Nanoscale mixing of soft solids

Area of Science:

• Materials Science
• Polymer Science
• Soft Matter Physics

Background:

• Assessing molecular-scale mixing in soft solids presents significant challenges.
• Concentrated solutions of polystyrene-block-poly(ethylene-alt-propylene) (PS-PEP) diblock copolymers in squalane form a body-centered cubic (bcc) lattice with glassy polystyrene (PS) cores.
• Understanding and controlling nanoscale mixing is crucial for material properties.

Purpose of the Study:

• To quantitatively assess the degree of nanoscale mixing in a soft solid.
• To demonstrate the effectiveness of a commercial mixer for achieving random distribution of polymer micelles.
• To validate the use of small-angle neutron scattering (SANS) for quantifying nanoscale randomness.

Main Methods:

• Utilized small-angle neutron scattering (SANS) for structural analysis.
• Employed isotopic labeling of polystyrene blocks (deuterium labeling, PS(D)) for contrast variation.
• Used a contrast-matching solvent (squalane and perdeuterated squalane mixture).

Main Results:

• Demonstrated that a commercial mixer can achieve completely random mixtures of PS-PEP micelles with normal (PS(H)) or deuterium-labeled (PS(D)) cores.
• Observed these random mixtures within a well-defined body-centered cubic (bcc) lattice.
• Quantitatively modeled the SANS intensity using the form factor of a single spherical core, confirming randomness.

Conclusions:

• Complete nanoscale mixing in a soft solid is achievable using conventional mixing techniques.
• SANS is a powerful tool for quantitatively measuring and verifying nanoscale randomness in complex materials.
• The findings have implications for the design and processing of soft materials with controlled molecular arrangements.