Abstract
Microgels are solvent-swollen nano- and microparticles that show prevalent colloidal-like behavior despite their polymeric nature. Here we study ultra-low crosslinked poly(N-isopropylacrylamide) microgels (ULC), which can behave like colloids or flexible polymers depending on dimensionality, compression or other external stimuli. Small-angle neutron scattering shows that the structure of the ULC microgels in bulk aqueous solution is characterized by a density profile that decays smoothly from the center to a fuzzy surface. Their phase behavior and rheological properties are those of soft colloids. However, when these microgels are confined at an oil-water interface, their behavior resembles that of flexible macromolecules. Once monolayers of ultra-low crosslinked microgels are compressed, deposited on solid substrate and studied with atomic-force microscopy, a concentration-dependent topography is observed. Depending on the compression, these microgels can behave as flexible polymers, covering the substrate with a uniform film, or as colloidal microgels leading to a monolayer of particles.
Highlights
Microgels are solvent-swollen nano- and microparticles that show prevalent colloidal-like behavior despite their polymeric nature
Our results show that while the ultra-low crosslinked (ULC) microgels present a colloidallike behavior in three dimensions, their nature changes once they are confined at interfaces
To summarize, in this study we have shown that ultra-low crosslinked microgels behave as colloids in three dimensions but not in two, where within a certain range of concentrations their properties are very similar to those of flexible polymers
Summary
Microgels are solvent-swollen nano- and microparticles that show prevalent colloidal-like behavior despite their polymeric nature. We study ultra-low crosslinked poly(N-isopropylacrylamide) microgels (ULC), which can behave like colloids or flexible polymers depending on dimensionality, compression or other external stimuli. Small-angle neutron scattering shows that the structure of the ULC microgels in bulk aqueous solution is characterized by a density profile that decays smoothly from the center to a fuzzy surface Their phase behavior and rheological properties are those of soft colloids. They have a spherical shape with sizes in the range of nm to μm These nano- and microparticles, constituted of polymeric networks, have properties of both flexible polymers and colloids. In the swollen state they are soft and can be compressed or interpenetrate once in concentrated suspensions[5,6] Their flow properties and phase behavior are the same as those of colloids interacting via soft potentials.
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