Siloxane Surfactants Research Articles

Surface activity and spreading properties of water-based avermectin microemulsions containing novel siloxane surfactants

GRAPHICAL ABSTRACT

Influence of SDS on the Lα-phases of siloxane surfactant swollen by glycerol

The interaction between SDS and the swollen lamellar phase of an A-B-A type nonionic siloxane surfactant IM-22 in 60 % glycerol has been investigated with macroscopic phase observation, FF-TEM, SAXS, conductivity, and rheology experiments. Without addition of SDS, 20 % IM-22 forms highly swollen planar lamellar phase stabilized by strong thermal undulations. Upon addition of 1 mM SDS, the lamellae were transformed into giant multilamellar vesicles. The size of the vesicles decreases with increasing the amount of SDS below 5 mM whereas the number density of the vesicles increases. Further increasing the concentration of SDS leads to break of the vesicles. In this self-assembly transition process, the viscosity of the system exhibits maximum at 5 mM SDS, where the system owns property of gels. Conductivity measurements suggest that SDS starts to bind IM-22 at a concentration below 2 mM, but SAXS results reveal that the interlamellar spacings were not affected up to 5 mM. This was explained by the special interactions in this system. On the one hand, the ionization degree of SDS in 60 % glycerol is very low due to the low dielectric constant, which results in lower charge density in the lamellae. Therefore, thermal undulations dominate the electrostatic forces at SDS concentration below 5 mM. On the other hand, the mutual phobic nature of SDS with IM-22 allows break of the lamellae at higher SDS concentrations.

Highly stretchable composites from PDMS and polyazomethine fine particles

Polyazomethine fine particles are obtained in reverse micelles of a siloxane surfactant and used as a dispersed phase in PDMS to afford materials with improved and tunable electric and mechanical properties.

Wetting Behavior of Tetrasiloxane Surfactants Containing Glucosamide on Low-Energy Surface

The wetting behavior of aqueous solutions of two types of siloxane surfactant (dicephalic and gemini) on two hydrophobic substrates was investigated. Solutions of dicephalic surfactant demonstrate rapid and complete wetting on Parifilm surface and only partial wetting on Teflon. An increase in surfactant concentration results in a transition from partial to complete wetting. The solutions of gemini surfactant show only partial wetting on both Teflon and Parifilm. It is demonstrated that wetting behavior depends crucially on surfactant structure; substrate surface affects the wetting behavior of siloxane surfactant.

Aqueous dispersion of metal oxide nanoparticles, using siloxane surfactants

Siloxane surfactants containing tromethamol or carboxylate groups, with very good surface properties, are tested for the first time for biocompatibility using MTT cytotoxicity test. They are used for encapsulation of superparamagnetic iron oxide nanoparticles (SPION), and of a combination of these with nystatin as model un-soluble drug, in order to obtain stable aqueous dispersions. The initial magnetite and chromite nanoparticles have been synthesized previously by thermal decomposition thus being covered by dodecylamine and oleic acid. Their aqueous dispersions were obtained by physical methods using very low concentrations of siloxane surfactants, and were investigated by DLS, TEM, cryo-TEM and EDX. One such formulation was tested by MTT method and the results showed high cell viability. The nanoparticles covered with siloxane surfactants exhibited various types of morphology: individual particles, vesicle-like aggregates or composite particles, all having diameters roughly between 20 and 200nm. The encapsulation of both SPION and nystatin confirmed our previous results on nystatin solubilization by encapsulation within the hydrophobic wall of surfactant vesicles.

Polysiloxane‐Based Block Copolymers as Structure‐Directing Agents in the Synthesis of Hierarchically Organized Silica Monoliths

AbstractIn this work the successful application of commercially available, linear PEO‐PDMS‐PEO block copolymers in the synthesis of hierarchically organized silica monoliths comprising a periodic arrangement of mesopores as well as a well‐defined macroporous morphology is presented. All silica monoliths were synthesized via the sol‐gel approach with an ethylene glycol‐modified silane (EGMS) as precursor. Beyond their use as structure‐directing agents, these siloxane surfactants can also be employed as agents to tailor the surface polarity by controlled thermal decomposition of the hydrophilic PEO blocks resulting in a hydrophobic organosiloxane‐covered surface.

