Oxyfluorinated iPP

In the example we elaborate here, we focus on oxyfluorinated iPP (e.g. oxy-fluorinated isotactic polypropylene films, SOLVAY ELTEX P KL 177 obtained from SOLVAY ALKOR-DRAKA Snc.). In principle, corona treated iPP films can be utilized similarly well. The freshly oxidized films are cut into small lxl cm2 sized samples and are inserted quickly after mounting to the metallic sample puck (using a minute amount of a fast curing epoxy). 

The operation and adjustment of the TM-AFM are identical to the procedures discussed in example 34 (oxyfluorinated iPP). 

Fig. 4.8 (a) Histograms of pull-off force values obtained with an unmodified Si3N4 tip on untreated and oxyfluorinated iPP films in ethanol. The total surface free energy y of the polymer film is shown, (b) Mean values of pull-off force measured with COOH-terminated tips on modified polyolefin surfaces (iPP, isotactic polypropylene LDPE, low-density polyethylene) in ethanol (top) and with OH-terminated tips on oxyfluorinated iPP in water (pH 3.8, bottom) as a function of cos 0 (contact angle measured with water). (Reprinted in part/adapted with permission from [26, 27]. Copyright 1998, 2000, American Chemical Society.)... 

Fig. 24 Force titration of an untreated iPP (top, left) and three oxyfluorinated iPP films using OH-terminated SFM tips. The total surface tension values are indicated. The error bars correspond to the standard deviation of the average value calculated from the corresponding histograms. (Reprinted with permission from [58]. Copyright 2000 American Chemical Society)...

Fig. 25 FV images of oxyfluorinated iPP (y = 39.6mN/m) at pH 6.8 (left) and pH 8.8 (right). Dark color indicates high adhesion (-0.3nN for pH 6.8, 0nN for pH 8.8), bright color indicates low adhesion (0 nN for pH 6.8 and pH 8.8). The arrows indicate areas of high pull-off forces, which were attributed to domains with the most hydrophobic character, i.e. lower density of polar - COOH and OH functional groups introduced by the oxyfluorination). (Reprinted with permission from [58]. Copyri t 2000 American Chemical Society)...

For flat samples, the extent of surface modification reactions can be conveniently followed. For the iPP films analyzed in Sect. 3.5 in Chap. 3, the roughness variations due to surface modification were minimal. Thus, crosstalk in the force analysis shown in Fig. 4.8a (acquired using unmodified Si3N4 tips in ethanol) subsequent to oxyfluorination is minimized. 

In these experiments, individual f-d curves were recorded at various locations of each film using the same tip (i.e., the tip radius is assumed to remain constant). Subsequently, the pull-off forces were evaluated off-line and were plotted in a histogram. The pull-off forces were observed to increase with the extent of oxyfluorination and the concomitant increase in surface energy (shown as values of surface tension). Using different tip functionalities and media on oxidized iPP and... 

---