Crosslinked polyacrylamide systems

This system is not in itself useful because the polymer is brominated and the reagents expensive but such a system has been used to generate periodic self-assembly of aggregates of acrylonitrile-derivatized gold nanocrystals (43). Kalyshyn et al. reported macroscopic patterns in crosslinked polyacrylamide with BZ waves (44). 

Resolvation may precede the preparation of polymer-immobiUzed nanoparticles. For example, the cryochemical synthesis of colloidal Ag particles is performed in acetone, which is then replaced by formamide. This dispersion is stable for a few days. The system Ag (2-5 nm) formamide is used as a solvent in the preparation of crosslinked polyacrylamide gel. Three dilferent synthetic resolvation methods are documented. In the first version, a Co-nonadecane system obtained by the cryochemical method was mixed with a solution of a polymer in nonadecane with subsequent sonication. In the second version, the nanoparticles of Co or Ni in toluene were added to a solution of low-pressure polyethylene (LPPE) in toluene at 363K. The third variant employs a toluene polymer solution cooled fi om 383K to 185K. The resulting gel-like system was mixed with nanoparticles obtained cryochemically and subjected to sonication. These techniques make it possible to virtually preclude the aggregation of particles at aU intermediate stages. However, along with the peptization and resolvation, more complex interactions of nanoparticles with the solvent may take place. 

Cationic polyacrylamide may be used in the initial treatment stages to promote rapid polymer adsorption (201). Adjustment of the pH may allow deeper penetration of the fluids in an aluminate crosslinking system prior to gelation (202). A process involving injection of alternate slugs of stoichiometrically equivalent amounts of partially hydrolyzed polyacrylamide and Al O ) has been evaluated in the laboratory permeability of sana packs were reduced by more than 96% (203). Mixtures of Al(IIl) and Zr(IV) have also been evaluated as partially hydrolyzed polyacrylamide crosslinkers (204). 

Soppimath, K.S. Kulkarni, A.R. Aminabhavi, T.M. Chemically modified polyacrylamide-g-guar gum-based crosslinked anionic microgels as pH-sensitive drug delivery systems preparation and characterization. J. Control. 

Another system similar to the microbaU is called inverse polymer emulsion. In this case, the polymer used is polyacrylamide (PAM). The inverse PAM emulsion is a W/O type of emulsion. The dispersed phase contains 6.4 to 10.5 million Daltons PAM and 1000 mg/L crosslinkers for a sample product. The external continuous phase is white oil. There is a surfactant interfacial film between the disperse phase and continuous phase, as shown in Figure 5.16. The emulsion is stable at the surface. When it is injected into a target formation, it is inverted into an 0/W type of emulsion under certain temperature and salinity, with the help of a phase inversion agent. Thus, the name inverse emulsion is used. 

Many crosslinked gel treatments are currently available for injection profile modification in secondary oil recovery waterflood operations. The gels usually consist of a water-soluble polymer, such as polyacrylamide or polysaccharide, crosslinked with a metal ion (A13+, Cr3+, Zr4+) or organic compounds. Due to the large number of systems available and possible conditions which must be considered, a rapid testing procedure must be used to screen these systems on a timely basis. 

A combination of circular dichroism, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, chemical crosslinking, and analytical ultracentrifugation studies showed that both the apo- and metallated derivatives of H21(31-mer) form two-stranded a-helical coiled coils in aqueous solution. Further characterization of these derivatives by EPR spin-label experiments helped to determine its three-dimensional backbone structure. In these studies, a Cys-21 mutant of the 31-mer coiled coil, H21/C21(31-mer), was prepared and labeled with a thiol-specific nltroxide spin label (MTSL = l-oxyl-2,2,5,5-tetramethyl-A -pyrroline-3-methyl-methanethiosulfonate) at position 21 of the peptide sequence which is the site of metal substitution in the ET heterodimer. Comparison of the low-temperature, dipolar-broadened spectrum of the spin-labeled dimer with those of magnetically dilute peptide samples yielded a backbone-to-backbone distance that was nearly identical to that of the GCN4 homodimer. Based on these results, computer modeling studies provided an estimate of the metal-to-metal distance in the ET heterodimer of m-m > 25 A. The electron-transfo properties of this system are now being studied by a combination of laser flash-quench and pulse radiolysis techniques. 

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