Fire Testing a New Fluorine-free AFFF Based on a Novel Class of Environmentally Sound High Performance Siloxane Surfactants

Fire Testing a New Fluorine-free AFFF Based on a Novel Class of Environmentally Sound High Performance Siloxane Surfactants

Superspreading: A possible mechanism

It is suggested that superspreading of droplets of dilute aqueous solutions of siloxane surfactants over a hydrophobic surface is driven by: (i) the spreading at their leading edges of the surfactant as bilayers, (ii) the suction of water in the hydrophilic atmosphere between the two layers and (iii) the displacement of the surfactant and water by a Marangoni effect intensified by the formation of bilayers. An explanation is provided for the observation that the rate of spreading passes through a maximum at an optimum degree of surface wettability (surface hydrophobicity).

METAL-COMPLEXING ABILITY OF TROMETHAMOL-MODIFIED SILOXANE SURFACTANTS

Tromethamol-modified siloxane surfactants (disiloxane and siloxane copolymers), which have previously been synthesized in the authors research group, were reacted with metal salts (Cu(II)acetate, Zn(II)acetate and Fe(III)sulfate). The obtained compounds were characterized by FT-IR and 1H-NMR spectroscopy. The evolution of the reactions was followed by UV-Vis spectra and the obtained data proved the afinity of the tromethamol-based siloxane compounds towards metal species. The formed Cu complexes showed significantly higher electronic absorption compared to Cu(II)acetate. The tested siloxane surfactants, which also act as chelating agents, could be used for improving metal detection or in certain decontamination processes.

NSGA-II-RJG applied to multi-objective optimization of polymeric nanoparticles synthesis with silicone surfactants

AbstractPolydimethylsiloxane nanoparticles were obtained by nanoprecipitation, using a siloxane surfactant as stabilizer. Two neural networks and a genetic algorithm were used to optimize this process, by minimizing the particle diameter and the polydispersity, finding in this way the optimum values for surfactant and polymer concentrations, and storage temperature. In order to improve the performance of the non-dominated sorting genetic algorithm, NSGA-II, a genetic operator was introduced in this study — the transposition operator — “real jumping genes”, resulting NSGA-II-RJG. It was implemented in original software and was applied to the multi-objective optimization of the polymeric nanoparticles synthesis with silicone surfactants. The multi-objective function of the algorithm included two fitness functions. One fitness function was calculated with a neural network modelling the variation of the particle diameter on the surfactant concentration, polymer concentration, and storage temperature, and the other was computed by a neural network modelling the dependence of polydispersity index on surfactant and polymer concentrations. The performance of the software program that implemented NSGA-II-RJG was highlighted by comparing it with the software implementation of NSGA-II. The results obtained from simulations showed that NSGA-II-RJG is able to find non-dominated solutions with a greater diversity and a faster convergence time than NSGA-II.

Block Copolymer Vesicle Permeability Measured by Osmotic Swelling and Shrinking

Vesicle response to osmotic shock provides insight into membrane permeability, a highly relevant value for applications ranging from nanoreactor experimentation to drug delivery. The osmotic shock approach has been employed extensively to elucidate the properties of phospholipid vesicles (liposomes) and of varieties of polymer vesicles (polymersomes). This study seeks to compare the membrane response for two varieties of polymersomes, a comb-type siloxane surfactant, poly(dimethylsiloxane)-g-poly(ethylene oxide) (PDMS-g-PEO), and a diblock copolymer, polybutadiene-b-poly(ethylene oxide) (PBut-b-PEO). Despite similar molecular weights and the same hydrophilic block (PEO), the two copolymers possess different hydrophobic blocks (PBut and PDMS) and corresponding glass transition temperatures (-31 and -123 °C, respectively). Dramatic variations in membrane response are observed during exposure to osmotic pressure differences, and values for polymer membrane permeability to water are extracted. We propose an explanation for the observed phenomena based on the respective properties of the PBut-b-PEO and PDMS-g-PEO membranes in terms of cohesion, thickness, and fluidity.

