Spatial distribution of core monomers in acrylamide-based core-shell microgels with linear swelling behaviour

Area of Science:

• Polymer Science
• Materials Science
• Soft Matter Physics

Background:

• Core-shell microgels combine polymers with distinct transition temperatures.
• Their linear swelling behavior is not fully understood.
• The interplay between core-shell architecture and swelling is complex.

Purpose of the Study:

• To elucidate the internal structure of poly(N-isopropylacrylamide)-(pNIPMAM) core and poly(N-n-isopropylacrylamide)-(pNNPAM) shell microgels.
• To correlate microgel structure with their linear temperature-dependent swelling.
• To investigate the influence of deuteration on microgel structure and swelling.

Main Methods:

• Small-angle neutron scattering (SANS) with selective deuteration.
• Photon correlation spectroscopy (PCS).
• Form-free multi-shell reverse Monte Carlo (RMC) modeling.

Main Results:

• SANS and RMC revealed gradient monomer density profiles with significant core-shell interpenetration.
• Core-shell microgels showed cores embedded in larger shells compared to core-only particles.
• Linear swelling behavior was confirmed and linked to interpenetration across various conditions.

Conclusions:

• The internal structure of pNIPMAM-core/pNNPAM-shell microgels is heterogeneous and interpenetrated.
• This interpenetration likely causes progressive core swelling between transition temperatures, leading to linear swelling.
• The findings provide a structural basis for the observed swelling behavior in these microgels.