Dynamics in Confining Nanoparticle Systems

Mustafa Akbulut
Department of Chemical Engineering
UCSB Doctoral Candidate

Date: Thursday, Dec. 14, 2006
Time: 4:00 p.m.
Place: Engineering II, Room 3361

ABSTRACT

Nanoparticles have electronic, optical and mechanical properties different from those of the bulk materials because of the large contribution of surface atoms. Hence, the precise size, shape and surface chemistry of nanoparticles may be expected to have major effects on these properties. The unique and tunable properties of nanoparticles make them suitable for various applications. Some of these applications require well-ordered large scale structures or films from smaller nanoparticles. It is known that the properties of such structures strongly depend on the nanoparticle ordering processes and, of course, the properties of the nanoparticle building blocks themselves. Thus, it is important to understand the various forces and interactions acting between nanoparticles, and the effects of confinement.  

The normal and lateral forces between mica surfaces across various size, shape and concentration of nanoparticles consisting of ZnS cores coated with a monolayer of physisorbed surfactant, dissolved in organic solvents were measured using a surface forces apparatus (SFA). Forces were found to be exponentially repulsive when the surfactant layers were strongly bound to the nanoparticles; and were roughly linear when there was adhesion between the nanoparticle cores, i.e., when the surfactant layers detached from the nanoparticles. In both cases, the range and magnitude of the forces were dependent upon the particle size and solution concentration. Fine details in the otherwise smooth force-distance profiles indicate specific effects due to particle chemistry and geometry, and the existence of first-order disorder-order phase transitions upon confinement. Understanding and controlling the effects of particle shape, size and concentration on particle-particle and particle-surface interactions provide important information for the processing of nanoparticles into ordered nanostructured materials.