04 Fakultät Energie-, Verfahrens- und Biotechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/5
Browse
4 results
Search Results
Item Open Access Acid catalyzed cross‐linking of polyvinyl alcohol for humidifier membranes(2021) Michele, Andre; Paschkowski, Patrick; Hänel, Christopher; Tovar, Günter E. M.; Schiestel, Thomas; Southan, AlexanderPolyvinyl alcohol (PVA) is a hydrophilic polymer well known for good film forming properties, high water vapor permeance JW, and low nitrogen permeance. However, depending on molar mass and temperature, PVA swells strongly in water until complete dissolution. This behavior affects the usability of PVA in aqueous environments and makes cross‐linking necessary if higher structural integrity is envisaged. In this work, PVA networks are formed by thermal cross‐linking in the presence of p‐toluenesulfonic acid (TSA) and investigated in a design of experiments approach. Experimental parameters are the cross‐linking period tc, temperature ϑ and the TSA mass fraction wTSA. Cross‐linking is found to proceed via ether bond formation at all reaction conditions. Degradation is promoted especially by a combination of high wTSA, tc and ϑ. Thermal stability of the networks after preparation is strongly improved by neutralizing residual TSA. Humidification membranes with a JW of 6423 ± 63.0 gas permeation units (GPU) are fabricated by coating PVA on polyvinyliden fluoride hollow fibers and cross‐linking with TSA. Summarizing, the present study contributes to a clearer insight into the cross‐linking of PVA in presence of TSA, the thermal stability of the resulting networks and the applicability as selective membrane layers for water vapor transfer.Item Open Access Unravelling parameter interactions in calcium alginate/polyacrylamide double network hydrogels using a design of experiments approach for the optimization of mechanical properties(2024) Gorke, Oliver; Stuhlmüller, Marc; Tovar, Günter E. M.; Southan, AlexanderCalcium alginate/polyacrylamide double network hydrogels were reported to be exceptionally tough. However, literature reports so far varied the sample compositions mainly by one parameter at a time approaches, thus only drawing an incomplete picture of achievable material properties. In this contribution, sample compositions are varied according to a face-centered central composite experimental design taking into account the four parameters of alginate concentration cAlg, high/low molar mass alginate mixing ratio RP, acrylamide concentration cAAm, and N,N′-methylenebisacrylamide concentration cMBA. Each sample composition is investigated in triplicate. Thus, 75 samples were investigated by tensile testing, and a detailed analysis of the significant parameters and parameter interactions influencing the mechanical properties is conducted. The data shows that two parameter interactions, involving all four tested parameters, have a large effect on the Young's modulus, the strength, the toughness and the strain at material failure. As a consequence, it becomes evident that the experimental procedure from previous studies did not always result in optimum sample compositions. The results allow optimization of the mechanical properties within the studied parameter space, and a new maximum value of the strength of 710 kPa is reported. The data also give rise to the assumption that other parameters and parameter interactions ignored also in this study may allow further tailoring of mechanical properties.Item Open Access Soft sub‐structured multi‐material biosensor hydrogels with enzymes retained by plant viral scaffolds(2023) Grübel, Jana; Wendlandt, Tim; Urban, Daniela; Jauch, Corinna O.; Wege, Christina; Tovar, Günter E. M.; Southan, AlexanderAn all‐soft multi‐material combination consisting of a hydrogel based on poly(ethylene glycol) (PEG) coated with spatially defined spots of gelatin methacryloyl (GM) containing selectively addressable viral nanorods is presented, and its basic application as a qualitative biosensor with reporter enzymes displayed on the tobacco mosaic virus (TMV) bioscaffolds within the GM is demonstrated. Biologically inert PEG supports are equipped with GM spots serving as biological matrix for enzymes clustered on TMV particles preventing diffusion out of the gel. For this multi‐material combination, i) the PEG‐based hydrogel surface is modified to achieve a clear boundary between coated and non‐coated regions by introducing either isothiouronium or thiol groups. ii) Cross‐linking of the GM spots is studied to achieve anchoring to the hydrogel surface. iii) The enzymes horseradish peroxidase or penicillinase (Pen) are conjugated to TMV and integrated into the GM matrix. In contrast to free enzymes, enzyme‐decorated TMVs persist in GM spots and show sustained enzyme activity as evidenced by specific color reaction after 7 days of washing, and for Pen after 22 months after dry storage. Therefore, the integration of enzyme‐coupled TMV into hydrogel matrices is a promising and versatile approach to obtaining reusable and analyte‐specific sensor components.Item Open Access Adsorption on inkjet-printable polyelectrolyte hydrogels allows refractive index sensing of diclofenac and metoprolol in aqueous solution(2024) Southan, Alexander; Tan, Jennifer; Schuster, Fabian; Rotenberger, Julia; Tovar, Günter E. M.Polyelectrolyte hydrogels containing negatively charged sulfonate groups or positively charged ammonium groups are characterized by their adsorption behavior toward the pharmaceuticals metoprolol (cationic) and diclofenac (anionic) in an aqueous solution. Additionally, the change in the hydrogel refractive index with metoprolol and diclofenac concentrations inside the hydrogel is investigated. Both metoprolol adsorption on sulfonate group containing hydrogels as well as diclofenac adsorption on the ammonium group containing hydrogels can be described using a modified Langmuir-type adsorption isotherm with Ks values around 0.1 and 10 mL μmol-1, respectively. In both cases, the adsorption capacities are close to the concentration of charged groups in the hydrogels. Thus, diclofenac concentrations inside the hydrogels are enhanced by a factor of approximately 1000 and metoprolol concentrations by a factor of approximately 10 compared to their concentrations in solution. In contrast, metoprolol was completely excluded from the ammonium group containing hydrogels, and diclofenac showed weak adsorption on the poly(ethylene glycol) fraction of the sulfonate group containing hydrogels, resulting in lower concentration enhancements. Hydrogel refractive indices increased linearly with the concentration of metoprolol and diclofenac inside the hydrogels. Thus, monitoring the refractive index of sulfonate group containing hydrogels is shown to be efficient in measuring the solution concentrations of metoprolol up to 10 μmol mL-1 and of ammonium group containing hydrogels for diclofenac concentrations up to 0.1 μmol mL-1, both values corresponding to the reciprocal of the Ks values. In the case of Langmuir-type adsorption, maximizing Ks values therefore leads to the best refractive index sensor sensitivities at low analyte concentrations, whereas lower Ks values lead to lower sensitivities at low concentrations but to superior sensitivities at rather high analyte concentrations. Inkjet printing of the hydrogel formulations is demonstrated to facilitate their future use as spatially resolved coatings on sensor surfaces.