Mixing order asymmetry in nanoparticle-polymer complexation and precipitation revealed by isothermal titration calorimetry

25 April 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


In recent years, there has been a renewed interest in complex coacervation, driven by concerted efforts to offer novel experimental and theoretical insights into electrostatic charge-induced association. While previous studies have primarily focused on polyelectrolytes, proteins or surfactants, our work explores the potential of using cerium (CeO2) and iron (γ-Fe2O3) oxide nanoparticles (NPs) to develop innovative nanomaterials. By combining various charged species, such as polyelectrolytes, charged neutral block copolymers and coated NPs, we study a wide variety of complexation patterns and compare them using isothermal titration calorimetry, light scattering and microscopy. These techniques confirm that the titration of oppositely charged species occurs in two steps: the formation of polyelectrolyte complexes and subsequent phase (or microphase) separation, depending on the system studied. Across all examined cases, the entropic contribution to the total free energy surpasses the enthalpic contribution, in agreement with counterion release mechanisms. Furthermore, our investigation reveals a consistent asymmetry in the reaction enthalpy associated with the secondary process, with exothermic profiles observed upon the addition of cationic species to anionic ones and endothermic profiles in the reverse case.


Isothermal titration calorimetry
Polymer coated nanoparticles
Polyelectrolyte complexes

Supplementary materials

Supporting Information
S1 – Transmission electron microscopy images of cerium and iron oxide nanoparticles S2 – Relationship between CeO2@PAA and γ-Fe2O3@PAA nanoparticle weight and charge concentrations S3 – Electrophoretic mobility obtained from PDADMAC/CeO2@PAA titration S4 – PTEA-b-PAm/PAA thermodynamic and structure titrations Supporting Information S5 S5 – ITC titration curve analysis for PTEA-b-Pam/PAA S6 – Results of fitting titration curves with the MNIS model (Eq. 2 and 3) S7 – Effect of titrant and titrate concentration on thermodynamic parameters extracted from MNIS model fitting


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