The behavior of amphoteric hydrogels based on vinyl 2-aminoethyl ether and sodium acrylate under the influence of pH, ionic and solvent composition, temperature, and dc electric field has been studied. The excess of positive or negative charges causes the swelling of polyampholyte networks. At the isoelectric point (IEP) the polyampholyte gel is in shrunken state due to the formation of intraionic contacts. An “antipolyelectrolyte” effect is observed at the IEP:  the gel considerably swells in the presence of neutral salt. The condensation of bulky anions to positively charged groups of polyampholyte gels enhances the shrinking rate. The shrinking process can be described by apparent first-order kinetics. Polyampholyte gel shrinks with the increasing of temperature when the overall charge is neutral (IEP), while it shrinks effectively with addition of acetone when the overall charge is negative. In dependence of the network net charge, the ionic strength of the external solution, and the direction of dc electric field, the polyampholyte specimen can bend, shrink, swell, and oscillate. Under the same conditions, positively and negatively charged precursors of polyampholytes only swell or shrink. Shrinking and swelling of amphoteric gels are determined by the concentration of mobile ions inside and outside of gel. To interpret the oscillation phenomenon the Donnan equilibrium and water hydrolysis are utilized. The realization of “antipolyelectrolyte” or polyampholyte and polyelectrolyte effects is probably the driving force of gel behavior. The oscillation−relaxation regimes are characterized by numerical value of 1/τ (where τ is the relaxation period). The phase portraits of all oscillation−relaxation curves are in good agreement with the Faraday law.

331Besides the surface activity of the amino resins used, the electrostatic interactions between the protonated amino resin and the negatively charged organic phase can be considered as driving force. Thereby the reaction rate of the polycondensation in the boundary phase is increased contrary to the volume phase with the result of capsule wall formation.These conceptions are supported by the fact t h a t in the presence of other non-reactive tensides no microcapsules will be formed. These tensides occupy the phase boundaries and prevent the enrichment of polycondensation active b u t less surface active amino resins.A detailled discussion of the mechanism of capsule formation will be given in connection with the discussion of surface activity of amino resins [Is]. The preparation of microcapsules is also possible with unmodified, nonetherified $IF-resins. In this case the suitable reaction conditions have to be evaluated by preliminary tests. Under t h e applied reaction conditions, pure urea-formaldehyde resins were not capable of wall formation.Results of biological testing of MP-microcapsules will be published elsewhere [ 2 4 ] .

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Isotachophoresis and viscometric measurements were performed on aqueous dispersions of non-stoichiometric polyelectrolyte complexes in order to elucidate the surface charge situation of the complex particles in dependence on component charge density, ratio of cationic to anionic groups in the complex, and pH and ionic strengths of the ambient medium. Components for complex formation were acryl-based anionic and cationic polyelectrolytes of the pendent type. From our results, an amphoteric character of the polyelectrolyte complex particles can be concluded, with an isoelectric point characterized by zero mobility and a minimum in reduced viscosity r/spec/c of the particle dispersion, and with the sign of net surface charge depending on ambient pH and component charge density. The influence of ionic strength on the rlspJc vs pH plots can be interpreted by assuming a competition between salting-out and electrostatic shielding effects. No correlation could be established between the overall molar ratio of cationic to anionic groups and the isoelectric point of the complex particles, which obviously indicates a different composition of "surface" and "bulk" of the polyelectrolyte complex particles.

Summary:The physico-chemical and rheological properties of low acyl gellan (LAG) were investigated in aqueous solutions of various salts.1 H NMR spectroscopic study of LAG was conducted in salt-free solutions at different temperatures. FTIR spectra revealed that the characteristic bands of both asymmetric and symmetric carboxylate groups are shifted to higher frequency regions as a result of effective surrounding of glucuronate residuesby mono-and divalent cations of salts. According to viscometricresults the effectiveness of salts to enhance gelation of gellan changes in the following order: BaCl 2 > CaCl 2 % MgCl 2 > KCl > NaCl. The behavior of LAG in model aqueous-salt solutions and real oilfield saline water was evaluated by means of rheological measurements.The shear rate (and effective viscosity) of 0.5 wt.% gellan solution versus shear stress increases (and decreases) in the sequence of CaCl 2 > MgCl 2 > KCl > NaCl demonstrating the pseudo plastic character. The sol-gel and liquid-solid phase transitions of gellan solutionswere observed upon addition of oilfield water containing 73 g Á L À1 of alkaline and alkaline earth metal ions. The effectiveness of salts to induce the separation of liquid and solid phases changes in the sequence: NaCl > KCl > MgCl 2 % CaCl 2 % BaCl 2 . The mechanical properties of gellan gels under compression were studied and the Young modules and breaking stresses were found. Sol-gel transition of gellan solution inside of sand pack model was demonstrated. The hydrodynamic behavior of 0.5 wt.% gellan solution injected into the sand pack model with high (20 d) and low (2 d) permeability is useful to model the oil reservoirs in the process of enhanced oil recovery. The influence of clay minerals -bentonite on the rheological characteristics of gellan solution was evaluated for simulation of drilling mud ability to carry up the drilled rock particles from the bottomhole of the well to the surface.