Siloxane surfactant induced self-assembly of gold nanoparticles and their application to SERS

A siloxane surfactant was used for the mild synthesis and simultaneous 1D assembly of gold nanoparticles. The length of the gold nanochains could be tuned by facile adjustment of the surfactant concentration. The multiple interactions between the siloxane surfactant and gold nanoparticles made the non-uniform spatial distribution of stabilizers at the nanoparticle surfaces and then led to the 1D assembly. Transmission electron microscopy (TEM) and UV-vis spectroscopy have been employed for characterizing the nanochains. The effect of ionic strength in the spontaneous linear assembly of gold nanoparticles was investigated to further elucidate the assembly of mechanism. These gold nanochains were shown to yield a large SERS enhancement for Rhodamine 6G.

Carbohydrate-Modified Siloxane Surfactants and Their Adsorption and Aggregation Behavior in Aqueous Solution

Four carbohydrate-modified siloxane surfactants, Si(n)N-GA and Si(n)N-LA (n = 3, 4), were designed and synthesized. Their surface activities, adsorption, and aggregation behavior in aqueous solution were investigated by surface tension measurements, dynamic light scattering (DLS) and transmission electron microscopy (TEM). Due to the bulky siloxane moiety at the end of hydrophobic chains, the surfactant solutions displayed low critical aggregation concentration (cac) and low surface tension. Surface tension measurement for all three surfactants are under 22 mN x m(-1), much lower than those of ordinary hydrocarbon surfactants. Due to its poor solubility in water, surface tension of Si(4)N-GA could not be measured. DLS and TEM analysis of Si(3)N-GA, Si(3)N-LA, and Si(4)N-LA aqueous solutions revealed self-assembled spherical vesicles, indicating potential applications as microsphere drug delivery systems and as models of biomembranes.

Phases confirmation of cloudy Silwet L-77 aqueous solution by dielectric relaxation spectroscopy

The phase transition of Silwet L-77 (a kind of siloxane surfactant) dilute aqueous solution with temperature was investigated by dielectric relaxation spectroscopy. In the initial heating process, a dielectric relaxation was found at about 10 6 Hz, which was considered as the interface polarization ascribed to the interface between water and liquid phases (W and L 1). With the temperature increasing further, a new dielectric relaxation was observed at about 10 4 Hz, which was assigned to the appearance of liquid crystal phase (L α). According to the dielectric parameters fitted by Cole–Cole equation, the coexistence temperature of W, L 1 and L α was determined at about 37.0 °C.

Silver nanoparticles obtained with a glucose modified siloxane surfactant

Silver nanoparticles were obtained in aqueous medium, at room temperature, by redox reactions, with or without glucose, in the presence of a glucose-containing cyclosiloxane. The siloxane surfactant can act as stabilizer when glucose is present in the system, but also as reducing agent and stabilizer when no glucose is added. The kinetics was followed by absorption UV–Vis spectroscopy, and different behaviors were found for the two versions of the redox process: first-order kinetics for the reaction with glucose and a much slower complex reaction with three zero-order steps when no glucose was added. The reactions were also investigated with IR absorption spectroscopy. The resulting nanoparticles were analyzed by dynamic light scattering (DLS), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) analysis, and transmision electron microscopy (TEM). All data showed evidence for the formation of silver spherical nanoparticles, with an average diameter of 14 nm (reaction with glucose) and 6.5 nm (reaction without glucose), respectively.

Exfoliation of Clays in Poly(dimethylsiloxane) Rubber Using an Unexpected Couple: A Silicone Surfactant and Water

Poly(dimethylsiloxane) (PDMS)/montmorillonite (MMT) composites have been prepared using a newly synthesized omega-ammonium functionalized poly(dimethylsiloxane) compatibilizer coupled with a dispersion technique in water. The organoclay containing the new siloxane surfactant was characterized by TGA and XRD. For the first time, a nanoscopic dispersion of MMT nanoplatelets in the PDMS composite cured by hydrosilylation and a good compatibility between clay layers and matrix were obtained. The beneficial effect of both the surfactant and the water onto clay nanoplatelet dispersion was evaluated by different microscopy techniques and by measuring different properties such as the viscosity of the uncured PDMS/MMT nanodispersions, and the swelling rate and Young's modulus of the cured PDMS/MMT nanocomposites.

