Siloxane Surfactants Research Articles

In-situ surface reconstruction of CsPbl3 perovskite for efficient and stable solar cells

All-inorganic perovskite is a promising candidate for solar cell applications. However, a significant challenge lies in its poor phase stability to environmental moisture. To address this problem, we develop a strategy for in-situ reconstruction of the CsPbI3 surface using siloxane surfactants such as 3-aminopropyltriethoxysilane (APTES) and 3-aminopropyltrimethoxysilane (APTMS), which both demonstrate multifunctional roles in surface engineering. The siloxanes undergo air-induced hydrolysis, leading to the formation of Si-O-Si networks. Additionally, the –NH2 convert to –NH3+, enabling interaction with the I− ions on the surface of CsPbI3. This facilitates the formation of a self-assembled siloxane cross-linked ligand layer, which offers extra function for providing water and oxygen shielding, consequently stabilizing the surface of CsPbI3. Furthermore, the siloxane surfactants can passivate uncoordinated Pb2+ ions, resulting in a reduction of non-radiative recombination at the interface, thereby significantly augmenting device performance and stability. Following research comparisons, APTES with longer alkyl chains displays superior performance. As a result, with the APTES passivation, the PCE is increased from 19.01 % to 21.42 %, which is one of the highest PCE devices in pure CsPbI3 PSCs reported so far. Meanwhile, the devices treated with APTES show superior moisture stability over those without APTES, especially in the absence of encapsulation.

Systematically varying zwitterionic-siloxane surfactant structure to affect interfacial properties, foam stability, and fire suppression

Zwitterionic siloxane-sulfobetaine (siloxaneSB) surfactants are developed to replace per- and poly-fluoroalkyl substances (PFAS) used currently in aqueous firefighting foams because PFAS pose significant threats to environment and human health. SiloxaneSB surfactant's head and tail structures are varied gradually, one step at a time, to vary hydrophilicity of the head and hydrophobicity, and oleophobicity of the tail. Identical methods and conditions are used across all the surfactants to correlate surfactant structure to interfacial and foam properties, and fire suppression. The results suggest that the amphiphilic balance of the siloxane surfactant have dramatic effects on CMC, interfacial tension, foam expansion ratio, foam degradation, heptane vapor permeation through a foam layer, and fire suppression but little effect on bubble size, coarsening, and liquid drainage. They show synergism between siloxaneSB and alkylpolyglycoside in gasoline fire suppression while trisiloxane-polyoxyethylene exhibited synergism in heptane fire suppression. A 28 ft2 gasoline pool-fire suppression results were consistent with the bench-scale findings for tetrasiloxaneSB and trisiloxane-polyoxyethylene formulations. Small changes to surfactant molecular structure can dramatically improve its amphiphilic balance, synergisms, fuel-foam interactions resulting in improved effectiveness of fluorine-free foams but depend very much on the fuel, unlike the fluorocarbon surfactants.

Surface activity, foamability, and foam stability of binary mixed systems based on siloxane-based Gemini and hydrocarbon surfactants

Aiming to explore the potential of siloxane-based Gemini surfactants in the development of environmentally friendly foam extinguishing agent to address the pollution caused by traditional fluorinated ones. A crucial step is to study the performance of binary mixed systems of siloxane-based Gemini and hydrocarbon surfactants in terms of surface activity, foamability, and foam stability. In this study, binary mixed systems of two types of siloxane-based Gemini surfactants and one siloxane surfactant with four different hydrocarbon surfactants are prepared. Parameters such as surface tension, foam height, drainage time, and coarsening rate are tested. The results show that the siloxane-based Gemini surfactant HY-4000 with double silane chains could effectively reduce the surface tension of hydrocarbon surfactants. In addition, the two types of Gemini surfactants performed better in enhancing the foamability of hydrocarbon surfactants. The siloxane OFX0193 even inhibits the foaming of cationic hydrocarbon surfactant CATC. Besides the HY-4000/APG0180 mixed system, the binary mixed systems of three silicone surfactants with AOS and APG0180 exhibit better foam stability, particularly the systems containing TEGO4100. For the coarsening process of foam bubbles, we develop a predictive model based on previous studies, where the relationship between bubble area and time follows a power function law. The findings of this study could provide guidance for the development of green foam extinguishing agent with siloxane-based Gemini and hydrocarbon surfactants as core components.

