CBET Award Achievements
Notable Accomplishments from CBET Awards

Controlling Liquid Crystal Ordering in Soft Materials Using Microfluidics

Shelley Anna  -  Carnegie-Mellon University

Background:  Large, anisotropic (material properties depend on direction) molecules such as liquid crystals, surfactants, and polymers are found in products ranging from coatings and adhesives to pharmaceuticals and foods. Because many of these products are synthesized, processed, and used in a liquid state, understanding the complex flow behavior of the constituent liquids is essential to their design and optimization. Some anisotropic molecules can aggregate to form ordered microstructures such as layered molecular sheets, or lamellae. Flow fields and surface interactions can lead to the formation of defects in the lamellae, which strongly modify the flow behavior.

Results:  To date, studying the role of these defects on flow of lamellar liquids has been difficult since it has not been possible to control the specific defect microstructure and the flow independently. A new method of controlling the defect microstructure is being developed. The presence of nearby walls with tailored surface interactions in microchannels drives the formation of ordered defect arrays, as shown in the accompanying figure, which can then be subjected to controlled flow fields. The dynamics of the defect structures can then be observed.

Microchannels have been used to synthesize linear arrays of monodisperse defects in lamellar liquid crystals, and it was shown that there is a critical microchannel size below which no defects can form. Additionally, a train of monodisperse defects can be generated when slow flows are driven past a small obstruction in a microchannel. Images of these structures are shown in the accompanying figure.

Shelley Anna Image 1
Confinement-induced formation of microscale defects in layered liquids.
Static defect arrays arise from competing boundary conditions.

Credit:  Shahab Shojaei-zadeh, Carnegie Mellon University

Shelley Anna Image 2
Confinement-induced formation of microscale defects in layered liquids.
Dynamic defect formation via surface-tension driven flow past a small

Credit:  Shahab Shojaei-zadeh, Carnegie Mellon University

  This work is notable because the structure of lamellar defects has been controlled, employing microfluidics, such that their dynamics could be studied at the microscopic scale.  The ability to synthesize ordered monodisperse microstructures could impact development of novel applications that exploit this order, including optoelectronic devices and displays and templates for information storage media.

This work involves multidisciplinary research.  It requires the knowledge of fluid dynamics, macromolecular self-assembly and dynamics, surface chemistry, and microscale fabrication.  Disciplines involved include mechanical engineering, chemical engineering, materials science, and physics.  This work is high risk since it offers an innovative yet untested new method of both controlling and probing liquid crystal ordering in soft materials using microfluidic technology.  The results of these studies have the potential to impact both new and mature applications from displays to pharmaceuticals, as well as to advance a fundamental understanding of the fluid dynamics of self-organizing materials.

Program Officer:   Michael Plesniak
NSF Award Number:   0527909
Award Title:   SGER: Microfluidics as a Platform to Study Confinement of Complex Fluid Microstructures at Intermediate Length Scales
PI Names:   Shelley Anna
Institution Name:   Carnegie-Mellon University
Program Element:   1443
CBET Nugget:   FY 2006

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This Nugget was Updated on 24 September 2008.