A quantum chemical model for assessment of the temperature dependence in monolayer formation of amphiphiles at the air/water interface

Abstract

In the present study it is shown that parameters used in the framework of the model for the assessment of the threshold temperature of spontaneous clusterization of nonionic amphiphiles at the air/water interface (T(Cl)) are independent of the amphiphile type used in the developed schemes. The temperature dependence of the clusterization Gibbs' energies of alkyl amides, α-amino acids and 2-hydroxycarboxylic acids obtained in the framework of several schemes is listed. The exploited schemes differ from each other by the degree of their theoretical validity. The values of the clusterization threshold temperature for substituted alkanes can be described by a fractionally linear function versus the number of CH···HC interactions in the framework of the simplest scheme taking into account the found corrections and agree well with available experimental data.

Dynamics driven by lipophilic force in Langmuir monolayers: In-plane and out-of-plane growth

“…Vysotsky et al observed in their series of papers the spontaneous clustering of aliphatic amides for alkyl chain length higher than a threshold value, forming dimers and tetramers [35][36][37], Goto et al showed that during compression the hydrophilic groups are protruded in a new geometric configuration to form trilayer (or multilayer) structures [38]. Our results for the longer-chain acids are consistent with their studies.…”

Quantum chemical assessment of the molecular area corresponding to the onset of the LE–LC phase transition for amphiphilic 2D monolayers at the air/water interface

“…of this model more than ten classes of nonionic surfactants were considered, for which the threshold chain lengths were determined, which allow the formation of condensed monolayers, the "temperature effect" of clusterization, the geometric parameters of the unit cells of monolayers, the peculiarities of the dendritic film formation, the effect of the clusterization process on the pK a value. [7][8][9][10] The calculated values of the thermodynamic parameters of clusterization based on the quantum chemical approach are in qualitative agreement with the results of a thermodynamic theory, based on the use of the Volmer-type equation for the phase transition gaseous monolayer -liquid-expanded monolayer. 5 Taking into account the nonideality of the mixing entropy for monomers and clusters in the fluid-condensed transition region makes it possible to describe this region of the π-A isotherm.…”

Quantum-chemical analysis of hexagonal crystalline monolayers of ethoxylated nonionic surfactants at the air/water interface

“…The values of the free term and the slope in the eqn (17) virtually coincide within the error and for the mentioned classes of amphiphilic compounds are (10.1 AE 1.3) K and (À1.3 AE 0.2) K per CHÁ Á ÁHC interaction. 70 This reveals the same reason for the existence of the error and allows one to use the values found for the regression coefficients in the case of other surfactant classes. Corrected values of the temperature are listed in Table 4 in separate columns.…”