The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review.

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Gas Sensors Based on Conducting Polymers

Flexible non-volatile memories have attracted tremendous attentions for data storage for future electronics application. From device perspective, the advantages of flexible memory devices include thin, lightweight, printable, foldable and stretchable. The flash memories, resistive random access memories (RRAM) and ferroelectric random access memory/ferroelectric field-effect transistor memories (FeRAM/FeFET) are considered as promising candidates for next generation non-volatile memory device. Here, we review the general background knowledge on device structure, working principle, materials, challenges and recent progress with the emphasis on the flexibility of above three categories of non-volatile memories.

Towards the development of flexible non-volatile memories.

Environmental Monitoring Ajeet Kaushik,*,†,‡ Rajesh Kumar,*,‡,§ Sunil K. Arya, Madhavan Nair,† B. D. Malhotra, and Shekhar Bhansali‡ †Center for Personalized Nanomedicine, Institute of Neuroimmune Pharmacology, Department of Immunology, Herbert Wertheim College of Medicine, Florida International University, Miami, Florida 33199, United States ‡Bio-MEMS Microsystems Laboratory, Department of Electrical and Computer Engineering, College of Engineering, Florida International University, Miami, Florida 33174, United States Department of Physics, Panjab University, Chandigarh 160014, India Bioelectronics Program, Institute of Microelectronics, A*Star, 11 Science Park Road, Singapore Science Park II, Singapore Department of Biotechnology, Delhi Technological University, Shahbad Daulatpur, Delhi 110042, India

Organic–Inorganic Hybrid Nanocomposite-Based Gas Sensors for Environmental Monitoring

Improvements in the efficiency of combustion within a vehicle can lead to reductions in the emission of harmful pollutants and increased fuel efficiency. Gas sensors have a role to play in this process, since they can provide real time feedback to vehicular fuel and emissions management systems as well as reducing the discrepancy between emissions observed in factory tests and ‘real world’ scenarios. In this review we survey the current state-of-the-art in using porous materials for sensing the gases relevant to automotive emissions. Two broad classes of porous material – zeolites and metal–organic frameworks (MOFs) – are introduced, and their potential for gas sensing is discussed. The adsorptive, spectroscopic and electronic techniques for sensing gases using porous materials are summarised. Examples of the use of zeolites and MOFs in the sensing of water vapour, oxygen, NOx, carbon monoxide and carbon dioxide, hydrocarbons and volatile organic compounds, ammonia, hydrogen sulfide, sulfur dioxide and hydrogen are then detailed. Both types of porous material (zeolites and MOFs) reveal great promise for the fabrication of sensors for exhaust gases and vapours due to high selectivity and sensitivity. The size and shape selectivity of the zeolite and MOF materials are controlled by variation of pore dimensions, chemical composition (hydrophilicity/hydrophobicity), crystal size and orientation, thus enabling detection and differentiation between different gases and vapours.

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Gas sensing using porous materials for automotive applications

This review describes the possibilities of using hard templates to create nanostructured “soft” materials, for example, polymer networks, carbon nitrides, or carbonaceous materials, that is, materials which are still organic in their nature. Examples are given for the whole range of hard templates described in the literature, starting from silica nanoparticles, zeolites, and periodic mesoporous silicas to aluminum oxide membranes and colloidal crystals.

Hard Templates for Soft Materials: Creating Nanostructured Organic Materials†

The effects of zeolite content, pore size and ion exchange capacity on electrical conductivity response to carbon monoxide (CO) of polyaniline/zeolite composites were investigated. Zeolite Y, 13X, and synthesized AlMCM41, all having the common cation Cu 2+ , were dry mixed with synthesized maleic acid (MA) doped polyaniline and compressed to form polyaniline (PANI)/zeolite pellet composites. The Y, 13X and AlMCM41 zeolite have the nominal pore sizes of 7, 10, 36 A, and the Cu 2+ exchange capacities of 0.161, 0.087, and 0.044 mol/g, respectively. With an addition of 13X zeolite to pristine polyaniline, the electrical conductivity sensitivity to CO/N 2 gas increases with zeolite content. For the effect of zeolite type, the highest electrical conductivity sensitivity is obtained with the 13X zeolite, followed by the Y zeolite, and the AlMCM41 zeolite, respectively. Poor sensitivity of zeolite AlMCM41 is probably due to its very large pore size and its lowest Cu 2+ exchange capacity. Y zeolite and 13X zeolite have comparable pore sizes but the latter has a greater pore free volume and a more favorable location distribution of the Cu 2+ ions within the pore. The temporal response time increases with the amount of zeolite in the composites but it is inversely related to the amount of ion exchange capacity.

