Soft Matter, 2019, Vol.15(32), pp.6536-6546
The preparation of poly( N -isopropylacrylamide) microgels via classical precipitation polymerization (batch method) and a continuous monomer feeding approach (feeding method) leads to different internal crosslinker distributions, i.e. , from coreshell-like to a more homogeneous one. The internal structure and dynamics of these microgels with low and medium crosslinker concentrations are studied with dynamic light scattering and small-angle neutron scattering in a wide q -range below and above the volume phase transition temperature. The influence of the preparation method, and crosslinker and initiator concentration on the internal structure of the microgels is investigated. In contrast to the classical conception where polymer microgels possess a coreshell structure with the averaged internal polymer density distribution within the core part, a detailed view of the internal inhomogeneities of the PNIPAM microgels and the presence of internal domains even above the volume phase transition temperature, when polymer microgels are in the deswollen state, are presented. The correlation between initiator concentration and the size of internal domains that appear inside the microgel with temperature increase is demonstrated. Moreover, the influence of internal inhomogeneities on the dynamics of the batch- and feeding-microgels studied with neutron spin-echo spectroscopy is reported.
Light Scattering ; Polymers ; Light Scattering ; Echo Surveys ; Polymerization ; Polymerization ; Feeding ; Crosslinking ; Domains ; Neutron Scattering ; Microgels ; Polymers ; Precipitation ; Core-Shell Structure ; Monomers ; Transition Temperature ; Neutron Scattering ; Feeding ; Poly(N-Isopropylacrylamide) ; Transition Temperatures ; Polymerization ; Isopropylacrylamide ; Spectroscopy ; Inhomogeneity ; Phase Transitions ; Dynamic Structural Analysis ; Temperature Effects ; Density Distribution ; Photon Correlation Spectroscopy ; Phase Transitions ; Phase Transitions;