A "nano-windmill" driven by a flux of water vapour: a comparison to the rotating ATPase.

We measure the frequency of collective molecular precession as a function of temperature in the ferroelectric liquid crystalline monolayer at the water-air interface. This movement is driven by the unidirectional flux of evaporating water molecules. The collective rotation in the monolayer with angular velocities ω ~ 1 s(-1) (at T = 312 K) to 10(-2) s(-1) (at T = 285.8 K) is 9 to 14 orders of magnitude slower than rotation of a single molecule (typically ω ~ 10(9) to 10(12) s(-1)). The angular velocity reaches 0 upon approach to the two dimensional liquid-to-solid transition in the monolayer at T = 285.8 K. We estimate the rotational viscosity, γ1, in the monolayer and the torque, Γ, driving this rotation. The torque per molecule equals Γ = 5.7 × 10(-8) pN nm at 310 K (γ1 = 0.081 Pa s, ω = 0.87 s(-1)). The energy generated during one turn of the molecule at the same temperature is W = 3.5 × 10(-28) J. Surprisingly, although this energy is 7 orders of magnitude smaller than the thermal energy, kBT (310 K) = 4.3 × 10(-21) J, the rotation is very stable. The potential of the studied effect lies in the collective motion of many (>10(12)) "nano-windmills" acting "in concerto" at the scale of millimetres. Therefore, such systems are candidates for construction of artificial molecular engines, despite the small energy density per molecular volume (5 orders of magnitude smaller than for a single ATPase).

Aggregation and layering transitions in thin films of X-, T-, and anchor-shaped bolaamphiphiles at the air-water interface.

Aggregation in Langmuir films is usually understood as being a disorderly grouping of molecules turning into chaotic three-dimensional aggregates and is considered an unwanted phenomenon causing irreversible changes. In this work we present the studies of 11 compounds from the group of specific surfactants, known as bolaamphiphiles, that exhibit reversible aggregation and, in many cases, transition to well-defined multilayers, which can be considered as a layering transition. These bolaamphiphiles incorporate rigid π-conjugated aromatics as hydrophobic cores, glycerol-based polar groups and hydrophobic lateral chains. Molecules of different shapes (X-, T-, and anchor) were studied and compared. The key property of these compounds is the partial fluorination of the lateral chains linked to the rigid cores of the molecules. The most interesting feature of the compounds is that, depending on their shape and degree of fluorination, they are able to resist aggregation and preserve a monolayer structure up to relatively high surface pressures (T-shaped and some X-shaped molecules), or create well-defined trilayers (X- and anchor-shaped molecules). Experimental studies were performed using Langmuir balance, surface potential and X-ray reflectivity measurements.

Reverse vesicles from a salt-free catanionic surfactant system: a confocal fluorescence microscopy study.

We give a detailed confocal fluorescence microscopy study on reverse vesicles from a salt-free catanionic surfactant system. When tetradecyltrimethylammonium laurate (TTAL) and lauric acid (LA) are mixed in cyclohexane at the presence of a small amount of water, stable reverse vesicular phases form spontaneously. The reverse vesicular phases can be easily labeled with dyes of varying molecular size and hydrophobicity while the dyes are nearly insoluble in cyclohexane without reverse vesicles. This indicates the reverse vesicular phases can be good candidates to host guest molecules. With the help of a fluorescence microscope combined a confocal method, the features of these interesting reverse supramolecular self-assemblies were revealed for the first time. Because of the absence of electrostatic repulsions and hydration forces between adjacent vesicles, the reverse vesicles have a strong propensity to aggregate with each other and form three-dimensional clusters. The size distributions of both individual reverse vesicles and clusters are polydisperse. Huge multilamellar reverse vesicles with closely stacked thick walls (giant reverse onions) were observed. Besides the spherical reverse vesicles and onions, other supramolecular structures such as tubes have also been detected and structural evolutions between different structures were noticed. These interesting supramolecular self-assemblies form in a nonpolar organic solvent may serve as ideal micro- or nanoreaction centers for biological reactions and synthesis of inorganic nanomaterials.

Reversible aggregation of X-shaped bolaamphiphiles with partially fluorinated lateral chains at the air/water interface.

Langmuir films of four X-shaped bolaamphiphiles were studied using surface pressure and Kelvin potential measurements, Brewster angle microscopy and X-ray reflectivity. The partially fluorinated bolaamphiphiles exhibit an unusual reversibility and reproducibility of Langmuir isotherms, and create very stable and well defined single- or triple layers which can be transferred to solid substrates.