Structure of nanoparticles embedded in micellar polycrystals

Area of Science:

• Soft matter physics
• Materials science
• Nanotechnology

Background:

• Pluronic block-copolymers form thermosensitive micelles in water.
• These micelles can self-assemble into crystalline structures.
• Silica nanoparticles are added to these systems as a composite component.

Purpose of the Study:

• To investigate the structural behavior of silica nanoparticles within Pluronic block-copolymer crystals.
• To understand how nanoparticles interact with the crystalline micelle lattice.
• To determine the influence of preparation conditions on nanoparticle distribution.

Main Methods:

• Contrast-matching small-angle neutron scattering (SANS) to probe nanoparticle and polymer structures independently.
• Static light scattering (SLS) to analyze sample heterogeneity.
• Light microscopy imaging to visualize nanoparticle distribution.

Main Results:

• Silica nanoparticles (≤2% by volume) do not perturb the face-centered cubic crystalline order of Pluronic micelles.
• A distinct structure peak for silica nanoparticles indicates spatial heterogeneity.
• Nanoparticles concentrate approximately 10-fold in silica-rich regions, identified as grain boundaries.
• Preparation temperature rate significantly affects nanoparticle segregation into grain boundaries.

Conclusions:

• Silica nanoparticles integrate into Pluronic crystals without disrupting the primary lattice structure.
• Nanoparticle segregation occurs at crystallite grain boundaries, creating heterogeneity.
• The rate of temperature change during sample preparation is a critical factor controlling nanoparticle distribution within the composite.