Correlating surfactant hydrophilic-lipophilic balance and nanoparticle radii via coarse-grained molecular dynamics simulations

COLL 378

Robert JB. Kalescky, robert.kalescky@student.utdallas.edu, Department of Chemistry, University of Texas at Dallas, 2601 North Floyd Road, Richardson, TX 75080, Wataru Shinoda, w.shinoda@aist.go.jp, Research Institute for Computational Sciences, National Institute of Advanced Industrial Science and Technology, Central 2, 1-1-1 Umezono, Tsukuba, 305-0035, Japan, Preston B. Moore, p.moore@usip.edu, Department of Chemistry & Biochemistry and West Center for Computational Chemistry and Drug Design, University of the Sciences in Philadelphia, 600 South 43rd Street, Philadelphia, PA 19104, and Steven O. Nielsen, steven.nielsen@utdallas.edu, Department of Chemistry, The University of Texas at Dallas, 2601 North Floyd Road, Richardson, TX 75083-0688.
Nanoparticles display unique properties, which have applications in many different areas such as medicine and the semiconductor industry. Many of these applications would require assembling these nanoparticles into specific crystal lattice structures to exploit their optoelectronic properties. One proposed method is to solubilize the nanoparticle with surfactants to control the subsequent crystallization by a combination of attractive (van der Waals) and repulsive (electrostatic, steric) forces. We use course-grain molecular dynamics simulations to measure the optimal number of polyoxyethylene surfactants (C12E2, C12E5, C12E8) on the surface of a generic hydrophobic nanoparticle as a function of the particle's radius. The ideal number is determined by evaluating the surface tension at the surfactant/particle interface using free energy techniques. We have tethered the surfactants to the surface, prohibiting them from leaving the particle regardless of whether or not the configuration is favorable. As the radius increases the optimal number of surfactants on the surface will increase. Here we quantify the functional dependence of the surface area per surfactant on the nanoparticle radius. As the surface curvature decreases, the hydrophilic surfactant heads have increasing steric interaction therefore causing each chain to need more surface area to be thermodynamically favorable.
 

Polymer-Nanoparticle Systems: Theory, Simulation, Experiments
9:00 AM-12:00 PM, Wednesday, April 9, 2008 Morial Convention Center -- Rm. 227, Oral

Division of Colloid & Surface Chemistry

The 235th ACS National Meeting, New Orleans, LA, April 6-10, 2008