Charge effects on density fluctuations in stretched gels

We present a theoretical analysis of density fluctuations in weakly charged polymer gel swollen in poor solvent and subjected to uniaxial extension. The calculated structure factor is suppressed along the stretching axis and enhanced along the perpendicular directions. In the absence of added salt, plots of the isointensity lines produced complicated contours with a maximum at a finite wave vector in the plane normal to the extension axis. As screening increases with the addition of salt, these contours are transformed into butterfly patterns oriented along a direction perpendicular to that observed in uncharged gels.