Spreading, trisiloxane

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

There are numerous studies on the spreading of trisiloxane surfactants on hydrophobic surfaces (for two comprehensive reviews, see [21,22]), but the... 

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

Stoebe T, Lin Z, Hill RM, Ward MD, Davis HT (1997) Superspreading of aqueous films containing trisiloxane surfactant on mineral oil. Langmuir 13 7282-7286 Stoebe T, Hill RM, Ward MD, Scriven LE, Davis HT (1996) Surfactant-enhanced spreading. Langmuir 12 337-344... 

Svitova TF, Hill RM, Radke CJ (2001) Spreading of aqueous trisiloxane surfactant solutions over liquid hydrophobic substrates. Langmuir 17 335-348... 

Wu Y, Rosen MJ (2002) Superspreading of trisiloxane surfactant mixtures on hydrophobic surfaces 2. Interaction and spreading of aqueous trisiloxane surfactant -n-alkyl pyrrolidinone mixtures in contact with polyethylene. Langmuir 18 2205-2215... 

Wagner, P., Wu, Y., van Berlepsch, H. and Perepelittchenko, L. (2000) Silicon-modified surfactants and wetting IV. Spreading behaviour of trisiloxane surfactants on energetically different solid surfaces. Appl. Organometallic Chem., 14(4), 177-88. 

Trisiloxanes represent a unique subset within conventional silicone polyether copolymers. Their well-defined compact siloxane backbone affords distinctive application benefits (e.g., spreading and wetting). However, they tend to be more prone to hydrolysis. 

Fig. 4. Spreading area (absolute values [cm ] relative to number of surfactant molecules expressed in number of bilayers O) as a firnction of concentration and relative humidity. Trisiloxane surfactant (Tegopren 5840) at (A) 50 % and (B) 100 % relative humidity Silane surfactant (K 4237) at (C) 50 % and (D) 100 % relative humidity.

The order of increased surfactant adsorption on the solid produced by the different alkyl pyrrolidinones parallels the order of their enhancement of superspreading. In addition, it was shown (Wu, 2002) (1) that the change in the spreading coefficient (equation 6.1) parallels enhancement of superspreading and (2) that the order of increased attractive molecular interaction between the different alkylpyr-rolidinones and the trisiloxane surfactant at the hydrophobic solid-aqueous solution interface, as measured by the interaction parameter Psl° (Chapter 11) n-butyl < n-cyclohexyl < -octyl < n-hexyl < 2-ethylhexyl, is exactly the same order as that of their enhancement of the superspreading. 

Trisiloxane surfactants have been used as adjuvants in agriculture. They increase the foliar uptake of pesticides, due to reduction of surface tension and superspreading. A method for improving the performance of agricultural compositions under conditions of low humidity has been developed, by using silicone surfactants that reduce the surface tension to less than 30 mN/m in 0.10% (w/w) aqueous solution, without concomitant spreading of the spray solution [60]. 

What Super Spreads — An Analysis of the Spreading Performance of the Single Components of the Trisiloxane Superspreader Type M2D -(CH2)3-(0CH2CH2) -0CH3... 

Aqueous solutions of certain trisiloxane surfactants wet rapidly low-energy surfaces (water contact angle > 90°) [1]. The spreading rate of a superspreader solution significantly exceeds that expected for a purely liquid diffusion controlled process [2, 3]. 

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. 

These theories, however, do not explain why only some trisiloxane surfactants exhibit superspreading behavior, and why minor variations in the hydrophilic head group can lead to dramatically reduced spreading. This effect is demonstrated in Table 1 for the four specific trisiloxane surfactants used in our studies. 

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