Buckling, fluctuations, and collapse in semiflexible polyelectrolytes

We present a systematic statistical mechanical analysis of the conformation al properties of a stiff polyelectrolyte chain with intrachain attractions that are due to counterion correlations. We show that the mean-field soluti on corresponds to an Euler-like buckling instability. The effect of the con formational fluctuations on the buckling instability is investigated, first , qualitatively, within the harmonic ("semiclassical") theory, then, system atically, within a 1/d expansion, where d denotes the dimension of embeddin g space. Within the "semiclassical" approximation, we predict that the effe ct of fluctuations is to renormalize the effective persistence length to sm aller values, but not to change thenature of the mean-field (i.e., buckling ) behavior. Based on the 1/d expansion we are, however, led to conclude tha t thermal fluctuations are responsible for a change of the buckling behavio r which is turned into polymer collapse. A phase diagram is constructed in which a sequence of collapse transitions terminates at a buckling instabili ty that occurs at a place that varies with the magnitude of the bare persis tence length of the polymer chain, as well as with the strength and range o f the attractive potential. [S1063-651X(99)04708-X].