Nanoclay Reinforcement of Liquid Silicone Rubber

Siloxane modified montmorillonite clay was prepared from sodium montmorillonite and quaternary ammonium-containing siloxane surfactant. X-ray diffraction and Fourier transform infrared analyses indicated that the polysiloxane oligomer chains were successfully grafted onto the surface of the montmorillonite clay platelets. The siloxane modified montmorillonite clay and commercial organo-modified montmorillonite and bentonite clays were incorporated into a rapid-cure liquid silicone rubber (LSR) matrix. The morphologies of the LSR/nanoclay composites were analyzed by SEM and TEM, and partial exfoliation of the silicate nanolayers of the clay platelets was observed. Up to a 20% reduction in water vapor permeability was achieved as well as a 24% improvement in tear strength and a 40% improvement in the compression set.

Molecular Exchange through the Vesicle Membrane of Siloxane Surfactant in Water/Glycerol Mixed Solvents

The effect of glycerol on the permeability of vesicle membranes of a siloxane surfactant, the block copolymer polyethyleneoxide-b-polydimethylsiloxane-polyethyleneoxide, (EO)15-(DMS)15-(EO)15, was studied with freeze-fracture transmission electron microscopy (FF-TEM) and pulsed-field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy. The FF-TEM results show that, in pure water, the surfactant can form small vesicles with diameters of less than 25 nm, as well as a few multilamellar vesicles with diameters larger than 250 nm. Gradual substitution of water with glycerol to a glycerol content of 40% leads to significant structural transformations: small vesicles are gradually swollen, and large multilamellar vesicles disappear. A glycerol content of 60% results in the complete disintegration of the vesicles into membrane fragments. PFG-NMR measurements indicate that the vesicle membrane does not represent an effective barrier for water molecules on the NMR time scale; hence, the average residence time of water in the encapsulated state is below tau b = 2 ms. In contrast, the average residence time of glycerol molecules in the encapsulated state can be as large as tau b = 910 ms. The permeability of the vesicle membrane increases with increasing glycerol concentration in the solvent: At a concentration of 40%, the residence time tau b is lowered to approximately 290 ms. After vesicle destruction at higher glycerol concentrations, a small glycerol fraction is still bound by membrane fragments that are formed after the disintegration of the vesicles.

Physico-chemical properties of siloxane surfactants in water and their surface energy characteristics

A simple but efficient method has been followed for the synthesis of water soluble siloxane amphiphile by grafting poly(ethylene glycol) (PEG) onto the hydrophobic poly(hydromethyl siloxane) backbone. Systematic variations in the amount of PEG incorporations were carried out to get water soluble oligomers. The structural analysis of the systems was done by 1H NMR and GPC analysis. The solution behavior of these amphiphiles was studied. The presence of nonpolar microdomains was observed at concentrations ≥0.01 g/dL for all the systems. Interestingly, I 3/ I 1 ratio of pyrene fluoroprobe solubilised in aqueous solution of amphiphile suggests greater nonpolarity of microdomains in the system containing a higher PEG graft. The oligomers were shown to be surface active wherein, critical aggregation concentration decreased systematically with the decrease in the hydrophilic PEG substitutions. However, the system with a higher PEG substitution shows the close packed aggregates in the solution as suggested from the viscosity and fluorescence measurements. The contribution of polar and dispersion component towards the total surface energy was studied by the contact angle measurement by the sessile drop method.

Effect of salt and pH on surface active properties of comb rake-type polysiloxane surfactants

Comb rake-type polysiloxane surfactants, [PA-oligo(PO- b-EO) series and PA-oligo(PO- b-EO)Me series] were synthesized by the hydrosilylation reaction. To investigate the surface active properties of polysiloxane surfactants that have multiple hydrophobic and hydrophilic groups, the surface tension and sedimentation time of the aqueous surfactant solution were measured. Surface tension and cloud point ( C P) tended to increase with an increase of the EO chain length and a decrease of the PO ratio. The surface tension of siloxane surfactants in the methoxy group was lower than that of the hydroxyl group. Surface tensions at pH 3 and 11 were higher than those in neutral pH values. When the inorganic electrolyte was added into the aqueous solution, the surface tension tended to decrease gradually due to the arrangement of surfactant molecules toward the interface of aqueous solution. The sedimentation time of the aqueous solution tended to decrease with an increase of the EO chain length, and a decrease of PO ratio. The sedimentation time according to the variation of pH values was similar to the results of surface tension.