| Siloxane surfactants consist of a nonpolar/hydrophobic moiety, siloxane. and various polar/hydrophilic moieties. As a unique class of surfactants, siloxane surfactants have been extensively used in the fields of cosmetic, textile, coating, paint, oil and agriculture. On the contrary, acetylenic diol-based surfactants, which contain carbon-carbon triple bond and two adjacent hydroxyl groups, have been widely used in the formulations of inks and coatings. Butynediol-ethoxylate modified polysiloxanes (PSi-EO) were designed and synthesized through the combination of siloxane and acetylenic diol surfactants. Their properties in aqueous solution were studied systematically, which leads to a wide variety of potential applications in industry.1. P8-2 (PSi-EO with m/n=8/2) was synthesized via two-step reactions. The hydrosilylation reaction conditions, such as material feeding ratio, reaction temperature, the dose of catalyst and reaction time were discussed. The results showed that the optimized reaction conditions for P8-2 were:material ratio n[Si-H]:n[C=C]= 1.1:1, reaction temperature 130 ℃, catalyst 100 ppm and reaction time 2.5 hours. PSi-EO with different unit ratios and siloxane backbone lengths were successfully synthesized according to the optimized reaction conditions. The chemical composition of each product was confirmed by FT-IR, 1H NMR and 29Si NMR, which revealed that the products PSi-EO were almost identical to the target molecules.2. The surface activities, aggregation behaviors, wetting and spreading abilities and foaming properties of PSi-EO with different unit ratios in aqueous solution were studied systematically using surface tension, dynamic light scattering (DLS), transmission electron microscopy (TEM), contact angle and Ross-Miles methodologies. Relatively low critical aggregation concentration (15-34 mg/L) and surface tension (-25 mN/m) were measured for PSi-EO aqueous solution. The rate of surface tension reduction increased both with increasing PSi-EO concentration and the percentage of BEO branches within the synthesized compounds. Furthermore, DLS and TEM studies revealed that PSi-EO self-assembled in aqueous solution to form spherical aggregates (50-600 nm). Contact angle measurement conducted upon paraffin film surfaces demonstrated that PSi-EO exhibited efficient wetting and spreading at concentrations above the critical aggregation concentration (CAC). Using the foam property test, PSi-EO all showed weak foaming abilities and effective anti-foaming properties in aqueous solution.3. The surface activities, aggregation behaviors, wetting and spreading abilities and foaming properties of PSi-EO with different lengths of siloxane backbone in aqueous solution were discussed using surface tension, transmission electron microscopy (TEM), contact angle and Ross-Miles techniques. With the increase of siloxane backbone length, the critical aggregation concentration (CAC) decreased and the surface tension at CAC (γCAC) increased, but the dynamic adsorption at the air/water interface had no significant change. Above the CAC, all of these three surfactants could self-assemble into spherical aggregates from 100 to 500 nm in aqueous solution. Moreover, the contact angle measurement on Paraffin film demonstrated that shorter siloxane backbone length of PSi-EO led to lower contact angle and showed better wetting and spreading abilities. Using the foam property test, PSi-EO with a shorter siloxane backbone exhibited better foaming and more effective anti-foaming properties in water.Overall, the unit ratios and siloxane backbone lengths of PSi-EO could play a significant role in their physicochemical properties and application performances. Hence, this work will be useful in allowing the design of novel siloxane surfactants that may find their potential applications in agricultural adjuvants, home care products, or coatings. |
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