Lukas Huber

Fast and Minimal‐Solvent Production of Superinsulating Silica Aerogel Granulate

With their low thermal conductivity (λ), silica aerogels can reduce carbon emissions from heating and cooling demands, but their widespread adoption is limited by the high production cost. A one-pot synthesis for silica aerogel granulate is presented that drastically reduces solvent use, production time, and global warming potential. The inclusion of the hydrophobization agent prior to gelation with a post-gelation activation step, enables a complete production cycle of less than four hours at the lab scale for a solvent use close to the theoretical minimum, and limits the global warming potential. Importantly, the one-pot aerogel granulate retains the exceptional properties associated with silica aerogel, mostly λ=14.4±1.0 mW m-1 ⋅K-1 for the pilot scale materials, about half that of standing air (26 mW m-1 ⋅K-1 ). The resource-, time-, and cost-effective production will allow silica aerogels to break out of its niche into the mainstream building and industrial insulation markets.

Monolithic nitrogen-doped carbon as a water sorbent for high-performance adsorption cooling

In the present study, we report on the development of carbon adsorbents for water adsorption heat pumps. Resorcinol-melamine-formaldehyde (RMF) resins were synthesized and molded into monolithic shapes before pyrolysis and chemical activation with KOH. The influence of the carbonization and activation treatments on the physicochemical properties and the water sorption behavior of the final adsorbent materials were investigated. Activated carbons with a one-to-one (C to KOH) impregnation mass ratio, an activation temperature of 800 °C and an activation time of one hour exhibited the highest water cycling ability. For isobaric adsorption at 23 mbar, the peak specific cooling power of the best monolithic activated carbon produced in this way was 192 W kg−1 for a temperature step from 90 °C to 50 °C compared to 255 W kg−1 for silica gel for a finned tube heat exchanger of comparable fin spacing. For a temperature step from 60 °C to 30 °C, the monolithic activated carbon exhibited a higher peak specific cooling power (389 W kg−1) compared to silica gel (240 W kg−1). In situ infrared thermography revealed superior thermal transport properties of the monolithic carbons compared to commercial silica gel.

Enzyme functionalized electrospun chitosan mats for antimicrobial treatment

This work presents electrospun chitosan mats, functionalized with glucose oxidase (GOX) to implement an in-situ hydrogen peroxide (H2O2) generation system. The as spun CTS-PEO mats exhibited a smooth and homogenous morphology in combination with a high specific surface area (5.4m2/g) providing an excellent basis for further functionalization and subsequent glutaraldehyde crosslinking provided them with superior mechanical stability in aqueous environments. GOX was covalently immobilized, as proven by XPS, and resulted in activity recoveries between 20 and 40%. The functional mats generated a steady state concentration of ∼60μM H2O2 per cm2 which resulted in growth inhibition of E. coli and of S. aureus already after two hours of incubation. Additional cytotoxicity tests of the modified mats against mouse fibroblasts did not show an influence on the viability of the cells which proved it a functional biomaterial of great potential for biomedical applications.

Water sorption behavior of physically and chemically activated monolithic nitrogen doped carbon for adsorption cooling

In this work, nitrogen doped resorcinol–melamine–formaldehyde (RMF) resins were synthesized, pyrolyzed and physically activated with CO2. The influence of the activation time on the physicochemical properties and the water sorption behavior produced in this way was investigated. Furthermore, a comparison between physical activation with CO2 and chemical activation with KOH is presented. Materials performance was validated in an adsorption chiller test setup with a temperature step from 90 °C → 50 °C. The CO2 activated RMF carbon exhibits a maximal specific cooling power which is a factor of 1.7 higher in comparison to a commonly used, commercial silica gel reference material (430 W kg−1 compared to 255 W kg−1). This is surprising considering that the hydrophilicity of the CO2 activated carbon is rather low. The superior performance of carbon based sorbents is attributed to originate from the superior thermal transport properties of monolithic carbons over commercial silica gels. At a more feasible temperature swing 60 °C → 30 °C, the RMF derived carbon yields a specific cooling power 3.2 times greater than that of the silica gel reference.

Controlling the surface structure of electrospun fibers: Effect on endothelial cells and blood coagulation

The influence of nano- or micron-sized structures on polymer films as well as the impact of fiber diameter of electrospun membranes on endothelial cell (EC) and blood response has been studied for vascular tissue engineering applications. However, the influence of surface structures on micron-sized fibers on endothelial cells and blood interaction is currently not known. In this work, electrospun membranes with distinct fiber surface structures were designed to study their influence on the endothelial cell viability and thrombogenicity. The thermodynamically derived Hansen-solubility-parameters model accurately predicted the formation of solvent dependent fiber surface structured poly(caprolactone) membranes. The electrospun membranes composed of microfibers (MF) or structured MF were of similar fiber diameter, macroscopic roughness, wettability, and elastic modulus. In vitro evaluation with ECs demonstrated that cell proliferation and morphology were not affected by the fiber surface structure. Similarly, investigating the blood response to the fiber meshes showed comparable fibrin network formation and platelet activation on MF and structured MF. Even though the presented results provide evidence that surface structures on MF appear neither to affect EC viability nor blood coagulation, they shed light on the complexity and challenges when studying biology-material interactions. They thereby contribute to the understanding of EC and blood-material interaction on electrospun membranes.