Conductivity percolation of carbon nanotubes (CNT) in polystyrene (PS) latex film S ¸ . Ug ˘ ur, O ¨ . Yargi, and O ¨ . Pekcan Abstract: In this study, the effect of multiwalled carbon nanotubes (MWNT) on film formation behaviour and electrical conductivity properties of polystrene (PS) latex film was investigated by using the photon transmission technique and elec- trical conductivity measurements. Films were prepared by mixing PS latex with different amounts of MWNTs, varying in the range between 0 and 20 wt%. After drying, MWNT content films were separately annealed above the glass transition temperature (Tg) of PS, ranging from 100 to 270 8C, for 10 min. To monitor film formation behavior of PS–MWNT com- posites, transmitted light intensity, Itr, was measured after each annealing step. The surface conductivity of annealed films at 170 8C was measured and found to increase dramatically above a certain fraction of MWNT (4 wt%) following the per- colation theory. This fraction was defined as the percolation threshold of conductivity, Rc. The conductivity scales with the mass fraction of MWNT as a power law with exponent 2.27, which is extremely close to the value of 2.0 predicted by percolation theory. In addition, the increase in Itr during annealing was explained by void closure and interdiffusion proc- esses. Film formation stages were modeled and the corresponding activation energies were measured. Key words: multiwalled carbon nanotubes, polystyrene, latex, nanocomposites, conductivity, transmission, percolation, film formation. Re ´sume ´: Faisant appel a ` la technique de transmission photonique et a ` des mesures de conductivite ´e ´lectrique, on a e ´tudie ´ l’effet de nanotubes de carbone a ` parois multiples (NCPM) sur le comportement de formation de films et sur les proprie ´te ´s de conductivite ´e ´lectrique de films de latex au polystyre `ne (PS). Les films ont e ´te ´ pre ´pare ´s en me ´langeant du latex de PS avec diverses quantite ´s de nanotubes de carbone a ` parois multiples allant de 0 a ` 20 % en poids. Apre `s les avoir soumis au se ´chage, les films contenant des nanotubes de carbone a ` parois multiples ont e ´te ´ recuits se ´pare ´ment a ` une tempe ´rature su- pe ´rieure a ` la celle de la de transition de verre (T v ) du PS, de 100 a ` 270 8C, pendant dix minutes. Afin de suivre le compor- tement de formation des films composites PS/NCPM, on a mesure ´ l’intensite ´ de la lumie `re transmise, I tr , apre `s chaque e ´tape de recuisson. On a aussi mesure ´ la conductivite ´ de surface des films recuits a ` 170 8C et on a observe ´ une augmenta- tion dramatique au-dessus d’une certaine fraction (4 % en poids), en accord avec la the ´orie de percolation. On a de ´fini cette fraction comme le seuil de percolation de conductivite ´, R c . Les e ´chelles de conductivite ´ utilisant la fraction massique des nanotubes de carbone a ` parois multiples avec une loi de puissance avec un exposant 2,27 sont tre `s pre `s de la valeur de 2,0 pre ´dite par la the ´orie de la percolation. De plus, l’augmentation de I tr durant la recuisson peut e ˆtre explique ´e par la fer- meture du vide et des processus d’interdiffusion. On a calcule ´ des mode `les des stages de formation des films et on a me- sure ´ les e ´nergies d’activation correspondantes. Mots-cle ´s : nanotubes de carbone a ` parois multiples, polystyre `ne, latex, nanocomposites, conductivite ´, transmission, perco- lation, formation de film. [Traduit par la Re ´daction] Introduction As a result of worldwide efforts by theorists and experi- mentalists, a very good understanding of the mechanisms of latex film formation has been achieved. 1 Traditionally, the film formation process of polymer latex is considered in terms of three sequential steps: (i) Water evaporation and subsequent packing of polymer particles. (ii) Deformation of the particles and close contact between the particles if their glass transition temperature (T g ) is less than or close to the drying temperature (soft or low T g latex). Latex with a T g above the drying temperature (hard or high T g latex) stays undeformed at this stage. In the annealing of a hard latex system, deformation of particles first leads to void closure 2–4 and then after the voids disappear, diffusion across particle– particle boundaries starts, i.e., the mechanical properties of hard latex films evolve during annealing, after all solvent has evaporated and all voids have disappeared. (iii) Coales- Received 13 August 2009. Accepted 16 November 2009. Published on the NRC Research Press Web site at canjchem.nrc.ca on 24 February 2010. This article is part of a Special Issue dedicated to Professor M. A. Winnik. S ¸. Ug ˘ur and O ¨ . Yargi. Department of Physics Istanbul Technical University, Istanbul 34469, Turkey. O ¨ . Pekcan. 1 Kadir Has University, Cibali. Istanbul 34230, Turkey. 1 Corresponding author (e-mail: pekcan@khas.edu.tr). 267 Can. J. Chem. 88: 267–276 (2010) doi:10.1139/V09-173 Published by NRC Research Press