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151. Controlling liquid crystal defects

Author

Gharbi, Mohamed A., primary, Beller, Daniel A., additional, Honglawan, Apiradee, additional, Stebe, Kathleen J., additional, Yang, Shu, additional, and Kamien, Randall D., additional

Published
2014
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157. Ring around the colloid

Author

Cavallaro Jr, Marcello, primary, Gharbi, Mohamed A., additional, Beller, Daniel A., additional, Čopar, Simon, additional, Shi, Zheng, additional, Kamien, Randall D., additional, Yang, Shu, additional, Baumgart, Tobias, additional, and Stebe, Kathleen J., additional

Published
2013
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158. Near field capillary repulsion

Author

Yao, Lu, primary, Botto, Lorenzo, additional, Cavallaro, Jr, Marcello, additional, Bleier, Blake J., additional, Garbin, Valeria, additional, and Stebe, Kathleen J., additional

Published
2013
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159. Direct mapping of local director field of nematic liquid crystals at the nanoscale.

Author

Yu Xia, Serra, Francesca, Kamien, Randall D., Stebe, Kathleen J., and Shu Yang

Subjects
NEMATIC liquid crystals, DIPOLE-dipole interactions, ANISOTROPY, PHASE separation, PHOTOPOLYMERIZATION
Abstract

Liquid crystals (LCs), owing to their anisotropy in molecular ordering, are of wide interest in both the display industry and soft matter as a route to more sophisticated optical objects, to direct phase separation, and to facilitate colloidal assemblies. However, it remains challenging to directly probe the molecular-scale organization of nonglassy nematic LC molecules without altering the LC directors. We design and synthesize a new type of nematic liquid crystal monomer (LCM) system with strong dipole-dipole interactions, resulting in a stable nematic phase and strong homeotropic anchoring on silica surfaces. Upon photopolymerization, the director field can be faithfully "locked," allowing for direct visualization of the LC director field and defect structures by scanning electron microscopy (SEM) in real space with 100-nm resolution. Using this technique, we study the nematic textures in more complex LC/colloidal systems and calculate the extrapolation length of the LCM. [ABSTRACT FROM AUTHOR]

Published
2015
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180. New technology and clinical applications of nanomedicine: Highlights of the second annual meeting of the American Academy of Nanomedicine (Part I)

Author

Wei, Chiming, primary, Lyubchenko, Yuri L., additional, Ghandehari, Hamid, additional, Hanes, Justin, additional, Stebe, Kathleen J., additional, Mao, Hai-Quan, additional, Haynie, Donald T., additional, Tomalia, Donald A., additional, Foldvari, Marianna, additional, Monteiro-Riviere, Nancy, additional, Simeonova, Petia, additional, Nie, Shuming, additional, Mori, Hidezo, additional, Gilbert, Susan P., additional, and Needham, David, additional

Published
2006
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196. In SituMechanical Testing of Nanostructured Bijel Fibers

Author

Haase, Martin F., Sharifi-Mood, Nima, Lee, Daeyeon, and Stebe, Kathleen J.

Abstract

Bijels are a class of soft materials with potential for application in diverse areas including healthcare, food, energy, and reaction engineering due to their unique structural, mechanical, and transport properties. To realize their potential, means to fabricate, characterize, and manipulate bijel mechanics are needed. We recently developed a method based on solvent transfer-induced phase separation (STRIPS) that enables continuous fabrication of hierarchically structured bijel fibers from a broad array of constituent fluids and nanoparticles using a microfluidic platform. Here, we introduce an in situtechnique to characterize bijel fiber mechanics at initial and final stages of the formation process within a microfluidics device. By manipulation of the hydrodynamic stresses applied to the fiber, the fiber is placed under tension until it breaks into segments. Analysis of the stress field allows fracture strength to be inferred; fracture strengths can be as high as several thousand Pa, depending on nanoparticle content. These findings broaden the potential for the use of STRIPS bijels in applications with different mechanical demands. Moreover, our in situmechanical characterization method could potentially enable determination of properties of other soft fibrous materials made of hydrogels, capillary suspensions, colloidal gels, or high internal phase emulsions.

Published
2016
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198. Exploiting imperfections in the bulk to direct assembly of surface colloids.

Author

Cavallaro, Jr., Marcello, Gharbi, Mohamed A., Belier, Daniel A., Čopar, Simon, Zheng Shi, Baumgart, Tobias, Shu Yang, Kamien, Randall D., and Stebe, Kathleen J.

Subjects
COLLOIDS, NEMATIC liquid crystals, DENSITY, MAGNETIC resonance imaging, MAGNETIC properties of thin films
Abstract

We exploit the long-ranged elastic fields inherent to confined nematic liquid crystals (LCs) to assemble colloidal particles trapped at the LC interface into reconfigurable structures with complex symmetries and packings. Spherical colloids with homeotropic anchoring trapped at the interface between air and the nematic IC 4-cyano-4'-pentylbiphenyl create quadrupolar distortions in the director field causing particles to repel and consequently form close-packed assemblies with a triangular habit. Here, we report on complex open structures organized via interactions with defects in the bulk. Specifically, by confining the nematic LC in an array of microposts with homeotropic anchoring conditions, we cause defect rings to form at well-defined locations in the bulk of the sample. These defects source elastic deformations that direct the assembly of the interfacially trapped colloids into ring-like assemblies, which recapitulate the defect geometry even when the microposts are completely immersed in the nematic. When the surface density of the colloids is high, they form a ring near the defect and a hexagonal lattice far from it. Because topographically complex substrates are easily fabricated and LC defects are readily reconfigured, this work lays the foundation for a versatile, robust mechanism to direct assembly dynamically over large areas by controlling surface anchoring and associated bulk defect structure. [ABSTRACT FROM AUTHOR]

Published
2013
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