Zhiping Du

Surface Activity and Aggregation Behavior of Siloxane-Based Ionic Liquids in Aqueous Solution.

Six novel siloxane-based surface-active ionic liquids (SAILs)--siloxane ammonium carboxylate [Si(n)N(2)-CA(1), (n = 3, 4)]--were designed and synthesized. Their melting points, surface activities, and self-aggregation behavior in aqueous solution were studied. The results showed that because of the bulky hydrophobic siloxane chains at the end of the tail, all six siloxane-based SAILs are room-temperature ionic liquids (RT-SAILs). The introduction of the siloxane group can reduce the melting point of ionic liquids to below room temperature and can promote the micellization and aggregation behavior more efficiently. These siloxane-based SAILs can greatly reduce the surface tension of water, as shown by the critical aggregation concentration (γCAC) values of 20 mN·m(-1); all six siloxane RT-SAILs can form a vesicle spontaneously in aqueous solution, indicating potential uses as model systems for biomembranes and vehicles for drug delivery.

Preparation and properties of comb-like surfactants containing poly(ethylene oxide) methyl ether grafts

The comb-like surfactants, poly(styrene-co-maleic anhydride)-g-(poly(ethylene glycol) monomethyl ether), poly(St-co-MA)-g-(MPEG), have been prepared using a macromonomer approach to get controlled molecular structures. The macromonomer (MAMPEG) was obtained by esterification of poly(ethylene glycol) monomethyl ether with maleic anhydride. Poly(St-co-MA)-g-(MPEG) with various molar ratios of St to MAMPEG (R) were then constructed by radical copolymerization. The comb-like structures of the surfactants were confirmed by infrared and (1)H nuclear magnetic resonance spectroscopy. It is found from gel permeation chromatography characterization that the molecular weight of the surfactants increases as R increases. The polydispersity index was in the range between 1.4 and 2.0 in all the cases. The surfactants with a higher St percentage are less soluble in water due to aggregation. The value of critical aggregation concentration (CAC) and the surface tension at the CAC (gamma(CAC)) decrease as R increases. The steady-shear measurements show that the surfactant solutions at 50 g/L are dilatant fluids. In addition, it appears that there are two break points in the viscosity-shear rate curve. Both break points increase with increasing R. It can therefore be concluded that the properties of comb-like surfactants poly(St-co-MA)-g-(MPEG) are related to molecular structure. The results demonstrate that the properties of these comb-like surfactants can be tailored through appropriate molecular design.

Aggregation Behavior of Trisiloxane-Tailed Surface Active Ionic Liquids in Aqueous Solution: Coarse-Grained Molecular Dynamics Study

The aggregation behaviors of two trisiloxane-tailed surface active ionic liquids in water have been investigated by coarse-grained (CG) molecular dynamics simulation on the basis of MARTINI force field. The new CG model is developed from the optimized molecule computed by using density functional theory. Direct comparison of angles and bonds obtained from all-atom (AA) simulations with those calculated from the CG model has been conducted to validate the latter model. Excellent agreement between AA and CG demonstrates that the potential of the new CG model can represent the complex system well. The long time CG simulation has been performed to understand the formation process of micelles when dissolving ionic liquids in water. Vesicles were observed at the final stage of the simulation and their partially truncated views and density profiles were obtained to describe the structure in detail.

Adsorption and Aggregation Behavior of n-Undecyl Ammonium Acetate Ionic Liquid in Aqueous Solution

A surface active ionic liquid (IL), [CH3(CH2)10NH3][OOCCH3], was synthesized and characterized by FTIR, 1H NMR, and 13C NMR. Its surface activity and aggregation behavior in aqueous solution were investigated using surface tension measurements, conductivity measurements, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The results reveal that the CAC and γcac of this IL are 15.3 mM and 23.1 mN/m, respectively. We observed a strong interaction between the counter-ions, leading to ion pairs that self-assemble into spherical vesicles in aqueous solution, with an average diameter in the range of 120 to 130nm.

Synthesis of hybrid silica nanoparticles grafted with thermoresponsive poly(ethylene glycol) methyl ether methacrylate via AGET-ATRP

Thermosensitive SiO2 nanoparticles were prepared with graft-on poly(ethylene glycol) methyl ether methacrylate (POEGMA, Mn ∼ 300 or 500 g mol−1) via atom transfer radical polymerization with activators generated through electron transfer (AGET ATRP). CuBr2/PMDETA and ascorbic acid (AA) were employed as the catalyst and reducing agent respectively in the fabrication process. The structure and surface composition of our hybrid materials were analyzed using Fourier Transform Infrared (FTIR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS) in detail. The results of Thermogravimetric Analysis (TGA) show that AGET-ATRP could provide a higher surface grafting density to get more pronounced thermosensitive properties. The morphology of our hybrid SiO2 nanoparticles was characterized by Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). measurements of turbidity, Dynamic Light Scattering (DLS), and phase transfer were conducted to investigate the thermal responses of the hybrid material. In addition, Pickering emulsions were prepared using such hybrid SiO2-POEGMA as an emulsifier. Moreover, its fast de-emulsification above a lower critical solution temperature (LCST) may be exploited for the efficient separation and recycling of catalysts in future.

