Multilayer anchor layer

Once the anchoring layer has been deposited, a second layer can be grown on top of this layer when the tails of the molecules in the first layer are functionalized to link covalently to the head groups of the molecules in the second layer [189]. Figure 32 shows the scheme of formation of zirconyl phosphate layers. By repeating the deposition steps, such as steps 2 and 3 in Figure 32, a number of times, it is possible to deposit multilayer films [182, 183, 194]. 

An example of this approach is represented by the growth of 3-D coordination polymers with SCO properties via stepwise adsorption reactions for multilayer films based entirely on intra- and interlayer coordination bonds Fe(pyrazine) [Pt(CN) ] [218, 219], Indeed, after functionalization of the surface with the appropriate anchoring layer the coordination polymer is built in a stepwise fashion, alternating the metal ion (Fe "), the platinum salt ([Pt(CN) ] ), and pyrazine. The polymer shows many interesting properties, with the SCO transition accompanied by a variation in the dielectric constant of the material accompanied by a room temperature hysteresis of the dielectric constants. This dielectric hysteretic property may be useful in building molecular memory devices that can store information by high- and low-capacitance states. What must be remarked here is that these appealing properties cannot be exploited in bulk materials, but only in thin films. 

The possibility of generating multilayered membrane assemblies employing PET membranes modified with PGMA anchoring layers was examined. The multilayered assemblies can be straightforwardly employed as an efficient tunable and upgradeable platform to fabricate breathable protective materials, where membranes of different natures with different pore sizes can be combined. An additional advantage of this is the possibility to load intermembrane space with functional micro- and nanoparticles, such as catalysts and/or adsorbents. 

A substrate functionalized with proper molecules can be used to anchor particles on its surface via surface exchange reaction, leading to controlled assembly of the particles. This self-assembly technique is known as molecule-mediated self-assembly and is commonly used for constructing various composite nanostructures [49-55]. Due to their excellent adhesion capability to various substrates, multifunctional polymers are routinely applied as templates to mediate the assembly of the particles. The assembly is carried out as follows a substrate is immersed into a polymer solution, and then rinsed, leading to a functionalized substrate. Subsequently, this substrate is dipped into the nanoparticle dispersion and then rinsed, leaving one layer of nanoparticles on the substrate surface. By repeating this simple two-step process in a cyclic fashion, a layer-by-layer assembled poly-mer/nanoparticle multilayer can be obtained. 

A very versatile approach to the formation of multilayer films has been developed by Decher, based on polyelectrolytes. If a solid substrate with ionic groups at the surface is dipped into a solution of a complementary polyelectrolyte, an ultrathin, essentially monomolecular film of the polyion is adsorbed [340]. The adsorption is based on pairing of surface bound ionic sites with oppositely charged ions, bound to the macromolecule. The polymers adsorb in an irregular flattened coil structure and only part of the polymer ions can be paired with the surface ions (Figure 29a). Ionic sites which remain with small counterions provide anchor points for a next layer formed by a complementary polyelectrolyte [342,343]. This way multilayer polyelectrolyte films can be prepared layer-by-layer just by dipping a suitable substrate alternately in an aqueous solution of polyanions and polycations. The technique can be employed with nearly all soluble charged polymers and results in films with a... 

In adsorption from solution, physisorption is far more common than chemisorption, although the latter is sometimes possible. Solute adsorption is usually restricted to a monomolecular layer, since the solid-solute interactions, although strong enough to compete successfully with solid-solvent interactions in the first adsorbed monolayer, do not do so in subsequent monolayers, because the interaction is screened by the solvent molecules. Thus, multilayer adsorption has only rarely been observed in a number of cases, and identified, when the number of adsorbate molecules exceeds the number of mono-layer molecules possible on the total adsorbent surface area. However, this analysis cannot be applied to polymer adsorption, because it is generally impossible to determine the surface area of a monomolecular layer of a polymer adsorbed flat on the solid surface. This is because the adsorbed polymer can only be anchored to the surface at a few points, with the remainder of the polymer in the form of loops and ends moving more or less freely in the liquid phase. 

In a clever attempt to form Langmuir monolayers of pure Cgo> Metzger and collaborators prepared an amphiphilic derivative by a thermally reversible Diels-Alder reaction (Scheme 7) [99], The temporary introduction of the car-boxyhc acid functionality guarantees an efficient anchoring of the fullerene spheroid to the water layer. The monolayers could be successfully transferred onto sohd substrates to form LB monolayers and multilayers. Upon heating, the Diels-Alder adduct decomposes, giving back Cgo. Thus, the final film consists of mixed layers of pure Cgo and Cgo/adduct. 

The preparation of multilayers based on the same or on different structural units may take advantage of the reactivity of the monolayers and particularly of the tail groups. Different strategies have been adopted as an example, dithiol molecules lead to multilayers thanks to the formation of an S-S bond between molecules on the surface [20-22]. The defects present in a single monolayer are inherited by the monomolecular layer anchored to its tail group. Hence, the degree of order of a multilayer is usually much lower with respect to the first monolayer oti the substrate. In the majority of cases, bi- or tri-layers are prepared, although few hundreds of micron thick multilayers can be also obtained. 

Previous studies show that exposure of the PEM to salt solutions or temperature treatment result in changes in the film structure. In order to extend information on the behaviour of multilayers in various conditions we treated PAH/PSS samples prepared with and without anchoring PEI layer in acid/base solutions with pH of 3/11 and respective ionic strength of 0.001 M. Changes in the PEM stmcture were obtained but they were not pH specific. This means that the observed changes were related to the ionic strength of the solutions. A small change in the film... 

A self-assembled multilayer system of Zr -EPPI-Zr -anchoring agent was successfully fabricated on the various substrates. The characterization of Zr-EPPl multilayer with UV-Vis, ellipsometry, and SPR proved the formation of well-ordered Zr-EPPl layer. Ellipsometry and SPR measurements provided quantitative information on the thickness of the Zr-EPPI multilayer films. Each average thickness of one layer of Zr-EPPI was 13.1 0.5 A. From the in-situ SPR measurements at various concentrations of EPPI solution, the adsorption process of EPPI on Zr-MUDP-gold surface was eonfirmed as a two-step model. In the first step, a self-assembled Zr-EPPI layer was formed very quickly but molecular orientation was not well ordered. In the second step, the disordered layer was rearranged and consolidated due to the interaction between the neighbouring EPPI molecules. The initial rate for Zr-EPPI layer formation increased the concentration of EPPI solution increase up to 1 mM and the initial adsorption rates were same over 1 mM solution of EPPI. 

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