Self‐Assembly and Properties of Main‐Chain Reversible Polymer Brushes

Abstract

in the potential range between 0 and 0.6 V. Impedance spectra were taken between 100 kHz and 50 MHz under sinusoidal potentials with an amplitude of 10 mV. To estimate the electrochemical parameters from the data, the whole system was represented by ideal elements of a simplified equivalent-circuit model composed of serial resistance, interface capacitance, and interface resistance. [4] and very limited experimental work has been reported. [5] Using DNA-based modules, we investigate here the compressive and adhesive mechanical properties of self-assembled polymer brushes, and we report the effects of surface anchor density, association strength, and monomer flexibility on those properties. Reversible polymer brush properties ( Fig. 1) were examined using atomic force microscopy (AFM). Patterned gold substrates were prepared using scanning electron microscopy (SEM), photolithography, and chemical vapor deposition. The patterning provided a background reference height and also allowed multiple samples to be introduced simultaneously into the AFM. Isolated gold dots (~1.4 lm in diameter) were spaced among quadrants of a ca. 1 cm 2 silicon surface. Each quadrant and its associated gold pattern were addressed independently with a solution of an oligonucleotide±thiol RP anchor 1, (5¢®3¢)GGTATACC±(CH 2 ) 3 ±SH, and a 6-mercapto-1-hexanol backlayer that resists non-specific adsorption of the RPs on the surface.[6] The relative concentration of the two components determined the surface density (0±1.2 10 12 cm ±2 )of the RP anchor within a self-assembled monolayer (SAM) on the pattern in each quadrant.[6] Using tapping-mode AFM in 1 M NaCl and phosphate buffer (pH 7.0), the heights of the gold dots in each quadrant were measured and found to be roughly equivalent at~40 nm (Table 1). All four quadrants were then immersed simultaneously into the RP solutions of interest and probed in rapid succession with a single gold-coated AFM tip that had also been treated with 1.The anchor 1 is complementary to the oligonucleotide RP monomer 2 ((5¢®3¢)GGTATACCGCTTAAGC). End-to-end duplex formation of 2 creates a linear, polymeric assembly that resembles larger duplex DNA, but in which the main chain is defined by the reversible base pairing.[7] The equilibrium RP solution structure of 2 has been thoroughly characterized, [8] and reversible polymers formed from oligonucleotide-based monomers have been found to be a useful model system for delineating molecule-to-material relationships in RPs. Polymer-brush synthesis is a facile, one-step self-assembly process. Immersing the 1-modified substrate into an 11 lM solution of 2 led, within minutes, to the formation of RP brushes, as revealed by changes in the AFM images (Table 1). The effective thickness of the brush is indicated by the difference in the height of the features in the two solutions, which increased with increasing surface density of anchors; the apparent brush thicknesses are 6 ± 2, 16 ± 2, and 23 ± 2 nm for surface anchor densities of 0.6 ± 0.1 10 11 , 1.1 ± 0.1 10 11 , ...

Rational Control of Viscoelastic Properties in Multicomponent Associative Polymer Networks

“…More generally, the results presented here speak to the potential of reversible and specific intermolecular interactions as effectors of the entanglements or polymer bridges 38,39,53 necessary to transmit force in materials. The sophistication available in the field of molecular recognition holds considerable promise as it is applied increasingly to areas of material science.…”

Molecularly Regulated Reversible DNA Polymerization

“…However, the spontaneous self-assembly and concomitant disassembly are not stable or molecularly regulatable. [18] …”

Single-molecule force spectroscopy of DNA-based reversible polymer bridges: Surface robustness and homogeneity

“…Similar observations have been made previously on related systems, although the details of the experimental procedure are different in all cases. [28, 29, 52]…”

“…Regions of different surface densities lead to different bridging probabilities. [52] An AFM-based bridging experiment on a single spot or small (~40 × 40 nm) grid samples a surface area that, apparently, is somewhat smaller than that necessary to represent the surface as a whole. Picking points that span a larger surface area, on the order of μm 2 , appears to be sufficient to overcome the surface inhomogeneity.…”

“…[40-44] Hydrogen bonds,[45] metal-ligand coordination,[17, 23, 42, 44, 46-49]and DNA base pairing between monomer units have all been used in the past to make reversible polymers. [28, 29, 50-52] Reversible polymers, because of their weakly interacting monomer units, are able to respond to their environment making their structure, and molecular weight amendable. Typically, this is exploited in the context of stimulus-responsiveness,[41, 42, 53] but it can be used to alter surface interactions in ways not possible using covalent polymers.…”