can be formed in a simple A-B amphipihile system. Such structures are likely to be
more long-lived in block copolymer systems due to their slower dynamics and
kinetics. This opens up exciting possibilities for achieving well-defined intricate
structures in simple two-component systems. However, in order to take full advantage
of these possibilities, the kinetic pathways and the kinetics of block copolymer
systems must be understood. On a more fundamental note, kinetic pathways in selfassembled systems and kinetic control are integral parts of the understanding and
intelligent use of these materials in a nanotechnological setting. Their importance can
be understood in much the same way as the importance of kinetics in chemical
reactions and how an understanding of kinetics has helped design products and
extended the use of both inorganic and organic chemistry in the twentieth century.
Apart from kinetic control and manipulation of structures, kinetics is also essential in
controlling the size and stability of nanoparticles formed by block copolymers for
their use as, e.g., drug delivery systems [11] or in industrial applications as
components of emulsions or non-foaming surfactant systems [12]. A great deal of
effort must therefore be made towards studies assessing kinetic processes and in
development of suitable experimental techniques.
Time resolved SAXS/SANS allow a structural observation of kinetic processes
on the nanoscale (1–100 nm) on a time scale ranging from milliseconds to hours.
This allows micellar kinetics to be followed in real time, giving direct structural
information of the process and its evolution. Synchrotron SAXS can reach smaller
time scales and exhibits better resolution compared to neutron-based methods.
However, SANS offers the possibility for contrast variation via simple H/D
exchange chemistry, which opens up a world of possibilities for the investigation
of kinetics in soft matter systems, in particular transport and exchange processes
that otherwise would be invisible in scattering experiments. As most of these
techniques have become available over recent years with advancements in both
instrumentation and sample environments, there is a need for an overview of the
development and the possibilities that are now available in the field of soft matter in
general and micellar systems in particular.
To this end, in this review we focus on the study of kinetic processes in micellar
systems using time-resolved SAXS and SANS. Particular attention will be given to
block copolymer systems and novel methodologies to study the kinetics using
TR-SAXS or TR-SANS. Secondly, labeling experiments to study equilibrium kinetics using SANS will be thoroughly presented. While several related reviews have
been presented [13–19], these contributions have been mostly devoted to low molecular weight surfactant systems and/or only focused on the general methodology of
either SANS or SAXS. Here, we will give a thorough overview of results on block
copolymer systems and show how both SAXS and SANS can be used as complementary methods to study kinetic processes in these systems. We will discuss both the
strength and weaknesses of these methods and compare the results with investigations
using other methods. Small-angle scattering methods are low-resolution methods that
give ensemble averages over a large number of (most often orientational averaged)
particles. The technique therefore requires a significant effort in data modeling and
the development of methodology to analyze the data and thereby optimize the
information content. Significant attention is therefore devoted to data modeling, in
Kinetics of Block Copolymer Micelles Studied by Small-Angle Scattering Methods
57
more long-lived in block copolymer systems due to their slower dynamics and
kinetics. This opens up exciting possibilities for achieving well-defined intricate
structures in simple two-component systems. However, in order to take full advantage
of these possibilities, the kinetic pathways and the kinetics of block copolymer
systems must be understood. On a more fundamental note, kinetic pathways in selfassembled systems and kinetic control are integral parts of the understanding and
intelligent use of these materials in a nanotechnological setting. Their importance can
be understood in much the same way as the importance of kinetics in chemical
reactions and how an understanding of kinetics has helped design products and
extended the use of both inorganic and organic chemistry in the twentieth century.
Apart from kinetic control and manipulation of structures, kinetics is also essential in
controlling the size and stability of nanoparticles formed by block copolymers for
their use as, e.g., drug delivery systems [11] or in industrial applications as
components of emulsions or non-foaming surfactant systems [12]. A great deal of
effort must therefore be made towards studies assessing kinetic processes and in
development of suitable experimental techniques.
Time resolved SAXS/SANS allow a structural observation of kinetic processes
on the nanoscale (1–100 nm) on a time scale ranging from milliseconds to hours.
This allows micellar kinetics to be followed in real time, giving direct structural
information of the process and its evolution. Synchrotron SAXS can reach smaller
time scales and exhibits better resolution compared to neutron-based methods.
However, SANS offers the possibility for contrast variation via simple H/D
exchange chemistry, which opens up a world of possibilities for the investigation
of kinetics in soft matter systems, in particular transport and exchange processes
that otherwise would be invisible in scattering experiments. As most of these
techniques have become available over recent years with advancements in both
instrumentation and sample environments, there is a need for an overview of the
development and the possibilities that are now available in the field of soft matter in
general and micellar systems in particular.
To this end, in this review we focus on the study of kinetic processes in micellar
systems using time-resolved SAXS and SANS. Particular attention will be given to
block copolymer systems and novel methodologies to study the kinetics using
TR-SAXS or TR-SANS. Secondly, labeling experiments to study equilibrium kinetics using SANS will be thoroughly presented. While several related reviews have
been presented [13–19], these contributions have been mostly devoted to low molecular weight surfactant systems and/or only focused on the general methodology of
either SANS or SAXS. Here, we will give a thorough overview of results on block
copolymer systems and show how both SAXS and SANS can be used as complementary methods to study kinetic processes in these systems. We will discuss both the
strength and weaknesses of these methods and compare the results with investigations
using other methods. Small-angle scattering methods are low-resolution methods that
give ensemble averages over a large number of (most often orientational averaged)
particles. The technique therefore requires a significant effort in data modeling and
the development of methodology to analyze the data and thereby optimize the
information content. Significant attention is therefore devoted to data modeling, in
Kinetics of Block Copolymer Micelles Studied by Small-Angle Scattering Methods
57