Christopher Dreimol

Last Name

Dreimol

First Name

Christopher

ORCID

0000-0002-0615-2385

Organisational unit

03917 - Burgert, Ingo / Burgert, Ingo

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Publications 1 - 10 of 21

Rationally designed conductive wood with mechanoresponsive electrical resistance
Mastantuoni, Gabriella G.; Tran, Van Chinh; Gaermark, Jonas; et al. (2024)
Composites Part A: Applied Science and Manufacturing
Porous cellular foams, combining lightweight, high strength, and compressibility, hold great promise in a wide range of advanced applications. Here, the native structure of pine wood was modified by in-situ lignin sulfonation and unidirectional freezing, resulting in an alveolate structure inside the wood cell wall with arrays of sub-100 nm channels. The obtained wood foam exhibited highly enhanced permeability while retaining the native cellular arrangement and high lignin and hemicellulose content. Such engineered cellular foam contributed to superior mechanical performance with compressive strength of 9 MPa and Young's modulus of 344 MPa in the longitudinal direction. The high porosity allowed homogeneous infiltration of conductive polymer PEDOT:PSS inside the wood cell wall. The resulting composite exhibited high conductivity, sponge-like compressibility and the ability to modulate electrical resistance in a reversible manner in the radial direction. This rationally designed conductive wood demonstrated potential in durable and ultrasensitive pressure-responsive devices and strain sensors.
Sustainable Wood-Based Electronics Towards Smart Buildings
Dreimol, Christopher (2025)
The transition from conventional construction practices to smart building technologies is reshaping how we design, inhabit, and interact with our built environments, offering real-time monitoring of environmental conditions and occupant behavior, and enhanced energy performance through adaptive control systems that optimize building operations. However, this advancement comes at a cost: the widespread use of sensors, control systems, and embedded electronics relies on rare, non-renewable resources and energy-intensive manufacturing, leading to significant environmental impacts and the accumulation of electronic waste. Reconciling these technological benefits with long-term sustainability goals remains a pressing and multifaceted, complex challenge. Motivated by this context, this thesis investigates iron-catalyzed laser-induced graphitization (IC-LIG), presented as a novel, eco-efficient approach that transforms wood from a passive substrate into an electrically conductive material, with the aim of contributing to the development of sustainable materials for future building technologies. The first step involves the application of a bio-based precursor ink, composed of tannic acid and iron salt, which smooths surface irregularities and facilitates catalytic graphitization. In the second step, CO₂ laser irradiation under ambient conditions induces localized graphitization via iron-catalyzed laser-induced graphitization, beginning with thermal decomposition and precarbonization of the precursor ink in the heat-affected zone, and yielding conductive graphitic structures with high electrical performance. This is achieved without the need for fire retardants, inert atmospheres, or complex laser systems, thereby streamlining the process and enhancing its scalability and compatibility with potential industrial manufacturing. As a result, sensing, energy storage, and interactive touch functionalities have been demonstrated in first proof-of-concept devices, highlighting the potential for direct integration into wood-based (construction) materials and alignment with the renewability and carbon storage potential of wood. Over the course of three publications, this thesis establishes IC-LIG as a scalable and versatile platform for the laser-based fabrication of functional carbon structures on wood. The first study introduces the IC-LIG approach and demonstrates its feasibility for large-scale processing, enabling the creation of conductive patterns with areas reaching up to 100 cm² on various wood species under ambient conditions. The second study investigates the catalytic mechanisms and structural evolution underlying laser-induced graphitization by analyzing the cross-sectional transition zone spanning untreated precursor ink to fully graphitized IC-LIG. This approach reveals a hierarchically layered electrode structure and enables the construction of a 3D model that integrates nanoscale insights within a mesoscopic framework. Based on post-process observations, it traces the migration and growth of catalytic iron nanoparticles across the IC-LIG electrode, highlighting their inferred role in the graphitization process. The third study focuses on process optimization towards industrial scalability, demonstrating that variations in the tannic acid-to-iron (TA:Fe) ratio directly affect ink rheology, which in turn enables diverse application methods, including spray coating, screen printing, and direct ink writing. These ink alterations influence the electrode architecture and electrochemical behavior for prospective energy storage applications. Collectively, these findings position IC-LIG as a promising approach for advancing green electronics that balances performance and scalabil-ity, with environmental sustainability identified as a potential avenue for fu-ture exploration, particularly through life cycle assessment (LCA). The IC-LIG platform reflects a broader, interdisciplinary vision for sustainable innovation in the built environment. By rethinking both materials and methods, this work marks a significant step within the emerging landscape of sustainable electronics toward integrating electronics directly into renewable building materials. While practical implementation challenges such as long-term environmental stability and integration with conventional electrical systems remain to be addressed, this work contributes to a future where buildings are not only smart, but fundamentally sustainable, bridging disciplines and fos-tering collaboration among materials scientists, engineers, architects, de-signers, and circular economy stakeholders.
