The surface pressure (Π) and electric surface potential (ΔV) vs. concentration (c) isotherms of n-decanoic acid (DA) in 1 × 10⁻³ mol/dm³ HCl were measured at the air/solution interface - the Π with a du Noüy ring, the ΔV with the vibrating plate (named also the dynamic condenser) method. The DA solutions fulfilled criterion of surface-chemical purity. The complementary Π-c and ΔV-c isotherms were jointly evaluated to obtain dependence of quotient of the effective dipole moment to the interface's permittivity, μ_⊥/ε_s, as a function of chosen adsorption ordinates such as the bulk concentration, c, partial molar area, A, and surface molar fraction of DA, X_DA^s. The crucial point for the analysis is knowledge of the surface excess (Γ) dependence on concentration (c). Since, experimental determination of a Γ-c course is problematic, so far, we used Γ-c courses calculated basing on different adsorption models (Gibbsian, the classical Frumkin’ model and the Lunkenheimer’ and Hirte’ two state approach). Despite, the Γ-c courses determined basing on the different adsorption models differ significantly, the μ_⊥/ε_s dependences on different adsorption's ordinates (c, A or X_DA^s) revealed consistently three local μ_⊥/ε_s maxima of their height increasing with the adsorption coverage. The μ_⊥/ε_s change was recalculated into inclination angle (α_incl) of the total dipole moment vector ($\overrightarrow{\mu }$) to the interface, assuming ε_s = 1. The μ_⊥/ε_s which reflects polarization orientation is an order parameter used by us for analysis of 2D phase transitions in the monolayer. The three μ_⊥/ε_s local maxima are ascribed by us to three 2D mono-phases, one transferring into the next one of the higher order in the sequence: liquid expanded (L1) → the liquid condensed tilted (L2) → the liquid condensed untilted (L2′). One inflection point appearing in the Π-A isotherm within the region between the μ_⊥/ε_s maxima 2 and 3 indicates that transition of the L2 into the L2’ 2D phase is of the first order. Decrease of the μ_⊥/ε_s above the maximum 3 indicates transition into two phase regime by nucleation of aggregates (possibly in form of lamellas) within the L2′ phase.

在空气/溶液界面上测量正癸酸（DA）在1×10 ^-3  mol / dm ³ HCl中的表面压力（Π）和表面电势（ΔV）相对于浓度（c）等温线-Π如果使用duNoüy环，则采用振动板（也称为动态冷凝器）方法的ΔV。DA溶液满足表面化学纯度的标准。互补Π-c和ΔV-C等温线共同评估，以获得有效的偶极矩的商数的依赖于界面的介电常数，μ _⊥ /ε_小号，作为选择吸附纵坐标的函数，如散装浓度c，部分摩尔面积A和DA的表面摩尔分数X _DA ^s。分析的关键点是了解表面过量（Γ）对浓度（c）的依赖性。由于Γ-c过程的实验确定是有问题的，因此到目前为止，我们使用了基于不同吸附模型（吉布斯模型，经典Frumkin模型和Lunkenheimer'和Hirte'两种状态方法）计算的Γ-c过程。尽管，在Γ-C课程确定基础上的不同吸附模型显著不同，则μ _⊥ /ε_小号上不同吸附的坐标（C，A或依赖性X _DA^小号）揭示一致三个本地μ _⊥ /ε_小号它们的高度的最大值随着吸附覆盖率的增加。所述μ _⊥ /ε_小号变化换算成倾斜角度（α_含总偶极矩向量的）（$\overrightarrow{\mu }$）到接口，假设ε_小号 = 1μ _⊥ /ε_小号反映偏振取向被用于单层2D相变的分析中使用由我们的命令参数。我们_将这三个_μ⊥ /εs_的局部最大值归结为三个2D单相，一个按顺序转移到下一个更高阶的相中：液体膨胀（L1）→液体倾斜倾斜（L2）→液体浓缩直到（L2'）。所述μ之间的区域内出现的Π-A等温线一个拐点_⊥ /ε_小号最大值2和3表示L2进入L2' 2D相过渡是一阶。_μ⊥ /εs_的减小 高于最大值3表示通过L2'相内的聚集体（可能以薄片形式）成核而转变为两相态。