A computer simulation and molecular-thermodynamic framework to model the micellization of ionic branched surfactants in aqueous solution

Surfactants, or surface active agents, are chemicals exhibiting amphiphilic behavior toward a solvent. This amphiphilic character leads to increased activity at interfaces and to self-assembly into micellar aggregates beyond a threshold surfactant concentration, referred to as the critical micelle concentration (CMC), in bulk solutions. As a result of these unique attributes, surfactants are used in many pharmaceutical, industrial, and environmental applications, including biological separations, fat metabolism during digestion, drug delivery, and water purification. Selection of the appropriate surfactant for a given application is often motivated by the need to control bulk solution micellization properties, such as the CMC and the micelle shape and size. The ability to make molecular-level predictions of these surfactant properties would allow formulators in industry to speed up the design and optimization of new surfactant formulations. In this thesis, a combined computer simulation/molecular-thermodynamic (CS-MT) modeling approach was developed and utilized to study the micellization behavior of ionic branched surfactants, which are a class of surfactants of great industrial relevance in applications such as detergency, emulsification, and enhanced-oil recovery. In the CSMT modeling approach, molecular dynamics (MD) simulations are used to obtain input parameters for molecular-thermodynamic (MT) modeling of surfactant micellization.This approach is motivated by the limitations inherent in computer simulations (the high computational expense associated with modeling self-assembly) and in MT modeling approaches (their restriction to structurally and chemically simple surfactants). One key input required for traditional MT modeling is the identification of the hydrated ("head") and the dehydrated ("tail") portions of surfactants in a self-assembled micellar aggregate. Using the results of MD simulations of surfactants in a micellar environment, a novel head and tail identification method was developed based on the determination of a conceptual micelle core-water interface. The introduction of an interfacial region consisting of partially hydrated, neutral atomic groups required formulating an improved surfactant tail packing approach.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Lin, Shangchao

Advisor dc:contributor.advisor

• Daniel Blankschtein.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/45641

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/45641