Braun Research Group - University of Illinois at Urbana-Champaign

News

December 2009, Frontispiece of Journal of Materials Chemistry, Vol. 19, No. 48

Complex three-dimensional conformal surfaces formed by atomic layer deposition.

November 2009, Nature Research Highlights, Vol. 462, No. 26

Featuring the publication by Jeong-Ho Park and Paul V. Braun: Coaxial Electrospinning of Self-Healing Coatings

SEE THE FORCE: MECHANICAL STRESS LEADS TO SELF-SENSING IN SOLID POLYMERS

Parachute cords, climbing ropes, and smart coatings for bridges that change color when overstressed are several possible uses for force-sensitive polymers being developed by researchers at the University of Illinois.

U of I News Bureau
Mechanochemically Active Polymers Web Page

February 2009, Frontispiece of Advanced Materials, Vol. 21 No.6
Dramatic reduction in corrosion of a steel plate coated with a self-healing coating (right) as compared to a conventional coating is demonstrated. Two samples were scratched and placed in 5% NaCl for 5 days. The background is an optical image (2× magnification), in the foreground is an SEM image of the scratch. In the self-healing sample, the scratch has almost completely self-healed, while in the control sample, the scratch remains all the way down to the substrate.

Self-healing Polymer Coatings
New polymer coatings prevent corrosion, even when scratched (see press release)

January 2009, Cover of Advanced Materials, Vol. 21 No.1
Here we report the use of direct laser writing topattern porous 3D structures from photo-responsive colloidal building blocks. Upon 2-photon exposure, the colloids become highly attractive, enabling localized control of aggregation behavior. 3D structures composed of porous walls are harvested by writing intoa colloidal sediment of these particles, followed by rinsing away unexposed colloidal species. Applications may include microfluidics, and studies of porous media, cellular growth and signaling, and colloidal physics. Cover art by Steven Eisenmann of the Beckman Institute VMIL.

Direct Laser Writing of Photoresponsive Colloids for
Microscale Patterning of 3D Porous Structures

January 2008, Cover of Nature Photonics,
Vol.2 No.1
Photonic crystals, artificially engineered nanoscale structures that can manipulate the flow of light, show great promise for building sophisticated optical circuitry that can route, filter, store or suppress optical signals. However, fabricating such circuitry presents a great challenge as defects need to be carefully incorporated into the photonic-crystal structure with great precision. Although this has been accomplished for two-dimensional designs that confine light in a plane, it is still an ongoing challenge for so-called complete-bandgap materials, where the defects need to be embedded into a three-dimensional structure. In this issue, Paul Braun and colleagues report the introduction of defects into a silicon three-dimensional photonic crystal by using a technique called two-photon polymerization. The result is waveguides that guide near-infrared light around sharp corners.
Article p52,News & Views p9, UIUC Press Release

Beckman Institute researchers, led by Paul Braun and Ben Grosser, receive $1.99 million National Science Foundation MRI award to acquire nano-CT instrument (see press release)

June 2007, Cover of Advanced Materials, Vol. 19, Issue 12
Germanium inverse woodpile 3D photonic crystals with a large (25%) photonic band gap in the infrared (background image) were fabricated through a multistep replication procedure. A polymer scaffold was first created by direct-write assembly, followed by the conformal growth of oxide and semiconductor layers, and removal of the polymer and oxide (foreground), ...as reported on p. 1567 by F. García-Santamaría, M. Xu, V. Lousse, S. Fan, P. V. Braun,
and J. A. Lewis.

May 2007: INVERSE WOODPILE STRUCTURE HAS EXTREMELY LARGE PHOTONIC BAND GAP
Researchers at the U. of I. have built an inverse woodpile structure of germanium, a material with a higher refractive index than silicon.
http://www.news.uiuc.edu/news/07/0521woodpile.html

November 2006, Cover of Advanced Functional Materials, Vol. 16, Issue 17
The direct ink writing of three-dimensional functional materials is detailed in the Feature Article by Lewis on p. 2193. The left side of the cover image displays schematic images that show the conversion of a direct-write polymer woodpile to a silicon hollow-woodpile structure. The 3 × 3 image matrix showcases the resulting silicon photonic crystal (center) surrounded by a higher-magnification view of a representative hollow silicon feature (ca. 1 m in diameter). The figure was prepared by F. Garcia-Santamaria, G. M. Gratson, and P. V. Braun.

The ability to pattern materials in three dimensions is critical for several technological applications, including composites, microfluidics, photonics, and tissue engineering. Direct-write assembly allows one to design and rapidly fabricate materials in complex 3D shapes without the need for expensive tooling, dies, or lithographic masks. Here, recent advances in direct ink writing are reviewed with an emphasis on the push towards finer feature sizes. Opportunities and challenges associated with direct ink writing are also highlighted.

June 22, 2004 Cover of Langmuir, Vol. 20, Issue 13
Cover illustration by Wonmok Lee and Paul V. Braun showing to the left a scanning electron microscope image of a substrate patterned with a periodic array of dimples formed through focused ion beam lithography and to the right a laser scanning confocal microscope cross section of a 3-D colloidal crystal formed by gravity-driven sedimentation from a binary mixture of 1.18 m diameter colloidal microspheres and 6 nm diameter highly charged nanoparticles onto this patterned substrate. After microsphere settling, the nanoparticle solution surrounding the colloidal crystal was gelled in situ by introducing ammonia vapor, which increased the pH and enabled drying with minimal microsphere rearrangement. The confocal image shown here was generated by infilling the dried colloidal crystal with an index-matched fluorescent dye solution prior to imaging. These colloidal crystals have very low defect densities and may be suitable for use as photonic crystals and as templates for photonic band gap materials. The dimple pitch and the volume fraction of microspheres in solution were found to strongly impact the quality of the resulting colloidal crystal. For more information see "Nanoparticle-Mediated Epitaxial Assembly of Colloidal Crystals on Patterned Substrates" by Wonmok Lee, Angel Chan, Michael A. Bevan, Jennifer A. Lewis, and Paul V. Braun on pages 5262-5270 of this issue. Copyright 2004 American Chemical Society

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