Multilayer Assemblies

Fukui M, Katayama N, Ozaki Y, Araki T and Iriyama K 1991 Struotural oharaoterization of phthalooyanine Langmuir-Blodgett multilayer assemblies by FTIR speotrosoopy Chem. Phys. Lett. 177 247-51... 

FIG. 5 Schematic of multilayer assembly by consecutive adsorption of polyanion and polycation. 

Fulda and coworkers [92,93], Bliznyuk and Tsukruk [94], and Serizawa and coworkers [95-97] were the first who tried to use this technique for the preparation of ordered bi- and multilayer assemblies of oppositely charged latex particles. The structure was investigated using scanning force microscopy (SFM) and SEM. In a further publication, Kampes and Tieke [98] studied the influence of the preparation conditions on the state of order of the monolayers. In the following section, the recent studies are more extensively reviewed. 

FIG. 4 Thickness of PDADMAC/PSS multilayers assembled on PS latices as a function of layer number. The layers were assembled by the consecutive adsorption of PDADMAC and PSS. The thicknesses were determined from SPLS data. 

TABLE 1 Thickness of Si02/PDADMAC Multilayers Assembled onto Negatively Charged PS Particles, as Determined by SPLS, SEM, and TEM... 

As the film is polymerized there is some reduction (=10%) in the total surface area of the films. The film can be transferred to a suitable substrate by dipping the substrate through the film and subsequently pulling it off while a fixed film surface pressure is maintained. Thus, in each "dipping" two monolayers are transferred onto the substrate. By successive dippings a multilayer assembly can be fabricated on the substrate. The preferred substrate for the multilayer dipping should have a hydrophobic character. This leads to an excellent adhesion between the aliphatic tails of the monomer to the substrate. 

Multilayer assemblies of -0.5 pm thickness were built up on quartz plates and the films were characterized in detail using spectroscopic (vis. IR) and electron microscopic techniques. 

Figure 4 is an optical absorption spectrum from a multilayer assembly and shows the sharp absorption in the visible characteristic of the polydiacetylenes. Electron diffraction reveals a crystalline layered structure. However, registry between layers is less than perfect. Electron diffraction from a few layers indicates a strong possibility for growing well-oriented structures, and this is being pursued in our laboratory. 

The films formed in these covalent layer-by-layer assembly procedures are similar to the ionic assemblies prepared by other layer-by-layer self assembly procedures. Unlike the more defined Langmuir-Blodgett multilayer assemblies that have well defined layers, the layers of electrophilic polymer and nucleophihc polymer are intermixed to an extent. Similar effects are seen in ionic layer-by-layer assembhes. 

Studies of the order within surfactant monolayers have been reported for many decades. Multilayer assemblies have been studied by electron as well as infrared absorption. Motivated by an older model proposed for the orientation of molecules (Langmuir, 1933 Epstein, 1950), and by recent theoretical calculations, these two potential models for tilt disorder in the monolayer have been examined. Both models arise because the monolayer structure tries to compensate for the difference between the equilibrium head-head and chain-chain distances that each piece of the molecule would want to attain if it were independent. In one model, the magnitude of the tilt is fixed, but the tilt direction wanders slowly through the lattice. In the second... 

The multilayer assembly of electroactive units protects the electrode surface and can prevent redox species in solution from contacting the underlying metal substrate. However, the electron transport properties of these electroactive units can be... 

The photochemistry and photophysics of trans-stilbene derivatives (24) have been utilized by Whitten and co-workers to understand the relaxation characteristics of media such as micelles, monolayers, and LB films [144,145]. For example, the d>,rans to Cis for stilbene derivatives show the following trend solvent system methylcyclohexane > SDS micelle multilayer assemblies (with arachidic acid). In fact, no isomerization is observed in multilayer assemblies. This is the trend expected on the basis of how readily the media can respond to stilbene shape changes during isomerization process. 

A novel capillary electrophoresis method using solutions of non-crosslinked PDADMAC is reported to be effective in the separation of biomolecules [211]. Soil studies conducted with PDADMAC report the minimization of run-off and erosion of selected types of soils [212]. In similar studies, PDADMAC has found to be a good soil conditioner [213]. The use of PDADMAC for the simultaneous determination of inorganic ions and chelates in the kinetic differentiation-mode capillary electrophoresis is reported by Krokhin [214]. Protein multilayer assemblies have been reported with the alternate adsorption of oppositely charged polyions including PDADMAC. Temperature-sensitive flocculants have been prepared based on n-isopropylacrylamide and DADMAC copolymers [215]. A potentiometric titration method for the determination of anionic polyelectrolytes has been developed with the use of PDADMAC, a marker ion and a plastic membrane. The end-point is detected as a sharp potential change due to the rapid decrease in the concentration of the marker due to its association with PDADMAC [216]. 

The liposomes prepared by this method are usually MLVs, but the structure inside the vesicles can be highly formulation dependent. MLVs composed entirely of neutral lipids tend to be very tightly packed multilayer assemblies with the adjacent bilayers stacked closely on one another, with very little aqueous space between them. The presence of negatively charged lipids in the membram tends to push the bilayers apart from each other and increase the aqueous volume of entrapmer signiLcantly for water-soluble compounds. 

Fig. 15 Internalization and gene expression of pDNA released from a multilayer assembly. Release of pDNA occurs upon degradation of T4 polyamide. Notable increase in fluorescence intensity overtime is observed in the flow histograms. Gene expression (measured by intracellular GFP fluorescence) does not increase at the same rate as DNA uptake. Figure adapted with permission from [151]. 2009 Elsevier...

Taori VP, Liu Y, Reineke TM (2009) DNA delivery in vitro via surface release from multilayer assemblies with poly(glycoamidoamine)s. Acta Biomater 5(3) 925-933... 

Rubner MF (2003) pH-controlled fabrication of polyelectrolyte-multilayers assembly and applications. In Decher G, Schlenoff JB (eds) Multilayer thin-films. Wiley-VCH, Weinheim, p133-154... 

Hammond PT (2004) Form and function in multilayer assembly new applications at the nanoscale. Adv Mater 16 1271-1293... 

Brynda E, Houska M (2000) Ordered multilayer assemblies albumin/heparin for biocompatible coating and monoclonal antibodies for optical immunosensors. In Lvov Y, Mohwald H (ed) Protein architecture interfacial molecular assembly and immobilization biotechnology. Dekker, New York... 

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