The ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) can form nonaqueous microemulsions with benzene by the aid of nonionic surfactant TX-100. The effect of water on ionic liquid-in-oil (IL/O) microemulsions was studied, and it was shown that the addition of small amount of water to the IL microemulsion contributed to the stability of microemulsion and thus increased the amount of solubilized bmimBF4 in the microemulsion. The conductivity measurements also showed that the attractive interactions between IL microdroplets were weakened, that is, the IL/O microemulsion becomes more stable in the present of some water. Fourier transform IR was carried out to analyze the states of the added water, and the result showed that these water molecules mainly behaved as bound water and trapped water, indicating that the water molecules are located in the palisade layers of the IL/O microemulsion. Furthermore, 1H NMR and 19F NMR spectra suggested that the added water molecules built the hydrogen binding network of imidazolium cations and H2O, BF4- anion and H2O, and at the same time the electronegative oxygen atoms of the oxyethylene units of TX-100 and water in the palisade layers, which made the palisade layers more firm and thus increased the stability of the microemulsion. The study can help in further understanding the formation mechanism of microemulsions. In addition, the characteristic solubilization behavior of the added water can provide an aqueous interface film for hydrolysis reactions and therefore may be used as an ideal medium to prepare porous or hollow nanomaterials.
The phase behavior of an aqueous catanionic surfactant system, composed of a long-chain imidazolium ionic liquid 1-dodecyl-3-methylimidazolium bromide (C(12)mimBr) and sodium dodecyl sulfate (SDS), is described. The phase diagram of the catanionic system was determined by electrical conductivity measurements and the formation of vesicles in a birefringent L(alpha) phase characterized by transmission electron microscopy (TEM) and freeze-fracture transmission electron microscopy (FF-TEM). Rheological measurements were used to characterize the macroscopic properties of the birefringent L(alpha) phase. Both electrostatic and hydrophobic interactions contribute to the vesicle formation in the catanionic system. Compared to the DTAB/SDS aqueous solution, differences between the imidazolium and trimethylammonium headgroups geometric packing and charge density induce the different phase behavior in each system. Silica hollow spheres, with diameters 30-60 nm and a wall thickness of 8-10 nm, were prepared by using the vesicles as the templates. The hollow silica spheres were characterized by TEM, scanning electron microscopy (SEM), and nitrogen adsorption-desorption. The results suggest additional application for ionic liquid based vesicles to be used as templates for the synthesis of hollow inorganic materials.
This paper studied
the strengthening effects of silica nanoparticles
on the polyacrylamide (PAM)/hydroquinone (HQ)–hexamethylenetetramine
(HMTA) composite gel. Pure PAM/HQ–HMTA gel and PAM/HQ–HMTA
gels containing silica nanoparticles up to 0.3 wt % were prepared
at 110 °C. Influences of silica nanoparticles on gelation performances
were systematically evaluated. By the addition of silica nanoparticles,
the gelation time became shorter and the gel strength was improved
observably. Rheological measurements showed that silica nanoparticles
enhanced both elasticity and viscosity of the gel significantly. Thermal
stability of the gel was studied by differential scanning calorimetry
(DSC) measurements. The maximum tolerated temperature of the gel was
improved from 137.8 to 155.5 °C by the addition of silica nanoparticles
with a concentration of 0.3 wt %. Furthermore, to study the strengthening
mechanisms of silica nanoparticles to the gel, the microstructure
and existing state of water within the gel were investigated by environmental
scanning electron microscopy (ESEM) and DSC measurements. Micrographs
of the gel showed that massive aggregations and arrangements of silica
nanoparticles existed in uniformly distributed three-dimensional network
structures of the gel, which greatly improved the structural strength
of the gel. Moreover, the mass fraction of bound water within the
gel increased from 22.5 to 39.9% by the addition of silica nanoparticles
with a concentration of 0.3 wt %. The hydrogen bonds and electrostatic
attractions between silica nanoparticles and water molecules/hydronium
ions make a higher bound water ratio, which contributes to better
water holding capacity and thermal stability of the gel.
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