- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Thermodynamic Analysis of the Transition of Liquid Crystals from Lamellar to Vesicular Phase
摘要： Here, we report the results of thermodynamic analyses on the lamellar-vesicular transition for a cationic amphiphilic species, namely 2-hydroxyethyl di(alkanol)oxyethyl methylammonium methylsulfate (DEAE). Previously, we have shown that spontaneous vesicle formation from a Lα-lamellar liquid crystal (LC) phase only occurs on the addition of a quantitative amount of additives to the DEAE LC at certain temperatures and that this change occurs without the input of any extra mechanical energy. These lamellar-vesicular transitions occur in two steps: the first step is the formation of an excited state, caused by the solubilization of organic substances in the bilayer structure. The second step, induced by the addition of a small amount of inorganic salt to the excited LC state, is the transition from lamellar to vesicular phase. From our experimental data, the change in the Gibbs free energy was estimated by assuming an ideal electrical chemical potential. As a result, the thermodynamic parameters at 303 K for the lamellar-vesicular transition from the initial state (lamellar) to the final state (vesicle) were found to be approximately －2.7 kJ/mol for the Gibbs free energy, －14.6 kJ/mol for the enthalpy change, and －11.9 kJ/mol for the entropy change. Each state change was due to structural changes not only in the LC bilayers but also in the hydration structure of the surrounding water. Moreover, the most significant finding is that the free energy change in lamellar-vesicular transition is negative, which may be explained based on the stabilization of solubilized vesicles with respect to the unsolubilized lamellar phases.
关键词： electrochemical potential,lamellar liquid crystal,chemical potential,vesicle,transition energy
更新于2025-09-23 15:21:01
-
Reductive Dissolution Mechanisms at the Hematite-Electrolyte Interface Probed by <i>In Situ</i> X-ray Scattering
摘要： The electron-catalyzed dissolution and reprecipitation of iron (oxyhydr)oxides constitute critical steps in natural geochemical iron cycling. However, the atomic-scale mechanisms of reductive dissolution and oxidative precipitation of Fe2+ remain poorly understood because they are difficult to directly experimentally probe. Using in situ synchrotron X-ray scattering and a novel electrochemical cell, we interrogate the interfacial structure between the hematite (α-Fe2O3) (1102) surface and acidic aqueous solution (5 mM Na2SO4, pH 4.0) under controlled electrochemical potential from open circuit to cathodic bias as the reductive dissolution potential is approached and then exceeded. The crystalline order of the surface improves under mild reducing conditions, and the surface Fe stoichiometry changes with cathodic bias. After significant reductive dissolution occurs and cathodic bias is removed, dissolved Fe is re-deposited, forming a disordered interface. Unlike at circumneutral pH, water layers at the hematite interface with acidic solution are poorly ordered, likely due to the adsorption of sulfate from the electrolyte. These results provide a novel atomic-scale view into the behavior of reducible transition metal oxide surfaces under fluctuating (electro)chemical conditions.
关键词： X-ray scattering,hematite,interface structure,electrochemical potential,reductive dissolution
更新于2025-09-04 15:30:14