Victor Lebedev

Carbon nanotubes on a spider silk scaffold

Understanding the compatibility between spider silk and conducting materials is essential to advance the use of spider silk in electronic applications. Spider silk is tough, but becomes soft when exposed to water. Here we report a strong affinity of amine-functionalised multi-walled carbon nanotubes for spider silk, with coating assisted by a water and mechanical shear method. The nanotubes adhere uniformly and bond to the silk fibre surface to produce tough, custom-shaped, flexible and electrically conducting fibres after drying and contraction. The conductivity of coated silk fibres is reversibly sensitive to strain and humidity, leading to proof-of-concept sensor and actuator demonstrations.

Silk/molecular conductor bilayer thin-films: properties and sensing functions

Since their discovery, organic conductors have attracted fundamental and device physics interest due to their diverse physical properties. However, conventional electrochemical growth methods produce millimeter-sized crystals that do not translate to the fabrication of large-scale thin-film devices. Of late a chemical-vapor annealing method has been proved to be capable of growing a conductive polycrystalline layer of (BEDT-TTF)2I3 molecular conductor on the surface of soluble polycarbonate (PC) thin films in a bilayer configuration. (Here BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene.) This has resulted in efficient piezoresistive organic molecular sensors. Conversely, solubility and other incompatibilities limit the direct application of the crystallite growth method to other substrates with arbitrary shape and composition. Here we report methods to circumvent these limitations. Specifically, we demonstrate the transfer of the active layer of a PC/(BEDT-TTF)2I3 bilayer film from the non-porous parent PC substrate to porous and humidity-dependent Bombyx mori silk target substrates. SEM analysis, temperature dependent resistance, and electromechanical measurements show no significant damage to the transferred (BEDT-TTF)2I3 layer. The silk/(BEDT-TTF)2I3 bilayer films exhibit additional functions that can be used for humidity sensing, electric current-driven actuators, and strain detection. Of particular significance is the piezoresistive function of the porous silk bilayer structure that allows the investigation of multi-stage diffusion processes.

Lightweight biocompatible physical sensors: Polymeric films “self-metallized” with organic molecular conductors

This paper reports a simple single-stage “metallization” process of polycarbonate films with highly strain resistive organic molecular conductors. The electro-mechanical studies showed that these metallized films that are termed bi-layer (BL) films hold the great interest for sensor engineering because important material properties, such as high conductivity, strain (pressure) sensitivity, excellent elasticity and biocompatibility, go together. Atomic force microscopy nano-indentation indicated that Youngs modulus (E) of polycrystalline layer of organic molecular conductors and polycarbonate films are of the same scale that imparts a good robustness and elasticity to BL films-based sensors. This type of “self-metallized” plastics may find a number of applications usually reserved for flexible, lightweight, strain and pressure sensors.

A new (TTF)11I8 organic molecular conductor: from single crystals to flexible all-organic piezoresistive films

This paper reports selective synthesis of two iodine-containing TTF (tetrathiafulvalene) salts: one, (TTF)11I8, is a new molecular conductor while another is the known non-conducting (TTF)I3 compound. Single crystals of both salts were prepared using different amounts of iodine in the redox process between TTF and I2. X-ray data showed that the resulting conducting (TTF)11I8 salt might be considered as a new modulated phase of the non-stoichiometric (TTF)I0.7+δ salts. The electrical resistance of single crystals of (TTF)11I8 reveals a semiconducting-like behaviour. The paper presents also a study of electromechanical properties of organic conductive bi-layer (BL) films prepared by covering different organic polymeric films with a thin network of oriented submicrocrystals of (TTF)I0.7+δ phases. These BL films exhibit a combination of flexibility, lightweight, and high piezo-resistivity properties showing therefore a potential interest for electronic sensing applications where lightweight, large area coverage and flexibility are required.

Z/E (C=C)-isomerization and fluorescence modulation of imines of 7-N,N-dialkylamino-4-hydroxy-3-formylcoumarins in organic solvents

Abstract Imines of 7-dialkylamino-3-formyl-4-hydroxycoumarins have been found to exist in Z-ketoenamine form in crystal state and undergo Z/E-isomerization around C=C bond in organic solvents at room temperature. Activation energies of isomerization have been measured experimentally and calculated by the DFT B3LYP method. Transition of ketoenamine form of p-nitrophenylimines into (hydroxy)imine form at low concentration (10-5 m) in polar solvents is accompanied by strong increase in fluorescence.

Highly sensitive multi-layer pressure sensor with an active nanostructured layer of an organic molecular metal

This work addresses to the modern technologies that need to be instrumented with lightweight highly sensitive pressure sensors. The paper presents the development of a new plain flexible thin pressure sensor using a nanostructured layer of the highly sensitive organic piezoresistive metal β-(BEDT-TTF)2I3 as an active component; BEDT-TTF=bis (ethylenedithio)tetrathiafulvalene. The original construction approach permits one to operate the developed sensor on the principle of electrical resistance variations when its piezoresistive layer is elongated under a pressure increase. The pressure sensing element and a set of gold electrodes were integrated into one compact multi-layer design. The construction was optimized to enable one generic design for pressure ranges from 1 to 400 bar. The pressure tests showed that the sensor is able to control a small pressure change as a well definite electrical signal. So the developed type of the sensors is very attractive as a new generation of compact, lightweight, low-cost sensors that might monitor pressure with a good level of measurement accuracy.

Piezoresistive biocompatible membranes for flexible pressure sensors

The article reports a promising approach to engineering biocompatible and highly piezoresistive membranes for flexible weightless transparent pressure sensors. The developed membranes are based on bi layer (BL) films composing a polycarbonate (PC) matrix “self-metallized” with organic molecular metal β-(ET)2I3, were ET=bis(ethylenedithio) tetrathiafulvalene. The presented approach permits engineering biocompatible all-organic membranes with sensitivity to pressure being of 13 Ω/mmHg; this value is significantly over the sensitivity of the previous reported BL film-based membrane sensors.

Fabrication and Application of Low Cost Flexible Film-Based Sensors to Environmental and Biomedical Monitoring Scenarios

The paper describes the development of flexible lightweight highly sensitive film-based sensors capable of monitoring pressure, deformation, temperature and humidity. In particular, we present a family of the developed simple devices that successfully adopted polycarbonate films covered with organic molecular conductors as conductive sensing components. Proof-of-concept experiments with these prototypes demonstrate that such bi layer films are promising as sensing devices for the environment and biomedical monitoring. Besides, we present the interfacing of the flexible film-based sensor with a wireless sensor node and evaluate the sensing capability of this system in a real monitoring scenario.

Approach to Engineering the Temperature Sensing E-textile: A Lightweight Thermistor as an Active Sensing Element

In this paper, we describe an approach to fabricating conductive textiles with temperature sensing capability. The key point of our approach is in combining electronic properties of a molecular organic semiconductor with clothing. A polycarbonate film covered with organic molecular semiconductor was used as the temperature measurement element. To minimize the electrical response of the developed bi layer thermistor to deformations, the thermistor was attached to a rigid film-like platform specifically fabricated in the textile by its local melting. Our study shows that the developed platform enables engineering of the conductive fabric the electrical resistance of which exclusively responded to temperature changes. Such e-textiles may be easily prepared using a simple fabrication procedure and, therefore, they are compatible with conductive sensing fabrics prepared by printing techniques. The developed organic thermistor, being cheap, lightweight and biocompatible, is highly attractive for applications in wearable biomedical technology.