Wetting Dynamics of Aqueous Surfactant Solutions on Polymer Surfaces - Drops and Bubbles in Contact with Solid Surfaces - page 84

Figure 12. Sessile drop method: θ —contact angle, d —base and h —height of the drop.
Figure 13. Contact angle of aqueous surfactant solutions on polypropylene surface as function of time
(c = cmc): ! SDS; E DTAS; 1 DTAB; C 12 E 5 .
ogy for analysis of wetting properties of surfactant solutions is meant including a
suitable measuring method as well as a number of appropriate model surfaces with
manufacturing and cleaning instructions.
The sessile drop method was used to investigate wetting of aqueous surfactant
solutions on solid surfaces. The measurement data are the contact angle, base and
height of the drop as shown in Fig. 12. For surfactant solutions, the contact angle
as a function of time may be significant as illustrated in Fig. 13.
In the time interval of 0 to 7 s, the most effective, i.e., the lowest contact
angle, surfactant for highly hydrophobic polypropylene (PP) surface is cationic
dodecyltrimethylammonium bromide (DTAB). Beginning at approximately 7 s,
a non-ionic pentaethylene glycol monododecyl ether (C 12 E 5 ) becomes more effec-
tive than DTAB, cationic dodecyltrimethylammonium sulfate (DTAS) and anionic
sodium dodecyl sulfate (SDS).
Dynamic wetting measurements were carried out with a FibroDAT 1122 dy-
namic contact angle tester (Fibro Systems AB, Sweden) equipped with a video
camera which allows collecting up to 1000 images per second. The device has some
advantages over other contact angle measuring systems, which are especially im-
portant for performing the dynamic wetting measurements with aqueous surfactant
solutions:
(i) Adjustment of a specified (small) drop volumes using a liquid delivery system;