DOI: 10.1002/asia.201000703 Lamellar-Structured Nanoflakes Comprised of Stacked Oligoaniline Nanosheets Zoran D. Zujovic,* [a] Cosmin Laslau, [a, b] and Jadranka Travas-Sejdic* [a, b] Dedicated to Professor Eiichi Nakamura on the occasion of his 60th birthday Conducting polymers (CPs), such as polyaniline (PANI) nanostructures, are novel materials with a wide range of ap- plications, [1] including sensors, [2] transistors, [3] and actuators. [4] This is due to their unique properties: the electrical conduc- tivity of CPs can be tuned between the insulator, semicon- ductor, and metal regimes, they have a reversible doping/de- doping process, and they also have controllable chemical, electrochemical, and physical properties. [5] However, synthe- sis pathways remain a problem, with some beset by compli- cated processes and low yields (e.g., hard templates, electro- spinning, lithography) whilst others are marred by poor re- peatability (e.g., self-assembly). [5–9] Overall, self-assembly may become the optimal pathway for the synthesis of PANI nanostructures, as its high yields and straightforward setup are ideal, but its poor reproducibility issues must be under- stood and addressed. [9–13] Very recently, it was discovered that critical nanosheet structural and morphological changes occur within the first few minutes of aniline polymerization, thus determining the course of the subsequent PANI nanostructure self-assem- bly. [12–15] The importance of this area of research is that in determining the intricacies underlying the process of PANI nanostructure self-assembly, a breakthrough in the synthesis of CPs may be achieved. Specifically, by understanding the formation mechanism, a synthesis may be designed to allow for the controlled, high-yielding, repeatable manufacture of PANI nanostructures. In our previous work, we proposed that oligoanilinic nanotube structures formed early in the “falling-pH” (here- after referred to without the quotation marks) reaction con- sist of very thin, rolled nanosheets. [12] Depending on the con- ditions (e.g., solution pH, concentrations of reagents, tem- perature) these individual nanosheets may either curl, thus forming cylindrical structures (i.e., nanotubes), or, as shown in Figure 1, stack onto each other, thus forming thicker flat structures, which we term nanoflakes. These structures rep- resent intermediate templates upon which PANI polymer- izes during the later stages of the falling-pH synthesis reac- tion. [6, 7, 9, 13, 16–20] How and why nanosheets form in the first place is still not clearly understood. Therefore, in this study we explore the initial conditions for the formation of nano- sheets and characterize their morphological and structural properties. This investigation should lead towards a better understanding of the self-assembly of low-dimensional PANI nanostructures. There are essentially two types of interactions that can be involved in the course of oligoanilinic nanosheet self-assem- bly: 1) strong, covalent bonding interactions which predomi- nantly occur within the nanosheets and 2) relatively weak van der Waals forces, hydrogen bonding (between the ÀOH, ÀNH, and =NÀ groups) and pÀp interactions which are active between individual nanosheet layers. [21] In addition to their role in subsequent stacking interactions, these forces may also be influential in the formation of individual nano- sheets. Aromatic molecules can interact with each other through a p À p stacking process: the p systems form two par- allel rings that overlap in a “face-to-face” orientation. [21] Ar- omatic molecules are also able to interact with each other in an “edge-to-face” orientation, where the slightly positive charge of the substituents on the ring atoms of one molecule are attracted to the slightly negative charge of the aromatic system on another molecule. This interaction, which is stron- ger than other noncovalent interactions, plays an important [a] Dr. Z.D. Zujovic, C. Laslau, Prof. J. Travas-Sejdic Polymer Electronics Research Centre Department of Chemistry, University of Auckland Private Bag 92019, Auckland 1142 (New Zealand) Fax: (+ 64)-9-373-7422 E-mail : z.zujovic@auckland.ac.nz j.travas-sejdic@auckland.ac.nz [b] C. Laslau, Prof. J. Travas-Sejdic MacDiarmid Institute for Advanced Materials and Nanotechnology Victoria University of Wellington PO Box 600, Wellington 6140, (New Zealand) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201000703. Chem. Asian J. 2011, 6, 791 – 796 # 2011 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 791