Ultrathin Binary Grafted Polymer Layers with Switchable Morphology

Abstract

Polymer surface layers comprised of mixed chains grafted to a functionalized silicon surface with a total layer thickness of only 1-3 nm are shown to exhibit reversible switching of their structure. Carboxylic acid-terminated polystyrene (PS) and poly (butyl acrylate) (PBA) were chemically attached to a silicon surface that was modified with an epoxysilane self-assembled monolayer by a "grafting to" routine. While one-step grafting resulted in large, submicron microstructures, a refined, two-step sequential grafting procedure allowed for extremely small spatial dimensions of PS and PBA domains. By adjusting the grafting parameters, such as concentration of each phase and molecular weight, very finely structured surfaces resulted with roughly 10-nm phase domains and less than 0.5-nm roughness. Combining the glassy PS and the rubbery PBA, we implemented a design approach to fabricate a mixed brush from two immiscible polymers so that switching of the surface nanomechanical properties is possible. Post-grafting hydrolysis converted PBA to poly(acrylic acid) to amplify this switching in surface wettability. Preliminary tribological studies showed a difference in wear behavior of glassy and rubbery surface layers. Such switchable coatings have practical applications as surface modifications of complex nanoscale electronic devices and sensors, which is why we restricted total thickness for potential nanoscale gaps.

Soft Nanopolyhedra as a Route to Multivalent Nanoparticles

“…for each struc- ture were also obtained through extensive simulations. These results will be useful guides to the nascent sciences of nanostructured nanoparticles [12] and environmentally responsive nanoparticles [15] and may facilitate construction of drug carriers with reversibly switchable structures [30]. I thank Professor Toshihiro Kawakatsu and Dr. Hiroya Kodama for discussions and Dr. Chin-Kun Hu for computational facilities.…”

Preparation and characterization of V-shaped PS-b-PEO brushes anchored on planar gold substrate through the trithiocarbonate junction group

“…Secondly, the mixed polymer brush is responsive to environmental stimuli, such as solvent atmosphere, and thus the surface composition and morphology of the mixed polymer brush is variable [12][13][14][15][16][17]. As a result, the surface properties of the mixed polymer brush can be tuned or switched by applying external stimuli [18][19][20][21][22][23][24][25][26][27][28][29]. Due to the interesting phase separation phenomena and the resulting smart properties of the mixed polymer brush, a substantial amount of theoretical [30][31][32][33][34][35][36][37][38][39][40][41][42] and experimental [43][44][45][46][47] work has been devoted to this field.…”

Polymer Brushes by the “Grafting to” Method

“…This approach brings a tremendous degree of flexibility to the choice of various functional groups suitable for the grafting procedures. Examples reported in the scientific literature include the utilization of reactions between epoxy and carboxy groups, [71,76,77,80,83,84,88,92,95,96] epoxy and amino groups, [37,67,73,74,88,95,97] and carboxy and amino groups. [62,98] Less frequent combinations of functional groups used for the ''grafting to'' procedure on oxide and/or gold surfaces are ''click'' chemistry, [99] reaction of epoxy group with maleic anhydride, [81,82] interaction between epoxy and thiol groups, [67] and alkylation of a pyridine ring in a polymer with a halogen atom attached to the surface via silane chemistry.…”