An Investigation of Critical Micelle Concentration and Aggregative Behavior of Amphiphilic Molecules Using Dissipative Particle Dynamics
Date Issued
2011
Date
2011
Author(s)
Wu, Ming-Zhe
Abstract
The micellization phenomena of the amphiphiles have been an important area of the research in colloid science for a long time. The ordered structure, micelle, which is formed in the amphiphile solution, exists only above a fairly well-defined concentration, CMC. Micelles could offer a powerful multifunctional platform for medical and industrial applications. Various factors, such as amphiphile concentration, amphiphile architecture, and additives, all significantly affect the properties of the micelles. Thus, to thoroughly investigate the solution behavior of the amphiphiles is of great importance.
The Dissipative Particle Dynamics was employed to study the CMC and aggregative behavior of the amphiphilic molecules. The effects of the tail/head length, amphiphile architecture (linear type, miktoarm star type, dendritic type, cyclic type and chain rigidity), nonpolar additives, and nonpolar solvent on the CMC and the aggregative patterns of the amphiphiles are systematically investigated. For the tail/head length, it is found that the CMC declines with increasing tail length but rises with increasing head length. Compared to head group, tail group has comparatively significant influence on the CMC. According to the analyses of the micelles, we found that amphiphiles with higher tail/head ratio or longer total length form the micelle in larger quantities. In addition to the tail and head length, amphiphile structures also have a considerable impact on the amphiphile solution properties. The branching and cyclic structures of either the hydrophobe or hydrophile lead to a striking increase in the CMC; nevertheless, as to the cases with rigid chain, amphiphiles with the greater degree of the rigidity on the tail group or head group have lower CMC. Form the analyses and morphologies of the micelles, we observed that the aggregative patterns of the amphiphiles with the changes in the tail structure and head structure are quite different. On the other hand, the changes in the concentration, length, and structure (cyclic and linear type) of the nonpolar additives were performed to study their effects on the behaviors of the amphiphiles in aqueous media, where some interesting supramolecular structures were observed. Besides the aqueous solvent, we investigated the properties of the inverted micelles formed in the nonpolar solvent. As the nonpolar solvent length increases, the CMC decreases sharply and then gradually.
This work could provide a thorough investigation on various factors which influence the amphiphile solution. The relationship between the CMC and these factors from our investigation is consistent with most experimental findings. For the amphiphiles with unique architectures or in special condition which have not been fully investigated, what we study could be a valuable reference for the future experimental works.
Subjects
Dissipative Particle Dynamics
Amphiphilic Molecules
Critical Micelle Concentration
Micelle
Type
thesis
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