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 γ_cac 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.     

Rheological Properties of SiC Suspensions with a Compound Surface Modification Using Ethyl Orthosilicate and Ethylene Glycol

Ultrafine silicon carbide (SiC) powders were surface-modified using ethyl orthosilicate (TEOS) combined with ethylene glycol. SiC suspensions with favorable rheological properties, low viscosity, and high solid loading were successfully obtained. The mechanisms of the compound surface modification for SiC powders as well as the influences of the compound surface modification not only on functional groups and charge state of the surface for SiC powders but also on the rheological properties of SiC suspensions were investigated in the present study. The results show that under alkaline conditions and acidic conditions, the surface charge states of SiC powders were [Si-OCH₂CH₂O]^? and [Si-OCH₂CH₂OH₂]⁺, respectively. The absolute value of zeta potential reached the maximum value of 22.69 mV at pH 11. Additionally, with added 1 wt% TEOS and 3 wt% ethylene glycol, the SiC suspensions exhibited good rheological properties, low viscosity and high stability due to the steric hindrance and electrostatic repulsion offered by the [Si-OCH₂CH₂O]^- with a high concentration.     

Characterization of polyethylenimine by electrospray ionization and matrix-assisted laser desorption/ionization

Branched polyethylenimines (PEIs) with lower average molecular weights (600, 1200 and 1800 Da) have been studied by Electrospray Ionization (ESI) and Matrix‐Assisted Laser Desorption/Ionization (MALDI) mass spectrometry. In both, ESI and MALDI mass spectra, the main distribution arises from protonated PEI oligomers with NH₂ end groups, [PEI + H]⁺, which are observed at m/z 43n + 18. A trace of sodium contamination in the PEI samples results in the presence of a series that appears at m/z 43n + 40 [PEI + Na]⁺. However, only the MALDI mass spectra show a [PEI + K]⁺ series at m/z 43n + 56, because of matrix contamination with potassium, and a series generated by condensation of the matrix with PEI at m/z 43n + 30. Collisionally activated dissociation tandem mass spectrometry (CAD (MS/MS)) of protonated PEI oligomers is shown to yield three fragment ion series b_n, and K_n. The experiments have demonstrated the capabilities of these mass spectrometry techniques, along with CAD MS/MS to detect and characterize such polar synthetic polymers. Copyright © 2011 John Wiley & Sons, Ltd.     

Kinetic and Mechanistic Studies on [Zn(II)-Gly-Phe]+–Ninhydrin Reaction in Aqueous and Cationic CTAB Surfactant Micelles

The rates of reaction between metal-dipeptide complex ([Zn(II)-Gly-Phe]⁺) and ninhydrin have been determined in aqueous and aqueous–cationic micelles of cetyltrimethylammonium bromide (CTAB) at 70°C and pH 5.0. The rate data indicate that the reaction follows the template reaction mechanism in both the media. The reaction followed a first-order and fractional-order kinetics with respect to [Zn(II)-Gly-Phe]⁺ and [ninhydrin], respectively, in the excess of ninhydrin over [Zn(II)-Gly-Phe]⁺. The rate constant is affected by [CTAB] changes and maximum rate enhancement is approximately three-fold. CTAB micelles decrease the activation enthalpy and make the activation entropy less negative. Quantitative kinetic analysis of rate constant (k _ψ)–[CTAB] data was performed on the basis of pseudophase model of the micelles (proposed by Menger and Portnoy and developed by Bunton). The values of binding constants K _S for [Zn(II)-Gly-Phe]⁺ and K _N for ninhydrin with micelles are calculated with the help of observed kinetic data. The results obtained in micellar medium are treated quantitatively on the basis of pseudophase model.