2 research outputs found
Nanoprotective Layer-by-Layer Coatings with Epoxy Components for Enhancing Abrasion Resistance: Toward Robust Multimaterial Nanoscale Films
Layer-by-Layer (LbL) assembled films offer many interesting applications (<i>e.g.</i>, in the field of nanoplasmonics), but are often mechanically feeble. The preparation of nanoprotective films of an oligomeric novolac epoxy resin with poly(ethyleneimine) using covalent LbL-assembly is described. The film growth is linear, and the thickness increment per layer pair is easily controlled by varying the polymer concentration and/or the adsorption times. The abrasion resistance of such cross-linked films was tested using a conventional rubbing machine and found to be greatly enhanced in comparison to that of classic LbL-films that are mostly assembled through electrostatic interactions. These robust LbL-films are then used to mechanically protect LbL-films that would completely be removed by a few rubbing cycles in the absence of a protective coating. A 45 nm thick LbL-film composed of gold nanoparticles and poly(allylamine hydrochloride) was chosen as an especially weak example for a functional multilayer system. The critical thickness for the protective LbL-coatings on top of the weak multilayer was determined to be about 6 layer pairs corresponding to about only 10 nm. At this thickness, the whole film withstands at least 25 abrasion cycles with a reduction of the total thickness of only about 2%
Altering the Static Dipole on Surfaces through Chemistry: Molecular Films of Zwitterionic Quinonoids
The adsorption of molecular films made of small molecules
with a large intrinsic electrical dipole has been explored. The data
indicate that such dipolar molecules may be used for altering the
interface dipole screening at the metal electrode interface in organic
electronics. More specifically, we have investigated the surface electronic
spectroscopic properties of zwitterionic molecules containing 12π
electrons of the <i>p</i>-benzoquinonemonoimine type, C<sub>6</sub>H<sub>2</sub>(<u>···</u>NHR)<sub>2</sub>(<u>···</u>O)<sub>2</sub> (R = H (<b>1</b>), <i>n</i>-C<sub>4</sub>H<sub>9</sub> (<b>2</b>), C<sub>3</sub>H<sub>6</sub>–S–CH<sub>3</sub> (<b>3</b>), C<sub>3</sub>H<sub>6</sub>–O–CH<sub>3</sub> (<b>4</b>), CH<sub>2</sub>–C<sub>6</sub>H<sub>5</sub> (<b>5</b>)), adsorbed on Au. These molecules are stable
zwitterions by virtue of the meta positions occupied by the nitrogen
and oxygen substituents on the central ring, respectively. The structures
of <b>2</b>–<b>4</b> have been determined by single
crystal X-ray diffraction and indicate that in these molecules, two
chemically connected but electronically not conjugated 6π electron
subunits are present, which explains their strong dipolar character.
We systematically observed that homogeneous molecular films with thickness
as small as 1 nm were formed on Au, which fully cover the surface,
even for a variety of R substituents. Preferential adsorption toward
the patterned gold areas on SiO<sub>2</sub> substrates was found with <b>4</b>. Optimum self-assembling of <b>2</b> and <b>5</b> results in ordered close packed films, which exhibit n-type character,
based on the position of the Fermi level close to the conduction band
minimum, suggesting high conductivity properties. This new type of
self-assembled molecular films offers interesting possibilities for
engineering metal–organic interfaces, of critical importance
for organic electronics