Following Sharpless' visionary characterization of several idealized reactions as click reactions, the materials science and synthetic chemistry communities have pursued numerous routes toward the identification and implementation of these click reactions. Herein, we review the radical-mediated thiol-ene reaction as one such click reaction. This reaction has all the desirable features of a click reaction, being highly efficient, simple to execute with no side products and proceeding rapidly to high yield. Further, the thiol-ene reaction is most frequently photoinitiated, particularly for photopolymerizations resulting in highly uniform polymer networks, promoting unique capabilities related to spatial and temporal control of the click reaction. The reaction mechanism and its implementation in various synthetic methodologies, biofunctionalization, surface and polymer modification, and polymerization are all reviewed.

Thiol–Ene Click Chemistry

This paper describes the compatibility of poly(dimethylsiloxane) (PDMS) with organic solvents; this compatibility is important in considering the potential of PDMS-based microfluidic devices in a number of applications, including that of microreactors for organic reactions. We considered three aspects of compatibility:  the swelling of PDMS in a solvent, the partitioning of solutes between a solvent and PDMS, and the dissolution of PDMS oligomers in a solvent. Of these three parameters that determine the compatibility of PDMS with a solvent, the swelling of PDMS had the greatest influence. Experimental measurements of swelling were correlated with the solubility parameter, δ (cal1/2 cm-3/2), which is based on the cohesive energy densities, c (cal/cm3), of the materials. Solvents that swelled PDMS the least included water, nitromethane, dimethyl sulfoxide, ethylene glycol, perfluorotributylamine, perfluorodecalin, acetonitrile, and propylene carbonate; solvents that swelled PDMS the most were diisopropylam...

Solvent compatibility of poly(dimethylsiloxane)-based microfluidic devices.

Porous carbon materials are of interest in many applications because of their high surface area and physicochemical properties. Conventional syntheses can only produce randomly porous materials, with little control over the pore-size distributions, let alone mesostructures. Recent breakthroughs in the preparation of other porous materials have resulted in the development of methods for the preparation of mesoporous carbon materials with extremely high surface areas and ordered mesostructures, with potential applications as catalysts, separation media, and advanced electronic materials in many scientific disciplines. Current syntheses can be categorized as either hard-template or soft-template methods. Both are examined in this Review along with procedures for surface functionalization of the carbon materials obtained.

Mesoporous Carbon Materials: Synthesis and Modification

Nanotechnology is being used to enhance conventional ceramic and polymeric water treatment membrane materials through various avenues. Among the numerous concepts proposed, the most promising to date include zeolitic and catalytic nanoparticle coated ceramic membranes, hybrid inorganic–organic nanocomposite membranes, and bio-inspired membranes such as hybrid protein–polymer biomimetic membranes, aligned nanotube membranes, and isoporous block copolymer membranes. A semi-quantitative ranking system was proposed considering projected performance enhancement (over state-of-the-art analogs) and state of commercial readiness. Performance enhancement was based on water permeability, solute selectivity, and operational robustness, while commercial readiness was based on known or anticipated material costs, scalability (for large scale water treatment applications), and compatibility with existing manufacturing infrastructure. Overall, bio-inspired membranes are farthest from commercial reality, but offer the most promise for performance enhancements; however, nanocomposite membranes offering significant performance enhancements are already commercially available. Zeolitic and catalytic membranes appear reasonably far from commercial reality and offer small to moderate performance enhancements. The ranking of each membrane nanotechnology is discussed along with the key commercialization hurdles for each membrane nanotechnology.

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A review of water treatment membrane nanotechnologies

Parallel processes for patterning densely packed nanometre-scale structures are critical for many diverse areas of nanotechnology. Thin films of diblock copolymers can self-assemble into ordered periodic structures at the molecular scale (approximately 5 to 50 nm), and have been used as templates to fabricate quantum dots, nanowires, magnetic storage media, nanopores and silicon capacitors. Unfortunately, perfect periodic domain ordering can only be achieved over micrometre-scale areas at best and defects exist at the edges of grain boundaries. These limitations preclude the use of block-copolymer lithography for many advanced applications. Graphoepitaxy, in-plane electric fields, temperature gradients, and directional solidification have also been demonstrated to induce orientation or long-range order with varying degrees of success. Here we demonstrate the integration of thin films of block copolymer with advanced lithographic techniques to induce epitaxial self-assembly of domains. The resulting patterns are defect-free, are oriented and registered with the underlying substrate and can be created over arbitrarily large areas. These structures are determined by the size and quality of the lithographically defined surface pattern rather than by the inherent limitations of the self-assembly process. Our results illustrate how hybrid strategies to nanofabrication allow for molecular level control in existing manufacturing processes.

