Grafting, from gold surfaces

In their study, Park et al.100 investigated the frictional properties of fluorine-terminated alkanethiol SAMs grafted to gold surfaces. The frictional properties of the system were investigated by sliding two SAMs past one another at velocities in the stick-slip regime under various external loads. The simulations yield the shear stress as and the kinetic friction coefficient pk can be estimated from the slope of a plot of as versus load, using the relationships contained in Eqs. [4] and [5]. 

Jin Z, Brash JL, Zhu S (2010) ATRP grafting of oligo(ethylene glycol) methacrylates from gold surface — effect of monomer size on grafted chain and EO unit densities. Can J Chem 88(5) 411-417... 

In a similar approach Riihe et al. [279] reported the preparation ofpoly(2-oxazoline) brushes by the grafting onto as well as grafting from method. For LCSIP of 2-ethyl-2-oxazolines silane functionalized undecane tosylate was first prepared and then immobilized on the substrate surface. SIP resulted in PEOx layers with thickness close to 30 nm. PEOx brushes were prepared by chemisorption of PEOx disulfides onto gold substrates. Preliminary static and dynamic swelling experiments are reported for these brushes. However, later observations [243] contradicted these findings. 

During the last 5 years, there have been several reports of multiblock copolymer brushes by the grafting-from method. The most common substrates are gold and silicon oxide layers but there have been reports of diblock brush formation on clay surfaces [37] and silicon-hydride surfaces [38]. Most of the newer reports have utilized ATRP [34,38-43] but there have been a couple of reports that utilized anionic polymerization [44, 45]. Zhao and co-workers [21,22] have used a combination of ATRP and nitroxide-mediated polymerization to prepare mixed poly(methyl methacrylate) (PMMA)Zpolystyrene (PS) brushes from a difunctional initiator. These Y-shaped brushes could be considered block copolymers that are surface immobilized at the block junction. 

Similarly, gold particles were surface-modified with norborn-5-ene-2-ylmethanthiol and the surface-immobilized norborn-2-ene groups were subsequently used for norborn-2-ene polymerization in a grafting-from approach. The resulting material was used to construct a field effect transistor [32]. 

Spherical gold nanoparticles coated with poly(N-isopropylacrylamide) (PNIPAM) grafts have been synthesized by controlled radical polymerization. The polymerization of N-isopropylacrylamide was initiated from the surface of the nanoparticles modified with 4-cyanopentanoic acid dithiobenzoate for reversible addition-fragmentation chain-transfer polymerization. The mean diameter of the Au core was 3.2 nm, as observed by means of high-resolution transmission electron microscopy [90]. 

Of course, a poly(ethylene oxide)-functionalized SAM may be further functionalized with suitable groups to ensure protein grafting on the SAM surface. The best choice for these purposes are active esters functionalization of oligo(ethylene oxide) SAMs with biotin85 has also been reported. The adsorption of poly(ethylene oxide)-functionalized disulfides on gold surfaces has been proven to give SAMs with protein-resistant surfaces comparable to those obtained from oligo(ethylene oxide)-functionalized thiols.86... 

Scheme 3 Schematic representation of the two-steps electrostatic grafting of a cationic Mni2 derivative on a prefunctionalized gold surface (reprinted from [99])...

Presently, significant work has been done to develop and optimize various LRP techniques. Commercial applications are still scarce. The general expectation is that the products of LRP will mainly be employed in high-value-added products. These may include specialty coatings, adhesives, personal care products, biomedical applications, and optoelectronical applications. Examples of biomedical applications can be foimd in the work of eg, Muller (128), Haddleton (129), and Wooley (130,131). For materials in optoelectronical applications it is of great importance that many of the techniques from FRP can be adopted to LRP. An example is surface grafting from or onto various substrates, like silica (132) and gold (133). Much of the work of Hawker and co-workers is dedicated to the application of LRP in electronical applications (134). 

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