Investigation of Morphology and Interface in Polymer Composite Thin Films
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Investigation of Morphology and Interface in Polymer Composite Thin Films C. K. Chiang, L. P. Sung and R. Popielarz Polymer Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8541 ABSTRACT Laser scanning confocal microscopy (LSCM) has been applied to examine the filler particles and their distribution in BaTiO3-polymer composite films. We have measured thin-slice images of the composite films at various depths from the film surface and visualized the submicron size particles and the polymer between them nondestructively. We have found that, although BaTiO3 particles appear to be uniformly dispersed in the composite films when observed under conventional microscope, the particles form clusters at low BaTiO3 concentrations. The lower the concentration the larger the cluster size. The particles appear to be better dispersed in the high concentration composites than at low concentrations. INTRODUCTION High dielectric constant (High-K) ferroelectric ceramic-polymer composite are important electronic materials. Detailed understanding of this class of materials will help electronic industry in planning, design and processing of these materials. Previously, we have synthesized a series of BaTiO3-polymer composite films and measured their dielectric properties over a wide volume fraction of BaTiO3 filler [1]. BaTiO3 was used, because it is the best-known ferroelectric ceramics. In this paper, we report the morphology of the polymer composite films as observed by laser scanning confocal microscopy (LSCM). LSCM. is known for visualization of micron-size particles in detail.[2,3] The LSCM affords imaging of smaller features than the conventional microscopy and with a better depth resolution. We applied LSCM to examine the distribution of the filler particles in the BaTiO3 ceramic-polymer composites, the particles size, and, the cluster shapes. EXPERIMENTAL Trimethylolpropane triacrylate (TMPTA monomer) was purchased from Monomer Polymer & Dajac Labs. Barium titanate powder (BaTiO3 filler) and 2,2-dimethoxy-2-phenylacetophenone (photoinitiator) were obtained from Aldrich. All materials were used as received.[4] First, 1 % solution of the photoinitiator in the monomer was prepared. Next, barium titanate powder was mixed into the solution to form liquid formulations of various filler concentrations. The formulations were cured by exposure of a few drops of each formulation squeezed between microscope slides to UV-light. During the exposure, the slides were kept at a constant distance using self-adhesive labels in the role of spacers. The cured composites did not adhere strongly to C5.27.1
the glass and were carefully separated from the slides in the form of thin films of the thickness of the order of 50 - 200 µm. In this way, we prepared a series of BaTiO3-polymer composite films with BaTiO3 volume fraction of 5%, 10%, 15%, 20%, 25%, 30%, and 35%. The films were examined directly by the laser scanning confocal microscopy. A Zeiss Laser Scanning Confocal Microscope Model LSM510a was applied to charac
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