1. Interfacial Structure and Fluctuations in Block Copolymer Brushes: Tailoring Switchable Surfaces
*Gokce Ugur, Mark D. Foster, Department of Polymer Science, The University of Akron
Fluctuations of the surfaces of polymer brushes and any interfaces within a block copolymer brush are key to switching of the brush structure in response to the environment. Observations of a stronge correlation between the structure of the brush interface with air and the structure of the brush interface with the substrate has provided a hint that the fluctuations of the surface are strongly changed by the fact that the chains are tethered. Therefore, the surface height fluctuations on densely grafted brushes in which the chains are homopolymers have been studied using an emerging technique, x-ray photon correlation spectroscopy (XPCS). We find that surface fluctuations of wavelengths from 620 to 3100 nm on annealed brushes of either polystyrene or poly(n-butyl acrylate) are “frozen” on the time and length scales probed by XPCS even at temperatures more than 130 C above the glass transition temperature of films of corresponding untethered chains. No relaxation of the surface is seen for a time window of 0.1 to 1000 seconds. This alteration of surface dynamics by tethering has implications for wetting, friction, and adhesion as well as the “switching” of brushes.
1.2
Example: Change in time correlation function of surface fluctuations:
Fluctuations on surface of brush do not relax in this time window
Fluctuations relax on surface of film of untethered chains do relax
T= 170 C
26 nm thick PS brush
1.15 2 g
1.1
29 nm thick untethered PS Chains
1.05
qװ= 5.3x10-3 nm-1 1
*Collaborators: Bulent Akgun, Suresh Narayanan, Zhang Jiang, Hyunjung Kim, Sunil Sinha
0.1 1 10
100
1000
t (sec)