Markus Biesalski

As interest in sustainable materials grows, paper is being reimagined as a multifunctional substrate with significant potential for future technologies for innovative, environmentally friendly solutions. This study investigates the swelling behavior and environmental responsiveness of a copolymer, poly(N,N-dimethylacrylamide-co-4-methacryloyloxybenzophenone) [P(DMAA-co-MABP)], when applied to cellulosic paper for use in humidity-sensitive actuators. The copolymer’s swelling behavior was characterized using dynamic vapor sorption (DVS) and in-situ atomic force microscopy (AFM). DVS measurements demonstrated that the polymer coating significantly enhances the hygroscopic properties of the paper, while AFM revealed the polymer’s fast response to relative humidity (RH) changes, shown by immediate height adjustments, increased adhesion, and decreased stiffness at higher RH levels. Studies on polymer-modified paper-based bilayer actuators demonstrate that incorporating the hydrophilic P(DMAA-co-MABP) results in actuation in response to relative humidity variations between 10 and 90% RH. From these findings, two models were proposed to assess key mechanisms in the swelling behavior: the correlation between the heterogeneity in crosslinking and the polymer swelling behavior, and the correlation between polymer-paper interactions and the hygro-responsive bending behavior. Additionally, thermal analysis was performed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), providing a comprehensive profile of the copolymer’s behavior.

Mechanical integrity of paper materials is crucial for many applications, yet reinforcement strategies with polymer strengthening agents that interact strongly often result in inhomogeneous coatings. In-sheet polymerization and adhesion (InSPA) methodology enables the in situ generation of reinforcing polymers, facilitating their uniform deposition on the cellulose fibers despite high interaction capabilities, and significantly increasing the dry and wet strength of commercial filter papers. A set of polymers containing highly adhesive thiol-catechol-connectivities (TCC) is prepared from o/m/p-isomers of benzenedithiol and bisquinone A by the InSPA thiol-quinone Michael-type polyaddition route. During polymerization, the interaction capabilities of the TCC-polymers are built up gradually, enabling effective cellulose fiber penetration and homogeneous fiber coating. Polymer loadings of up to 48 wt.-% are reached, transferring rigidity and hydrophobicity to the paper fibers without jeopardizing paper porosity. The noncovalently modified papers show a doubling in tensile index in the dry and a 7-fold increase in the wet state, paving the way for effective oil/water separation membranes, where end-of-life recyclability by removal of the polymer coating in a water-based process is demonstrated.

A solvent‐free approach to the formation of freestanding photonic material from amphiphilic polystyrene‐ block ‐poly(2‐hydroxyethyl methacrylate) (PS‐ b ‐PHEMA) is reported, where the application of shear force and pressure induces phase separation. This work demonstrates access to high molecular weight (HMW; >100 kg mol ⁻¹ ) PS‐ b ‐PHEMA with PHEMA contents up to 62 vol% using sequential anionic polymerization. By exploring hot pressing, the dependency of microstructure formation on temperature, pressure, and time is demonstrated using transmission electron microscopy and small‐angle X‐ray scattering measurements. Within 30 min, phase‐separated block copolymer (BCP) films are obtained. Although no highly ordered equilibrium structures are formed, photonic properties are observed for PS‐ b ‐PHEMA films with molecular weights higher than 140 kg mol ⁻¹ and PHEMA contents between 20 and 51 vol%. The photonic properties are investigated by ultraviolet–visible (UV–vis) and fluorescence spectroscopy as well as confocal fluorescence microscopy. The BCP films exhibit tailored transmittance that is dependent on molecular weight and microstructure, making them suitable for UV and blue light filter applications. Also, structure‐dependent reflection and fluorescence are demonstrated. Finally, the application in the field of sensors is addressed by demonstrating a reversible color change of BCP films with a co‐continuous microstructure, achieved through polar solvent infiltration and evaporation.

Lactate is a key metabolite with applications ranging from monitoring training efficiency to early sepsis detection and monitoring the metabolic state of cell cultures. In this study, a paper-based lactate sensor utilizing a fluorescent readout was developed. Unlike common lactate dehydrogenase (LDH)-based methods, these sensors use a green fluorescent protein (GFP) or mApple-coupled lactate binding domain, which provides a fluorescent readout upon lactate binding. We demonstrate that immobilizing these proteins on paper does not affect their ability to bind lactate and produce a fluorescent readout, by monitoring lactate levels in the cell culture supernatant applying different cell culture conditions.

Superhydrophobic paper has demonstrated significant potential for efficient water harvesting. Previous studies have indicated that the incorporation of pinning structures on superhydrophobic surfaces can enhance water collection efficiency. This study explores the feasibility of creating such pinning structures through femtosecond laser ablation of wax‐based superhydrophobic coatings. Static contact angle measurements and the roll‐off behavior of droplets on laser‐treated surfaces are conducted to evaluate the effects of laser ablation. Additionally, fogging tests are performed to assess the water collection performance, revealing an improvement of above 10% in comparison to unmodified superhydrophobic paper without localized pinning structures. Notably, the laser ablation process minimally affects the load‐bearing capacity of the paper, ensuring that its structural integrity is preserved. The ability to design laterally resolved pinning structures opens new possibilities for further optimization, such as the creation of flow paths, ultimately enhancing the overall efficiency of water harvesting systems.

Fatty acid cellulose esters (FACEs) have great potential as biogenic alternatives to petroleum-based plastics. Nevertheless, their thermal property profiles have been the subject of controversial discussion, particularly with respect to their crystallization behavior. A thorough understanding of the crystallization behavior of FACEs is fundamentally important for gaining deep insights into their solid-state characteristics and thermal properties. This systematic study succeeds in elucidating the crystallization behavior of FACEs as bulk materials. Differential scanning calorimetry combined with rheological analysis and X-ray diffraction of cellulose esters bearing side chains with varying numbers of fatty acid residues (C-12-C-20) and degrees of substitution (ranging from partial to full esterification, i.e., 0.1-3.0) revealed that crystallization of FACEs occurs in multiple stages. These stages involve the distinct crystallization of inter and intramolecular side chains and polysaccharide backbones. A quantitative multistep crystallization mechanism is proposed based on the study findings.

Here the performance of phase change material (PCM)‐coated paper made from unbleached kraft pulp is introduced. The applied PCM consists of a mixture of ethylene glycol distearate (EGDS), a well‐known PCM wax material, and a fully substituted cellulose stearoyl ester (CSE). Transfer of the PCM material onto/into paper is achieved by spray as well as blade coating of EGDS + CSE mixture. It is shown that the kind of coating method used does not interfere with observed PCM properties. The significantly higher melt viscosity of the EGDS + CSE blends ensures that the EGDS wax is not bleeding out of the paper, which avoids the use of further encapsulation processes. The PCM behavior, as observed by thermal load measurements, and the thermal buffering of the coated paper is a function of the applied mass of the PCM material applied. The thermal retention exhibited a quasi‐isothermal behavior at ≈65 °C with EGDS + CSE coatings. These effects can offset fluctuations in temperature, and the PCM papers can be employed to achieve a more uniform temperature setting. PCM‐modified papers are therefore interesting candidates for paper‐based packaging or for use in paper‐based sensors, where overheating can strongly affect reliability of results.

Screen printing was employed for the first time to examine the effect of electrode size and arrangement on the performance of a microfluidic paper-based electroanalytical device for clozapine sensing.