CHARGE-FLUCTUATION FORCES BETWEEN RODLIKE POLYELECTROLYTES - PAIRWISESUMMABILITY REEXAMINED

We formulate low-frequency charge-fluctuation forces between charged c ylinders, parallel or skewed. in salt solution. At high-salt concentra tions. forces are exponentially screened. In low-salt solutions, dipol ar fluctuation energies go as R-5 or R-4; monopolar energies vary as R -1 or lnR, where R is the minimal separation between cylinder axes. Th e most important result is not the derivation of long-sought pair pote ntials but rather the demonstration that pairwise summability of rod-r od ion-fluctuation forces is easily violated under low-salt conditions .