Effect of pH on complex coacervate core micelles from Fe(III)-based coordination polymer

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Colloid Science

Background:

• Complex coacervate core micelles [Fe(III)-C3Ms] are formed from poly(N-methyl-2-vinylpyridinium iodide)-b-poly(ethylene oxide) [P2MVP(41)-b-PEO(205)] and anionic iron coordination polymers [Fe(III)-L(2)EO(4)].
• Understanding the influence of environmental factors like pH is crucial for controlling the properties of these self-assembled nanostructures.

Purpose of the Study:

• To investigate the effect of pH on the structural characteristics and properties of iron-containing complex coacervate core micelles [Fe(III)-C3Ms].
• To elucidate the pH-dependent changes in micellar core structure and hydrodynamic radius.

Main Methods:

• Light scattering measurements to determine hydrodynamic radius.
• Cryo-transmission electron microscopy (Cryo-TEM) to visualize micellar core morphology.
• Magnetic relaxation measurements to assess core properties.

Main Results:

• The hydrodynamic radius of [Fe(III)-C3Ms] remained largely unchanged across a broad pH range, primarily dictated by the copolymer corona.
• Cryo-TEM and magnetic relaxation data revealed significant pH-dependent alterations in the micellar core structure.
• At higher pH, cores exhibited a more crystalline and elongated morphology, accompanied by reduced relaxivity, attributed to the formation of mixed iron-hydroxide complexes stabilized by the diblock copolymer.

Conclusions:

• The diblock copolymer effectively stabilizes the [Fe(III)-C3Ms] against precipitation across varying pH conditions.
• The pH-induced changes in the micellar core structure, particularly at higher pH, are linked to the formation of specific iron complexes.
• These findings highlight the potential for pH control in tuning the properties of iron-containing complex coacervate core micelles for specific applications.