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We have controlled the structure of self-assembled systems by introducing charges (charge effect) and polymeric tails (steric effects) on a spherical–cylindrical shape of nonionic surfactant micelles. In detail, we studied the effects of a phospholipid (DL-α-phosphatidycholine dimyristol: DMPC) on the shape of nonionic surfactant micelles (penta-ethyleneglycol mono- n -dodecyl ether: C 12 E 5 ), which has been studied in terms of an aggregation number, critical micellization concentration (CMC), second virial coefficient ( A 2 ), and hydrodynamic diameter ( D H ) by laser light scattering. DMPC, DOPC (DL-α-phosphatidylcholine dioleoyl), and DMPE (DL-α-phosphoethanolamin dimyristol) molecules added in C 12 E 5 micelle solutions decrease the spontaneous curvatures, leading to an increase of the end-cap energy E c that favors micellar growth. Based on the CMC values, the total free energy per micelle of C 12 E 5 /DMPC mixtures is estimated. The free energy per micelle of C 12 E 5 /DMPC mixtures decreases as DMPC is added. This is consistent with the decrease of A 2 and the strong hydrophobicity of DMPC compared with C 12 E 5 . The average contour length, the diffusion coefficient, and the end-cap energy of mixed micelles are estimated based on the CMC and molecular specific volumes of the moiety. The end-cap energy of the mixed micelles and the average contour length increase as DMPC is added, which is also reasonable considering the molecular structure of DMPC. Furthermore, the diffusion coefficients obtained from dynamic laser light scattering are in excellent agreement with the estimated diffusion coefficients obtained from a one-dimensional growth model based on static light scattering measurements. Charged lipid (1,2-dioleoyl-3-trimethylammonium-propane) and polymer lipid (1,2-dimyristoyl- sn -glycero-3-phosphoethanolamine-[poly(ethylene glycol)]) increase the spontaneous curvatures, resulting in breaking micelles into small size. When the lipids are added, the hydrodynamic diameter of the micelles of C 12 E 5 /lipids is nearly temperature independent due to the strong charge or steric repulsion. |
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