Search Results (12)

Measurements of the surface tension of aqueous solutions of some trisiloxane surfactants containing various polyether groups (HOL7, HOL9, and HOL12) at 293 K, 303 K, and 313 K were performed. The studied surfactants were synthesized by hydrosilylation reaction and their structural analysis was carried out by the ¹H NMR, ¹³C NMR, ²⁹Si NMR, as well as FT-IR techniques. The thermal stability of HOL7, HOL9, and HOL12, as well as their molecular weight distributions, were also studied. On the basis of the obtained experimental results of the surface tension of aqueous solutions of HOL7, HOL9, and HOL12, the activity of the studied surfactants at the water–air interface was determined and discussed in the light of intermolecular interactions. Using the measured values of the surface tension, the Gibbs surface excess concentration, the area occupied by the surfactant molecule in the adsorption layer, and the standard Gibbs free energy of adsorption of the studied surfactants at the water–air interface were also calculated. Based on the obtained thermodynamic parameters of adsorption of the studied surfactants at the water–air interface, temperature, as well as a number of polyether groups in the hydrophilic part of surfactant, impact on particular surfactant adsorption was deduced. In general, the changes in the standard Gibbs free energy of adsorption of the studied surfactants at the water–air interface indicate that their adsorption tendency decreases with decreasing temperature. In addition, that tendency also diminishes as the number of the polyether groups in the hydrophilic part of the surfactant increases. Full article

A series of Si-H- or Si-Vi-terminated, branched and linear oligomers containing Me₂SiO segments were prepared by equilibrium polymerization or non-equilibrium polymerization initiated by living anions, respectively. These oligomers were used to improve the defects of concentrated crosslinking points and the high hardness of crosslinked products when using phenyltris(dimethylsiloxy)silane or 1,1,5,5-tetramethyl-3,3-diphenyl trisiloxane as crosslinking agents in the preparation of silicone gel. NMR, FT-IR, and GPC characterized the structure and molecular weight information of the prepared oligomers. The effects of equilibrium polymerization and the anionic non-equilibrium ring-opening polymerization methods on the structure of oligomers were investigated in detail, together with the structure, the molar ratio of SiH to SiVi, and the phenyl content on the thermal properties and the transmittance retention yield of the silicone gel. The introduction of phenyl groups increases the glass transition temperature of silicone gel from −121.29 °C to −117.71 °C when the phenyl content increased from 0.88 wt% to 3.17 wt%. Meanwhile, the thermal decomposition temperature of silicone gel at 10% weight loss in the N₂ atmosphere increased from 440.5 °C to 480.0 °C. When the SiH/SiVi molar ratio is close to 1.0, the transmittance retention yield of the prepared silicone gel using Si-Vi-terminated phenyl T-shaped polysiloxane as the matrix and α, ω-dimethylsiloxyl-terminated PDMS as the crosslinking agent could reach 88.9% after 25 min of UV irradiation. Full article

CO₂ fracturing is known as the best solution to improve the efficiency of the CO₂ replacement of natural gas hydrates, but the effect of CO₂ thickeners on CH₄-CO₂ replacement are barely noticed. In this work, the effect of four kinds of CO₂ thickener—including DL-Lactic acid, polyvinyl acetate, ethyl trifluoroacetate and octamethyl trisiloxane—on the CH₄-CO₂ replacement in quartz sand was measured thermodynamically and kinetically. The results show that the majority of the CO₂ thickeners had no effect on the equilibria of the CH₄ and CO₂ hydrates, except for DL-Lactic acid, where the temperature depression caused by the addition of 5.5 wt% DL-Lactic acid was about 0.52 and 0.48 K for the CH₄ and CO₂ hydrates, respectively. In the kinetic measurements, the CH₄-CO₂ replacement was promoted via the addition of the CO₂ thickeners, except DL-Lactic acid. The CO₂ thickeners were suggested to strengthen the CH₄-CO₂ replacement by enhancing the gas exchange in the pore space. Octamethyl trisiloxane, which could promote CH₄ recovery and CO₂ capture at a low concentration, was suggested to be an ideal CO₂ thickener for CH₄-CO₂ replacement. Full article