The structure-activity relationship for the ABA triblock siloxane surfactant in aqueous-ethanol system

It is challenging to improve the foam stability in high concentration ethanol solution. In this paper, well-defined polyether-modified siloxane surfactants were synthesized, and their structures were characterized through infrared spectroscopy and one- and two-dimensional Nuclear magnetic resonance (NMR) spectroscopy. Furthermore, the relationships of between their chemical structure, surface activity, and foam property in high concentration ethanol solution were investigated in detail. The results showed that the target surfactant exhibited an ABA-type structure. They can effectively reduce the surface tension and produce the excellent foam in 75 % ethanol. In particular, these surfactants with loner siloxane chain confer strong foaming power in 75 % solution. This ability with good surface activity in water-ethanol system suggests a wide range of potential applications in low surface tension solvent system.

Foam formation in aqueous-ethanol system triggered by the ABA triblock siloxane surfactant

The foam formation is difficult in aqueous-ethanol mixed system with lower surface tension. In this work, we reported an ABA triblock siloxane surfactant, with A representing the polyoxyethylene (PEO) and B the polysiloxane chain that can reduce the surface tension of ethanol solution and generate stable foam. The siloxane surfactant molecules can adsorb onto the surface of ethanol solutions due to the hydrophobic-oleophobic property. The foam behaviors show slower Ostwald ripening and drainage process in aqueous-ethanol system. The closer arrangement of ABA triblock siloxane surfactant molecules provides higher surface film elasticity for efficient migration during the surface repair process. Our work provided a surfactant to form stable foam without the additional surfactants in the water–ethanol system, and will open an avenue for foam research in mixed systems.

Investigation on thermal stability of highly stable fluorine-free foam co-stabilized by silica nanoparticles and multi-component surfactants

Nanoparticles (NPs) have shown promising applications in developing the novel environmental-friendly firefighting foams. Hydrophilic silica NPs, siloxane surfactant (CoatOsil-77), and hydrocarbon surfactant (BS-12) were used to prepare mixed foam dispersions. The adsorption between surfactant molecules and NPs, and foamability of the mixed dispersions were analyzed. Thermal stability of foam was evaluated by using foam drainage, coarsening, and volume decay under thermal radiation. The strengthening mechanism of NPs on thermal stability of foam was analyzed. Results indicate that the intense interaction exists between NPs and surfactants. The presence of NPs with a concentration below 1 wt% leads to the deterioration of foam stability by accelerating foam drainage and coarsening, while a concentration of NPs above 1.5 wt% enhances foam stability. The foam coarsening, drainage, and foam volume decay were obviously delayed by NPs under thermal radiation. This research can give theoretical guidance for NP application in invention of fluorine-free firefighting foams.

Effect of spacer length on the micellization of cationic trisiloxane surfactants

Siloxane surfactants, hydrophobic (poly)siloxane chain and hydrophilic polar headgroup linking with spacer ((CH2)3 or (CH2)3S(CH2)3), exhibit peculiarly chemical and physical properties. The aggregation behavior and surface properties of siloxane surfactant can be influenced by the hydrophobicity of spacer. Cationic trisiloxane surfactants ([Si3-C3-Min]Br, [Si3-C4-Min]Br, and [Si3-C5-Min]Br) with the same imidazolium group, hydrophobic heptamethyltrisiloxane, and spacer (different number of methylene) were synthesized. The effect of the spacer on micellization in aqueous solution was investigated. Compared with 1-methyl-3- trisiloxaneimidazolium chloride ([Si3Min]Cl), critical micelle concentration (CMC), effectiveness (πCMC), and minimum area occupied by a surfactant molecule (Αmin) values of the investigated surfactants decrease with increase the number of methylene in spacer, while, γCMC value increases as the length of spacer increase. The micellization process was enthalpy driven. The ΔHm0 value becomes more exothermic for [Si3-C5-Min]Br attributed to the increasing hydrophobicity of spacer. The ΔHm0 of [Si3-C3-Min]Br is less exothermic than that of [Si3-C4-Min]Br and [Si3-C5-Min]Br. Spherical aggregates with the range of 20–500 nm were formed in aqueous solution at 2 times CMC.

