Anisotropic Microgels Show Their Soft Side

Langmuir, vol. 38, pp. 5063–5080

Abstract

Anisotropic, submicrometer-sized particles are versatile systems providing interesting features in creating ordering in two-dimensional systems. Combining hard ellipsoids with a soft shell further enhances the opportunities to trigger and control order and alignment. In this work, we report rich 2D phase behavior and show how softness affects the ordering of anisotropic particles at fluid oil-water interfaces. Three different core-shell systems were synthesized such that they have the same elliptical hematite-silica core but differ with respect to thickness and stiffness of the soft microgel shell. Compression isotherms, the shape of individual core-shell microgels, and their 2D order at a decane-water interface are investigated by means of the Langmuir-Blodgett technique combined with ex-situ atomic force microscopy (AFM) imaging as well as dissipative particle dynamics (DPD) simulations. We show how the softness, size, and anisotropy of the microgel shell affect the side-to-side vs tip-to-tip ordering of anisotropic hybrid microgels as well as the alignment with respect to the direction of compression in the Langmuir trough. A large, soft microgel shell leads to an ordered structure with tip-to-tip alignment directed perpendicular to the direction of compression. In contrast, a thin and harder microgel shell leads to side-to-side ordering orientated parallel to the compression direction. In addition, the thin and harder microgel shell induces clustering of the microgels in the dilute state, indicating the presence of strong capillary interactions. Our findings highlight the relevance of softness for the complex ordering of anisotropic hybrid microgels at interfaces.

Authors 9

1. Anne C. Nickel Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany, European Union

2. Timon Kratzenberg Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany, European Union

3. Steffen Bochenek Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany, European Union

4. Maximilian M. Schmidt Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany, European Union

5. Andrey A. Rudov Aachen DWI - Leibniz Institute for Interactive Materials

   Lomonosov Moscow State University · DWI – Leibniz Institute for Interactive Materials

   Affiliation as printed

   DWI Leibniz-Institute for Interactive Materials, 52056 Aachen, Germany, European Union

   Physics Department, Lomonosov Moscow State University, Moscow 119991, Russia

6. Andreas Falkenstein Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany, European Union

7. Igor I. Potemkin Aachen DWI - Leibniz Institute for Interactive Materials

   South Ural State University · Lomonosov Moscow State University · DWI – Leibniz Institute for Interactive Materials

   Affiliation as printed

   DWI Leibniz-Institute for Interactive Materials, 52056 Aachen, Germany, European Union

   National Research South Ural State University, Chelyabinsk 454080, Russia

   Physics Department, Lomonosov Moscow State University, Moscow 119991, Russia

8. Jérôme J. Crassous Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany, European Union

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

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany, European Union

   RWTH Aachen University