Trisiloxane solution, hydrophobic surfac

Spreading of Aqueous Trisiloxane Solution on a Hydrophobic Surface. . 119... 

Chengara A, Nikolov A, Wasan D (2002) Surface tension gradient driven spreading of trisiloxane solution on hydrophobic solid. Colloid Surf A 206 31-39... 

The wetting exhibited by some trisiloxane surfactants is so extensive and rapid that it has been referred to as superspreading [3]. Typically, a small drop (50 pL) of a diluted aqueous solution (0.1 % w/w) of such a trisiloxane spreads out on a hydrophobic surface such as a polypropylene sheet into a thin, wetting film approx. 80 mm in diameter within tens of seconds. This is about 20 times the area wetted by a 1 % w/w solution of a conventional organic surfactant such as a nonylphenol ethoxylate. 

FTIR-ATR spectroscopy was used to study the absorbance kinetics of trisiloxane and hydrocarbon surfactants on different hydrophobic solids from aqueous solutions. The surface of AMTIR (the internal reflection element) was used as low hydrophobic surface, and Teflon AF coated AMTIR surface was chosen as a highly hydrophobic surface. It has been shown that the absorbance of all surfactants studied on Teflon AF is considerably higher than that on AMTIR surface. Irrespectively of the surface energy of solid substrates the absorbance of trisiloxanes increased over 10 minutes of the experiment, while the absorbance of hydrocarbon surfactants reached equilibrium in seconds on AMTIR and in a few minutes on Teflon AF surfaces. The continuous growth of absorbance with increasing bulk concentration of surfactants has been detected in case of trisiloxanes on both substrates even at C > CWC while hydrocarbon surfactants... 

For a series of lV-alkyl-2-pyrrolidinones that produce enhanced superspreading of the POE trisiloxane mentioned above on polyethylene film, it has been shown (Rosen, 2001) that the addition of the alkylpyrrolidinone to the trisiloxane surfactant produces little or no increase in the total surfactant at the hydrophobic solid-air or aqueous solution-air interfaces, but a considerable increase in the total surfactant adsorption at the hydrophobic solid-aqueous solution interface. This enhanced adsorption of surfactant at the aqueous solution-solid interface relative to that at the aqueous solution-air interface produces a decrease in the surfactant concentration at the air-solution interface in the thin precursor film at the wetting front (Figure 6-8). This results in a surface tension gradient in the precursor film promoting movement of the aqueous phase to the wetting front. 

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