gregates, and their further organization in the bulk, clearly stands out as a fine example of one such approach. An alternative approach using significantly higher
molecular weight polymers, wherein the rod-block is made up of a conjugated
segment and the coil block is made up of poly(styrene) has recently been demonstrated [73, 74]. Unlike in most cases discussed so far, where using a block selective solvent that dissolves the coil-block generated the nanostructures, the prime
driving force being the aggregation (crystallization) of the rod segment, Jenekhe
et al. showed that utilizing a solvent that solubilized the rod-segment could lead to
the formation of rather unexpected hollow spherical aggregates [73]. Rod–coil
block copolymers, thus present unique opportunities that combine both the possibilities of generation and fixation of nano-size molecular objects while at the same
time permitting the retention of ordered domains within these structures.
15.8
Nanostructures from Polymerized Surfactant Assemblies
The approaches to the preparation of nanostructured polymeric materials discussed thus far have focused on the use of block copolymers as the basic molecular
entity. The domain sizes have typically been varied from ca. 10 nm to tens of mm.
To access even smaller nanostructures, one will need to exploit aggregates formed
from small molecules. Surfactants are one of the most extensively studied systems,
which are known to form a variety of organizates (Figure 15.21), typically when
dissolved in water, due to the presence of both hydrophobic and hydrophilic molecular segments. Reverse micelles and inverted mesophases are formed when they
are dissolved in a hydrocarbon solvent, in most cases requiring small amounts of
water to aid the aggregate formation. Surfactant molecules, when appropriately
modified to include a polymerizable group, either within the hydrocarbon tail or as
a part of the hydrophilic head group, or even as a counter-ion, could serve as a very
useful approach to the generation of very small nano-size structures of various
sizes and shapes, ranging from a few nanometers to 100s of nanometers. Polymerization of surfactant assemblies has been extensively studied for over two decades. The early efforts focused largely on the more stable assemblies, like vesicles,
lipid microtubules and other lamellar bilayer assemblies, and the objectives then
were largely focused on stabilizing vesicular structures by polymerization, primarily for use as drug-carriers [75]. One of the overriding problems of structural fixation of the geometrically more complex and relatively less stable nonlamellar
phases is the retention of the original phase structure during and after polymerization. Thus, it was only more recently that fixation of a variety of other nonlamellar phases, such as the hexagonal and the bicontinuous cubic phases was
successfully established. My review of this approach will focus only on some of the
more recent approaches that deal with the polymerization of the more complex
structures for the generation of nanostructured polymeric structures. Readers may
refer to several reviews that deal with this broad area of polymerizable surfactants
in order to gain a better insight into the evolution of this field [10–12, 75].
15.8 Nanostructures from Polymerized Surfactant Assemblies 507
molecular weight polymers, wherein the rod-block is made up of a conjugated
segment and the coil block is made up of poly(styrene) has recently been demonstrated [73, 74]. Unlike in most cases discussed so far, where using a block selective solvent that dissolves the coil-block generated the nanostructures, the prime
driving force being the aggregation (crystallization) of the rod segment, Jenekhe
et al. showed that utilizing a solvent that solubilized the rod-segment could lead to
the formation of rather unexpected hollow spherical aggregates [73]. Rod–coil
block copolymers, thus present unique opportunities that combine both the possibilities of generation and fixation of nano-size molecular objects while at the same
time permitting the retention of ordered domains within these structures.
15.8
Nanostructures from Polymerized Surfactant Assemblies
The approaches to the preparation of nanostructured polymeric materials discussed thus far have focused on the use of block copolymers as the basic molecular
entity. The domain sizes have typically been varied from ca. 10 nm to tens of mm.
To access even smaller nanostructures, one will need to exploit aggregates formed
from small molecules. Surfactants are one of the most extensively studied systems,
which are known to form a variety of organizates (Figure 15.21), typically when
dissolved in water, due to the presence of both hydrophobic and hydrophilic molecular segments. Reverse micelles and inverted mesophases are formed when they
are dissolved in a hydrocarbon solvent, in most cases requiring small amounts of
water to aid the aggregate formation. Surfactant molecules, when appropriately
modified to include a polymerizable group, either within the hydrocarbon tail or as
a part of the hydrophilic head group, or even as a counter-ion, could serve as a very
useful approach to the generation of very small nano-size structures of various
sizes and shapes, ranging from a few nanometers to 100s of nanometers. Polymerization of surfactant assemblies has been extensively studied for over two decades. The early efforts focused largely on the more stable assemblies, like vesicles,
lipid microtubules and other lamellar bilayer assemblies, and the objectives then
were largely focused on stabilizing vesicular structures by polymerization, primarily for use as drug-carriers [75]. One of the overriding problems of structural fixation of the geometrically more complex and relatively less stable nonlamellar
phases is the retention of the original phase structure during and after polymerization. Thus, it was only more recently that fixation of a variety of other nonlamellar phases, such as the hexagonal and the bicontinuous cubic phases was
successfully established. My review of this approach will focus only on some of the
more recent approaches that deal with the polymerization of the more complex
structures for the generation of nanostructured polymeric structures. Readers may
refer to several reviews that deal with this broad area of polymerizable surfactants
in order to gain a better insight into the evolution of this field [10–12, 75].
15.8 Nanostructures from Polymerized Surfactant Assemblies 507