Research
Particle Films • Surface Modification • Three-dimensional Assembly • Particles as TemplatesTwo-dimensional Nano- and Microparticle Films
This research area is concerned with the development of simple methods for the fabrication of highly ordered, close-packed particle monolayers. Our objectives are the reproducible formation of monolayer areas and the minimization of defects within the monolayers. Particle monolayers are intersting precursors for:
• chemical and pressure sensors
• particle modification technology
• shadow masks.
We have developed a simple cell set-up which allows the control of the miniscus of the drying suspension (Fig. 1a).[1] The set-up enables us to create a concave miniscus, which leads to the fromation of a two-dimensional particle film in the center of the cell as the particle suspension dries (Fig. 1b).
Within the two-dimensional particle film, immersion capillary forces[2] are at work which cause attraction between particles (Fig. 2a) leading to close packing of the particles. In addition, evaporation occurs in the area of the monolayer particle film. As a result, solvent needs to be replenished in the monolayer region by a convective flow from the cell wall towards the cell center. Particles are transported by the convective flow towards the 2D-particle film in the center of the cell leading to the growth of the monolayer (Fig. 2b).
In our studies, we find that the particle volume fraction and the evaporation rate are the determining factors in the convective assembly of particles. We are able to form large area monolayers of ~45 mm 2using the above described set-up. The monolayers show packing defects (grain boundaries) due to small size of the domains. Best monolayer crystals are obtained with: f = 0.002, tdrying ~ 90 min, and a cell load of 25 ml (see Poster).
Students:
Current Graduate Students: Amar B. Pawar
Current Undergraduate Students: Anton Dela Cruz, Mohammad Mahmud, Ralph Eddy Daniel
Former Contributors: Carlos Alberto Silvera Batista, Charlotte König, Saumya Banerjee
Posters:
1)“Assembly of Two-dimensional Monolayers from Micro- and Nanoscale Particle Dispersions” C. A. Silvera Batista and I. Kretzschmar* Columbia NSEC Retreat, Spring 2006 PDF
Relevant Literature:
[1]“Two-dimensional Micro- and Nanoparticle Monolayer Films” C. A. Silvera Batista and I. Kretzschmar* Proceedings of the Junior Scientist Conference '06, 2006. PDF
[2]“Capillary forces and structuring in layers of colloid particles” P. A. Kralchevsky and N. D. Denkov Current Opinion in Colloid & Interface Sci., 2001. 6 383-401.
Funding:
• New York City Louis Stokes Alliance for Minority Participation (LSAMP) Program
• CCNY and CUNY start-up funds and CCNY travel funds
• This work was partially supported by the Nanoscale Science and Engineering Initiative of the National Science Foundation under NSF
Award Number CHE-0117752,and by the New York State Office of Science, Technology, and Academic Research (NYSTAR).