Morphology control of structured polymer brushes

The surface-initiated photopolymerization (SIPP) of vinyl monomers on structured self-assembled monolayers, as defined by two-dimensional (2D) initiator templates for polymer growth, is investigated. The 2D templates are prepared by electron-beam chemical lithography (EBCL) of 4'-nitro-4-mercaptobiphenyl (NBT) and chemical conversion to an asymmetric azo initiator (4'-azomethylmalonodinitrile-1,1'-biphenyl-4-thiol). Ex situ kinetic studies of the SIPP process reveal a linear increase in the thickness of the polymer layer with the irradiation/polymerization time. The effect of the applied electron dosage during the EBCL process upon the final thickness of the polymer layer is also studied. The correlation between the electron-induced conversion of the 4'-nitro to the 4'-amino group and the layer thickness of the resulting polymer brush indicates that the polymer-brush grafting density can be directly controlled by the EBCL process. NBT-based template arrays are used for the combinatorial study of the influence of the lateral structure size and the irradiation dosage on the morphology of the resulting polymer-brush layer. Analysis of the array topography reveals the dependence of the thickness of the dry polymer layer on both electron dosage and structure size. This unique combination of EBCL as a lithographic technique to locally manipulate the surface chemistry and SIPP to amplify the created differences allows the preparation of defined polymer-brush layers of controlled morphologies.     

聚合物刷子的合成及应用

概述了聚合物刷子的最新进展情况，并着重介绍了固定于固体基体表面的线型聚合物刷子。讨论了聚合物刷子的结构特征；聚合物刷子的合成途径，包括物理吸附法和将聚合物分子以化学键结合到基体表面上的方法，后者又可分为“接枝到表面”和“从表面接枝”两种技术．最后简略地介绍了聚合物刷子的特性及应用。     

A single-step photolithographic interface for cell-free gene expression and active biochips

We have developed a biochip platform technology suitable for controlled cell-free gene expression at the micrometer scale. A new hybrid molecule, "Daisy", was designed and synthesized to form in a single step a biocompatible lithographic interface on silicon dioxide. A protocol is described for the immobilization of linear DNA molecules thousands of base pairs long on Daisy-coated surfaces with submicrometer spatial resolution and up to high densities. On-chip protein synthesis can be obtained with a dynamic range of up to four orders of magnitude and minimal nonspecific activity. En route to on-chip artificial gene circuits, a simple two-stage gene cascade was built, in which the protein synthesized at the first location diffuses to regulate the synthesis of another protein at a second location. We demonstrate the capture of proteins from crude extract onto micrometer-scale designated traps, an important step for the formation of miniaturized self-assembled protein chips. Our biochip platform can be combined with elastomeric microfluidic devices, thereby opening possibilities for isolated and confined reaction chambers and artificial cells in which the transport of products and reagents is done by diffusion and flow. The Daisy molecule and described approach enables groups not proficient in surface chemistry to construct active biochips based on cell-free gene expression.     

Organic Semiconductor Growth and Morphology Considerations for Organic Thin‐Film Transistors

Analogous to conventional inorganic semiconductors, the performance of organic semiconductors is directly related to their molecular packing, crystallinity, growth mode, and purity. In order to achieve the best possible performance, it is critical to understand how organic semiconductors nucleate and grow. Clever use of surface and dielectric modification chemistry can allow one to control the growth and morphology, which greatly influence the electrical properties of the organic transistor. In this Review, the nucleation and growth of organic semiconductors on dielectric surfaces is addressed. The first part of the Review concentrates on small‐molecule organic semiconductors. The role of deposition conditions on film formation is described. The modification of the dielectric interface using polymers or self‐assembled mono­layers and their effect on organic‐semiconductor growth and performance is also discussed. The goal of this Review is primarily to discuss the thin‐film formation of organic semiconducting species. The patterning of single crystals is discussed, while their nucleation and growth has been described elsewhere (see the Review by Liu et. al). 1 The second part of the Review focuses on polymeric semiconductors. The dependence of physico‐chemical properties, such as chain length (i.e., molecular weight) of the constituting macromolecule, and the influence of small molecular species on, e.g., melting temperature, as well as routes to induce order in such macromolecules, are described.     

聚合物"刷子"的研究进展

采用活性聚合方法在材料表面制备聚合物"刷子"可有效控制材料表面性质,在分子结构设计中具有突出的优越性,所制备"刷子"的分子量可控、分布窄,近年来引起了研究者的广泛关注.主要综述了聚合物"刷子"的各种制备方法.     

Tip-Induced Nanopatterning of Ultrathin Polymer Brushes

Patterned, ultra-thin surface layers can serve as templates for positioning nanoparticlesor targeted self-assembly of molecular structures, for example, block-copolymers. This work investigates the high-resolution, atomic force microscopebased patterning of 2 nm thick vinyl-terminated polystyrene brush layers and evaluates the line broadening due to tip degradation. This work compares the patterning properties with those of a silane-based fluorinated self-assembled monolayer (SAM), using molecular heteropatterns generated by modified polymer blend lithography (brush/SAM-PBL). Stable line widths of 20 nm (FWHM) over lengths of over 20000 µm indicate greatly reduced tip wear, compared to expectations on uncoated SiO_x surfaces. The polymer brush acts as a molecularly thin lubricating layer, thus enabling a 5000 fold increase in tip lifetime, and the brush is bonded weakly enough that it can be removed with surgical accuracy. On traditionally used SAMs, either the tip wear is very high or the molecules are not completely removed. Polymer Phase Amplified Brush Editing is presented, which uses directed self-assembly to amplify the aspect ratio of the molecular structures by a factor of 4. The structures thus amplified allow transfer into silicon/metal heterostructures, fabricating 30 nm deep, all-silicon diffraction gratings that could withstand focused high-power 405 nm laser irradiation.     

Polymeric Materials: Patterned Polymer Carpets (Small 5/2011)

For the development of polymer carpets as active devices for micro‐ and nanotechnology, a control of the polymer carpet morphology and especially control of the stimulus responsive polymer brush is needed. Here, we report on the first example for the fabrication of patterned polymer carpets. On a two‐dimensional framework of fully crosslinked and chemically patterned nanosheets, polymer brushes of styrene and 4‐vinyl pyridine were grafted by self‐initiated surface photopolymerization and photografting (SIPGP). It was found that polymer grafting by SIPGP occurred over the entire nanosheets but with a preferred grafting on the amino functionalized nanosheet areas. This results in continuous polymer carpets with an intact nanosheet framework but with amplification of the chemical patterning into a three dimensional topography of the grafted polymer brush. In the case of negative patterned nanosheets, the patterned carpet could be prepared as freestanding ultrathin membranes. Furthermore, swelling experiments with poly(4‐vinyl pyridine) carpets showed that the patterns induces a directional buckling of the flexible polymer carpet. This may open the possibility of the development of micro‐ or nanoactuator devices with anisotropic responds upon environmental changes.