John M. Colwell

A Highly Sensitive Diketopyrrolopyrrole‐Based Ambipolar Transistor for Selective Detection and Discrimination of Xylene Isomers

An ambipolar poly(diketopyrrolopyrrole-terthiophene)-based field-effect transistor (FET) sensitively detects xylene isomers at low ppm levels with multiple sensing features. Combined with pattern-recognition algorithms, a sole ambipolar FET sensor, rather than arrays of sensors, can discriminate highly similar xylene structural isomers from one another.

A study of the chemical and physical effects of ion implantation of micro-porous and nonporous PTFE

In a comparative study, N2+, Ar+ and Ca+ ion implantation was used to modify subcutaneous augmentation material (SAM), a micro-porous form of polytetrafluoroethylene (PTFE) and nonporous PTFE, with a view to assessing the effect of ion implantation on the chemical and physical structure of these materials as well as the effect of porosity on the response to ion implantation. SAM is used as an implant material for reconstructive surgery, and this study is part of a larger investigation into methods of modifying SAM to improve its tissue integration potential. Ion implantation was carried out at an energy of 30 keV, with doses of 1×1015 and 1×1016 ions/cm2. SRIM.2000.39 was used to simulate N2+, Ar+ and Ca+ implantation of PTFE. X-ray photoelectron spectroscopy (XPS) was used for the characterisation of chemical structural changes in the ion-implanted samples, while scanning electron microscopy (SEM) was used for the characterisation of physical structural changes. Rutherford backscattering spectroscopy (RBS) was used to determine the elemental surface composition of Ca+ and Ar+ implanted samples. Advancing and receding water contact angles were measured using the sessile drop method. XPS analysis showed that all ion-implanted samples had undergone chemical structural changes. Some variation was noted between samples implanted with different ions and at different doses. SEM analysis showed that physical structural changes were independent of ion mass with some variation between doses. Water contact angle measurements showed some variation between samples, with nonporous samples showing dose dependent behaviour.

Prognostic Tools for Lifetime Prediction of Aircraft Coatings: Paint Degradation

A direct interrogation, portable analysis technique (portable FT-IR) and a novel environment-monitoring profluorescent sensor for studying aircraft coating degradation have been developed. For the direct interrogation approach, a standard military aircraft paint: 459-line Anzothane flexible polyurethane (lead free) has been used to illustrate a new potential field technique to evaluate coating service lifetime, portable FT-IR. This technique allows direct analysis of chemical changes within the degrading coatings and has the potential to evaluate service lifetime when coupled with advanced statistical analysis methods (chemometrics). The degradation environment monitoring sensors are embodied in a profluorescent environment-sensitive witness patch that may be analysed in-service by a field-deployable fluorescence spectrometer. Accelerated ageing for both the paint and the witness patches has been undertaken and their capabilities as aircraft paint degradation monitors assessed.

A profluorescent azaphenalene nitroxide for nitroxide-mediated polymerization

A novel nitroxide‐mediated polymerization (NMP) control agent; 1,1,3,3‐tetramethyl‐2,3‐dihydro‐2‐azaphenalen‐2‐yloxyl (TMAO), was used in the free‐radical polymerization of styrene. The conversion of styrene during NMP was studied using FT‐Raman spectroscopy and the effectiveness of TMAO as a NMP control agent was assessed by GPC analysis. Fidelity of the TMAO‐alkoxyamine end‐group on the synthesized polymers was confirmed by GPC, UV‐Vis and fluorescence spectroscopic analyses. Comparison to the well known NMP control agent, TEMPO was made. TMAO showed control of molecular weight approaching that of TEMPO. Attempts to improve the properties of TMAO as an NMP control agent by synthesizing an analogue with bulkier substituents around the nitroxide did not generate the target molecule but demonstrated some of the interesting chemistry of the azaphenalene ring system.

Sensors: A Highly Sensitive Diketopyrrolopyrrole-Based Ambipolar Transistor for Selective Detection and Discrimination of Xylene Isomers (Adv. Mater. 21/2016).

An ambipolar organic field-effect transistor (OFET) based on poly(diketopyrrolopyrrole-terthiophene) (PDPPHD-T3) is shown by P. Sonar, H. Haick, and co-workers on page 4012 to sensitively detect xylene isomers at low to 40 ppm level in multiple sensing features. Combined with pattern-recognition algorithms, a sole ambipolar FET sensor, rather than arrays of sensors, is able to discriminate highly similar xylene structural isomers from each other.