Global and Local Mechanical Properties of Responsive Microgels Adsorbed to Solid-Liquid Interfaces*

Microgels are highly interfacial active, although not being amphiphilic. They readily adsorb to liquid/liquid, liquid/air or solid interfaces and deform [1]. We studied microgels with unique internal structures, (i) one with a rigid silica core and a PNIPAM shell, (ii) hollow microgels obtained by dissolving the silica core, and (iii) ultra-low cross-linked microgels. These responsive microgels were investigated at the solid-liquid interface by scanning force microscopy. An important parameter is the size of the probe compared to the dimensions of the microgel [2]. Colloidal probe experiments lead to a compression of the whole microgel and provide information on their global mechanical properties. Changing the probe dimensions, we will demonstrate that indentation experiments using sharp tips lead to a local penetration of the porous swollen microgel network. Therefore, force-distance curve measurements enable to probe the segment density distribution orthogonal to the substrate of adsorbed single microgels.

[1] A. Mourran, et al., Langmuir 2016, 32, 723-730.
[2] A. Halperin, et al., Langmuir 2010, 26, 8933-8940.