Cubic phase bicontinous

Many single-chain amphiphiles form cubic phases when added to water in a given composition. Two of the most well known are didodecyl-phosphatidyl ethanolamine, and mono-olein. Figure 9.18 shows some idealized bicontinous cubic structures of the former, including typical inverse ones. This is also highly viscous and optically transparent as are most of the other cubic phases. 

Micellar cubic (OD), hexagonal columnar (ID), lamellar (2D), and bicontin-uous cubic (3D) nanostructures are formed by self-assembly of 13. For the complexes with IiC104, the ionic conductivities show discontinuous changes following the phase transitions with change of temperature or molecular structure of the dendritic moiety. For example, the conductivity of the complex of 13 with LiC104 drops from 4.6 x 10 6 to 1.2 x 10 9 S cm, along the phase transition from crystalline lamellar to micellar cubic phases. 

Related to these structures and also of relevance for the preparation of nanoparticles are some amphiphile-based nanostructured phases which do not possess any long range order. For example, another type of bicontinuous phase with relation to the inverse bicontinous cubic phases is the so-called sponge phase (L3). Its curved bilayer structure is disordered so that the water channels adopt a sponge-like structure. Sometimes this phase is referred to as a "melted cubic (v2) phase". Moreover, also dispersions of inverse micellar phases (L2) have been described which may be regarded as "melted I2 phase". Although such disordered phases do not represent a liquid crystalline phase in a strict sense they are included here since they are of relevance for nanoparticulate drug delivery purposes. 

Fig-1 Mean-field predication of the morphologies for conformationally symmetric diblock melts. Phases are labeled as S (bcc spheres), C (hexagonal cylinders), G (bicontin-uous la 3 d. cubic), L (lamellar)./a is the volume fraction... 

The classical picture of spheres, cylinders and lamellae was first challenged by the discovery of a new morphology in styrene/isoprene diblocks (Hasegawa et al. 1987) and styrene/isoprene star diblocks (Thomas et al. 1986). In the latter case the morphology has subsequently been identified as a so-called gyroid phase (Hajduk et al. 1995) this is a bicontinous nework with cubic symmetry that has now been identified in a number of different diblock systems (Schulz et al. 1994, Hajduk et al. 1995). Other non-classical phases have also been identified these include a perforated layer phase and a modulated lamellar phase (Bates et al. 1994). 

Another important aspect of adding homopolymer to a block copolymer is the ability to change morphology (without synthesis of additional polymers). Furthermore, morphologies that are absent for neat diblocks such as bicontin-uous cubic double diamond or hexagonal-perforated layer phases have been predicted in blends with homopolymers [183], although not yet observed. Transitions in morphology induced by addition of homopolymer are reviewed elsewhere [1], where a list of experimental studies on these systems can also be found. 

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