CAREER: Selective Grafting of Responsive Polymer Brushes on Topographically Structured Surfaces: A New Route for Surface and

Interface ManipulationShu Yang, University of Pennsylvania, DMR 0548070

Fig.2. At 40oC (above LCST), the tips of pillars grafted with PNIPAAm is hydrophobic, the droplet containing silica nanoparticles (~ 100 nm) is repelled from the surface. At 25oC (below LCST), the tips become hydrophilic, and the nanoparticles are absorbed on the tips.

5 μm

A major goal of this research is to combine the chemical heterogeneity and surface topography by selectively grafting responsive polymer brushes on different parts of a nanostructured surface to spatially control surface wettability and transition in response to a small change of environment.

We have selectively grafted thermoresponsive polymer brushes, poly(N-isopropylacrylamide) (PNIPAAm), on well-defined, high-aspect-ratio micropillar arrays at different locations (tips only or everywhere), which allows us to locally control and tune the wetting behaviors (Fig. 1). We compare the experimental data to theory to elucidate the site-specific wetting transition near LCST of PNIPAAm. The site-dependent wetting further enable us to direct assembly of nanoparticles (Fig. 2).

Fig. 1. When PNIPAAm brushes were grafted everywhere on the pillars, the non-wettable surface (Cassie state) became completely wetted (Wenzel state), whereas that grafted with PNIPAAm brushes on tips only became partially wetted only on the tips but maintained in Cassie state.

themoresponsive PNIPAAm brushes

Tips only

EverywhereT > LCST (32oC)

non-wettingContact angle: 135+1o

T < LCST

complete wettingContact angle: < 5o

non-wettingContact angle: 132+2o

partial wettingContact angle: 122+3o

CAREER: Selective Grafting of Responsive Polymer Brushes on Topographically Structured Surfaces: A New Route for Surface and

Interface ManipulationShu Yang, University of Pennsylvania, DMR 0548070

Outreach for pre-school-12 Education:• Two RET teachers, Sunila Gorde (Germantown High

school), and Medha Malgaonkar (West Philadelphia HS), worked in our lab in the summer. They have experienced fabrication and characterization of polymer pillars and colloidal assembly. They will bring their experience to their high school students.

• The PI outreached the Penn Children Center and did 3 science demonstration to the preschool to pre-k students (3-5 years old) on how to make white instant snow, pink snow and hatching duck eggs. Each kid was offered one duck egg and hatch it at home such that they can show and share with their parents or friends. The activities offered the kids first-hand experience on responsive hydrogels.

Education at Graduate and Undergraduate Levels:• Two Ph.D. students: Ying Zhang (3rd yr), Miriam Berdichevsky (2nd yr).• One REU undergraduate student: Billy Yau (Cornell University)• One international exchange undergraduate student from ETH (Switzerland): Anna Peter• In PI's classes, both undergraduate and graduate level, specific examples of nanofabrication,

synthesis of polymer brushes and their applications were illustrated and case studied.