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RISS 인기검색어
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- 저자 : Bockstaller, Michael R. (검색결과 2 건)
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Role of Grain Boundary Defects During Grain Coarsening of Lamellar Block Copolymers
Ryu, Hyung Ju,Fortner, David B.,Lee, Sukbin,Ferebee, Rachel,De Graef, Marc,Misichronis, Konstantinos,Avgeropoulos, Apostolos,Bockstaller, Michael R. American Chemical Society 2013 Macromolecules Vol.46 No.1
<P>The evolution of grain size and shape as well as type and frequency of grain boundary structures during thermal annealing of lamellar diblock copolymer microstructures is established using large area image reconstruction and analysis. Grain coarsening is found to proceed via an initial transient stage that is characterized by the rapid relaxation of unstable “frozen-in” defects such as kink boundaries and the subsequent quasi-stationary coarsening that is dominated by the continuous relaxation of low-angle symmetric tilt boundaries. The particular relevance of low-angle symmetric tilt boundaries to grain coarsening is interpreted as the consequence of both the associated decrease of boundary energy as well as the availability of favorable kinetic pathwayssuch as grain boundary splittingto facilitate the coarsening process. The inverse relation between grain boundary energy and frequency suggests that the reduction of boundary energy is a relevant governing parameter for the evolution of grain boundary structuresas it is in inorganic materials. The existence of “inert” boundary types (such as asymmetric tilt and twist) thatwithin the experimental windowdo not participate in the coarsening process is expected to have dominant influence on the final morphology that can be attained by thermal annealing of the microstructure. The reduction of the density of inert boundaries during the film preparation process should therefore provide a strategy for increasing the coarsening kinetics in block copolymer films during thermal annealing and thus a path toward a higher degree of order in block copolymer microstructures.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2013/mamobx.2013.46.issue-1/ma3015382/production/images/medium/ma-2012-015382_0015.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ma3015382'>ACS Electronic Supporting Info</A></P>
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Schmitt, Michael,Choi, Jihoon,Min Hui, Chin,Chen, Beibei,Korkmaz, Emrullah,Yan, Jiajun,Margel, Shlomo,Burak Ozdoganlar, O.,Matyjaszewski, Krzysztof,Bockstaller, Michael R. The Royal Society of Chemistry 2016 SOFT MATTER Vol.12 No.15
<P>The effect of polymer modification on the deformation characteristics and processibility of particle assembly structures is analyzed as a function of particle size and degree of polymerization of surface-tethered chains. A pronounced increase of the fracture toughness (by approximately one order of magnitude) is observed as the degree of polymerization exceeds a threshold value that increases with particle size. The threshold value is interpreted as being related to the transition of tethered chains from stretched-to-relaxed conformation (and the associated entanglement of tethered chains) and agrees with predictions from scaling theory. The increase in toughness is reduced with increasing particle size - this effect is rationalized as a consequence of the decrease of entanglement density with increasing dimension of interstitial (void) space in particle array structures. The increased fracture toughness of particle brush materials (with sufficient degree of polymerization of tethered chains) enables the fabrication of ordered colloidal films and even complex 3D shapes by scalable polymer processing techniques, such as spin coating and micromolding. The results, therefore, suggest new opportunities for the processing of colloidal material systems that could find application in the economical fabrication of functional components or systems compromised of colloidal materials.</P>
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