Interactions in the mixed micelles of monomeric and gemini surfactants: Influence of some co-solvents as a function of temperature

Troubleshooting the influence of trace chemical impurities on nanoparticle growth kinetics via electrochemical measurements

Reproducibility issues resulting from particle growth solutions made with cetyltrimethylammonium bromide (CTAB) surfactant from different lots and product lines in a newly developed synthesis of monometallic palladium (Pd) tetrahexahedra (THH) nanoparticles are investigated via a multi-pronged approach. Time-resolved electrochemical measurements of solution potential, variation of chemical parameters in colloidal synthesis, and correlation to electrodeposition syntheses are used together to uncover the effects of the unknown contaminants on the chemical reducing environment during nanoparticle growth. Iodide-a known impurity in commercial CTAB-is identified as one of the required components for equalizing the reducing environment across multiple CTAB sources. However, an additional component-acetone-is critical to establishing the growth kinetics necessary to enable the reproducible synthesis of THH in each of the CTAB formulations. In one CTAB variety, the powdered surfactant contains too much acetone, and drying of the as-received surfactant and re-addition of solvent is necessary for successful Pd THH synthesis. The relevance of solvent impurities to the reducing environment in aqueous nanoparticle synthesis is confirmed via electrochemical measurement approaches and solvent addition experiments. This work highlights the utility of real-time electrochemical potential measurements as a tool for benchmarking of nanoparticle syntheses and troubleshooting of reproducibility issues. The results additionally emphasize the importance of considering organic solvent impurities in powdered commercial reagents as a possible shape-determining factor during shaped nanomaterials synthesis.

Thermodynamic and Interfacial Properties of Cationic Gemini Surfactant in the Presence of Alcohols

The micellar properties of the cationic Gemini surfactant ethanediyl-1,2-bis(dimethyldodecyl ammonium bromide), C12H25 · (CH3)2N+–(CH2)2–N+(CH3)2C12H25 · 2Br− (12-2-12), with short chain alcohols have been studied by conductivity and surface tension measurements within the temperature range 293.15 K–313.15 K and alcohol percentage. The critical micelle concentration (CMC) of 12-2-12 solution, degree of ionization (α) and standard Gibbs free energy of micellization (ΔG°m), standard enthalpy of micellization (ΔH°m) were calculated from conductivity and surface tension data. The experimental data show that the CMC values of cationic Gemini surfactants increased with addition of methanol, ethanol and n-propanol. The thermodynamic parameters (ΔG°m), (ΔH°m) and (ΔS°m) of micellization of 12-2-12 in alcohol were also calculated from the temperature dependence of the CMC values. CMC, (α), (ΔH°m) and (ΔS°m) increased linearly with increasing temperature. In the mixture of dimeric cationic surfactant (12-2-12) and alcohol solutions, the CMC values showed a slight increase with increasing alcohol concentration. CMC, maximum surface excess concentration at the solution/air interface, Γmax, minimum area per surfactant molecule, Amin, and the surface pressure at CMC, ¶CMC, values calculated from the surface tension measurements and thermodynamic parameters have been evaluated at same temperatures.