Interactions between a responsive microgel monolayer and a rigid colloid: from soft to hard interfaces

Physical Chemistry Chemical Physics, vol. 23, pp. 16754–16766

Abstract

Responsive poly-N-isopropylacrylamide-based microgels are commonly used as model colloids with soft repulsive interactions. It has been shown that the microgel-microgel interaction in solution can be easily adjusted by varying the environmental parameters, e.g., temperature, pH, or salt concentration. Furthermore, microgels readily adsorb to liquid-gas and liquid-liquid interfaces forming responsive foams and emulsions that can be broken on-demand. In this work, we explore the interactions between microgel monolayers at the air-water interface and a hard colloid in the water. Force-distance curves between the monolayer and a silica particle were measured with the Monolayer Particle Interaction Apparatus. The measurements were conducted at different temperatures and lateral compressions, i.e., different surface pressures. The force-distance approach curves display long-range repulsive forces below the volume phase transition temperature of the microgels. Temperature and lateral compression reduce the stiffness of the monolayer. The adhesion increases with temperature and decreases with a lateral compression of the monolayer. When compressed laterally, the interactions between the microgels are hardly affected by temperature, as the directly adsorbed microgel fractions are nearly insensitive to temperature. In contrast, our findings show that the temperature-dependent swelling of the microgel fractions in the aqueous phase strongly influences the interaction with the probe. This is explained by a change in the microgel monolayer from a soft to a hard repulsive interface.

Authors 5

1. Steffen Bochenek Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   52074 Aachen

   Germany

   Institute of Physical Chemistry

   RWTH Aachen University

   Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52074, Aachen, Germany

2. Cathy E. McNamee

   Shinshu University

   Affiliation as printed

   Department of Chemistry and Materials

   Faculty of Textile Science and Technology

   Japan

   Shinshu University

   Ueda

   Department of Chemistry and Materials, Faculty of Textile Science and Technology, Shinshu University, Tokida 3-15-1, Ueda, Nagano, Japan

3. Michael Kappl

   Max Planck Society · Max Planck Institute for Polymer Research

   Affiliation as printed

   Germany

   Mainz

   Max Planck Institute of Polymer Research

   Max Planck Institute of Polymer Research, Ackermannweg 10, Mainz, Germany

4. Hans‐Jürgen Butt

   Max Planck Society · Max Planck Institute for Polymer Research

   Affiliation as printed

   Germany

   Mainz

   Max Planck Institute of Polymer Research

   Max Planck Institute of Polymer Research, Ackermannweg 10, Mainz, Germany

5. Walter H. Richtering corresponding Aachen Institute of Physical Chemistry

   Jülich Aachen Research Alliance · RWTH Aachen University

   Affiliation as printed

   52074 Aachen

   Germany

   Institute of Physical Chemistry

   JARA-SOFT

   RWTH Aachen University

   Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52074 Aachen, Germany