Structure and universal property of nonionic surfactant and phospholipid mixed micelle in the semidilute regime

Abstract

On the mixed system of nonionic surfactant $C_{12}E_5$ (Pentaethyleneglycol mono n-dodecylether) and phospholipids molecules DMPC (DL-a-phosphatidylcholine Dimyristoyl) in the semidilute regime, we found that dilute-semidilute transition concentration $(c^*)$ decreased as increasing DMPC`s quantities. In spite of having different transition point, their viscosity and correlation length followed the scaling law $(η-η_o)~(c/c^*)^{1.91+/-0.03}$ and $(ξ/ξ^*)~ (c/c^*)^{0.585+/-0.005}$ in the viscosity measurements and DLS (Dynamic Light Scattering) experiment when scaled using solvent viscosity $(η_o)$ and concentration $(c^*)$ and correlation length $(ξ^*)$ at transition point. These are different from wormlike micellar solution with counterions in which exponent values of the viscosity and correlation length change according to salt`s quantities. These exponents in the experiments are almost same as $η ~ c^2$ and $ξ ~ c^{-0.5}$ that are results from the mean field theory applied to the branched wormlike micelle system with the sliding effect. As the result, the semidilute regime of nonionic surfactant /phospholipids mixed systems is expected to be the network structure. Though transition point is controlled by DMPC`s quantities, their properties are all influenced by the sliding and break-recombination effect.