The onset and early stages of dynamic wetting on different hydrophobic surfaces is investigated experimentally for aqueous solutions of two commercial trisiloxane surfacants of similar chemical structure, one of which exhibits superspreading behaviour, in order to investigate the spreading dynamics independently of the surface activity. Superspreading, or the ability of a surfactant solution to spread on a surface beyond the state determined by thermodynamic equilibrium, has been investigated for more than 30 years however its physical mechanism remains poorly understood to date despite its important applications in the formulation of agrochemicals. Surfactant solutions were prepared by dissolving S233 and S240 surfactants (Evonik Industries AG, Essen, Germany) into de-ionised water at a weight concentration of 0.1%. Drops of surfactant solutions and pure water were deposited on three horizontal substrates with different wettability (equilibrium contact angle of water ranging between ${55}^{\circ }$ and ${100}^{\circ }$), and observed from below with a high-frame rate camera to visualise the advancing contact line. The spreading ratio of drops as a function of time was extracted from high-speed videos by digital image processing. Results reveal that the superspreading solution exhibits an intermittent spreading rate, as well as peculiar features of the contact line, which are not observed for the non-superspreading solution, and confirm the superspreading effect becomes less significant when the surface energy of the substrate is decreased. Full article

It is a challenge to research and develop silicon surfactants with good acid and alkali stability. In the present paper, methylpropenyl polyether modified nonionic silicone surfactant (MPNTS), an alkali-resistant and hydrolysis-resistant silicone surfactant, was synthesized by hydrosilylation of 1,1,1,3,5,5,5-heptamethyl trisiloxane (MD^HM) and methylpropenyl polyether (EO(7)). The polyether segments are grafted onto the main chain of organosilicon heptamethyl trisiloxane at a molar ratio of 1:1.05 (n(Si-H):n(C=C)). To evidence product formation, the MPNTS were analyzed by FT-IR and ¹H NMR spectroscopy. The surface tension of NPNTS is 18.68 mN/m, and the CMC value is 78 mg/L by a contact angle tester. MPTNS shows hydrolytic stability and maintains that it could keep surface activity after standing for 60 days at pH = 7–10. The compatibility performance analysis shows that MPNTS has good compatibility and synergy with cationic, anionic, and nonionic surfactants, and it reveals the application prospects in daily chemicals, agricultural adjuvants, and other products. Full article

The wetting behavior of droplets of aqueous surfactant solutions over hydrophobic thin PVDF porous membrane and non-porous hydrophobic PVDF film is investigated for small (~10 μL) droplets of aqueous trisiloxane surfactant solutions: superspreader S 240. The time dependencies of contact angle, droplet radius, wetted area and volume were monitored as well as penetration into the porous substrate. It is shown that the fast spreading of droplets of trisiloxane solutions takes place both in the case of porous and non-porous substrates at a concentration above some critical concentration. It was found that the trisiloxane droplets penetrate into the hydrophobic porous substrates and disappear much faster than on a corresponding hydrophobic non-porous substrate, which was not observed before. This phenomenon is referred to as “superpenetration”. Full article

Pesticide foliage treatment is used in agricultural production to protect plants from diseases, pests, or weeds. Tank-mix adjuvants added to the barrel can improve the effective utilization rate of pesticides. Herein, a comparative study was conducted to investigate the effect of three kinds of tank-mix adjuvant on the deposition, absorption, and permeation behavior of epoxiconazole and chlorantraniliprole solutions. Surface tension and contact angle results indicate that polyether-modified trisiloxane may be the best surface-active agent for pesticides, whereas methyl oleate and green-peel orange essential oil were found to be more suitable for improving pesticide deposition, absorption, and permeation in some cases. These findings indicate that various tank-mix adjuvants had different effects on pesticide application on plants. Appropriate tank-mix adjuvants need to be selected for comprehensive practical application. Full article

Organosilicone molecules represent important components of surfactants added to pesticides to improve pest control efficiency, but these molecules also have pesticidal properties in their own right. Here, we examined toxicity and control efficacy of Silwet 408, a trisiloxane ethoxylate-based surfactant, to the two-spotted spider mite (TSSM), Tetranychus urticae and its crop hosts. Silwet 408 was toxic to nymphs and adults of TSSM but did not affect eggs. Field trials showed that the control efficacy of 1000 mg/L Silwet 408 aqueous solution reached 96% one day after spraying but declined to 54% 14 days after spraying, comparable to 100 mg/L cyetpyrafen, a novel acaricide. A second spraying of 1000 mg/L Silwet 408 maintained control efficacy at 97% when measured 14 days after spraying. However, Silwet 408 was phytotoxic to eggplant, kidney bean, cucumber, and strawberry plants, although phytotoxicity to strawberry plants was relatively low and declined further seven days after application. Our study showed that while the organosilicone surfactant Silwet 408 could be used to control the TSSM, its phytotoxicity to crops should be considered. Full article