Epitaxial self-assembly of block copolymers on lithographically defined nanopatterned substrates

One of the key challenges in nanotechnology is to control a self-assembling system to create a specific structure. Self-organizing block copolymers offer a rich variety of periodic nanoscale patterns, and researchers have succeeded in finding conditions that lead to very long range order of the domains. However, the array of microdomains typically still contains some uncontrolled defects and lacks global registration and orientation. Recent efforts in templated self-assembly of block copolymers have demonstrated a promising route to control bottom-up self-organization processes through top-down lithographic templates. The orientation and placement of block-copolymer domains can be directed by topographically or chemically patterned templates. This templated self-assembly method provides a path towards the rational design of hierarchical device structures with periodic features that cover several length scales.

Templated Self‐Assembly of Block Copolymers: Top‐Down Helps Bottom‐Up

Self-assembling materials are the building blocks for bottom-up nanofabrication processes, but many self-assembled nanostructures contain defects and lack sufficient long-range order for certain nanotechnology applications. Here we investigate the formation of defects in a self-assembled array of spherical block-copolymer microdomains, using topographical templates to control the local self-assembly. Perfect ordered sphere arrays can form in both constant-width templates and width-modulated templates. For modulated templates, transition between configurations having a constant number of rows and configurations of stable arrays with varying numbers of rows is shown to be analogous to dislocation formation in an epitaxial thin film system. Based on the configuration transition energy and fluctuation energy, designed templates with a high tolerance for lithographical imperfections can direct precisely modulated block-copolymer nanostructures. This study provides insights into the design of hybrid systems combining top-down and bottom-up fabrication.

Nanostructure engineering by templated self-assembly of block copolymers.

Single-domain cobalt dot arrayswith high magnetic particle density, patterned over large areas (e.g., 10 cm diameter wafers) are fabricated by self-assembled block copolymer lithography, using a polystyrene-poly(ferrocenyldimethylsilane) copolymer as a template. By varying the copolymer type and etching conditions the magnetic properties can be tuned. The Figure shows a typical array of Co dots with tungsten caps obtained via this procedure.

Formation of a Cobalt Magnetic Dot Array via Block Copolymer Lithography

We are inspired by the beauty and simplicity of self-organizing materials and the promise they hold for enabling continued improvements in semiconductor technology. Self assembly is the spontaneous arrangement of individual elements into regular patterns," under suitable conditions, certain materials self organize into useful nanometer-scale patterns of importance to high-performance microelectronics applications. Polymer self assembly is a nontraditional approach to patterning integrated circuit elements at dimensions and densities inaccessible to traditional lithography methods. We review here our efforts in IBM to develop and integrate self-assembly processes as high-resolution patterning alternatives and to demonstrate targeted applications in semiconductor device fabrication. We also provide a framework for understanding key requirements for the adoption of polymer self-assembly processes into semiconductor technology, as well as a discussion of the ultimate dimensional scalability of the technique.

Polymer self assembly in semiconductor microelectronics

Block copolymer lithography makes use of the self-assembling properties of block copolymers to pattern nanoscale features over large areas. Although the resulting patterns have good short-range order, the lack of long-range order limits their utility in some applications. This work presents a lithographically assisted self-assembly method that allows ordered arrays of nanostructures to be formed by spin casting a block copolymer over surfaces patterned with shallow grooves. The ordered block copolymer domain patterns are then transferred into an underlying silica film using a single etching step to create a well-ordered hierarchical structure consisting of arrays of silica pillars with 20 nm feature sizes and aspect ratios greater than 3.

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Joy Cheng

Papers

Templated Self‐Assembly of Block Copolymers: Top‐Down Helps Bottom‐Up

Nanostructure engineering by templated self-assembly of block copolymers.

Formation of a Cobalt Magnetic Dot Array via Block Copolymer Lithography

Polymer self assembly in semiconductor microelectronics

Fabrication of nanostructures with long-range order using block copolymer lithography