David Gendron

Parylene-Coated Ionic Liquid–Carbon Nanotube Actuators for User-Safe Haptic Devices

Simple fabrication, high power-to-weight and power-to-volume ratios, and the ability to operate in open air at low voltage make the ionic electroactive polymer actuators highly attractive for haptic applications. Whenever a direct tactile stimulation of the skin is involved, electrical and chemical insulation as well as a long-term stability of the actuator are required. Because of its inherent physicochemical properties such as high dielectric strength, resistance to solvents, and biological inactivity, Parylene C meets the requirements for making biocompatible actuators. We have studied the displacement and the generated force of Parylene-coated carbon nanotube actuators as well as the encapsulation quality. A 2 μm coating creates an effective electrical insulation of the actuators without altering the blocking force at frequencies from 50 mHz to 1 Hz. Moreover, the generated strain is preserved at higher frequencies (from 0.5 to 5 Hz). We employed a simple mechanical model to explain the relation between the key parameters-flexural stiffness, displacement, and force-for uncoated and coated actuators. In addition, we demonstrated that our Parylene-coated actuators are not damaged by rinsing in liquid media such as 2-propanol or water. In conclusion, our results indicate that Parylene C encapsulated actuators are safe to touch and can be used in contact with human skin and in biomedical applications in direct contact with tissues and physiological fluids.

Synthesis and properties of pyrrolo[3,2-b]pyrrole-1,4-diones (isoDPP) derivatives

The synthesis of three pyrrolo[3,2-b]pyrrole-1,4-dione (isoDPP) derivatives is described, namely 1,3,4,6-tetraphenylpyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dione 2, 1,4-diphenyl-3,6-di(thiophen-2-yl)pyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dione 3, and 1,4-bis(4-(hexyloxy)phenyl)-3,6-di(thiophen-2-yl)pyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dione 7 in which the molecular structures differ in the aromatic ring (phenyl or thiophene) attached to the nitrogen atom. Thin films of 2, 3, and 7 could be formed by evaporation under vacuum. In the case of 2 and 3 GIWAXS measurements showed that the film structural ordering was similar to that measured in single crystals. In contrast GIWAXS showed that 7 had features associated with liquid crystalline materials. Time dependent density functional theory (TDDFT) calculations predicted that the transition between the lowest energy singlet excitation (S1) and the ground state (S0) would be optically forbidden due to the centrosymmetric geometries of compounds. Photophysical measurements showed that the compounds were weakly luminescent, with low radiative rates in solution of order 106 s−1, which are consistent with the TDDFT predictions. Furthermore, photoinduced absorption (PIA) spectroscopy showed that there is a long-lived low energy state, which has been assigned as a triplet and provides a further non-radiative decay pathway for the excited state.

A thiocarbonyl-containing small molecule for optoelectronics

We report the synthesis and characterization of a novel thiocarbonyl iso-DPP derivative, namely 1,3,4,6-tetraphenylpyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dithione. Even without solubilising alkyl chains, the small molecule could be processed from organic solvents such as dichloromethane, chloroform or dichlorobenzene, and it was found that the optical properties of neat thin films were strongly dependent on the solvent used. Field effect hole mobilities were of the order 10−4 cm2 V−1 s−1, with mobilities measured in a diode configuration solvent dependent and at least an order of magnitude lower. Importantly, blends of the iso-DPP derivative with PC70BM, a typically used electron acceptor in bulk heterojunction solar cells, were found to possess hole mobilities of up to 10−3 cm2 V−1 s−1 in a diode configuration, which was an order of magnitude larger than the electron mobility. Finally, simple bulk heterojunction solar cells were fabricated with maximum power conversion efficiencies of 2.3%.

Synthesis and Reactions of Halo-substituted Alkylthiophenes. A Review

[Extract] Introduction: Thiophene chemistry is a flourishing area of organic semiconductors as they are useful for field effect transistors, solar cells and light-emitting diodes.1 This interest stems from the unique optical and electronic properties of thiophene oligomers and polymers coupled with the ease of synthesis and their unique reaction selectivity. Therefore, the preparation of thiophenes is pivotal in this burgeoning area of science. Although there have been several reviews that have focused on the preparation of poly(alkylthiophene)s, this is not the case for oligomeric and monomeric materials. Halo-substituted alkylthiophenes are very useful compounds that react under various conditions to give a plethora of derivatives, which can then be used in the field of materials chemistry. This review summarizes recent advances (from 1986-2013) in the synthesis and reactivity of these systems to provide a stepping-stone for the design and preparation of more complex thiophene-based molecular architectures for the next generation of materials in photonics and electronics. We will focus first on the preparation of halo-substituted alkylthiophenes by electrophilic aromatic substitution and then their reactivity using various metal-catalyzed cross-coupling methods.

Functional materials from polymer derivatives

This chapter summarizes properties and characterization of a broad range of functional polymeric materials. The attention is drawn toward hybrid polymers for electroactive applications. The first section describes photoactive polymer materials for optoelectronics with a focus on the properties and characterization techniques. The second section examines the physicochemical properties of polymeric materials for storing and transducing energy as well as techniques to characterizing them. More specifically, functional materials that have found applications in supercapacitors and carbon nanotube-based hybrid actuators will be discussed. Each section comprises an overview of material characterization techniques with chosen literature examples preceded by an introduction of the necessary general background.

Cross-linked carbon nanotubes buckygel actuators: an in-depth study

Recently, materials that can convert electrical energy into mechanical work have drawn great attention. Applications in robotics, tactile or optical displays and microelectrochemical systems are currently investigated. Likewise, interest in actuators devices is increasing toward applications where low voltage and low weight properties are required. One way to achieve such prerequisites is to combine the mechanical and electronic properties of carbon nanotubes (CNTs) with the stability and conductivity of ionic liquids. Indeed, the CNTs can be dispersed in ionic liquids to form hybrid composites also named bucky gels, thanks to the non-covalent (π-π stacking and cation-π) interactions. In our previous studies, we demonstrated an improvement in actuator performance whilst using cross-linked CNTs. Indeed, our preliminary results showed an increase in the capacitance together with a faster response of the actuator. At the time, these results were explained by an actuation mechanism model. Herein, we designed new experiments in order to allow us to get a deeper insight in the effect the crosslinking process on the carbon nanotubes properties. Thus, we present a set of electromechanical and electrochemical data that shed light on the chemical modification of the CNTs, the different cross-linking strategies and also on the uses of cross-linked CNTS polymer blends. Finally, corresponding bucky gels actuators performances will also be discussed.

Parylene coated carbon nanotube actuators for tactile stimulation

Ionic liquid/carbon nanotube based actuators have been constantly improved in recent years owing to their suitability for applications related to human-machine interaction and robotics thanks to their light-weight and low voltage operation. However, while great attention has been paid to the development of better electrodes and electrolytes, no adequate efforts were made to develop actuators to be used in direct contact with the human skin. Herein, we present our approach, based on the use of parylene-C coating. Indeed, owning to its physicochemical properties such as high dielectric strength, resistance to solvents, biological and chemical inactivity/inertness, parylene fulfils the requirements for use in biocompatible actuator fabrication. In this paper, we study the influence of the parylene coating on the actuator performance. To do so, we analyzed its mechanical and electrochemical properties. We looked into the role of parylene as a protection layer that can prevent alteration of the actuator performance likely caused by external conditions. In order to complete our study, we designed a haptic device and investigated the generated force, displacement and energy usage.