Electronically conductive polymer films microscopy

Another approach to deposit conducting polymers can be achieved by photochemical polymerization of the monomer precursors. This procedure provides a means by which different composites (metals and/or various alloy materials with or without biomolecules) can be deposited from an electrolyte onto a non-conducting surface. Such a procedure was optimized and applied for polymerization of pyrrole in the presence of metal nanoparticles [61]. Photopolymerized films containing metals analyzed by environmental scanning electron microscopy (SEM) appeared to be typical of amorphous polypyrrole in which bright Ag particles were found on the surface (Fig. 7.6). 

Other workers have used additives to enable the preparation of effectively water-soluble conductive polymer colloids. As early as 1986, Bjorklund and Liedberg102 observed that when pyrrole was oxidized by FeCl3 in the presence of aqueous methylcellulose (MWt 100,000), a PPy/methylcellulose sol was formed that could be characterized by scanning electron microscopy. Thin films could be obtained from the sol, exhibiting a conductivity of ca. 0.2 S cm-1. Subsequently, a range of neutral, water-soluble steric stabilizers such as poly(vinylalcohol), poly(ethyleneoxide) (PEO), or poly(vinylpyridine) have been successfully... 

Finally the conductivity and electrochemical activity of the polymer film, at the working potential used for driving the electrocatalytic reaction, is also essential for commentating on the observed electrocatalytic properties. Many experimental methods are available for such characterizations, such as electronic microscopies, electrical and electrochemical characterizations, which... 

In situ conductivity measurements [52, 53, 164, 189, 195-202], luminescence techniques [203], different spectroscopies in combination with electrochemical methods [35-39, 82, 114, 115, 153-156, 204-208], and surface plasmon resonance [209] have also supplied valuable information about the ionic and electronic charge-transfer and charge transport processes. Microscopies have given new insights into the structure and morphology of surface polymer films, as well as their changes with the experimental conditions [151-159, 210-218]. The successful... 

AFM, especially when used in noncontact modes, is an ideal tool to image delicate morphological details of surfaces of polymer films [8a]. When these films are coated with gold for scanning electron microscopy (SEM), features with typical dimensions of less than —50 run become buried and may disappear from SEM images. In AFM imaging this is not a problem as no conductive coating is required. 

Another conductivity mechanism could be suggested for LB films of this polymer with Ag+ cations. Such cations can accept or release electrons easily, so in the layer of such cations the conductivity could be caused by electron transitions between the ions with different degrees of oxidation. With tunneling microscopy an anomaly in the dl/dV(V) curves near zero bias was discovered for the LB films in Ag form with an odd number of layers there was a conductivity peak some 150-200 mV wide (Figure 7.4, Curves 1, 3) but no anomaly for these same films with an even number of layers (Figure 7.4, Curve 2). For LB films with an odd number of layers the ordered superstructure of the scale 11.5 x 11.5 x lO cm has been found in a conductivity dl/dV (x,y) measurement regime. The scale of such a structure corresponds to 3 x 2 surface reconstruction (Figure 7.5). 

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