• Polymer(Korea)
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• v.30 no.5
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• pp.385-390
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• 2006

In this work, the effect of carbon nanofiber (CNF) on thermal properties, and friction and wear behavior of CNF/PMMA composites were examined. While thermal properties of the composites were investigated with differential scanning calorimetry, thermograyimetric analyzer, and dynamic mechanical analyzer friction and wear behaviors were examined using a friction and wear tester. The glass transition temperature (Tg), integral procedural decomposition temperature (IPDT), storage modulus (E'), and tan ${\delta}$ appeared at higher temperatures with increasing CNF content, which were probably attributed to the presence of strong interactions between the carbonaceous fillers and the PMMA resins matrix. The wear loss in the composites decreased at 0.1 wt% CNF and then increased with 5-10 wt% CNF content. This was due to the existence of large aspect ratio CNF in PMMA which led to an alignment of PMMA chains and an increase of mechanical interlocking, resulting in the formation of crosslinked structures between CNF and PMMA in the composite.

• Macromolecular Research
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• v.16 no.8
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• pp.686-694
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• 2008

We studied the molecular shapes and structural characteristics of a 33-armed, star polystyrene (PS-33A) and two $3^{rd}$-generation, dendrimer-like, star-branched poly(methyl methacrylate)s with different architectures (pMMA-G3a and PMMA-3Gb) and 32 end-branches under good solvent and theta ($\Theta$) solvent conditions by using synchrotron small angle X-ray scattering (SAXS). The SAXS analyses were used to determine the structural details of the star PS and dendrimer-like, star-branched PMMA polymers. PS-33A had a fuzzy-spherical shape, whereas PMMA-G3a and PMMA-G3b had fuzzy-ellipsoidal shapes of similar size, despite their different chemical architectures. The star PS polymer's arms were more extended than those of linear polystyrene. Furthermore, the branches of the dendrimer-like, star-branched polymers were more extended than those of the star PS polymer, despite having almost the same number of branches as PS-33A. The differences between the internal chain structures of these materials was attributed to their different chemical architectures.

• Polymer(Korea)
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• v.33 no.4
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• pp.347-352
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• 2009

Charged organic-inorganic composite particles were prepared for the application to electrophoretic display technology such as electronic paper. $TiO_2$ and $Co_3O_4$ particles were used for core particles and were coated with poly(methyl methacrylate) by dispersion polymerization. Composite particles were endowed with charge moiety for electrophoresis; positive charge for $TiO_2$ and negative charge for $Co_3O_4$ composite particles. Scanning electron microscopic results revealed that the charged composite particles have spherical shape. Densities of the composite particles were controlled to be that of medium of electrophoresis. Density of $TiO_2$ particle changed from 4.02 to 1.44 g/$cm^3$ after the polymer coating, and that of $Co_3O_4$ particles changed from 6.11 to 1.49 g/$cm^3$. Urea, melamine, and formaldehyde were used as wall materials for capsule, and microcapsule containing black or white particles inside were prepared by in-situ polymerization. Microcapsule showed the inspection by a video microscope demonstrated the formation of uniform transparent capsules.

• Applied Chemistry for Engineering
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• v.22 no.5
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• pp.551-554
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• 2011

One of the key issues in the research of organic field-effect transistors (OFETs) is the low-voltage operation. To address this issue, we synthesized poly(styrene-r-benzocyclobutene-r-methyl methacrylate) (P(S-r-BCB-r-MMA)) as a thermally cross-linkable gate dielectrics. The P(S-r-BCB-r-MMA) showed high quality dielectric properties due to the negligible volume change during the cross-linking. The pentacene FETs based on the 34 nm-thick P(S-r-BCB-r-MMA) gate dielectrics operate below 5 V. The P(S-r-BCB-r-MMA) gate dielectrics yielded high device performance, i.e. a field-effect mobility of $0.25cm^2/Vs$, a threshold voltage of -2 V, an sub-threshold slope of 400 mV/decade, and an on/off current ratio of ${\sim}10^5$. The thermally cross-linkable P(S-r-BCB-r-MMA) will provide an attractive candidate for solution-processable gate dielectrics for low-voltage OFETs.

• Applied Chemistry for Engineering
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• v.18 no.1
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• pp.71-76
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• 2007

We have demonstrated the resonant resistance pattern changes of the polymer film in the quartz crystal analysis by the function of the molecular polarity phase transition phenomena. PVA and PMMA/PVAc blend films were used as hydrophilic and/or hydrophbic film, respectively. In the comparison between the hydrophilic shows the pattern changes near by the phase transition temperature. For more detailed explanation, the static capacity in the oscillation parameter was measured and the morphology of Au quartz crystal electrode was studied by AFM. It is suggested that the different resonant resistance pattern change is reliable in the condition of different polarity, and the conclusion is important to analysis of the real mechanism a normal quartz crystal experiments.

