chips by various techniques and investigation of material characteristics(Elsevier, 2016) Yavuz, C.; Oliaei, S. N. B.; Cetin, B.; Yesil-Celiktas, O.The sterilization of microfluidic chips is a vital step of the fabrication process prior to the customer use in biomedical applications. The aim of this study was to analyze the influence of different sterilization techniques and to compare the characteristics of the material before and after sterilization of polymethylmethacrylate (PMMA) microchips. For this, supercritical carbon dioxide (SC-CO2) along with standard sterilization methods such as ultraviolet (UV), heat (autoclaving), ethylene oxide (EtO) and hydrogen peroxide (H2O2) were applied. The treated microchips were analyzed by Scanning Electron Microscopy, Differential Scanning Calorimetry, Fourier Transform Infrared Spectroscopy and Laser Scanning Microscopy in order to ascertain any changes in the chemical structure and surface morphology. The optimum sterilization parameters for SC-CO2 were elicited as 120 bar, 40°C and 60 min which provided complete sterility and did not alter the main properties of the polymer along with EtO and H2O2 sterilizations unlike heat and UV treatments. However, surface roughness and microchannel profiles were negatively affected. Although complete sterility was achieved, each protocol has its own strengths and weaknesses. © 2015 Elsevier B.V. All rights reserved.