The design and development of a compact wireless gas sensor with a surface modified multiwalled carbon nanotube (f-CNT) chemiresistor as the sensing element is presented in this paper. f-CNT/polymer composite sensing film is patterned on a printed circuit board and is integrated to the wireless system. The change in resistance of the CNT/polymer composite film due to exposure of different gases is utilized as the principle of this gas sensor. The response for different organic vapors are evaluated and it is observed that the f-CNT/PMMA composite film shows fast response and change in resistance of the order of 10 2-10 3 due to its surface modification.

The design and development of composite thin films of polymethylmethacrylate (PMMA) with multiwalled carbon nanotubes (CNTs) and surface-modified multiwalled carbon nanotubes (f-CNTs) for gas-sensing applications are presented in this paper. The responses of these composites for different organic vapors were evaluated by monitoring the change in the resistance of thin films of composite when exposed to gases like dichloromethane, chloroform, acetone, methanol, ethyl acetate, toluene and hexane. It was observed that the f-CNT/PMMA composite showed a higher response. There was an increase in resistance of the order of 10 2 -10 3 , due to surface modification, when exposed to dichloromethane, chloroform and acetone. The sensing mechanism is explained on the basis of volume expansion and polar interaction of various vapors on the CNT surface.

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A nanocomposite of a multiwalled carbon nanotube and polythiophene was prepared by functionalizing the nanotube surface with a polythiophene, poly[3-(2-hydroxyethyl)-2,5-thienylene], containing pendant hydroxyl groups. The composite was characterized by IR, high resolution TEM and conductivity measurements. The poly[3-(2-hydroxyethyl)-2,5-thienylene] (PHET) was synthesized by the oxidation polymerization of 2-(3-thienylethanol) using FeCl3 and CHCl3. Multiwalled carbon nanotubes were synthesized by a microwave CVD method and oxidized with potassium permanganate using a phase transfer catalyst in mild conditions. The COOH groups formed on the nanotube surface were converted to COCl using thionyl chloride and it was then condensed with the polythiophene at high temperature in anhydrous DMF. High resolution TEM images showed that the functionalization provided a firm coating of the conducting polymer on nanotube walls. This nanocomposite with PHET grafted to CNT showed higher conductivity than a nanocomposite of PHET and CNT in the same percentage weight composition prepared by ultrasonic mixing of the two. Such a material was designed and synthesized with a view to electronic and sensor applications.

The synthesis and characterization of a new series of chiral poly(ester-amide)s are reported. They were prepared by the simple reaction of diacid chlorides with biphenolic azo chromophores and optically active dihydroxy compound (isosorbide) in dimethyl acetamide at 100°C. The polymers containing isosorbide units were optically active. The polymers showed T g between 100 and 190°C and were stable up to 400°C. These poly(ester-amide)s showed a positive solvatochromism in UV±visible absorption spectra. Second harmonic generation activities were measured by the powder method.

A series of polyesters with -conjugated donor-acceptor segments was synthesized by the condensation of azobenzene-4,4Ј-dicarbonylchloride with 1,4:3,6dianhydro-D-sorbitol ([␣] D 25 ϭ ϩ 42.5°) and biphenolic chromophores, bis(4-hydroxyphenylazo)-2,2Ј-dinitrodiphenylmethane and bis(4-hydroxyphenylazo)-2,2Ј-dinitrodiphenylsulfone. The polymers were characterized by spectral methods (IR, ultravioletvisible, and NMR), thermal methods (thermogravimetry and differential scanning calorimetry), wide-angle X-ray scattering, and polarimetry. The polymers containing isosorbide units were optically active and crystalline. They exhibited glass-transition temperature values between 100 and 160°C and were stable up to 400°C. The second-harmonic generation (SHG) efficiency of the polymers was experimentally verified by a powder-reflection technique with 2-methyl-4-nitroaniline as a reference. The SHG efficiencies of the polymers were compared to those of the chromophores and explained as a function of the percentage of chiral composition. The hyperpolarizability ␤ values were also determined by a two-level model solvatochromic method and computational methods.

In tubular nanocomposites prepared from carbon nanotubes and polyaniline, carbon nanotubes can improve the structural ordering, compactness, delocalization of charges and carrier mobility. Such properties are very much critical in the case of organic semiconducting materials for electronics applications. In this paper we describe the synthesis of a nanotubular composite of polyaniline and carbon nanotube using p-phenylenediamine functionalized multiwalled carbon nanotubes. This functionalization helped to disperse the nanotubes well in acidic solution. The in situ polymerization of aniline in the presence of these well dispersed nanotubes gave rise to a new tubular composite of carbon nanotubes having a uniform encapsulation of doped polyaniline. It also improved the structural order, molecular packing and delocalization of the charges in the material.

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