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    EXC 3120 BlueMat - Research Topic A3: Water Absorption-Driven Nanoporous Materials
    We aim to establish and enhance mechanical actuation based on the reversible switching of soft, water-filled hydrogels in response to external triggers (e.g., pH, ionic strength, electrical potential, CO2). For the first time, we aim to realize such an actuation on both nm- (ligament/pore scale) and mm-scopic levels by embedding soft responsive hydrogels in a hard, porous matrix (np-Au from A2) with responsive hydrogels, thus combining reversible switchability in aqueous media with significant macroscopic response and local controllability. We will focus on cellulose-based hydrogels, known for their inherent responsiveness in aqueous environments [Don21]. The envisioned materials will refine and optimize hydrogel actuation for broader applicability in diverse devices. The precise control of mechanical properties of hydrogels needed for active control of actuation is a challenge: although fundamental mechanisms are understood, there is a lack of research aiming at the predictable control of overall hydrogel actuation, which is necessary to pave the way for the application of these sustainable materials in devices [Che22]. Key scientific questions include: How can we tune hydrogel/wall interactions for optimal integration of hydrogels into a porous metal matrix forming a hybrid material? How can we use engineered biofilm matrix-enzyme interactions to maximize the actuation of hydrogel/metal hybrid systems in response to external stimuli? How can we predict/model the hybrid material response and thus define optimal mechanical actuation?
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    EXC 3120 BlueMat - Research Topic C1: Tunable Microwave and MIR Permittivity by Control of Water Distribution
    The nanoporous structures considered in BlueMat are orders of magnitude smaller than the wavelength of microwave and MIR radiation. Thus, we will utilize water-driven materials in the effective medium regime. In the microwave range, bulk water has a high permittivity of 80, attributed to the reorientation of water dipoles. The permittivity is expected to become anisotropic at interfaces, with the component orthogonal to the interface reducing to 2. Utilizing samples with anisotropic porosity, e.g., porous silica and alumina, we envisage for the first time experimentally clarifying this water anisotropy. In the MIR range, the permittivity of bulk water reduces to 2, but water is characterized by significant absorption with an attenuation length in the order of 10 ?m. We intend to employ polyolefin aerogels, which have intrinsically high transmittance in the MIR range, and add optical tunability via reversible adsorption of water on the surface of the aerogel. The key scientific questions are: How can we control the complex permittivity of water and its anisotropy by nanoconfinement? How can we utilize water and its confinement to tune the effective permittivity of nanostructured media? How can we utilize these effects to switch microwaves and thermal radiation?
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