Chemical Engineering

Chemical Engineering Colloquia Seminar: Robert E. Cohen, MIT

Speaker:  Prof. Robert E. Cohen, St. Laurent Professor of Chemical Engineering, MIT

http://web.mit.edu/cohengroup

Surface Engineering Using Polymers and Nanoparticles

Functional ultrathin films can be fabricated conformably on a variety of substrates via a layer-by-layer (LbL) deposition process that relies on sequential adsorption of nanoparticles and/or polymers. In one example, high- and low-refractive-index regions of quarter-wave stacks were generated by calcining LbL-assembled multilayers containing TiO2 and SiO2 nanoparticles. The physical attributes of each region were characterized by a recently-developed ellipsometric method. The structural color characteristics of the resultant nanoporous Bragg stacks could be precisely tuned in the visible region by varying the number of stacks and the optical thickness of the high- and low-refractive-index regions. These Bragg stacks also exhibited potentially useful superhydrophilicity (antifog) and self-cleaning properties. Issues of poor mechanical integrity and non-robust environmental stability have been addressed successfully by advantageous exploitation of capillary condensation phenomena in these ultrathin nanoporous coatings. In a second example, functional polyelectrolyte multilayer (PEM) patches are attached to a fraction of the surface area of living, individual lymphocytes. Surface-modified cells remain viable at least 48 h following attachment of the functional PEM patch, and patches carrying a cargo of magnetic nanoparticles allow the cells to be manipulated spatially using a magnetic field. The patch does not completely occlude the cell surface from its surrounding environment, thereby allowing a functional payload to be attached to a cell that is still free to perform its native functions.

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