Temperature structural transformations of reverse micelles of oxyethylated surfactants

Kinetic Factors in the Synthesis of Silver Nanoparticles by Reduction of Ag+ with Hydrazine in Reverse Micelles of Triton N-42

“…At V s / V o = 0.01, the size of initial micelles measured by DLS was d hm = 8.6 nm. Then we can calculate the area of a spherical surface for the polar cavity of one micelle S p = π( d hm – 2 l h ) 2 = π(8.6 – 2) 2 ≈ 137 nm 2 and estimate N ag = S p / S 0 ≈ 260, where S 0 = 0.52 nm 2 is the area occupied by one TN molecule on the polar cavity surface, a known independently measured value . So, the molar concentration of micelles in decane was about [(TN) N ag ] = c TN / N ag ≈ 0.25/260 ≈ 1 × 10 –3 M. As the total concentration in dispersed aqueous phase was fixed at c ’ Ag = 0.012 M for silver and varied within the range of c ′ N2H4 ≈ 0.3–1.8 M for hydrazine, their initial concentrations in micellar solution were c Ag = c ′ Ag ( V s / V o ) = 1.2 × 10 –4 M and c N2H4 = c ′ N2H4 V s / V o ≈ (0.3–1.8) × 10 –2 M. The obtained relations c Ag /[(TN) 260 ] ≈ 0.12 and c N2H4 /[(TN) 260 ] ≈ 3–18 mean that not all the micelles, only ∼10% of them, contained Ag + ion at the beginning of the reaction while all the micelles were loaded with N 2 H 4 .…”

“…"Dry" micelles at c TN = 0.25 M are spherical aggregates of the TN molecules, (TN) Nag , with the average aggregation number N ag = 79 and hydrodynamic diameter d 0 = 5.6 nm, which is twice as large as the length of TN molecule, l = 2.8 nm. 23 Hydrocarbon C 9 H 19 radicals of the TN molecules, having the length l h ≈1.0 nm, form the outer hydrophobic coat of the micelle while the rest fragments of the molecules fill an inner polar cavity (Scheme 2). The polar cavities are able to absorb small volumes of water or aqueous solutions.…”

“…Then we can calculate the area of a spherical surface for the polar cavity of one micelle S p = π(d hm − 2l h ) 2 = π(8.6 − 2) 2 ≈ 137 nm 2 and estimate N ag = S p /S 0 ≈ 260, where S 0 = 0.52 nm 2 is the area occupied by one TN molecule on the polar cavity surface, a known independently measured value. 23 So, the molar concentration of micelles in decane was about [(TN) Nag ] = c TN /N ag ≈ 0.25/260 ≈ 1 × 10 −3 M. As the total concentration in dispersed aqueous phase was fixed at c' Ag = 0.012 M for silver and varied within the range of c′ N2H4 ≈ 0.3− 1.8 M for hydrazine, their initial concentrations in micellar solution were…”

Preparation of Ultradispersed KNO3 Powders in Mixed Reverse Micelles of Tergitol NP-4 + AOT by Isothermal Evaporation Crystallization

“…The entropy of mixing cannot anymore compensate for this significant growth in the enthalpy component of Gibb's energy, and the system goes beyond thermodynamic stability. 33,34 The obtained results allow selection of starting reverse micellar systems and the temperature range for crystallization. The w o varied from 1.1 to 4.4, and the concentration of KNO 3 changed from 0.8 to 2.5 M. To decrease the contamination of KNO 3 crystals by Na + ions, for isothermal crystallization, we used solutions with low contents (to 0.05 M) of AOT.…”

“…Most likely, the reason for the instability of mixed reverse micellar systems at elevated temperatures is the significant increase in interfacial tension. The entropy of mixing cannot anymore compensate for this significant growth in the enthalpy component of Gibb’s energy, and the system goes beyond thermodynamic stability. , …”