Structural changes in PNIPAM microgel particles as seen by SANS, DLS, and EM techniques

Thermo-sensitive poly(N-isopropylacrylamide) (PNIPAM) microgels with differ ent cross-linker density have been investigated by complementary scattering methods and high-resolution imaging techniques. The swelling behavior of t he colloidal particles as probed by dynamic light scattering (DLS), is disc ussed together with information on local structure and dynamics of the part icles as obtained from small angle neutron scattering (SANS). Below the vol ume phase transition the static structure factor reveals liquid-like contri butions. This is similar to macroscopic gels, but for low q the scattering behavior is different because of the influence of the particle form factor Pig). Beyond the phase transition temperature, T-c, the system becomes comp letely phase separated and interfacial scattering dominates the measured SA NS profiles (I(q) proportional to q(-4)). Slight deviations from the ideal Pored behavior can be interpreted in terms of surface roughness of the coll apsed particles. This corresponds to structures visible on AFM micrographs. (C) 2001 Elsevier Science Ltd. All rights reserved.