Orientational switching mesogens microdomains


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FULL PAPER Orientational Switching of Mesogens and Microdomains in Hydrogen Bonded Side Chain Liquid Crystalline Block Copolymers Using AC Electric Fields By Chi Yang Chao Xuefa Li Christopher K Ober Chinedum Osuji and Edwin L Thomas In this report we show that the microstructures of hydrogen bonded side chain liquid crystalline block copolymers can be rapidly aligned in an alternating current AC electric field at temperatures below the order disorder transition but above the glass transition The structures and their orientation were measured in real time with synchrotron X ray scattering Incorporation of mesogenic groups with marked dipolar properties is a key element in this process A mechanism related to the dissociation of hydrogen bonds is proposed to account for the fast orientation switching of the hydrogen bonded blends 1 Introduction Block copolymers BCPs can self assemble into highly regular microphase separated structures at length scales of several tens of nanometers 1 Desirable microstructures can be selected by varying the number of blocks the relative volume ratio between different blocks and their chemical composition Specific potential applications including template formation for nanolithographic patterning 2 or high density arrays of nanowires en route to thin films for optoelectronic devices 3 require not only well ordered microdomains but also macroscopic alignment of the microstructure Though a single BCP grain may have a highly anisotropic structure a bulk sample usually exhibits isotropic properties due to its polygrain nature The orientation of microstructures of thin films which is necessary for most potential electro optical applications depends on a variety of processing conditions and on such features as interfacial properties among polymers substrates and air unless some ordering field is applied One successful approach to alignment of BCPs is by means of applied mechanical fields BCP melts can be oriented by oscillatory shear 4 or

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