3D printing interface-modified PDMS/MXene nanocomposites for stretchable conductors

Additive manufacturing has rapidly evolved over recent years with the advent of polymer inks and those inks containing novel nanomaterials. The compatibility of polymer inks with nanomaterial inks remains a great challenge. Simple yet effective methods for interface improvement are highly sought-after to significantly enhance the functional and mechanical properties of printed polymer nanocomposites. In this study, we developed and modified a Ti3C2 MXene ink with a siloxane surfactant to provide compatibility with a polydimethylsiloxane (PDMS) matrix. The rheology of all the inks was investigated with parameters such as complex modulus and viscosity, confirming a self-supporting ink behaviour, whilst Fourier-transform infrared spectroscopy exposed the inks’ reaction mechanisms. The modified MXene nanosheets have displayed strong interactions with PDMS over a wide strain amplitude. An electrical conductivity of 6.14 × 10−2 S cm−1 was recorded for a stretchable nanocomposite conductor containing the modified MXene ink. The nanocomposite revealed a nearly linear stress-strain relationship and a maximum stress of 0.25 MPa. Within 5% strain, the relative resistance change remained below 35% for up to 100 cycles, suggesting high flexibility, conductivity and mechanical resilience. This study creates a pathway for 3D printing conductive polymer/nanomaterial inks for multifunctional applications such as stretchable electronics and sensors.

Enhancing foam fire suppression analysis through CO2 TDLAS quantification

Tunable diode laser absorption spectroscopy (TDLAS) was used to monitor CO2 concentrations above a pool fire as experimental firefighting foams were applied to the pool surface. A 2.0 μm diode laser was used in a modified section of ventilation duct above a 19 cm diameter heptane pool fire. Laser signal intensity and temperature were measured to calculate CO2 concentration with time. The concentration profiles were determined for a reference fluorosurfactant foam and a series of fluorine-free foams containing siloxane surfactants blended with a hydrocarbon surfactant (Glucopon 215 UP), and solvent. Seven mixtures were evaluated: three foams fully covered the fuel pool and two foams extinguished the fire. Due to the rapid response of the measurement technique, a dramatic drop in CO2 concentration was observed as the fire was extinguished. Pool coverage corresponded to an observed peak in CO2 concentration. The concentration profiles allowed for a more accurate assessment of foams that were unable to extinguish a pool fire. Further analysis of these profiles may elucidate time-scales important for rapid fire suppression. Defining and characterizing mechanisms of foam fire suppression at these time-scales may improve and accelerate research efforts for the development of fluorine-free surfactants in firefighting foams.

Hansen solubility parameters obtained via molecular dynamics simulations as a route to predict siloxane surfactant adsorption

Hypothesis: The Hansen Solubility Parameters (HSP) derived from Molecular Dynamics (MD) simulations can be used as a fast approach to predict surfactants adsorption on a solid surface.Experiments and simulations: We focused on the specific case of siloxane-based surfactants adsorption on silicon oxide surface (SiO2), encountered in inkjet printing processes. A simplified atomistic model of the SiO2 surface was designed to enable the computation of its solubility parameter using MD, and to subsequently determine the interactions of the SiO2 surface with the siloxane-based surfactant and the various solvents employed. Surfactant adsorption was characterized experimentally using contact angle goniometry, ellipsometry, XPS and AFM.Findings: Comparison of the numerical results with experiments showed that the HSP theory allows to identify the range of solvents that are likely to prevent surfactant adsorption on the SiO2 surface. The proposed approach indicates that polar solvents, such as acetone and triacetin, which are strongly attracted to the silicon oxide surface might form a shield that prevents siloxane-based surfactants adsorption. This simple approach, can guide the selection of adequate solvents for surfaces and surfactants with specific chemical structures, providing opportunities for controlling interfacial adsorption.

Phase Diagrams and Structural Characterization of Mixtures of Silicone Surfactants + Silicone Oils + Water.

