Chemistry / Kimya
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Article Citation - WoS: 195Optical Properties of Composites of Pmma and Surface-Modified Zincite Nanoparticles(American Chemical Society, 2007) Demir, Mustafa Muammer; Koynov, Kaloian; Akbey, Ümit; Bubeck, Christoph; Park, Insun; Lieberwirth, Ingo; Wegner, GerhardLocate full-text(opens in a new window)|Full Text(opens in a new window)|View at Publisher| Export | Download | Add to List | More... Macromolecules Volume 40, Issue 4, 20 February 2007, Pages 1089-1100 Optical properties of composites of PMMA and surface-modified zincite nanoparticles (Article) Demir, M.M.a, Koynov, K.a, Akbey, Ü.a, Bubeck, C.a, Park, I.ab, Lieberwirth, I.a, Wegner, G.a a Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany b Seoul National University, School of Chemistry, Korea, South Korea View references (65) Abstract Composites that show visible light transmittance, UV absorption, and moderately high refractive index, based on poly(methyl methacrylate) (PMMA) and zinc oxide (zincite, ZnO) nanoparticles, were prepared in two steps. First, surface-modified ZnO nanoparticles with 22 nm average diameter were nucleated by controlled precipitation via acid-catalyzed esterification of zinc acetate dihydrate with pentan-1-ol. The surface of growing crystalline particles was modified with tert-butylphosphonic acid (tBuPO3H2) in situ by monolayer coverage. Particle size and graft density of -PO3H 2 on the particle surface were controlled by the amount of surfactant applied to the reaction solution. Second, the surface-modified particles were incorporated into PMMA by in-situ bulk polymerization. Free radical polymerization was carried out in the presence of these particles using AIBN as initiator. Volume fraction (0) of the particles was varied from 0.10 to 7.76% (0.5 to 30 wt %). Although the particles are homogeneously dispersed in monomer, segregation of the individual particles upon polymerization was observed. Optical constants of the films ca. 2.0 μm including absorption and scattering efficiencies, indices of refraction, and dispersion constants were determined. The absorption coefficient at 350 nm increases linearly with ZnO, obeying Beer's law at low particle contents. However, it levels off toward a value of about 5000 cm-1 and shows a negative deviation at high concentrations because of aggregation of the individual particles. Waveguide propagation loss coefficients of the composite films were examined by prism coupling. A steep increase of the loss coefficient was found with a slope of 52 dB cm-1 vol %-1 as the volume fraction of the particle increases. The refractive index of the composites depends linearly on volume fraction of ZnO and varies from 1.487 to 1.507 (φ = 7.76%) at 633 nm. The dispersion of refractive index was found to be consistent with Cauchy's formula.Article Citation - WoS: 185Pmma/Zinc Oxide Nanocomposites Prepared by In-Situ Bulk Polymerization(John Wiley and Sons Inc., 2006) Demir, Mustafa Muammer; Memesa, Mine; Castignolles, Patrice; Wegner, GerhardDispersing surface-modified zinc oxide nano-particles (ZnO) in methyl methacrylate (MMA) improves the free radical bulk polymerization process as well as the thermal stability of the formed polymer. Hydroxy groups available on the ZnO surface may induce a degenerative transfer. This suppresses the gel effect, which leads to a better control of the heat evolution during the late stages of polymerization. The formation of chains having vinylidene end groups and head-to-head links is suppressed, which shifts the onset of thermal decomposition to the regime where decomposition occurs by random chain scission.Article Citation - WoS: 5Citation - Scopus: 6Tailored Ceo2 Nanoparticles Surface in Free Radical Bulk Polymerization of Methyl Methacrylate(American Chemical Society, 2013) Tunusoğlu, Özge; Demir, Mustafa MuammerPolymerization of monomer/nanoparticle dispersion, namely in situ polymerization, has been frequently used for the fabrication of polymer nanocomposites. However, the interference of nanoparticle surface with polymerization in the course of composite formation has been tacitly neglected. In this work, surface-functionalized ceria nanoparticles were prepared using various capping agents: 3-(mercaptopropyl) trimethoxy silane, thioglycolic acid, 3-mercaptopropionic acid, and hexadecyltrimethyl ammonium bromide. Both in situ and ex situ approaches were applied for surface functionalization. The particles were dispersed into methyl methacrylate and free radical polymerization was carried out. The process of nanocomposite formation was examined in terms of conversion, molecular weight, and molecular weight distribution. The polymerization responded merely to the in situ functionalized particles. Regardless of the capping agents used, the particles function as a retarder and inhibitor. Their interaction with polymerization medium showed many complexities such that molecular weight was found to be strongly dependent on the capping agent employed.Article Citation - WoS: 51Citation - Scopus: 53Challenges in the Preparation of Optical Polymer Composites With Nanosized Pigment Particles: a Review on Recent Efforts(John Wiley and Sons Inc., 2012) Demir, Mustafa Muammer; Wegner, GerhardBlends of nanosized pigment particles and polymers are widely believed to offer the potential for the design of novel or at least improved materials. This review critically evaluates the recent literature with regard to the following issues: (a) why and how does the size of the particles matter, (b) what are the requirements to create compatibility between amorphous polymers and nanoparticles, (c) carbon allotropes as nanosized pigments, (d) bulk polymerization of monomer/pigment mixtures, (e) interaction of growing chains with the particles in the polymerization, (f) depletion flocculation as a mechanism to counteract homogeneous distribution of the particles in the polymer matrix and ways to suppress the undesirable flocculation, and (g) optical properties of the blends as well as methods of optical characterization.