Fibrillar and Globular Morphology

On a microscopic or nanoscopic scale, untreated, as-synthesized CPs generally fall into three categories in terms of outward topology fibrillar, the most typical globular, and more rarely, truly filmlike (which is actually extremely fine-structured globular). Typically, standard Shirakawa-P(Ac) is produced in fibrillar form, electrochemically polymerized P(Py) in globular form and electrochemically polymerized P(DPA) in filmlike form. 

contain dispersed, single, globular particles of P(ANi) of ca. 250 nm diameter, each of which is supposedly an aggregation of smaller spheres [274]. 

In the case of as-prepared fibrillar CPs, e.g. the Shirakawa-P(Ac), fibril diameters can vary from as little as 3 nm to 1 jum [304, 305], very much dependent on polymerization conditions (time, solvents used, etc.). 

Fibril formation in fibrillar CPs is generally through precipitation and coalescing of the growing polymer once a critical chain length is reached. It is important to note however that the bulk density of CPs appears to change little with morphology, or with other parameters such as nature of dopant, as shown below. 

Some workers [306, 307] have claimed that CPs such as P(ANi) can show folded/coiled and uncoiled forms, interconverted through the presence of electrolytes in solution, somewhat like proteins. Evidence for this however is highly inferential and circumstantial. 

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Cyclic voltammetry of polyaniline obtained in the presence of the three polyelectrolytes was very similar and presented two redox pairs. The absence of the third intermediate redox pair is evidence of linear chain formation. The scanning electron micrographs indicate a fibrillar morphology for polyanilines obtained with perchloric and p-toluene sulfonic acids and globular for those blended with the other polyelectrolytes. 

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