• Korean Chemical Engineering Research
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• v.46 no.6
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• pp.1100-1106
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• 2008

In this study, we presented rapid and simple fabrication method of functionalized surface on various substrates as a universal platform for the selective immobilization of cells. The functionalized surface was achieved by using deposition of polyelectrolyte such as poly(allyamine hydrochloride) (PAH), poly(diallyldimethyl ammonium chloride) (PDAC), poly(4-ammonium styrene sulfonic acid) (PSS), poly(acrylic acid) (PAA) and fabrication of poly(ethylene glycol) (PEG) microstructure through micro-molding in capillaries (MIMIC) technique on each glass, poly(methyl methacrylate) (PMMA), polystyrene (PS) and poly(dimethyl siloxane) (PDMS) substrate. The polyelectrolyte multilayer provides adhesion force via strong electrostatic attraction between cell and surface. On the other hand, PEG microstructures also lead to prevent non-specific binding of cells because of physical and biological barrier. The characteristic of each modified surface was examined by using static contact angle measurement. The modified surface onto several substrates provides appropriate environment for cellular adhesion, which is essential technology for cell patterning with high yield and viability in the micropatterning technology. The proposed method is reproducible, convenient and rapid. In addition, the fabrication process is environmentally friendly process due to the no use of harsh solvent. It can be applied to the fabrication of biological sensor, biomolecules patterning, microelectronics devices, screening system, and study of cell-surface interaction.

• The Journal of Advanced Prosthodontics
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• v.4 no.1
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• pp.30-36
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• 2012

PURPOSE. The aim of this in-vitro investigation was to describe the effect of reinforcement with different fibers on impact strength of heat polymerized poly-methyl methacrylate (PMMA) denture base resin and to analyze the effect of surface treatment of the fibers on the impact strength. MATERIALS AND METHODS. The specimens were fabricated from the dies formed as per standard ASTM D4812. 2% by weight of glass, polyethylene and polypropylene fibers were incorporated in the PMMA resin. The Izod impact testing was performed on the unnotched specimens and the values obtained were analyzed using appropriate one way ANOVA, followed by unpaired t-test. Fractured ends of the samples were subjected to the SEM analysis. RESULTS. The polypropylene fibers with plasma treatment showed the highest impact strength ($9.229{\times}10^2$ J/m) followed by the plasma treated polyethylene fibers ($9.096{\times}10^2$ J/m), untreated polypropylene fibers ($8.697{\times}10^2$ J/m), untreated polyethylene fibers ($7.580{\times}10^2$ J/m), silane treated glass fibers ($6.448{\times}10^2$ J/m) and untreated glass fibers ($5.764{\times}10^2$ J/m). Also the surface treatment of all the fibers has shown the significant improvement in impact strength. Findings of the SEM analysis justified the improvement in impact strength after surface treatment. CONCLUSION. Reinforcement with the fiber is an effective method to increase the impact strength of PMMA denture base resin. The surface treatment of fibers further increases the impact strength significantly.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.76-76
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• 2012

Surface engineering of polymers has a broad array of scientific and technological applications that range from tissue engineering, regenerative medicine, microfluidics and novel lab on chip devices to building mechanical memories, stretchable electronics, and devising tunable surface adhesion for robotics. Recent advancements in the field of nanotechnology have provided robust techniques for controlled surface modification of polymers and creation of structural features on the polymeric surface at submicron scale. We have recently demonstrated techniques for controlled surfaces of soft and relatively hard polymers using ion beam irradiation and plasma treatment, which allows the fabrication of nanoscale surface features such as wrinkles, ripples, holes, and hairs with respect to its polymers. In this talk, we discuss the underlying mechanisms of formation of these structural features. This includes the change in the chemical composition of the surface layer of the polymers due to ion beam irradiation or plasma treatment and the instability and mechanics of the skin-substrate system. Using ion beam or plasma irradiation on polymers, we introduce a simple method for fabrication of one-dimensional, two-dimensional and nested hierarchical structural patterns on polymeric surfaces on various polymers such as polypropylene (PP), polyethylene (PE), poly (methyl methacrylate) PMMA, and polydimethylsiloxane (PDMS).

• Steel and Composite Structures
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• v.23 no.5
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• pp.529-541
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• 2017

In the present study, vibration analysis of functionally graded carbon nanotube reinforced composite (FGCNTRC) plate moving in two directions is investigated. Various types of shear deformation theories are utilized to obtain more accurate and simplest theory. Single-walled carbon nanotubes (SWCNTs) are selected as a reinforcement of composite face sheets inside Poly methyl methacrylate (PMMA) matrix. Moreover, different kinds of distributions of CNTs are considered. Based on extended rule of mixture, the structural properties of composite face sheets are considered. Motion equations are obtained by Hamilton's principle and solved analytically. Influences of various parameters such as moving speed in x and y directions, volume fraction and distribution of CNTs, orthotropic viscoelastic surrounding medium, thickness and aspect ratio of composite plate on the vibration characteristics of moving system are discussed in details. The results indicated that thenatural frequency or stability of FGCNTRC plate is strongly dependent on axially moving speed. Moreover, a better configuration of the nanotube embedded in plate can be used to increase the critical speed, as a result, the stability is improved. The results of this investigation can be used in design and manufacturing of marine vessels and aircrafts.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.301.1-301.1
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• 2016

We report an ultraclean, cost-effective, and easily scalable method of transferring and patterning large-area graphene using pressure sensitive adhesive films (PSAFs) at room temperature. This simple transfer is enabled by the difference in wettability and adhesion energy of graphene with respect to PSAF and a target substrate. The PSAF transferred graphene is found to be free from residues, and shows excellent charge carrier mobility as high as ${\sim}17,700cm^2/V{\cdot}s$ with less doping compared to the graphene transferred by thermal release tape (TRT) or poly(methyl methacrylate) (PMMA) as well as good uniformity over large areas. In addition, the sheet resistance of graphene transferred by recycled PSAF does not change considerably up to 4 times, which would be advantageous for more cost-effective and environmentally friendly production of large-area graphene films for practical applications.