Silicone surfactants display unique properties and are widely employed in pharmaceutical and cosmetic products. In this work, we study water incorporation into silicone oils using silicone surfactants. Despite their importance, there are only a few studies reporting their phase equilibrium and structural characterization. Here, we determined the phase diagram of systems containing silicone oils, silicone surfactants, and water. In particular, we investigated the self-assembly behavior of two siloxane surfactants with the different hydrophilic-lipophilic balance: M(D'E7OH)M and MD18(D'3E18OAc)M and two silicone oils (cyclic oil-D4 and linear oil-MD15M). The phase behavior of the mixtures was investigated through optical inspection and structural characterization of aggregated states (microemulsions and mesophases) using small angle X-ray scattering (SAXS). These water-in-oil microemulsions or bicontinuous microemulsions incorporated a maximum amount of approximately 20 wt % water for the two surfactants with cyclic oil. A similar behavior was also identified with linear silicone oil, though with smaller water contents. We also observed the formation of anisotropic states, with a predominance of lamellar phases and a small region of a hexagonal phase. A quantitative analysis of the SAXS curves in the lamellar region reveals that this mesophase swells continuously after the addition of water lamellar periods ranging from 50 Å (with 18 wt % water) to 64 Å (with 40 wt % water). Our results confirm and expand the earlier literature on similar compounds, indicating their potential in incorporating water into silicone mixtures and forming interesting mesophases. Accompanying this characterization, we also report a comprehensive and systematic set of structural details for the different systems (microemulsions, bicontinuous phases and mesophases) formed by these mixtures, derived from the SAXS measurements.

Synthesis and properties of a novel asymmetric gemini surfactant based on siloxane skeleton

The paper introduced a kind of hydrogen-containing epoxy polysiloxane skeleton of different chain lengths with a defined molecular weight. Based on the skeleton, a novel asymmetric gemini siloxane surfactant (AGSS) was synthesized by reacting with maleic anhydride monoester and taurine. The chemical structure of AGSS was characterized by 1H NMR and FT-IR. At the same time, the physical and chemical properties of the three oil displacants were systematically studied. The results show that the minimum surface tension of the series of oil displacing agents is 29.02 mN/m, and the corresponding critical micelle concentration (cmc) is 0.416 mmol/L. As the silica chain in the polysiloxane backbone increases from n = 0 to n = 8, the surface tension corresponding to the critical micelle concentration decreases, much lower than conventional hydrocarbon surfactants. Besides, the study results show that the AGSS have good temperature resistance, salt resistance and resistance to divalent ions (Ca2+, Mg2+), and the above properties meet the needs of oil displacement applications.

Synergisms between siloxane-polyoxyethylene and alkyl polyglycoside surfactants in foam stability and pool fire extinction

Fluorocarbon surfactants in firefighting foams must be replaced with environmentally friendly surfactants without loss of fire suppression performance. Aqueous foams generated from commercial siloxane-polyoxyethylene and alkyl polyglycoside surfactants were characterized individually and as mixtures in a formulation by measuring the solution and foam properties, foam degradation and fuel transport rates through a foam layer on a hot heptane pool, and foam’s ability to suppress a heptane pool fire rapidly using minimum amount of foam. The results showed significantly smaller fire extinction times for the surfactant mixtures than for either of the individual components exhibiting a synergistic fire extinction rather than following the law of averages; 5 times enhancement in extinction performance. The measured foam degradation rate with the foam exposed to a hot heptane pool also showed a similar synergism. The reduced foam degradation rate resulted in a reduced fuel vapor transport for longer times and a more rapid fire extinction for the siloxane-glycoside mixture. By increasing the hydrophilicity with increased size of the polyglycoside head, the synergistic effect was enhanced. Both benchtop (19 cm diameter) and large scale (6 ft diameter) heptane pool fire extinction with the siloxane-glycoside surfactant mixture showed that the extinction time was 1.5 times (60% effectiveness of AFFF) that of an equivalent AFFF formulation containing a fluorosurfactant in place of the siloxane surfactant at a fixed foam application rate (22 L m−2 min−1). An understanding of the molecular interactions at the interface causing the synergistic effects may lead to improved siloxane-glycoside systems and other novel surfactant systems with performance matching that of fluorocarbon surfactants.

