The isotropic-cholesteric phase transition of filamentous virus   suspensions as a function of rod length and charge
  The viruses studied are genetically engineered, charged, semiflexible filamentous bacteriophages that are structurally identical to M13 virus, but differ either in contour length or surface charge. While varying contour length (L) we assume the persistence length (P) remains constant, and thus we alter the rod flexibility (L/P). Surface charge is altered both by changing solution pH and by comparing two viruses, fd and M13, which differ only by the substitution of one charged for one neutral amino acid per virus coat protein. We measure both the isotropic and cholesteric coexistence concentrations as well as the nematic order parameter after unwinding the cholesteric phase in a magnetic field. The isotropic-cholesteric transition experimental results agree semi-quantitatively with theoretical predictions for semiflexible, charged rods. 
Kirstin Purdy and Seth Fraden