George M. Whitesides

Bio: George M. Whitesides is an academic researcher from Harvard University. The author has contributed to research in topics: Microcontact printing & Self-assembled monolayer. The author has an hindex of 240, co-authored 1739 publications receiving 269833 citations. Previous affiliations of George M. Whitesides include University of California, Davis & University of Texas at Austin.

Complex Optical Surfaces Formed by Replica Molding Against Elastomeric Masters

Abstract: Complex, optically functional surfaces in organic polymers can be fabricated by replicating relief structures present on the surface of an elastomeric master with an ultraviolet or thermally curable organic polymer, while the master is deformed by compression, bending, or stretching. The versatility of this procedure for fabricating surfaces with complex, micrometer- and submicrometer-scale patterns was demonstrated by the production of (i) diffraction gratings with periods smaller than the original grating; (ii) chirped, blazed diffraction gratings (where the period of a chirped grating changes continuously with position) on planar and curved surfaces; (iii) patterned microfeatures on the surfaces of approximately hemispherical objects (for example, an optical surface similar to a fly's eye); and (iv) arrays of rhombic microlenses. These topologically complex, micropatterned surfaces are difficult to fabricate with other techniques.

Foldable Printed Circuit Boards on Paper Substrates

Abstract: This paper describes several low-cost methods for fabricating flexible electronic circuits on paper. The circuits comprise i) metallic wires (e.g., tin or zinc) that are deposited on the substrate by evaporation, sputtering, or airbrushing, and ii) discrete surface-mountable electronic components that are fastened with conductive adhesive directly to the wires. These electronic circuits—like conventional printed circuit boards—can be produced with electronic components that connect on both sides of the substrate. Unlike printed circuit boards made from fiberglass, ceramics, or polyimides, however, paper can be folded and creased (repeatedly), shaped to form three-dimensional structures, trimmed using scissors, used to wick fluids (e.g., for microfluidic applications) and disposed of by incineration. Paper-based electronic circuits are thin and lightweight; they should be useful for applications in consumer electronics and packaging, for disposable systems for uses in the military and homeland security, for applications in medical sensing or low-cost portable diagnostics, for paper-based microelectromechanical systems, and for applications involving textiles.

Direct measurement of interfacial interactions between semispherical lenses and flat sheets of poly(dimethylsiloxane) and their chemical derivatives

Abstract: The deformations resulting on contacting small (1-2 mm) semispherical lenses of elastomeric poly-, (dimethylsiloxane) (PDMS) *ith the flat sheets of this material were measured in air and in mixtures of water and methanol. The measurements in air were carried out in two ways: as a function of external loads, and under zero load but with variations in the sizes of the lenses. The measurements in liquids were carried out under zero load and varied the composition of the liquid mixtures. These experimental data were analyzed by using a theory of Johnson, Kendall and Roberts to obtain the works of adhesion between PDMS suifaces in the air and liquid media. The strength of interaction between PDMS surfaces decreased in mixtures of water and methanol as the concentration of methanol increased. A small interaction persisted even in pure methanol. The interfacial free energies (t.r) of the PDMS-liquid interfaces obtained from these measurements, together with the contact angles of these liquids on PDMS, were analyzed by using Young's equation. This analysis provided an estimate of the surface free energ-v of the polymer (y.") that was consistent both with the value obtained from measurements made in air and with the value estimated from the analysis of the contact angles of nonpolar liquids on PDMS using the Good-Girifalco-Fowkes equation. This research also developed ways to modify the surface of PDMS chemically and thus to control its properties. The chemically derivatized poly(dimethylsiloxanes), in the form of lenses and flat sheets, were subjected to load-deformation measurements similar to those used for unmodified PDMS. These functionalized PDMS surf'aces exhibited hysteresis in contact deformations, whereas no hysteresis was detected for unmodified PDMS. The origin of this hysteresis is not clear at present. The observation of hysteresis at solid-solid interfaces is relevant to understanding adhesion to these surfaces. 1013

Components for integrated poly(dimethylsiloxane) microfluidic systems.

Abstract: This review describes the design and fabrication of microfluidic systems in poly(dimethylsiloxane) (PDMS). PDMS is a soft polymer with attractive physical and chemical properties: elasticity, optical transparency, flexible surface chemistry, low permeability to water, and low electrical conductivity. Soft lithography makes fabrication of microfluidic systems in PDMS particularly easy. Integration of components, and interfacing of devices with the user, is also convenient and simpler in PDMS than in systems made in hard materials. Fabrication of both single and multilayer microfluidic systems is straightforward in PDMS. Several components are described in detail: a passive chaotic mixer, pneumatically actuated switches and valves, a magnetic filter, functional membranes, and optical components.

Structures of self-assembled monolayer films of organosulfur compounds adsorbed on gold single crystals: electron diffraction studies

Abstract: : Transmission electron microscopy and diffraction have been used to study the packing arrangements of docosyl thiol (RSH), didocosyl sulfide (RSR), and didocosyl disulfide (RSSR) on gold single crystal foils. The specimens include gold films in (100) and (111) orientations. Docosyl thiol and didocosyl disulfide adsorbed on (111) faces assemble in coincidence lattice structures yielding hexagonal overlayers c(7 x 7) in which the short interchain distance indicates freely rotating methylene chains. On a (100) surface both alkyl groups exhibit an in-plane structure consisting of a base-centered square array in which the interchain distance implies a hindered chain movement. We have presented evidence that substrate crystallography does control the packing of monolayer alkyl sulfides adsorbed from the solution phase.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

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。

The Theory of Island Biogeography

Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

Large-scale pattern growth of graphene films for stretchable transparent electrodes

Abstract: Problems associated with large-scale pattern growth of graphene constitute one of the main obstacles to using this material in device applications. Recently, macroscopic-scale graphene films were prepared by two-dimensional assembly of graphene sheets chemically derived from graphite crystals and graphene oxides. However, the sheet resistance of these films was found to be much larger than theoretically expected values. Here we report the direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers, and present two different methods of patterning the films and transferring them to arbitrary substrates. The transferred graphene films show very low sheet resistance of approximately 280 Omega per square, with approximately 80 per cent optical transparency. At low temperatures, the monolayers transferred to silicon dioxide substrates show electron mobility greater than 3,700 cm(2) V(-1) s(-1) and exhibit the half-integer quantum Hall effect, implying that the quality of graphene grown by chemical vapour deposition is as high as mechanically cleaved graphene. Employing the outstanding mechanical properties of graphene, we also demonstrate the macroscopic use of these highly conducting and transparent electrodes in flexible, stretchable, foldable electronics.

Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites

Abstract: Multilayer films of organic compounds on solid surfaces have been studied for more than 60 years because they allow fabrication of multicomposite molecular assemblies of tailored architecture. However, both the Langmuir-Blodgett technique and chemisorption from solution can be used only with certain classes of molecules. An alternative approach—fabrication of multilayers by consecutive adsorption of polyanions and polycations—is far more general and has been extended to other materials such as proteins or colloids. Because polymers are typically flexible molecules, the resulting superlattice architectures are somewhat fuzzy structures, but the absence of crystallinity in these films is expected to be beneficial for many potential applications.