Electrical conductivity of polyaniline/zeolite composites and synergetic interaction with CO

Polyaniline (PANI) was synthesized via oxidative coupling polymerization in acid conditions and de-doped in solution of ammonia. The electrorheological (ER) properties of the PANI/silicone oil suspensions were investigated in oscillatory shear as functions of electric field strength, particle concentration, and host fluid viscosity. Consistent with literature, the PANI ER fluid exhibits viscoelastic behavior under the applied electric field and the ER response is strongly enhanced with increasing electric field strength and particle concentration. The dynamic moduli, G' and G'' increase dramatically, by 5 orders of magnitude, as the electric field strength is increased to 2 kV/mm. A viscoelastic liquid to solid transition occurs at a critical electric field strength, in the range Ec = 50-200 V/mm, whose value depends on particle concentration and host fluid viscosity. The fibrillar structure formed in the presence of the applied field has a static yield strength tau(y), whose value scales with electric field strength as tau(y) approximately E(1.88). When the field is switched off a residual structure remains, whose yield stress increases with the strength of the applied field and particle concentration. When the applied stress exceeds the yield stress of the residual structure, fast, fully reversible switching of the ER response is obtained.

Electrorheological properties of polyaniline suspensions : Field-induced liquid to solid transition and residual gel structure

Polyaniline/zeolite LTA composites and electrical conductivity response towards CO

An electrorheological (ER) fluid, consisting of polydisperse dedoped polyaniline (PANI) particles, having irregular shapes, dispersed in silicone oil, was subjected to cyclic strain annealing treatments using oscillatory shear, under an external electric field After each annealing period, the sample was subjected to a controlled-strain sweep, to determine the yield stress, and to erase the ER structure During each annealing cycle, the storage modulus and the yield stress were observed to increase, and the loss modulus to decrease, each eventually approaching an asymptotic constant value These observations in oscillatory shear complement our previous observations of a strain-hardening effect in a PANI/silicone oil ER fluid subjected to unidirectional creep tests

Strain-hardening in the oscillatory shear deformation of a dedoped polyaniline electrorheological fluid

Electrorheological properties of polyisoprene and polythiophene/polyisoprene blends were investigated for electroactive actuator applications. Experiments were carried out under the oscillatory shear mode and with an applied electric field strength varying from 0 to 2 kV/mm. The dynamic moduli, G ′ and G ″, of the pure polyisoprene were measured in terms of the crosslinking ratio and electric field strength. In the absence of an electric field, the storage modulus ( G ″) increased but the loss loss modulus ( G ″) decreased with increasing crosslinking ratio. In the uncrosslinked polyisoprene fluid, the storage modulus ( G ′) exhibited no change in value with increasing electric field strength. For polyisoprene with crosslinking ratios of 2, 3, 5, and 7, the storage modulus sensitivity increased with electric field strength and attained maximum values of 10%, 60%, 25%, and 30%, respectively, at an electric field strength of 2 kV/mm. The dynamic moduli, G ′ and G ″, of blends of polythiophene with undoped particle concentrations of 5%, 10%, 20%, and 30% vol% were generally higher than those of crosslinked polyisoprene. The storage modulus sensitivity of these blends increased with electric field strength and attained maximum values of 50%, 35%, 110% ,and 45%, respectively, at an electric field strength of 2 kV/min.

Piyanoot Hiamtup

Papers

Electrical conductivity of polyaniline/zeolite composites and synergetic interaction with CO

Electrorheological properties of polyaniline suspensions : Field-induced liquid to solid transition and residual gel structure

Polyaniline/zeolite LTA composites and electrical conductivity response towards CO

Strain-hardening in the oscillatory shear deformation of a dedoped polyaniline electrorheological fluid

Electric field induced stress moduli in polythiophene/polyisoprene elastomer blends