Continuous isotropic-nematic liquid crystalline transition of F-actin solutions

The phase transition from the isotropic (I) to nematic (N) liquid crystalline suspension of F-actin of average length ł> or =3 microm was studied by local measurements of optical birefringence and protein concentration. Both parameters were detected to be continuous in the transition region, suggesting that the I-N transition is higher than first order. Thus we report experimental evidence for a continuous I-N transition for a suspension of rodlike macromolecules. Our findings are consistent with a recent theory by Lammert, Rokhsar, and Toner [Phys. Rev. Lett. 70, 1650 (1993)], predicting that the I-N transition may become continuous due to suppression of disclinations.