The trisiloxane polyether surfactant (3-[3-(hydroxy)(polyethoxy)propyl]-1,1,1,3,5,5,5 -heptamethyltrisiloxane) (TS-EO12) was successfully synthesized by a hydrosilylation reaction in the presence of Karstedt catalyst. The structural analysis of the surfactant was done by ¹H-NMR, ¹³C-NMR, ²⁹Si-NMR and FT-IR analysis. In addition the thermal stability of TS-EO12 was studied by the thermogravimetric measurements. On the one hand the surface properties of TS-EO12 at the water-air interface were investigated by surfactant aqueous solutions surface tension measurements carried out at 293 K, 303 K and 313 K, and on the other the aggregation properties were analyzed based on the solubilization properties of TS-EO12 aggregates at different temperatures. On the basis of the obtained thermodynamic parameters of adsorption and micellization of studied surfactant the temperature impact on its surface and volume properties were deduced. It was proved that the tendency of the studied surfactant molecules to adsorb at the water-air interface and to form micelles weakens with decreasing temperature. It was also concluded that the structure of the adsorption layer changes with temperature. Optical microscopy measurements were used for the TS-EO12 micelle morphology determination. Full article

Shattering of pods of oilseed rape (Brassica napus L.) is a major cause of seed yield losses prior to and during harvesting. In order to reduce shattering, researchers have been engaged in the development of special preparations that are known as pod sealants (PS). Despite the fact that there are already developed and commercialized PSs that have only been effective on seed yield preservation under certain environmental conditions, there is still a need to create a more versatile and efficient PS. Currently, the most promising method of controlling pod shattering in oilseed rape is the application of our developed novel acrylic- and trisiloxane-based pod sealant (PS4). The effectiveness of PS4 and three commercial pod sealants (PS1, PS2, and PS3) was assessed in this comparative study. By spraying an oilseed rape crop with PS4, natural seed loss can be reduced by 20–70%, depending on the prevailing weather conditions, and loss of seeds during harvest can be reduced by more than three-fold compared with that by the control treatment. Thus, the overall results demonstrated that by applying a novel pod sealant (PS4) to oilseed rape crops 2 weeks before harvest can increase the net profit margin by €30–€150 ha⁻¹. The life cycle assessment showed that during 2014–2016 oilseed rape cultivation, the largest effect on global warming emission (kg CO₂ eq) reduction was experimental sealant PS4, i.e., approximately 17% compared to the control. Full article

The spreading of solutions of three trisiloxane surfactants on two hydrophobic substrates, polyethylene and polyvinylidenefluoride, was studied with the addition of 0–40 mass % of glycerol. It was found that all the surfactant solutions spread faster than silicone oil of the same viscosity, confirming the existence of a mechanism which accelerates the spreading of the surfactant solutions. For the non-superspreading surfactant, BT-233, addition of glycerol improved the spreading performance on polyvinylidenefluoride and resulted in a transition from partial to complete wetting on polyethylene. The fastest spreading was observed for BT-233 at a concentration of 2.5 g/L, independent of glycerol content. For the superspreading surfactants, BT-240 and BT-278, the concentration at which the fastest spreading occurs systematically increased with concentration of glycerol on both substrates from 1.25 g/L for solutions in water to 10 g/L for solutions in 40% glycerol/water mixture. Thus, the surfactant equilibration rate (and therefore formation of surface tension gradients) and Marangoni flow are important components of a superspreading mechanism. De-wetting of the solutions containing glycerol, once spread on the substrates, resulted in the formation of circular drop patterns. This is in contrast to the solely aqueous solutions where the spread film shrank due to evaporation, without any visible traces being left behind. Full article

A series of new organosiloxane ferroelectric liquid crystalline (FLC) materials have been synthesized, and their mesomorphic and physical properties have been characterized. Four new disiloxanes and trisiloxanes, containing biphenyl 4-hydroxybenzoate and phenyl 4-hydroxybiphenylcarboxylate as mesogenic units and eleven methylene unit as spacers and (2S,3S)-2-chloro-3-methylvalerate unit as chiral end groups. The molecule, using three phenyl ring as a mesogenic unit, formulates much wider liquid crystalline phase temperature ranges than that of a two phenyl ring unit. The phenyl arrangement differences of mesogenic unit result in the greater differences of the liquid crystal phase formation. The siloxane molecule induction is helpful to the more regular smectic phase formation and smectic phase stabilization, such as chiral S_C (S_C*) and S_B phases. The siloxane molecule is helpful to reduce the phase transition temperature and broaden the liquid crystal temperature range of the S_C* phase and, simultaneously, it will not induce chain crystallization phenomenon and dilute the Ps value. The synthesis and characterization of the new FLCs materials, which exhibit a room temperature S_C* phase and higher spontaneous polarization are presented. Full article