The viscosity of solutions containing polyelectrolyte-grafted nanoparticles (PENPs) is governed by a complex interplay between electrostatic interactions, hydrogen bonding, and chain entanglement. Using molecular dynamics (MD) simulations, this study investigates how the degree of ionization, graft length, and the presence of chain extenders influence the rheological behavior of PENP dispersions in explicit solvent. The grafted chains are modeled as charged polymers with hydrogen bonding sites, where electrostatic repulsion between ionized monomers causes chain stretching and an increase in hydrodynamic size. This stretching enhances interparticle repulsion, increasing the average distance between nanoparticle cores and reducing lubrication layer thickness, thereby elevating solution viscosity. At low degrees of ionization (low pH), chains remain compact, leading to minimal viscosity increase. However, as ionization increases, the electrostatic repulsion dominates, causing chains to extend and interpenetrate, promoting entanglement and friction between particles.
Hydrogen bonding plays a critical role at intermediate ionization levels, where both charged and neutral monomers coexist on the grafted chains. These charge-assisted hydrogen bonds can form not only within individual particles but also between different nanoparticles, especially when graft lengths exceed the entanglement threshold. Such interparticle bridging leads to network formation, significantly enhancing viscosity. For shorter grafts (lg = 10–20), most hydrogen bonds are intraparticle, limiting network development. However, longer grafts (lg = 30) enable cross-linking across particles, resulting in a percolated structure that dramatically increases resistance to flow. Furthermore, the addition of short polymer chain extenders—designed to bridge multiple PENPs via hydrogen bonding—amplifies this effect. The efficiency of bridging depends strongly on chain stiffness; stiffer chains maintain extended conformations, increasing the probability of forming interparticle links. Flexible chains tend to fold back onto the same particle, reducing bridging efficiency.
Systematic variation of graft length, degree of ionization, and chain extender concentration reveals that viscosity peaks at moderate ionization levels (e.g., 50–80%) due to optimal balance between chain stretching and hydrogen bond formation.Galectin-3 Antibody custom synthesis At full ionization (100%), although chains are maximally stretched, hydrogen bonding is suppressed because all donor/acceptor sites are occupied by charges, eliminating available partners for interparticle bonding.c-Jun Antibody custom synthesis In contrast, at lower ionization, insufficient chain extension limits entanglement.PMID:34581945 Thus, maximum viscosity occurs at an intermediate state where both electrostatic expansion and hydrogen bond-mediated network formation are synergistic. Additionally, increasing nanoparticle concentration reduces core-to-core distance, further enhancing friction and viscosity, particularly when hydrodynamic sizes surpass interparticle spacing.
These findings demonstrate that the rheology of PENP solutions can be precisely tuned through control of graft architecture, ionization level, and auxiliary chain design. By leveraging hydrogen bonding and chain stiffness, it becomes possible to engineer high-viscosity, structurally stable dispersions suitable for applications such as drug delivery, coatings, and functional membranes. The results provide a foundational understanding for designing next-generation nanocomposites with tailored flow properties.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
