J. Appl. Cryst.の発刊に際して

Low Molecular Mass Gelators of Organic Liquids and the Properties of Their Gels

Cationic liposomes complexed with DNA (CL-DNA) are promising synthetically based nonviral carriers of DNA vectors for gene therapy. The solution structure of CL-DNA complexes was probed on length scales from subnanometer to micrometer by synchrotron x-ray diffraction and optical microscopy. The addition of either linear lambda-phage or plasmid DNA to CLs resulted in an unexpected topological transition from liposomes to optically birefringent liquid-crystalline condensed globules. X-ray diffraction of the globules revealed a novel multilamellar structure with alternating lipid bilayer and DNA monolayers. The lambda-DNA chains form a one-dimensional lattice with distinct interhelical packing regimes. Remarkably, in the isoelectric point regime, the lambda-DNA interaxial spacing expands between 24.5 and 57.1 angstroms upon lipid dilution and is indicative of a long-range electrostatic-induced repulsion that is possibly enhanced by chain undulations.

https://science.sciencemag.org/content/sci/275/5301/810.full.pdf

Structure of DNA-Cationic Liposome Complexes: DNA Intercalation in Multilamellar Membranes in Distinct Interhelical Packing Regimes

In certain surfactant solutions, such as aqueous cetyltrimethylammonium bromide (CTAB) in 0.1 M KBr, the amphiphiles are found to assemble reversibly into long, flexible worm-like micelles. Above a few per cent surfactant, these form an entangled viscoelastic fluid, reminiscent of a polymer solution. The authors review some recent experimental and theoretical progress concerning the equilibrium statistics and dynamics of these systems, which differ from normal polymer solutions in that the chains can break and reform reversibly.

http://iopscience.iop.org/article/10.1088/0953-8984/2/33/001/pdf

Statics and dynamics of worm-like surfactant micelles

Journal of Physics Condensed Matter: Preface

Laboratoire d'Ultrasona et de Dynamique des Fluides Complexes, URA du CNRS No. 851, Universit6 Louis Pasteur, 4 rue Blaise Pascal, 67070 Strasbourg cedex, France, Groupe de Dynamique des Phases Condensi?es, URA du CNRS No. 233, Universite des Sciences et Techniques du Languedoc, 34095 Montpellier cedex 05, France, and Laboratoire de Physique Statistique, associ6 au CNRS, 24 rue Lhomond, 75231 Paris cedex 05, France

Entangled versus multiconnected network of wormlike micelles

Linear rheology of entangled wormlike micelles

We report on the linear and nonlinear rheology of surfactant solutions of elongated wormlike micelles. The surfactant solutions placed under scrutiny are made of cetylpyridinium chloride (CP + , Cl - ) and sodium salicylate (Na + , Sal - ) diluted in 0.5 M NaCl-brine. Both semidilute and concentrated regimes of entangled micelles were investigated. Rheological experiments were performed at ambient temperature (T=25 o C) for surfactant concentrations O=1%-30%. When submitted to a steady shear high enough (for shear rate γ typically higher than 1-10 s -1 ) the solutions of wormlike micelles exhibit a first-order isotropic-to-nematic transition for all surfactant concentrations O≥6%. The transition is characterized by a true plateau in the shear rate dependence of the shear stress σ (γ). For γ above the transition rate γ 1/N , σ remains constant at σ 1/N . In the concentrated regime, the transition is clearly first-order. However, the first-order character weakens upon increasing dilution, suggesting that at some critical concentration O c it becomes second-order. Below O c , the transition ceases to occur: the σ(γ)-behavior rather indicates a progressive and homogeneous orientation of the micelles throughout the sample. Moreover, in the two-phase domain (where both isotropic and nematic phases coexist) a characteristic transient behavior of the shear stress σ (γ) measured at constant γ 1/N as a function of time has been observed and investigated in detail. In agreement with the picture of the first-order phase transition (in the domain of metastability), the transient behavior could be interpreted quantitatively in terms of nucleation and one-dimensional growth process. These results are finally compared to recent predictions by Spenley, Cates and MacLeish (Ref, [7]) who described the nonlinear rheology of wormlike micelles in terms of mechanical instability of shear-banding type

/pdf/isotropic-to-nematic-transition-in-wormlike-micelles-under-1vz24mcao1.pdf

Isotropic-to-nematic transition in wormlike micelles under shear

Experimental investigations on the flexibility of elongated cetylpyridinium bromide micelles

The growth of cetylpyridinium micelles in high NaBr concentration aqueous solutions is observed by the use of quasi-elastic light scattering. The variations of the mean hydrodynamic radius, are measured over wide ranges of temperature (27 < T < 75 C), detergent concentration (1.5 x 10/sup -3/-40 x 10/sup -3/ M), and added NaBr concentration (0.2, 0.4, 0.6, and 0.8 M). These results are interpreted in the frame of a multiple equilibrium description of the micellar elongation. This classical description is rewritten in order to incorporate the counterion influence through the use of the crude ion binding approximation. A quantitative geometrical model is developed for the elongated micelles which are known to have the shape of long flexible spherocylinders. The obtained relation between the mean hydrodynamic radius and the mean aggregation number allows qualitative comparison of the experimental results to the predictions of the theory. 26 references.

Grégoire Porte

Papers

Entangled versus multiconnected network of wormlike micelles

Linear rheology of entangled wormlike micelles

Isotropic-to-nematic transition in wormlike micelles under shear

Experimental investigations on the flexibility of elongated cetylpyridinium bromide micelles

Growth and size distributions of cetylpyridinium bromide micelles in high ionic strength aqueous solutions