Substrate contact angle governs microgel shape, stiffness and deposition pattern

arXiv (Cornell University)

Abstract

Soft microgels are widely used as deformable building blocks for two-dimensional assemblies, yet solid substrates are often treated as passive supports after interfacial deposition. Here, we show that substrate wettability mechanically preconditions soft microgels before drying. Using in-liquid force-volume atomic force microscopy, we find that the same microgels adopt markedly different hydrated shapes and stiffness profiles depending on substrate contact angle: hydrophobic substrates induce spreading, flattening, and internal stiffening, whereas hydrophilic substrates preserve taller, softer microgels with smaller contact areas. These single-microgel states can explain how Langmuir-Blodgett-deposited monolayers respond during drying. On hydrophilic substrates, the observed assemblies are consistent with soft and weakly immobilized microgels rearranging under immersion-capillary forces, producing distinct corona-corona and core-core contact states and an apparent isostructural transition. On hydrophobic substrates, the flattened and stiffened microgels are more strongly immobilized, likely suppressing capillary-driven rearrangements and largely preserving the transferred interfacial assembly structure. These findings establish substrate-controlled microgel mechanics as the missing link between interfacial self-assembly and the final structures observed after transfer and drying.

Authors 10

1. M. Frieda Schulte

   University of Münster

   Affiliation as printed

   Institute of Physical Chemistry , University of Münster , Germany

2. Sebastian Meyer

   University of Münster

   Affiliation as printed

   Institute of Physical Chemistry , University of Münster , Germany

3. Timon Kratzenberg Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry , RWTH Aachen University , Germany

4. Simon Schog Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry , RWTH Aachen University , Germany

5. Jesco Schönfelder

   University of Münster

   Affiliation as printed

   Institute of Physical Chemistry , University of Münster , Germany

6. Silke Klein-Kormelink

   University of Münster

   Affiliation as printed

   Institute of Physical Chemistry , University of Münster , Germany

7. Tim Blinzer

   University of Münster

   Affiliation as printed

   Institute of Physical Chemistry , University of Münster , Germany

8. Matthias Karg

   Martin Luther University Halle-Wittenberg

   Affiliation as printed

   Physical Chemistry of Functional Polymers , Martin Luther University Halle-Wittenberg , Germany

9. Walter H. Richtering Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry , RWTH Aachen University , Germany

10. Marcel Rey

    University of Münster

    Affiliation as printed

    Institute of Physical Chemistry , University of Münster , Germany