Polyion complex technique

Preparation of polymeric bilayer cast films by polyion complex technique... 

Polyion complex technique [40] is a unique method for immobilization of bilayer membranes with polymers. Water-insoluble complex is precipitated as the polyion complex when an aqueous solution of the charged bilayer membrane is mixed with a water solution of the counter charged polyelectrolyte. Stoichiometric ion pair formation is often found. Aging of the precipitate in a hot mixture kept above phase transition temperature of the bilayer membrane completes the ion exchange reaction [41], Chloroform solution of the polyion complex is washed by water several times to remove water soluble components [42]. 

Photochemical switching of the phase transition is also found in the polyion complex film. Figure 29 shows reversible cycles of the absorption at 370nm by the coupling of the thermal and photoinduced phase transition of the complex film with carboxymethylcellulose 8. In conclusion, we indicate that the immobilized bilayer membranes containing the azobenzene chromophore are available to the erasable memory materials based on the phase transition triggered by thermal and photochemical processes. The polyion complex technique is clearly shown to be a very useful method for materialization of the immobilized bilayer membranes. 

The Langmuir-Blodgett (LB) technique is one of the most conventional methods of nano-film fabrication. The polyion complex technique [221] was proposed to immobilize water-soluble bilayer forming amphiphiles and counter-charged polymers as polymeric LB films. Water-insoluble polyion complexes are formed at the air/water interface when the charged amphiphiles are directly spread on the surface of the aqueous polyelectrol 4 e solution. Alternative multilayers of the polymer and the amphiphile with stoichiometric ion pairing can be deposited onto solid substrates by the conventional LB technique [222]. The principle of the... 

The polyion complex technique [15] was proposed as a convenient preparative method to immobilize water-soluble, bilayer-forming amphiphiles and polymers as composite thin films. A water-insoluble polyion complex is precipitated when the aqueous solution of the charged bilayer membrane is mixed with a water solution of the countercharged polyelectrolyte. The polyion complex mono-layer also can be formed in situ when the charged amphiphiles are directly spread on the surface of the aqueous polyelectrolyte solution. The principle of the polyion complex LB technique has been expanded into a general and simple alternative deposition method of charged polymers by Decher [16] (this volume chapter 12). 

III. PREPARATION OF POLYMERIC LAYER-BY-LAYER FILMS BY POLYION COMPLEX TECHNIQUE... 

Polyion complex technique is a unique method of supramolecular polymerization of bilayer membranes without conventional polymerization procedures [14,50], Water-insoluble polyion complexes are precipitated when the aqueous solution of the charged bilayer membrane is mixed with a water solution of the countercharged polyelectrolyte. The polyion complexes can be formed as thin films by usual casting from organic solutions. The fundamental bilayer structure and characteristics are essentially maintained in the immobilized cast films of the polyion complexes. X-ray diffraction of the solvent cast polyion complex films reveals the layered structure with repeating spacing corresponding to the bilayer thickness [50-52]. 

B. Langmuir-Blodgett Films Prepared by Polyion Complex Technique... 

Aiming toward the functional applications of DNA as novel molecular devices, polynucleic acids have been immobilized as two-dimensional molecular assemblies by means of the specific intermolecular interaction at the air-water interface [82,83] as well as by the polyion complex technique [84]. We describe here the effect of DNA on photoinduced electron transfer in polyion complex LB monolayers deposited on an ITO electrode [85], or cast in polyion complex films [86]. 

RA and transmission techniques [3], and applied it to the studies of LB films of cadmium stearate [3], azobenzene-containing long-chain fatty acids and their barium salts [4], dipalmitoylphosphatidylcholine (DPPC) [5], and polyion complexes [6]. Furthermore, we explored the relationship between the molecular orientation evaluated by this method and pyroelectricity in alternating (noncentrosymmetric) Y-type LB films consisting of a phenylpyrazine-containing long-chain fatty acid and deuterated stearic acid and of their barium salts [7]. 

Figure 21 shows three possible routes to obtain oriented PAV films by the LB technique. In these route, it is anticipated that orientational orderliness of precursor polymers is introduced in the precursor LB films through the formation of two-dimensionally oriented monolayer of a polyelectrolyte precursor-anionic amphiphile polyion complex at the air/subphase interface and orientation of the precursor monolayers along the dipping direction dining the deposition process. As a result, it is expected to obtain oriented PAV LB films with well-developed jt-coryugation system. In this study, we successfully prepared oriented PAV films using two routes of them, b-1 and b-2 route [35-37]. The chemical structures of PAVs, their polyelectrolyte precursors and an anionic amphiphile used in this study are shown in Fig.22. 

In the preparation of the MOPPV LB films, the polyion complex monolayer were formed by the adsorption of the precursor onto the anionic amphiphile monolayer (route b-2 in Fig.5) [36,37]. The monolayer of 2C12SUC was spread on a aqueous solution of the MOPPV precursor polymer (repeating unit concentration about 10"4 M). The monolayer was allowed to stand for 4 hours to adsorb the precursor after being compressed to a surface pressure of 30 mNm 1. The monolayer was deposited on fused quartz substrate by the LB technique. At last, the deposited polyion complex was converted to MOPPV by the heat treatment at 200 C in vacuo (about 10 2 torr). 

The polyion complex LB technique is the most precise fabrication method of layer-by-layer polymer assemblies because the lateral molecular ordering and layer structure (X-, Y-, and Z-type deposition and heterogeneous deposition) of the polymer films can be controlled. The molecular assembly in polyion complex monolayers can be switched by pH change [105] or photochemical reaction [106]. Film uniformity of the polyion complex monolayer was improved by in situ ther-... 

By the systematic work on the complexation equilibrium analyses of both weak acidic and weak basic polyelectrolytes, the Gibbs-Donnan approach is validated to provide deep insights into the complexation behaviors of linear polymer ligands. This concept does not need any adjustable parameter it only uses the logic of phase separation of polyelectrolyte aqueous solutions. The electrostatic nonideality (polyelectrolytic effect) observed in the acid dissociation equilibria of a polyion can directly be used to correct for the electrostatic nonideality for metal complexation. The potentiometric titration technique with concurrent measurements of pH and pM is most suit-... 

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