Precipitation polyionic solutions

For most samples investigated, the temperature interval during which precipitation occurs, is quite small, i.e. 2-5 °C, as shown in Fig. 10. The upper dotted curve in Fig. 10 represents the temperature dependence which would be expected for the polyion solution if no precipitation occurs and if the fraction of free counterions would not increase with temperature, i.e. the increase in conductivity is solely caused by the decrease of the viscosity of water. Act may be utilized to determine the effective charge density f by the equation... 

Sodium sulfadiazine and sulfafurazole diolamine in therapeutic doses (1 mg) added to 5% dextrose and 5% dextrose and saline solution have been found to be compatible, yet when added to commercial polyionic solutions (such as Abbott lonosol B, Baxter electrolyte No.2) both rapidly form heavy precipitates. pH and temperature are two vital parameters, but the pH effect is not simply a solubility-related phenomenon. Polyionic solutions of a lower initial pH (4.4-4.6) cause crystallisation of sulfafurazole at room temperature within 2.5 h, the pH values of the admixtures being 5.65 and 5.75 respectively. Other solutions with slightly higher initial pH levels (6.1-6.6) formed crystals only after preliminary cooling to 20°C at pH values from 4.25 to 4.90. If the temperature remains constant, the intensity of precipitation varies with the composition and initial pH of the solution used as a vehicle. 

The precipitation of polyelectrolytes by the addition of multivalent counterions may be explained in these terms. When there are no multivalent ions in solution there is a strong repulsive force between polyions and the osmotic pressure is large. The solubility of polyions is a result of these repulsive forces. 

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]. 

Using the b-1 route, PPV LB films were successfully fabricated [35], The precursor polymer of PPV was prepared according to ref.27. Anionic amphiphile 2C12SUC was purchased from Sogo Pharmaceutical Co. and used without further purification. An aqueous solution of the precursor polymer was added dropwise to an aqueous 2C12SUC solution. Then, the precursor-anionic amphiphile polyion complex was precipitated. The precipitates were filtered and washed with deionized... 

Counter ions play a decisive role in the isolation of polyoxoanions. Ions occurring in negligible amounts in solution such as [Mo6Oi9]2 can be precipitated from aqueous solution with the cation [(C4H9)4N]+ while major species remain in solution. Different ions can be isolated at the same pH by using different cations. Conditions favorable for the precipitation of some polymolybdates from aqueous solution with the cations NH4, [(NH2)3C]+, [(CH3)4N]+, and [(n-C4H9)4N)]+ have been determined (98). The polyions isolated with these and some other cations are listed in Table VII. Most of these polyions have been structurally characterized. 

In close vicinity to the salting out phase transition, the effective charge density was determined by conductivity measurements in combination with the known and estimated electrophoretic mobilities of the counterions and the polyions, respectively. The procedure is based on the fact that, shortly before the precipitation of the polyion, the conductivity comprises contributions of polyions, free counterions and added salt. After precipitation of the polyion by reducing the temperature the conductivity is given solely by the supernatant aqueous salt solution, thus the difference Act is due to polyions and free counterions... 

There is ample experimental evidence that identically charged polymers in the presence of ordinary univalent counterions have a tendency to form loose clusters in solution [65-70], and we have asked whether the attractive polyion-polyion potential discussed in Sec. Ill can stabilize a finite-sized cluster of parallel rodlike polyions without leading to precipitation [71,72]. The theoretical problem is complicated by a failure of pairwise additivity the work of assembling N polyions is not equal to the work of assembling the N(N — l)/2 polyion pairs, each in isolation from the other N 2 polyions. To be sure, the Debye-Htickel interaction term for a cluster (the generalization of Eq. 5 above) takes the form of a pairwise sum over polyions,... 

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). 

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]. 

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