Abstract
Wetting performance of aqueous solutions of trisiloxane surfactants (TEOn) and polyoxyethylene alkyl ethers (C10EOn) on polypropylene, Parafilm and Teflon AF surfaces in a wide range of concentrations has been investigated. Surfactants C10EOn only facilitate partial wetting of water on all surfaces, but TEOn surfactants induce superspreading on polypropylene and Parafilm at room temperature (22°C) at critical wetting concentration (CWC). Influence of the length of EO chains on wetting ability has a completely different character for C10EOn and TEOn surfactants. In the case of C10EOn the final contact angle increases on all substrates used with increasing number of EO units. However, the final contact angles for droplets of TEOn solutions decrease with increasing of n(EO) reaching a minimum values at n(EO)=6 at the critical aggregation concentration (CAC), or show complete spreading (the final contact angle is nearly zero) for n(EO)=5–8 at 1 CWC on moderately hydrophobic substrates. Temperature-dependent spreading behaviour of both TEOn and C10EOn surfactant solutions has also been studied. It has been shown for the first time, that tuning of spreading performance with temperature for polyoxyethylene alkyl ether surfactants is possible. The increase of spreading capability for both trisiloxane surfactant solutions and polyoxyethylene alkyl ethers solutions is observed at temperature close to the cloud point for a given surfactant.
Highlights
The improvement of spreading ability of water-based solutions over hydrophobic surfaces is of great importance in such industrial processes as herbicide spreading [1,2,3], paper and plastic
Comparative study of spreading performance of aqueous solutions of trisiloxane surfactants with 4–9 ethylene oxide (EO) units and polyoxyethylene alkyl ethers with 10 hydrocarbon groups, and 3–8 EO units on polypropylene, Parafilm and Teflon AF in a wide range of concentrations and at different temperatures has been carried out
That both kinds of surfactants demonstrate three mode of spreading at room temperature depending on the concentration surfactants and the substrate used: (i) non-wetting when both an initial (Â0) and a quasi-equilibrium final contact angle (Â∞) were above 90◦; (ii) transition from non-wetting (Â0 ≥ 90◦) to partial wetting (Â∞ < 90◦), and (iii) partial wetting (Â0 < 90◦ and Â∞ < 90◦)
Summary
The improvement of spreading ability of water-based solutions over hydrophobic surfaces is of great importance in such industrial processes as herbicide spreading [1,2,3], paper and plastic. Droplets of surfactant solutions reach constant quasi-equilibrium final contact angles with increasing concentration above the CMC [9,10] Another class of widely used nonionic surfactants are trisiloxane surfactants (TEOn) consisting of silicone-based hydrophobic moiety with methyl groups [1,2]. The CWC is several times higher than the CAC; no change in the water–air interfacial tension at concentrations above CWC was detected It was shown in [17,18] that the droplets of surfactant solutions reach a constant final contact angles at concentrations above CWC (C ≥ CWC). We presented results of systematic comparison of spreading behaviour of alcohol ethoxylated C10EOn where n(EO) = 3–8 and trisiloxanes TEOn where n(EO) = 4–9 depending on concentration of surfactants, the length of the oxyethylene (EO) chains, properties of polymer substrates and temperature. Some data on behaviour of aqueous trisiloxane solutions have been taken from our previous works [17,18]
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