Impact of Molecular Architecture on Surface Properties and Aqueous Stabilities of Silicone-Based Carboxylate Surfactants

Silicone surfactants consist of siloxane or carbosilane hydrophobic groups that possess better surface activity compared with alkane surfactants. The surfactants, containing Si atoms which bring excellent bond flexibility and low cohesive energy properties are a promising class of materials for unique surface working, but there are few studies to elaborate their surface activity mechanism with regard to the molecular architecture. Herein, two novel carboxylate surfactants with different silicone hydrophobic groups (Si-O-Si and Si-C-Si) were synthesized and their surface activities, aggregate behaviors, and solution stabilities were systematically investigated. Results showed that both surfactants had excellent surface activities which are attributed to the hydrophobic structure of silicone. The hydrolysis resistance of the carbosilane-based carboxylate surfactant was better than that of the siloxane-based carboxylate surfactant. The differences in hydrolysis processes for the surfactants were confirmed by the mass spectrum and kinetic analysis. Meanwhile, the aggregation number of Si-C-Si surfactants was also determined by the fluorescence quenching method for the first time.

Effect of surfactant shape on solvophobicity and surface activity in alcohol-water systems

Here we study the relationship between a surfactant's molecular shape and its tendency to partition to the interface in ethanol-water mixtures. In general, finding surfactants that are effective in alcohol-water mixtures is more challenging than finding ones that are effective in pure water. This is because the solvophobic effect that partitions surfactants from bulk solution to the interface becomes weaker as ethanol concentration increases. We use experiments and molecular dynamics to observe the effects of increasing surfactant tail length or width. The results show that increasing surfactant tail length causes the surfactant to partition to the surface better in low ethanol concentrations, but not at high ethanol concentrations. In comparison, increasing surfactant tail width causes the surfactant to partition to the surface better at higher concentrations of ethanol. We examine the liquid structure to elucidate the mechanisms that weaken the partitioning effect as ethanol concentration increases. Ethanol-water mixtures are nanoscopically heterogeneous with protic and aprotic regions in the bulk solution. We see that the surfactant tail is most likely to be solvated in the aprotic regions where it perturbs fewer hydrogen bonds.

Synthesis and Solution Properties of New Polysiloxane Bola Surfactants Containing Carbohydrate

Three polysiloxane bola surfactants containing carbohydrate (ATPS-LA) were synthesized using a two-step method. Structure characterization was performed by infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H NMR). Their surface activities and aggregation properties in aqueous solution were investigated by surface tension measurements and transmission electron microscopy (TEM). The results indicated that these three surfactants have much higher surface activity than those of conventional hydrocarbon bola surfactants, such as sodium eicosanedioate, in aqueous solution, and they can self-assemble into spherical micelles with average diameters in the range from 100 to 600 nm.

Synthesis and Properties of Lactobionamide-Based Polysiloxane Surfactant

A lactobionamide-based polysiloxane surfactant (LBPS) with well-defined structure was prepared via a two-step method. Structure characterization of the LBPS was performed by Fourier Transform Infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR). Surface activity and aggregation behavior in aqueous solution of the LBPS were investigated by surface tension measurements, dynamic light scattering (DLS) and negative-stain transmission electron microscopy (TEM). The results show that the critical micelle concentration (CMC) and surface tension (γCMC) at the CMC in aqueous solution of the LBPS are 7.7 mg · L−1 and 27.5 mN · m−1, respectively, and the surfactants can self-assemble into spherical micelles with diameters in the range from 30 to 250 nm.

Nanoscale aggregate structures of trisiloxane surfactants at the solid-liquid interface

The self-associating structures at the solid-liquid interface of three nonionic trisiloxane surfactants ((CH3)3SiO)2Si(CH3)(CH2)3(OCH2CH2)n OH (n = 6, 8, and 12), or BEn, are studied as a function of substrate properties by atomic force microscopy (AFM) imaging and force measurement. These trisiloxane surfactants are known as superwetters, which promote rapid spreading of dilute aqueous solutions on low-energy surfaces. This study also attempts to relate the BEn surface aggregate structures at the solid-liquid interface to their superwetting behavior. Four substrates are used in the study: muscovite mica, highly oriented pyrolytic graphite, and oxidized silicon wafer with and without a full monolayer of self-assembled n-octadecyltrichlorosilane (OTS). The concentration of BEn is fixed at 2 times the critical aggregation concentration (CAC). The BEn surfactants are only weakly attracted to hydrophilic surfaces, more on oxidized silicon than on mica. All three form ordinary planar monolayers on HOPG and OTS-covered oxidized silicon. The significance of surfactant adsorption on the AFM tip is investigated by comparing the force curves obtained by tips with and without thiol modification. The surface aggregate structures of the BEn surfactants correlate with their bulk structures and do not exhibit anomalous adsorption behavior. The adsorption behavior of the BEn superwetters is similar to that of the CmEn surfactants. Thus, our results confirm previous work showing that superwetting shares its main features with other classes of surfactants.