Pierre Wiltzius

Bio: Pierre Wiltzius is an academic researcher from University of Illinois at Urbana–Champaign. The author has contributed to research in topics: Colloidal crystal & Photonic crystal. The author has an hindex of 28, co-authored 55 publications receiving 4783 citations. Previous affiliations of Pierre Wiltzius include Alcatel-Lucent.

Template-directed colloidal crystallization

Abstract: Colloidal crystals are three-dimensional periodic structures formed from small particles suspended in solution. They have important technological uses as optical filters1–3, switches4 and materials with photonic band gaps5,6, and they also provide convenient model systems for fundamental studies of crystallization and melting7–10. Unfortunately, applications of colloidal crystals are greatly restricted by practical difficulties encountered in synthesizing large single crystals with adjustable crystal orientation11. Here we show that the slow sedimentation of colloidal particles onto a patterned substrate (or template) can direct the crystallization of bulk colloidal crystals, and so permit tailoring of the lattice structure, orientation and size of the resulting crystals: we refer to this process as 'colloidal epitaxy'. We also show that, by using silica spheres synthesized with a fluorescent core12,13, the defect structures in the colloidal crystals that result from an intentional lattice mismatch of the template can be studied by confocal microscopy14. We suggest that colloidal epitaxy will open new ways to design and fabricate materials based on colloidal crystals and also allow quantitative studies of heterogeneous crystallization in real space.

Electrochemically grown photonic crystals

Abstract: Colloidal crystallization has been explored for several years as a fabrication method for photonic crystals. While macroporous materials grown with silica or polymer colloids might exhibit pleasing opalescence, truly novel photonic behavior such as photonic band-gaps, is expected only for very high index of refraction contrast systems. This can possibly be achieved through electrodeposition of semiconductors, polymers, or metals in the interstitial space of self-assembled colloids. 2002 Elsevier Science Ltd. All rights reserved.

Patterned colloidal deposition controlled by electrostatic and capillary forces.

Abstract: We use substrates chemically micropatterned with anionic and cationic regions to govern the deposition of charged colloidal particles. The direct observation of the colloidal assembly suggests that this process includes two steps: an initial patterned attachment of colloids to the substrate and an additional ordering of the structure upon drying. The driving forces of the process, i.e., screened electrostatic and lateral capillary interactions, are discussed. This approach makes it possible to fabricate complex, high-resolution two-dimensional arrays of colloidal particles.

