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Acharya Himadri,Srivastava Suneel K. The Polymer Society of Korea 2006 Macromolecular Research Vol.14 No.2
The dispersion of organoclay in ethylene propylene diene terpolymer (EPDM) matrix was correlated with the rheological and swelling properties of nanocomposites. X-ray diffraction pattern (XRD) and transmission electron microscopic (TEM) analysis exhibited the disordered-intercalated structure of EPDM/organoclay nanocomposite. The extent of the disordered phase increased with increasing organoclay content up to a limiting value of 3 wt% after which equilibrium tended towards intercalation. The dispersion effect of organoclay in EPDM matrix was clarified by the physicochemical properties like rheological response and swelling thermodynamics in toluene. The increase in viscoelastic properties of EPDM nanocomposite with increasing organoclay content up to 3 wt%, followed by a subsequent decrease up to 4 wt%, was correlated in terms of the disordered and ordered states of the dispersed nano-clay sheets. Swelling measurements revealed that the change in entropy of the swelling increased with the increase in disorder level but decreased with the increase in intercalation level of organoclay in the disordered-intercalated nanocomposite. The increase in solvent uptake was comparable with the free volume in EPDM matrix upon inclusion of silicate particles, whereas the inhibition in solvent uptake for higher organoclay loading was described by bridging flocculation.
Block Copolymer Micelles with Near Infrared Metal Phthalocyanine Dyes for Laser Induced Writing
Acharya, Himadri,Yoon, Bokyung,Park, Youn Jung,Bae, Insung,Park, Cheolmin WILEY-VCH Verlag 2010 Macromolecular Rapid Communications Vol.31 No.12
<P>A route has been developed to disperse metal-containing phthalocyanine dyes in a non-polar medium based on amphiphilic block copolymer micelles of poly[styrene-block-(4-vinylpyridine)] (PS-b-P4VP) and poly[styrene-block-(acrylic acid)] (PS-b-PAA) copolymers. Polar P4VP and PAA efficiently encapsulate cobalt(II), manganese(II), and nickel(II) phthalocyanine dyes by axial coordination of nitrogen and µ-oxo bridged dimerization with the transition metals, respectively. Good dispersion of the dyes is confirmed by the linear enhancement of Q-bands in UV–vis absorption spectra with dye concentration. A thin monolayered PS-b-P4VP micelle film that contained a nickel(II) phthalocyanine dye which efficiently adsorbs a laser beam on a localized area to generate a local heat higher than the glass transition temperatures of both blocks. One-dimensional laser writing on the dye-containing film allows the fabrication of a few submicrometer wide line patterns in which the self-assembled nanostructure of the block copolymer is modified by the directional heat arising from laser scanning.</P><P> <img src='wiley_img_2010/10221336-2010-31-12-MARC201000032-gra001.gif' alt='wiley_img_2010/10221336-2010-31-12-MARC201000032-gra001'> </P> <B>Graphic Abstract</B> <P>Metal-containing (Co<SUP>II</SUP>, Mn<SUP>II</SUP>, and Ni<SUP>II</SUP>) phthalocyanine (Pc) dyes dispersed in a non-polar medium based on amphiphilic block copolymer micelles of poly[styrene-block-(4-vinylpyridine)] (PS-b-P4VP) and poly[styrene-block-(acrylic acid)] (PS-b-PAA) copolymers are investigated. Linear enhancement of Q-bands in the UV–vis absorption spectra with dye concentration confirms the good dispersion. Laser absorption by a thin monolayered PS-b-P4VP micelle film with Ni-Pc allowed the writing of line patterns. <img src='wiley_img_2010/10221336-2010-31-12-MARC201000032-content.gif' alt='wiley_img_2010/10221336-2010-31-12-MARC201000032-content'> </P>
Lee, Geun-Tak,Yoon, Bo-Kyung,Acharya, Himadri,Park, Cheol-Min,Huh, June The Polymer Society of Korea 2009 Macromolecular Research Vol.17 No.3
We fabricated ordered micro/nano patterns induced by controlled dewetting on the topographically patterned PS/P4VP bilayer thin film. The method is based on utilizing microimprinting lithography to induce a topographically heterogeneous bilayer film that allows the controlled dewetting upon subsequent thermal annealing. The dewetting that was initiated strictly at the boundary of the thicker and thinner regions was guided by the presence of the topographic structure. The dewetting front velocity of the microdomains in the confined regions was linearly proportional to the measurement time, which enabled us to control the size of the dewet domain with annealing time. In particular, the submicron sized dot arrays between lines were generated with ease when the dewetting was confined into geometry with a few microns in size. The kinetically driven, non-lithographical pattern structures accompanied the pattern reduction to 400%. The pattern arrays on a transparent glass substrate were especially useful for non-circular microlens arrays where the focal length of the lens was easily tunable by controlling the thermal annealing.
Kim, Tae Hee,Hwang, Jiyoung,Acharya, Himadri,Park, Cheolmin American Scientific Publishers 2010 Journal of Nanoscience and Nanotechnology Vol.10 No.10
<P>We investigate the effect of water/benzene co-solvent vapor on the ordering of poly(styrene-b-ethylene oxide) (PS-b-PEO) copolymer thin film on silicon substrate upon solvent annealing. In-plane cylindrical PEO microdomains were observed after exposure of benzene vapor. The addition of water vapor dominantly produced the cylindrical PEO domains aligned perpendicular to the substrate. The best ordering of the cylinders was obtained at the water fraction of approximately 0.05. The degree of ordering decreases while the periodicity of haxagonally packed PEO cylinders increases with the amount of water in the vapor mixture. The average center-to-center distance of hexagonally packed cylindrical PEO microdomains increases with the water fraction from approximately 25 nm to 40 nm. As one way of utilizing the dewetting of thin films inevitable during solvent annealing, PS-b-PEO micropatterns prepared by microcontact printing were treated with co-solvent vapor, which allows us to fabricate the controlled dewet structures guided by the micropatterns. Cylinder-to-sphere phase transition of PEO microdomains also occurred upon solvent annealing in the micropatterned PS-b-PEO films.</P>