Aggregation properties of siloxane surfactants with phenyldimethylsiloxyl groups in aqueous solution

Two siloxane surfactants (Ph-Si3-EO16 and Ph-Si4-EO16) with two or three phenyldimethylsiloxyl groups were successfully synthesized by Piers-Rubinsztajn and thiol-ene reaction. The aggregation behavior in aqueous solution was investigated by surface tension, dynamic light scattering (DLS), transmission electron microscopy (TEM), and freeze-fracture transmission electron microscopy (FF-TEM). Owing to the steric hindrance and hydrophobicity of phenyldimethylsiloxyl groups, Ph-Si3-EO16 (40.4 mN·m−1) and Ph-Si4-EO16 (35.4 mN·m−1) have higher γCMC values. In comparison with Ph-Si3-EO16, Ph-Si4-EO16 has smaller CMC, γCMC, and Amin values attributed to the three phenyldimethylsiloxyl groups and intermolecular interaction. In the aqueous solution of Ph-Si4-EO16, the coexistence of spherical and rodlike aggregates resulting from intermolecular interaction (π-π interactions) was confirmed by TEM and FF-TEM. The results show that phenyldimethylsiloxyl groups play a vital role in the aggregation behavior of siloxane surfactants.

Synthesis, characterization and surface properties of novel polyether based siloxane surfactants

A series of poly(ethylene glycol) based trisiloxane or tetrasiloxane surfactants have been synthesized via thiol-ene reaction and confirmed by 1H NMR, 13C NMR, 29Si NMR, and FT-IR. The effect of the trimethylsiloxy groups and length of the ethylene glycol (EO) chain on the physicochemical properties, surface tension (γ), critical micelle concentration (CMC), surface tension at the CMC (γcmc), adsorption efficiency (pC20), surface pressure at the CMC (πCMC), maximum surface excess (Γmax), single siloxane surfactant molecule at the air/water interface (Amin), and the standard free energy of adsorption (), of these polyether based siloxane surfactants was investigated by surface tension, DLS, and TEM measurement. It indicated that all investigated polyether based siloxane surfactants can reduce the surface tension of water to approximately 21–24 mN·m−1 and the surface activities of silicone surfactants were enhanced with increasing the branched trimethylsiloxy groups and length of the EO chain.

Aggregation Behavior of Polyether Based Siloxane Surfactants in Aqueous Solutions: Effect of Alkyl Groups and Steric Hindrance.

A series of polyether based siloxane surfactants with different branched chain and alkyl groups were synthesized by thiol-ene reaction and Piers-Rubinsztajn reaction. The effect of the siloxane structures (alkyl groups and branched chains) on the adsorption and aggregation behavior in aqueous solution was investigated by surface tension, fluorescence, dynamic light scattering (DLS), freeze-fracture transmission electron microscopy (TEM), and TEM. The molecular structures of siloxane can obviously influence their surface activities and thermodynamics. Replacing the methyl of trimethylsiloxyl groups with longer alkyl groups (ethyl, propyl, and butyl) and branching trimethylsiloxyl resulted in an obvious decrease of the values of critical micelle concentration (CMC) and surface tension at CMC (γCMC). Dense surface films packed with CH3 groups result in the lower surface tensions being disordered by longer alkyl groups or branched chains of siloxane hydrophobic groups. And the minimum surface area per surfactant molecule ( Amin) values of Si3-PG, Et-Si3-PG, Pro-Si3-PG, and But-Si3-PG successively decrease about 3.5 Å with each increasing -CH2- group. All polyether based siloxane surfactants can form nonuniform size spheroidal aggregates in aqueous solution. Concerning the driving force, the micellization process was spontaneous but less spontaneous compared with adsorption.

Effects of polyether siloxane surfactant on the hydrophilic capacity of polypropylene films

Abstract To evaluate the hydrophilic capacity, polypropylene and surfactant (polyether siloxane) samples were extruded in the proportions of 0.0, 0.5, 1.0 and 3.0 (wt%) and films were obtained in a heated press. The samples were submitted to measurements of contact angle, surface tension, melt flow index and surface roughness. The results indicated that increasing surfactant content promoted better wettability and consequently higher hydrophilicity. Using water, the increase in the surfactant content reduced the contact angle (92.58° to 68.10°) and increased the surface tension (26.7 to 56.9 mN.m-1). However, with ethylene glycol, increasing the surfactant content promoted a small variation on the contact angle (59.14° to 65.10°) and on the surface tension (5.5 to 5.0 mN.m-1). The surfactant promoted a slight change in the melt flow index but not affected the roughness of the samples.

