The lyotropic phase behaviour of ester quaternary surfactants

Impact of Additives on the Microstructural Properties of DIDMAMS Bilayers: Studied by Molecular Dynamics Simulations

To further understand the mechanism of the impact of perfume raw materials (PRMs) such as allyl heptoate (AHT) and cashmeran (CMR) on distearoyl isopropyl dimethylammonium methyl sulfate (DIDMAMS) bilayers, 90 ns molecular dynamics simulations were conducted to investigate the structure of bilayers consisting of DIDMAMS and PRMs at 350 K on the molecular scale. Structural properties such as density profiles, order parameters, radial distribution functions (RDFs), and bilayer thickness were analyzed. The bilayers appear to be the structure of the ripple phase whether PRMs are added or not. The RDF and density profiles show that CMR molecules tend to locate in the region close to head groups and AHT molecules prefer to uniformly distribute among hydrocarbon chains. The special distribution of CMR molecules results in hydrocarbon chains twining around CMR molecules. The existence of CMR molecules between bilayers and the consequent highest bilayer thickness may be the main cause of higher viscosity. We expect that this work can help to screen stable vesicular formula and understand the relationship between microstructures of the vesicles and macroscopic fluidic properties.

Lyotropic Lamellar Structures of a Long-Chain Imidazolium and Their Application as Nanoreactors for X-ray-Initiated Polymerization

The lyotropic behavior of the ternary system formed by 1-tetradecyl-3-methylimidazolium chloride, 1-decanol, and water is investigated. A lamellar mesophase is formed for a wide range of compositions and is characterized by polarized optical microscopy, low-temperature scanning electron microscopy, small- and wide-angle X-ray scattering with synchrotron radiation, and differential scanning calorimetry. This phase presents onionlike structures. Two lamellar structures are formed: an L_α mesophase between 25 and 50 °C, with an isobaric thermal expansivity of the bilayer thickness of -3.2 × 10^-3 K^-1, and a lamellar gel phase, when the temperature decreases below 25 °C. This new medium is employed to perform in situ X-ray-initiated polymerization of N-isopropylacrylamide. When the monomer is incorporated in the lamellar structure, it is distributed between the water layer and bilayer interface and its polymerization can be followed by variations in the diffractograms with time.

Temperature-dependent structural changes on DDAB surfactant assemblies evidenced by energy dispersive X-ray diffraction and dynamic light scattering

Cationic amphiphile DDAB (dimethyl-dioctadecyl-ammonium-bromide) can spontaneously form water-dispersed and solid supported mimicking biomembrane structures as well as valuable DNA delivery vehicles whose shape, stability and transfection efficiency can be easily optimized on varying temperature, water content and chemical composition. In this framework, disclosing the thermotropic behavior of DDAB assemblies can be considered as an essential step in conceiving and developing new non-viral vector systems. Our work has been focused primarily on understanding the mesophase structure of silicon supported DDAB thin film on varying temperature at constant relative humidity by energy dispersive X-ray diffraction (EDXD). Diffraction results have then been employed in providing a more comprehensive dynamic light scattering (DLS) analysis of corresponding thermotropic water dispersed vesicles made up of DDAB alone and in combination with helper lecithin DOPC (1,2-dioleoyl-sn-glycero-3-phosphatidylcholine) liposomes. We found that above 55 °C silicon-supported DDAB films undergo a significant thinning effect, whilst DDAB-water vesicles exhibit a reduction in size polydispersity. Upon cooling to 25 °C a distinct silicon supported DDAB mesophase, exhibiting a relative humidity-dependent spacing, has been pointed out, and modeled in terms of a lyotropic metastable gel-crystalline phase.DDAB/DOPC-water vesicles show a temperature-dependent switching in size distribution, leading to promising biomedical applications.