Synthesis, Surface Activities, and Aggregation Behaviors of Butynediol-ethoxylate Modified Polysiloxanes.

Five different butynediol-ethoxylate modified polysiloxanes (PSi-EO) were designed and synthesized via two-step reactions: the preparation of low-hydrogen containing silicone oil (LPMHS) by acid-catalyzed polymerization and the following hydrosilylation reaction with 1,4-bis(2-hydroxyethoxy)-2-butyne. The chemical composition of each product was confirmed by FT-IR, (1)H NMR, and (29)Si NMR. The surface activities and aggregation behaviors of PSi-EO surfactants in aqueous solution were studied systematically using surface tension, dynamic light scattering (DLS), transmission electron microscopy (TEM), and contact-angle methodologies. Relatively low critical aggregation concentration (15-34 mg·L(-1)) and surface tension (∼25 mN·m(-1)) were measured for PSi-EO aqueous solution. The rate of surface tension reduction increased both with increasing PSi-EO concentration and with increases in the proportion of hydrophilic moieties within the synthesized compounds. Furthermore, DLS and TEM studies revealed that PSi-EO self-assembled in aqueous solution to form spherical aggregates. Contact-angle measurements conducted upon low-energy paraffin film surfaces demonstrated that PSi-EO exhibited efficient spreading at concentrations above the critical aggregation concentration.

One-step strategy for synthesis of yolk–shell silica spheres using trisiloxane-tailed ionic liquids as a template

Yolk–shell silica spheres consisting of a core and an outer shell were prepared by a one-step method using a new class of eco-friendly templates, trisiloxane-tailed surface active ionic liquids. The effects of pH, calcination, and template concentration were investigated in detail. Our results showed that yolk–shell silica spheres could be obtained only in alkaline conditions when using trisiloxane-tailed ionic liquids as templates. The particle diameter, core diameter, dimension of void space, and shell thickness, which we measured by transmission electron microscopy and nitrogen adsorption–desorption techniques, could be tuned by precisely varying the template concentration. The organosilicon component of the ionic liquid template contributes to the reaction during the formation of yolk–shell nanostructures, which leads to a firm silica sphere skeleton resulting in essentially identical morphology and void structure before and after calcination. This investigation provides a convenient approach to fabricate yolk–shell silica spheres, which may expand the application of organosilicon ionic liquids in the field of nanomaterials and could be expected to generate tailor-made yolk–shell silica with functionality in both the core and shell.

Thermostable mesoporous silica nanospheres produced through the use of a trisiloxane-tailed ionic liquid as a template

Mesoporous silica nanospheres can be prepared by a facile route using a new class of eco-friendly template: trisiloxane-tailed ionic liquids. The organosilicone component of the ionic liquids template contributes to the reaction during the formation of mesoporous material, which leads to a firm skeleton of pores resulting in excellent thermal stability.

Properties of Glucosamide-Based Tetrasiloxane Surfactants

The interfacial properties of new glucosamide-based tetrasiloxane surfactants were studied. Members of the glucosamide-based tetrasiloxane surfactants reduce the surface tension of water to approximately 21 mN · m−1 at concentration levels of 10−5 mol · L−1. The wetting and spreading behavior of the glucosamide-based tetrasiloxane surfactants on Teflon and Paraffin were investigated and compared with that of trisiloxane. A new glucosamide-based tetrasiloxane β shows the best spreading ability both on Teflon and Paraffin, which is similar with that of trisiloxane. It is suggested that a lower surface tension is a necessary but not sufficient condition for enhanced spreading. The spreading performance was affected by the hydrophilic-lipophilic balance (HLB) significantly. Furthermore, the molecular structure of the surfactant and the hydrophobic substrate also play important roles for showing spreading behavior.

Formulation and physicochemical properties of promising avermectin microemulsion with biodegradable surfactant and oil

ABSTRACT Green microemulsion suitable for oil-soluble pesticide delivery has been prepared using butyl acetate as oil phase, alkyl polyglycoside (APG) and linear alkylbenzene sulfonate (LAS) as mixed surfactant, and short-chain alcohol as cosurfactant. Pseudoternary phase diagrams were constructed to investigate the effects of APG and LAS mixing ratio, the chain length of the cosurfactant on the microemulsion phase behavior. A fully dilutable region run through the phase diagram can be observed and the structure of the microemulsion transformed from water-in-oil, bicontinuous to oil-in-water along with the addition of water according to the result of conductivity measurement. Based on the phase diagram, the avermectin microemulsion formulations were chosen from the fully dilutable line with the minimum surfactant-to-oil ratio. Dilution stability of the microemulsion with hard water was studied by dynamic light scattering (DLS), the microemulsion can maintain the uniform and homogeneous appearance although the droplet size increased after dilution. The diluted microemulsion were also studied by dynamic surface tension and dynamic contact angle, and the excellent wetting and spreading properties on hydrophobic surface was demonstrated. GRAPHICAL ABSTRACT