Determination of Solvent Systems for Blade Coating Thin Film Photovoltaics

With lab‐scale solution‐processed thin film photovoltaic (TFPV) devices attaining market relevant efficiencies, the demand for environmentally friendly and scalable deposition techniques is increasing. Replacing toxic halogenated solvents is a priority for the industrialization of solution‐processed TFPV. In this work, a generalized five‐step process is presented for fabricating high‐performance devices from nonhalogenated inks. Resulting from this process, several new solvent systems are introduced based on thiophene, tetralin, 1,2,4‐trimethylbenzene, o‐xylene, and anisole for blade coating of three different diketopyrrolopyrrole‐based (pDPP5T‐2, pPDPP5T‐2S, and P390) bulk heterojunctions applied in organic photovoltaic devices. Devices based on pDPP5T‐2S and P390 attain 5.6% and 6.1% efficiency, respectively, greater than the efficiency either material reached when processed from the halogenated solvent system commonly used. These processes are implemented without post‐deposition annealing treatments or additives. The Hansen solubility parameters of the pDPP5T‐2 material are obtained, and are used, along with wettability data on a variety of substrates, to determine optimum solvent combinations and ratios for deposition. This generalized five‐step process results in new nonhalogenated solvent pathways for the scalable deposition of thin film photovoltaic materials.     

Modular and Versatile Spatial Functionalization of Tissue Engineering Scaffolds through Fiber‐Initiated Controlled Radical Polymerization

Native tissues are typically heterogeneous and hierarchically organized, and generating scaffolds that can mimic these properties is critical for tissue engineering applications. By uniquely combining controlled radical polymerization (CRP), end‐functionalization of polymers, and advanced electrospinning techniques, a modular and versatile approach is introduced to generate scaffolds with spatially organized functionality. Poly‐ε‐caprolactone is end functionalized with either a polymerization‐initiating group or a cell‐binding peptide motif cyclic Arg‐Gly‐Asp‐Ser (cRGDS), and are each sequentially electrospun to produce zonally discrete bilayers within a continuous fiber scaffold. The polymerization‐initiating group is then used to graft an antifouling polymer bottlebrush based on poly(ethylene glycol) from the fiber surface using CRP exclusively within one bilayer of the scaffold. The ability to include additional multifunctionality during CRP is showcased by integrating a biotinylated monomer unit into the polymerization step allowing postmodification of the scaffold with streptavidin‐coupled moieties. These combined processing techniques result in an effective bilayered and dual‐functionality scaffold with a cell‐adhesive surface and an opposing antifouling non‐cell‐adhesive surface in zonally specific regions across the thickness of the scaffold, demonstrated through fluorescent labelling and cell adhesion studies. This modular and versatile approach combines strategies to produce scaffolds with tailorable properties for many applications in tissue engineering and regenerative medicine.     

In the Pursuit of Pleasure: The Not so Fleeting Life of the Pavilion and its Ilk

Author and architecture critic for the London Evening Standard, Robert Bevan reflects on the enduring appeal of the temporary structure, speaking ‘to a latent desire for freedom and movement’ as a hangover of our nomadic past in a sedentary ‘civilised’ society. He highlights the type's historical apex in Henry VIII's palatial pop-up on the Field of the Cloth of Gold, questioning the purpose and purposelessness of more recent examples.     

Theory and Practice and the Neutral's Persona

Editor's note: Longtime Alternatives columnist Bob Creo, a veteran Pittsburgh neutral, is revisiting his classic CPR Institute website columns of a decade ago in a Back to Basics Series that he has subtitled “Human Problems, Human Solutions.” These updated and expanded columns, in print for the first time, began late last year. He has revisited and re‐examined mediation‐room techniques and practice issues. This month, he returns to the second column he wrote at www.cpradr.org a decade ago, and brings it forward.     

Dealing with the One‐Hour SO2 NAAQS Implementation

In June 2010, the US Environmental Protection Agency (EPA) finalized a new, very stringent National Ambient Air Quality Standard (NAAQS) for sulfur dioxide¹ (SO₂).     

A portable data system for reindeer herd management

A portable computer system is described which supports timely data management for reindeer herding. An initial version has been in use for two years, supporting research on reindeer diseases. Versions are being developed which will expand the system to support commercial herd management. The hardware system is integrated from commercially available equipment. The software is currently composed of a set of ten programs, with others under development for enhancements and modifications. At field roundups, the computer allows new animals to be added to the data base plus rapid access to information on existing individual animals. Historical information can be displayed, including detailed historical records of reproductive activity, medical treatments, serological exam results, and observations of anomalies (e.g. infections, injuries, etc.). In the field, or in the lab, the data base may be accessed for information on specific animals and for summaries of herd data.     

Structural Response of World Trade Center Buildings 1, 2 and 7 to Impact and Fire Damage

The National Institute of Standards and Technology (NIST) conducted an extensive investigation of the collapse of World Trade Center towers (WTC 1 and WTC 2) and the WTC 7 building. This paper describes the component, subsystem, and global analyses performed for the reconstruction of the structural response of WTC buildings 1, 2, and 7 to impact and fire damage. To illustrate the component and subsystem analyses, the approach taken for simulating the performance of concrete slabs and shear stud connectors in composite floors subject to fire conditions are presented, as well as steel floor framing connections for beams and girders. The development of the global models from the component and subsystem analyses is briefly described, including the sets of input data used to bound the probable conditions of impact and fire damage. The final analysis results that were used to develop the probable collapse hypotheses, and a comparison of the results against observed events, are presented for each building. A review of research activities focused on improving understanding of structural system response to multi-floor fires following the WTC disaster is also provided.