In this paper, we give an overview of our studies by static and time-resolved X-ray diffraction of inverse cubic phases and phase transitions in lipids. In [section sign] 1, we briefly discuss the lyotropic phase behaviour of lipids, focusing attention on non-lamellar structures, and their geometric/topological relationship to fusion processes in lipid membranes. Possible pathways for transitions between different cubic phases are also outlined. In [section sign] 2, we discuss the effects of hydrostatic pressure on lipid membranes and lipid phase transitions, and describe how the parameters required to predict the pressure dependence of lipid phase transition temperatures can be conveniently measured. We review some earlier results of inverse bicontinuous cubic phases from our laboratory, showing effects such as pressure-induced formation and swelling. In [section sign] 3, we describe the technique of pressure-jump synchrotron X-ray diffraction. We present results that have been obtained from the lipid system 1:2 dilauroylphosphatidylcholine/lauric acid for cubic-inverse hexagonal, cubic-cubic and lamellar-cubic transitions. The rate of transition was found to increase with the amplitude of the pressure-jump and with increasing temperature. Evidence for intermediate structures occurring transiently during the transitions was also obtained. In [section sign] 4, we describe an IDL-based 'AXcess' software package being developed in our laboratory to permit batch processing and analysis of the large X-ray datasets produced by pressure-jump synchrotron experiments. In [section sign] 5, we present some recent results on the fluid lamellar-Pn3m cubic phase transition of the single-chain lipid 1-monoelaidin, which we have studied both by pressure-jump and temperature-jump X-ray diffraction. Finally, in [section sign] 6, we give a few indicators of future directions of this research. We anticipate that the most useful technical advance will be the development of pressure-jump apparatus on the microsecond time-scale, which will involve the use of a stack of piezoelectric pressure actuators. The pressure-jump technique is not restricted to lipid phase transitions, but can be used to study a wide range of soft matter transitions, ranging from protein unfolding and DNA unwinding and transitions, to phase transitions in thermotropic liquid crystals, surfactants and block copolymers.

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Addition of divalent cations to a solution of a naphthalene-diphenylalanine that forms worm-like micelles at high pH results in the formation of a rigid, self-supporting hydrogel.

We report a new method for the production of ordered 3D metal-nanowire network fi lms. The method utilizes a coating of lipid inverse cubic phase as the template for electrodeposition. We have produced platinum fi lms which show a previously unreported "single diamond" nanoarchitecture with Fd3m symmetry and a lattice parameter of approximately 132 Å. Their electrochemically accessible surface area is estimated to be > 40 m 2 g − 1 . The new methodology represents a facile route to 3D cubic nanostructures and thus provides a synthetically attractive route to the preparation of 3D nanostructured devices with diverse potential applications.Nanostructured metals and semiconductors have many important technological uses. They are commonly produced by templating soft materials such as diblock copolymers [ 1 ] or lyotropic liquid-crystal phases that form by amphiphile selfassembly. [ 2 ] These soft templates exhibit a range of different nanostructures that include hexagonal phases, based on simple 2D arrays of cylinders, and the more complex 3D bicontinuous cubic structures, based on mathematical surfaces known as the triply periodic minimal surfaces. Three different symmetries of bicontinuous cubic structure have been reported, based on the gyroid (G), double diamond (D), and primitive (P) minimal surfaces, which correspond to the space groups Ia3d (Q 230 ), Pn3m (Q 224 ), and Im3m (Q 229 ), respectively. In the inverse (Type II) cubic phases whose use as an electrochemical template is described here, the minimal surface lies at the centre of a continuous amphiphile bilayer which separates two continuous, but non-intersecting, water channel networks.Direct electrodeposition of nanostructured materials from normal topology (Type I) lyotropic liquid-crystal phases was fi rst reported by Attard and co-workers in 1997. [ 3 ] The method represents a reliable route to a range of nanostructured materials [ 4 ] under conditions that are suffi ciently mild to preserve the lyotropic mesophase structure during the electrodeposition process. Reported uses of direct electrochemical lyotropic templating using the normal (Type I) hexagonal phase are numerous, but in contrast there is only one reported case involving electrochemical templating from normal topology cubic phases. [ 5 ] There are two main reasons for this: fi rst, the cubic phase typically occupies only a small region of the composition-temperature phase diagram, and second, perhaps more importantly, the bicontinuous cubic phases are much more viscous than their hexagonal counterparts; [ 6 ] the combined result being that electrochemical templating from a cubic phase via the true liquid-crystal templating route is very difficult to achieve in practice.Nonetheless, the production of nanostructured materials with a bicontinuous cubic morphology is highly desirable, and even though the lyotropic liquid-crystal templating route has not been used extensively in this way, some alternative (albeit multi-step) approaches have been reported in the literature. The resulting bicon...

This paper describes time-resolved x-ray diffraction data monitoring the transformation of one inverse bicontinuous cubic mesophase into another, in a hydrated lipid system. The first section of the paper describes a mechanism for the transformation that conserves the topology of the bilayer, based on the work of Charvolin and Sadoc, Fogden and Hyde, and Benedicto and O'Brien in this area. We show a pictorial representation of this mechanism, in terms of both the water channels and the lipid bilayer. The second section describes the experimental results obtained. The system under investigation was 2:1 lauric acid: dilauroylphosphatidylcholine at a hydration of 50% water by weight. A pressure-jump was used to induce a phase transition from the gyroid ͑Q II G ͒ to the diamond ͑Q II D ͒ bicontinuous cubic mesophase, which was monitored by time-resolved x-ray diffraction. The lattice parameter of both mesophases was found to decrease slightly throughout the transformation, but at the stage where the Q II D phase first appeared, the ratio of lattice parameters of the two phases was found to be approximately constant for all pressure-jump experiments. The value is consistent with a topologypreserving mechanism. However, the polydomain nature of our sample prevents us from confirming that the specific pathway is that described in the first section of the paper. Our data also reveal signals from two different intermediate structures, one of which we have identified as the inverse hexagonal ͑H II ͒ mesophase. We suggest that it plays a role in the transfer of water during the transformation. The rate of the phase transition was found to increase with both temperature and pressure-jump amplitude, and its time scale varied from the order of seconds to minutes, depending on the conditions employed.