Effect of the Mobility of Charged Units on the Microphase Separation in Amphiphilic Polyelectrolyte Hydrogels

Abstract

The effect of the migration of charged units on the structure of hydrophobically modified polyelectrolyte gels swollen by D(2)O was studied by small-angle neutron scattering on an example of gels of terpolymers of acrylic acid, n-dodecylacrylate, and 2-acrylamido-2-methyl-1-propanesulfonic acid (quenched charged units) and gels of copolymers of partially neutralized acrylic acid and n-dodecylacrylate (annealed charged units). The content of charged units did not exceed 20 mol %, so that the electrostatic repulsion was too weak to disrupt the hydrophobic domains formed by self-assembled n-dodecyl chains, which was evidenced by NMR data. It was shown that upon increasing the charge content both types of gels undergo microphase separation with the formation of hydrophobic clusters consisting of several densely packed hydrophobic domains and hydrophilic regions swollen by water, where most of the charged repeat units and counterions are located. The dimensions of the nanostructure of the gels with quenched and annealed charged groups were compared. It was shown that the size of clusters in the gels with annealed charged units is much bigger than that in the gels with the same fraction of quenched charged units. This effect was attributed to a much weaker electrostatic repulsion in the corona of the hydrophobic clusters in the gels with annealed charged groups, because the charged units repelling each other are able to move farther apart.

Chitosan and its hydrophobic derivatives: Preparation and aggregation in dilute aqueous solutions

“…This stabil ity of aggregates is presumably related to the formation of the well defined core-shell structure in them, in which the majority of associating groups are concen trated in cores, while the majority of hydrophilic groups form the shell. Note that, because not all units are protonated under the experimental conditions, charged groups may move [137,138] from the core of the aggregate to the shell and additionally stabilize the system. In such aggregates, stabilization occurs owing to a small amount of charged groups in shells and to steric hindrances created by hydrophilic chain frag ments (loops, free ends, etc.)…”

“…The incorporation of hydrophobic substitu ents into chitosan is a very promising approach. These substituents form hydrophobic domains [22][23][24][25][26][27] that may absorb drugs poorly soluble in water; as a result, the application areas of chitosan as a drug carrier become wider. Moreover, hydrophobic substituents may enhance transfection [28][29][30]; therefore, the effi ciency of chitosan as gene delivery vehicle may be improved.…”

Polymer‐Surfactant Networks Highly Responsive to Hydrocarbons

“…The data were recorded in the range of the scattering vectors q of 0.009 – 0.5 Å −1 . The details of the experiments are described elsewhere 11–14. For fitting the experimental curves by different models, the program “Fitter” was used 11…”

PFG‐NMR diffusometry: A tool for investigating the structure and dynamics of noncommercial purified pig gastric mucin in a wide range of concentrations

“…Indeed, in addition to the similarities of rheological properties mentioned earlier, the collapse of hydrophobic clusters also takes place in HM-polyelectrolyte solutions such as hydrophibically modified polyacrylic acid. 29,36,37 In fact, a decrease to low pH in these systems induced phase separation. At this point, the hydrophobic attractions become dominant and the polymer depleted …”