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.

Flowing crystals: nonequilibrium structure of foam.

Abstract: Bubbles pushed through a quasi-two-dimensional channel self-organize into a variety of periodic lattices. The structures of these lattices correspond to local minima of the interfacial energy. The "flowing crystals" are long-lived metastable states, a small subset of possible local minima of confined quasi-two-dimensional foams [P. Garstecki and G. M. Whitesides, Phys. Rev. E 73, 031603 (2006)10.1103/PhysRevE.73.031603]. Experimental results suggest that the choice of the structures that we observe is dictated by the dynamic stability of the cyclic processes of their formation. Thus, the dynamic system that we report provides a unique example of nonequilibrium self-organization that results in structures that correspond to local minima of the relevant energy functional.

Patterned polymer multilayers as etch resists

Abstract: This paper describes the synthesis and characterization of patterned polymer multilayers on self-assembled monolayers (SAMs) and the use of these structures as etch resists for gold The procedure used to build polymer multilayers consisted of five steps: (i) A polar thiolHS(CH2)15COOHwas patterned on gold or silver films by microcontact printing (μCP) with a poly(dimethylsiloxane) (PDMS) stamp (ii) The patterned surface was placed in a solution containing CH3(CH2)15SH to form a nonpolar, methyl-terminated SAM on the remaining bare metal surface (iii) The regions of the SAM patterned with CO2H groups were activated for further chemical reaction by conversion into interchain anhydride groups (iv) The activated substrate was allowed to react with poly(ethylene imine) (PEI, branched chain, Mw 750 000) (v) A second polymer layer was attached to the PEI layer by allowing the amine-terminated surface to react with poly(octadecene-alt-maleic anhydride) (POMA, Mw 30 000) or poly(styrene-alt-maleic anhydride)

Customization of Poly(dimethylsiloxane) Stamps by Micromachining Using a Femtosecond‐Pulsed Laser

Abstract: This work describes the use of focused, high-intensity light from a Ti:sapphire laser that generates femtosecond pulses to create topographical structure in a flat surface of poly(di-methylsiloxane) (PDMS), and the use of the PDMS surfaces patterned using this procedure for a range of purposes. PDMS patterned in surface bas-relief is the material most widely used for printing and stamping in soft lithography, [1,2] and a material widely used in microfluidic systems. [3] The bas-relief patterns required in these applications are usually fabricated by casting PDMS against a complementary bas-relief pattern in photoresist, fabricated in turn by photolithography. This process works well, but is not applicable to the preparation of PDMS stamps required for all types of problems; printing on spherical surfaces is an example. The technique described here permits the non-photolitho-graphic generation of surface topography for use in soft lithography and microfluidics; this technique has three useful characteristics: i) It generates features smaller than those generated by standard rapid-prototyping techniques based on printed transparency masks. [1,2] ii) It is applicable to fabrication on non-planar surfaces. iii) It can be used in fabrication of large-area patterns. The rough, recessed features generated by this technique are useful for applications where large surface area to volume ratios are desired, e.g., in catalysis, [7] for super-hydrophobic surfaces, [8±10] in surface-enhanced Raman scattering, [11,12] and as magnetic field concentrators. [13±15] It has the disadvantages that it is a serial process, and that the laser and positioning equipment are relatively specialized. The only requirement for the material is that it must be transparent to 800 nm light: PDMS works well, but other transparent elastomeric polymers should also work. Laser ablation is a common technique for direct writing of patterns into the surfaces of metals, semiconductors, and polymers. [16,17] Most of the techniques that have been described for laser writing work through an absorption mechanism for light that is linear in light intensity. This sort of photochemistry typically requires doping of the material with sensitizers [18±20] and/or the use of UV lasers. [21,22] We have previously described the production of stamps for microcontact printing (lCP) by ablation of a doped polymer with a diode-pumped Nd:YVO 4 laser. [20] Line widths of the features produced through this technique are ~ 5 lm. This technique, as described, is substantially less useful than rapid prototyping. Another process, developed by Hull and co-workers, used a focused ion beam (FIB) to write …

Contact de-electrification of electrostatically charged polymers.

Abstract: The contact electrification of insulating organic polymers is still incompletely understood, in part because multiple fundamental mechanisms may contribute to the movement of charge. This study describes a mechanism previously unreported in the context of contact electrification: that is, “contact de-electrification”, a process in which polymers charged to the same polarity discharge on contact. Both positively charged polymeric beads, e.g., polyamide 6/6 (Nylon) and polyoxymethylene (Delrin), and negatively charged polymeric beads, e.g., polytetrafluoroethylene (Teflon) and polyamide-imide (Torlon), discharge when the like-charged beads are brought into contact. The beads (both with charges of ∼±20 μC/m2, or ∼100 charges/μm2) discharge on contact regardless of whether they are made of the same material, or of different materials. Discharge is rapid: discharge of flat slabs of like-charged Nylon and Teflon pieces is completed on a single contact (∼3 s). The charge lost from the polymers during contact de-...

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.