Structural Properties and Phase Behavior ... 25chain architecture and interspecies interactions. The interplay between
polymer/solvent interaction driving the macrophase separation and intra chain
A/B repulsion inducing microphase separation is demonstrated in the
simplified symmetrical limit. Mismatch of monomer/solvent interaction due to
differences in the values of as and bs to mimic the hydrophilic and
hydrophobic nature of A and B blocks, respectively, was also considered. The
focus, however, was made more on the case of partially charged DCPs in
solution to evaluate the impact of long range electrostatic interaction
depending on the degree of ionization of the hydrophilic charged block and the
ionic strength inhibiting the long range repulsion between charged monomers.
The partial structure factor due to the A block contribution exhibits a peak at a
finite wave vector qm indicating the presence of a microstructure of
characteristic size qm^1. When the conditions of microphase separation are
approached, this peak moves to higher q’s while its height diverges. For a
charged hydrophilic block, a strong compatibility enhancement is induced and
scrutinized by considering both the position qm and the height Saa(qm) of the
peak. Consistent with experimental findings, the peak position decreases while
its height Saa(qm) drops significantly with increasing f. The added salt
concentration salt yields also consistent tendencies between RPA formalism of
the SANS experiments. Adding more salt shifts the peak to smaller q’s while
its height increases. The RPA has been used extensively to analyze small angle
neutron scattering experimental data from block copolymer systems. However,
the case of dispersed partially charged DCPs in solution has not been given
sufficient attention in spite of its importance in practical applications. Indeed,
for the development of efficient drug delivery carries, it is necessary to control
all parameters responsible for aggregation. Moreover, in the process of
delivering the drugs, micelles should dissociate into dispersed DCPs for a safe
evacuation avoiding the risks of aggregation again and toxicity. According to
[28], the region where the RPA can be applied for such DCPs is quite large in
view of the fact that long range electrostatic repulsion between charged blocks
introduces significant compatibility enhancements inhibiting aggregation and
promoting DCPs dispersion into the solution. More efforts are needed both on
the experimental and theoretical fronts to explore in details the structural
properties and phase behavior of partially charged DCPs dispersed in solution
prior to aggregation.
A brief discussion is presented under aggregation conditions focusing on
the critical micelle concentration mic and the aggregation number Nag.
Depending on the micelle’s conditions, different scaling approaches are