Entropic Effects in Solvent-Free Bidisperse Polymer Brushes Investigated Using Density Functional Theories

Area of Science:

• Colloid and Surface Science
• Polymer Physics
• Materials Science

Background:

• Solvent-free polymer-functionalized nanoparticles are colloids with inorganic cores and grafted polymer layers.
• These systems lack intervening solvent molecules, relying on tethered polymers for fluidity and interparticle interactions.

Purpose of the Study:

• To investigate the structure and interaction of neighboring polymer-grafted surfaces in solvent-free conditions.
• To analyze the influence of brush polydispersity on system energy and brush profiles.
• To determine favorable interparticle spacing for solvent-free nanoparticle design.

Main Methods:

• Utilized mean-field density functional theories to study polymer-grafted surfaces.
• Semianalytically investigated brush configuration and energy landscape for opposing flat surfaces.
• Employed two bidisperse models to account for variations in chain length and grafting density.

Main Results:

• Observed steric repulsion upon brush compression and unique entropic attraction at increased interwall separation.
• Demonstrated changes in brush profiles from bell-like to step-function-like with increasing spacing.
• Characterized the energy landscape and identified favorable interparticle spacing based on free energy minima.

Conclusions:

• The study provides a comprehensive exploration of the parameter space for solvent-free polymer-functionalized nanoparticles.
• Findings offer guidance for the experimental design of these nanoparticles by understanding their unique solventless interactions.
• The unique entropic attraction is a key characteristic for designing self-assembled structures.