Institute of Physical Chemistry, RWTH Aachen University, 52056, Aachen, Germany.
Laboratory for Interfaces, Soft Matter and Assembly, Department of Materials, ETH Zurich, 8093, Zurich, Switzerland.
Nat Commun. 2019 Mar 29;10(1):1418. doi: 10.1038/s41467-019-09227-5.
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.
微凝胶是溶剂溶胀的纳米和微粒子，尽管具有聚合物性质，但表现出普遍的胶体样行为。在这里，我们研究超低交联聚（N-异丙基丙烯酰胺）微凝胶（ULC），其可以根据维度、压缩或其他外部刺激表现为胶体或柔性聚合物。小角中子散射表明，在本体水相溶液中，ULC 微凝胶的结构特征是从中心到模糊表面的密度分布平稳衰减。它们的相行为和流变性质是软胶体的性质。然而，当这些微凝胶在油水界面受限时，它们的行为类似于柔性大分子。一旦超低交联微凝胶的单层被压缩、沉积在固体基底上并通过原子力显微镜进行研究，就会观察到浓度依赖性的形貌。根据压缩程度，这些微凝胶可以作为柔性聚合物，在基底上覆盖一层均匀的薄膜，或者作为胶体微凝胶导致颗粒的单层。