Direct‐Write Assembly of 3D Hydrogel Scaffolds for Guided Cell Growth

Abstract: The ability to pattern soft materials at the microscale is critical for several emerging technologies, including tissue-engineering scaffolds, photonic crystals, sensors, and self-healing materials. Hydrogels are an important class of soft materials that can be fabricated in the form of 3D microperiodic structures by colloidal templating or interference lithography. However, neither approach allows one to omnidirectionally vary the spacing between patterned features over length scales ranging from sub-micrometer to tens of micrometers. By contrast, direct-write assembly enables a wide array of materials to be patterned in nearly arbitrary shapes and dimensions. Here, we report the fabrication of 1D and 3D microperiodic hydrogel scaffolds by direct-write assembly of an acrylamide-based ink. For the first time, we combine direct ink writing with in situ photopolymerization to obtain hydrogel scaffolds with micrometer-sized features (see Fig. 1). By plating 3T3 murine fibroblasts onto one-, two-, and four-layer hydrogel scaffolds, we demonstrate their cytocompatibility and, hence, potential suitability for tissue-engineering applications. Direct ink writing (DIW) is a layer-by-layer assembly technique in which materials are patterned in both planar and 3D forms with lateral feature sizes that are at least an order of magnitude smaller than those achieved by ink-jet printing and other rapid prototyping approaches, and nearly comparable in size to those produced by two-photon polymerization and interference holography. Central to our approach is the creation of concentrated inks that can be extruded through fine deposition nozzles in filamentary form, and then undergo rapid solidification to maintain their shape even as they span gaps in the underlying layer(s). Unlike prior efforts on polyelectrolyte inks that required reservoir-induced coagulation to enable 3D printing, we report the creation of hydrogel inks that can be printed directly in air, where they undergo solidification via photopolymerization (see Fig. 1a and b). The ink is created by first mixing monomeric acrylamide, glycerol, and water. Upon ageing for several hours under ambient conditions, the monomeric species polymerizes to yield a gel composed of 30w/o polyacrylamide chains. H NMR reveals that peaks associated with acrylamide, which are initially present, disappear after polymerization, followed by the emergence of two new peaks that correspond to alkyl chains (data not shown). Concomitantly, as the solution ages, sharp rises in both the shear elastic, G0, and loss, G00, moduli are observed, suggesting that the resulting gel is composed of physically entangled polyacrylamide chains (see Fig. 2a). To determine their degree of polymerization, N, the intrinsic viscosity, [h]0, of diluted polymer solutions is measured by capillary viscometry, and found to be [h]0 270mL g 1 (see Fig. 2b). Using the Mark– Houwink relation, h 1⁄2 01⁄4 KM, their molecular weight is determined to be 8.9 10 gmol , where K is 9.3 10 3 and a is taken to be 0.75 for polyacrylamide dissolved in an aqueous solution (0.5M NaCl). Hence, this initial polymerization process yields polyacrylamide chains with an average degree of polymerization N1⁄4 1.3 10 that is well above the entanglement value of Ne1⁄4 128. To further optimize the ink for direct-write assembly, this polymerizedmixture is diluted by addingmonomeric acrylamide, a crosslinking agent, N, N methylene bisacrylamide, a photoinitiator, diethoxyacetophenone, and deionized water at weight ratios (w/w) of 0.480, 0.036, 0.004, and 0.480, respectively. Notably, the initial polymerization step could be eliminated simply by adding high-molecular-weight polyacrylamide chains

Monolithically integrated, flexible display of polymer-dispersed liquid crystal driven by rubber-stamped organic thin-film transistors

Abstract: This letter describes the monolithic integration of rubber-stamped thin-film organic transistors with polymer-dispersed liquid crystals (PDLCs) to create a multipixel, flexible display with plastic substrates. We report the electro-optic switching behavior of the PDLCs as driven by the organic transistors, and we show that our displays operate robustly under flexing and have a contrast comparable to that of newsprint.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Chemistry and properties of nanocrystals of different shapes.

Abstract: The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Self-assembly at all scales.

Abstract: Self-assembly is the autonomous organization of components into patterns or structures without human intervention. Self-assembling processes are common throughout nature and technology. They involve components from the molecular (crystals) to the planetary (weather systems) scale and many different kinds of interactions. The concept of self-assembly is used increasingly in many disciplines, with a different flavor and emphasis in each.

Synthesis and Characterization of Monodisperse Nanocrystals and Close-Packed Nanocrystal Assemblies

Abstract: ▪ Abstract Solution phase syntheses and size-selective separation methods to prepare semiconductor and metal nanocrystals, tunable in size from ∼1 to 20 nm and monodisperse to ≤5%, are presented. Preparation of monodisperse samples enables systematic characterization of the structural, electronic, and optical properties of materials as they evolve from molecular to bulk in the nanometer size range. Sample uniformity makes it possible to manipulate nanocrystals into close-packed, glassy, and ordered nanocrystal assemblies (superlattices, colloidal crystals, supercrystals). Rigorous structural characterization is critical to understanding the electronic and optical properties of both nanocrystals and their assemblies. At inter-particle separations 5–100 A, dipole-dipole interactions lead to energy transfer between neighboring nanocrystals, and electronic tunneling between proximal nanocrystals gives rise to dark and photoconductivity. At separations <5 A, exchange interactions cause otherwise insulating ass...