Abstract In this thesis, preparation of carbon nanotube (CNT) inks and inkjet printing of aqueous dispersions of CNTs for certain electrical applications are studied. The nanotube inks prepared in this work are based on chemically oxidized CNTs whose polar side groups enable dispersion in polar solvents. Subsequent centrifugation and decanting processes are used to obtain stable dispersions suitable for inkjet printing. The inks are based on either carboxyl functionalized multi-walled carbon nanotubes (MWCNTs), carboxyl functionalized single wall carbon nanotubes (SWCNTs) or SWCNT-polymer composites. The applicability of MWCNT inks is firstly demonstrated as printed patterns of tangled nanotube networks with print resolution up to ∼260 dpi and surface resistivity of ∼40 kΩ/□. which could be obtained using an ordinary inkjet office printer. In addition, MWCNT inks are found to exhibit spatial ordering in external magnetic fields due to entrapped iron catalyst nanoparticles in the inner-tubular cavity of the nanotubes. Ordering of nanotubes in the inks and in drying droplets placed in relatively weak magnetic fields (B ≤ 1 T) is demonstrated and studied. The high electrical conductivity and optical transparency properties of SWCNTs are utilized for enhancing the conductivity of transparent poly(3,4-ethylenedioxythiophene):poly(styrenesulphonate) (PEDOT:PSS) films. Polymer-nanotube composite materials are inkjet printed on flexible substrates. It is demonstrated that incorporation of SWCNTs in the thin polymer films significantly increases the electrical conductivity of the film without losing the high transparency (> 90%). The structure of composite films is studied using atomic force microscopy (AFM). The electronic properties of deposited random SWCNT networks are studied. The amount of deposited SWCNT is controlled by the inkjet printing technique. In dense networks the current-voltage behaviour is linear whereas for sparse films the behaviour is nonlinear. It is shown that the conduction path in dense films is through the metallic nanotubes, but in sparse films the percolation occurs through random networks of metallic and semiconducting SWCNTs having Schottky-type contacts. The existence of Schottky-junctions in the films is demonstrated with field-effect transistors (FET) on Si-chips and on polymer substrates. The latter is demonstrated as fully printed transistors using a single ink as a material source. FETs are further utilized as chemical-FET sensor applications. The performance of resistive CNT sensors and their comparisons with chem-FETs in terms of selectivity are studied for H2S gas.

In smart textiles, electrical conductivity is often required for several functions, especially contacting (electroding) and interconnecting. This thesis explores electrically conductive textile surfaces made by combining conventional textile coating methods with the intrinsically conductive polymer complex poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS). PEDOT:PSS was used in textile coating formulations including polymer binder, ethylene glycol (EG) and rheology modifier. Shear viscometry was used to identify suitable viscosities of the formulations for each coating method. The coating methods were knife coating, pad coating and screen printing. The first part of the work studied the influence of composition of the coating formulation, the amount of coating and the film formation process on the surface resistivity and the surface appearance of knife-coated textiles. The electrical resistivity was largely affected by the amount of PEDOT:PSS in the coating and indicated percolation behaviour within the system. Addition of a high-boiling solvent, i.e. EG, decreased the surface resistivity with more than four orders of magnitude. Studies of tear strength and bending rigidity showed that textiles coated with formulations containing larger amounts of PEDOT:PSS and EG were softer, more ductile and stronger than those coated with formulations containing more binder. The coated textiles were found to be durable to abrasion and cyclic strain, as well as quite resilient to the harsh treatment of shear flexing. Washing increased the surface resistivity, but the samples remained conductive after five wash cycles. The second part of the work focused on using the coatings to transfer the voltage signal from piezoelectric textile fibres; the coatings were first applied using pad coating as the outer electrode on a woven sensor and then as screen-printed interconnections in a sensing glove based on stretchy, warp-knitted fabric. Sensor data from the glove was successfully used as input to a microcontroller running a robot gripper. These applications showed the viability of the concept and that the coatings could be made very flexible and integrated into the textile garment without substantial loss of the textile characteristics. The industrial feasibility of the approach was also verified through the variations of coating methods.