Preparation, Surface Activities, and Biodegradability of a Bola‐Type Collagen Hydrolysate‐Based Siloxane Surfactant

Abstract2 bola‐type collagen hydrolysate‐based siloxane surfactants (CBES) were prepared via grafting of an epoxy‐terminated polydimethylsiloxane oligomer onto 2 collagen hydrolysates with different molecular weights. Their structure was characterized by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR) spectroscopy, and the degree of grafting was determined by calculating the free amino content, which confirmed the successful synthesis of CBES. Subsequently, their physicochemical properties, such as particle size and isoelectric point, were evaluated. Besides, surface activities, application functionalities, and biodegradability of CBES were investigated. The results showed that CBES‐1, prepared with the lower‐molecular‐weight collagen hydrolysate, possessed superior surface activity, excellent foaming ability, and good emulsifying capacity comparable to those of a typical emulsifier such as the fatty alcohol polyoxyethylene ether (AEO‐9). In addition, their BOD5/CODCr value and CO2 evolution demonstrated that the CBES are readily biodegradable. There is, therefore, great potential for the bola‐type CBES to be applied in fields such as leather treatment and textile industries.

Properties of ABA and BA polysiloxane amphiphiles modified by polyether

ABSTRACTTo investigate the effect of content of polyether (F400) grafted on the properties of polysiloxane amphiphiles, polyether was grafted on the polysiloxane by hydrosilylation reaction with H2PtCl6 catalyst. The modified polysiloxanes were divided into two types; moreover, the ratio of polyether and polysiloxane was 1:1 or 1:2. The first one was similar to the conventional surfactant structure that is BA polysiloxane amphiphile, which own one hydrophobic chain and one hydrophilic group. Another one was ABA polysiloxane amphiphile, which possess one hydrophobic chain and two hydrophilic groups at the terminal. In our work, we compared the property of modified polysiloxanes with various contents of polyether in aqueous solution at room temperature to analyze the impact of polyether content on siloxane surfactants. The conclusion was that siloxane amphiphiles possess good solubility, high surface activity, and excellent spreading property.

Wetting Agent Influence on Putting Green Surface Firmness

Soil wetting agents are commonly used in the golf course industry for managing soil moisture. Recently, there has been an interest in the influence wetting agents have on the firmness characteristics of putting surfaces. To date, there has been no established relationship between wetting agents and surface firmness of putting greens. Research was conducted in St. Paul, MN, to evaluate the surface firmness impacts from 13 commercially available wetting agents applied individually or in combination to a creeping bentgrass (Agrostis stolonifera L.) research green. Treatments were evaluated as season‐long wetting agent programs with applications every 4 wk. Data collection included surface firmness (Clegg Impact Soil Tester), turfgrass quality (TQ), chlorophyll index (CI), volumetric water content (VWC), and spring water drop penetration tests (WDPT) to assess residual of fall‐applied wetting agents. Firmness measurements were not affected by wetting agent applications in 2014. In 2015, Duplex (15% alcohol ethoxylates, 2% alkyl sulfonate, 7% ethylenediaminetetraacetic acid), Aquicare (100% blend of alkoxylated alcohols), and Primer Select (100% alkoxylated polyols) provided the firmest surfaces. Ratings for TQ and CI demonstrated only minor influence of wetting agent applications, as did VWC measurements. Spring WDPT tests indicated wetting agent residual from late‐fall applications, and persistence was most evident at shallow depths. Revolution (100% modified alkylated polyol) demonstrated the greatest residual, whereas Duplex and Aquiflo (45% poloxanlene, 2‐butoxyethanol, siloxane surfactants) had the least residual. These results indicate that firmness can be influenced by wetting agent applications, and that persistence in the soil through the winter months is possible.