Comparing the ice nucleation properties of the kaolin minerals kaolinite and halloysite
Klumpp, Kristian; Marcolli, Claudia; Alonso-Hellweg, Ana; et al. (2023)
Atmospheric Chemistry and Physics
Heterogeneous ice nucleation on dust particles in the atmosphere is a key mechanism for ice formation in clouds. However, the conditions of a particle surface for efficient ice nucleation are poorly understood. In this study, we present results of immersion freezing experiments using differential scanning calorimetry on emulsified mineral dust suspensions, involving the two chemically identical, but morphologically different, kaolin minerals of kaolinite and halloysite. Kaolinite occurs in a platy morphology, while halloysites form predominantly tubular structures. We investigated six different halloysite and two different kaolinite samples. Our results show that, on average, the halloysite samples not only exhibit a higher ice nucleation (IN) activity than the kaolinite samples but also a higher diversity in terms of freezing onset temperatures and heterogeneously frozen fraction. Repeating the freezing experiments after shortly milling the samples led to a decrease in freezing onset temperatures and in the heterogeneously frozen fraction of the halloysite samples, bringing their IN activity closer to that of the kaolinites. To interpret these findings, the freezing experiments were complemented by dynamic vapor sorption (DVS), BET (Brunauer-Emmett-Teller) surface area measurements, pore ice melting experiments with slurries, and transmission electron microscopy (TEM) before and after milling. These measurements demonstrate an increase in surface area and the destruction of tubes by milling and provide evidence for the influence of the tubular structure of the halloysites on their IN activity. We identify the OH-Al-O-Si-OH functionalized edges as being the most likely site for ice nucleation, as the high geometric diversity of the edges best accounts for the high diversity in IN activity of halloysites. We hypothesize that the stacking of layers and the number of stacks in halloysite tubes and kaolinite platelets affect the freezing temperature, with thicker stacks having the potential to freeze water at higher temperatures. The notion that the edges constitute the IN-active part of kaolin minerals is further supported by comparing kaolin minerals with montmorillonites and feldspars, all of which exhibit enhanced IN activity in the presence of ammonia and ammonium-containing solutions. As OH-Al-O-Si-OH functionalized edge surfaces are the only surface type that kaolin particles have in common with montmorillonites and feldspars, the common feature of IN activity enhancement in ammoniated solutions can only be explained by ice nucleation occurring at the edges of kaolin minerals.
Water-vapour sorption of welded bond-line of European beech and Scots pine
Vaziri, Mojgan; Dreimol, Christopher; Abrahamsson, Lars; et al. (2023)
Holzforschung
The wood-water interactions of welded bond-lines of European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.) were in this paper studied for the first time with dynamic vapour sorption equipment. The aim of this study was to characterize the water sorption in the welded bond-line and to define to which extent it deviates from water sorption of the unwelded wood. The objective was to provide deepened knowledge about water sorption of the welded bond-line, which could be used to improve the moisture resistance of welded wood in the future. The welded wood generally had lower equilibrium moisture contents than the unwelded wood. The welded bond-lines of beech and pine showed greater hysteresis than the unwelded wood from 0 to 55 % relative humidity. All specimens showed faster adsorption than desorption. However, the welded wood showed slower adsorption but faster desorption than unwelded wood. The time to complete half of the fractional change in moisture content (E(t) = 0.5) increased as the moisture content increased. The adsorption diffusion coefficients of beech and welded beech were higher than those of pine and welded pine up to 50 % and 40 % RH, respectively. In desorption, pine had a higher diffusion coefficient than beech in the whole range of 85-0 % RH. Analogously, welded pine had a higher diffusion coefficient than welded beech in the range of 85-5 % RH. In contrast to the desorption, the welded wood always had lower adsorption diffusion coefficients than the corresponding unwelded wood. The diffusion coefficients showed irregular patterns in some ranges of the RH. Therefore, it was hard to make a clear conclusion about the water-sorption behaviour of the specimens based on the defined diffusion coefficients.
Biodegradable and Flexible Wood-Gelatin Composites for Soft Actuating Systems
Koch, Sophie; Dreimol, Christopher; Goldhahn, Christian; et al. (2024)
ACS Sustainable Chemistry & Engineering
Compliant materials are indispensable for many emerging soft robotics applications. Hence, concerns regarding sustainability and end-of-life options for these materials are growing, given that they are predominantly petroleum-based and non-recyclable. Despite efforts to explore alternative bio-derived soft materials like gelatin, they frequently fall short in delivering the mechanical performance required for soft actuating systems. To address this issue, we reinforced a compliant and transparent gelatin-glycerol matrix with structure-retained delignified wood, resulting in a flexible and entirely biobased composite (DW-flex). This DW-flex composite exhibits highly anisotropic mechanical behavior, possessing higher strength and stiffness in the fiber direction and high deformability perpendicular to it. Implementing a distinct anisotropy in otherwise isotropic soft materials unlocks new possibilities for more complex movement patterns. To demonstrate the capability and potential of DW-flex, we built and modeled a fin ray-inspired gripper finger, which deforms based on a twist-bending-coupled motion that is tailorable by adjusting the fiber direction. Moreover, we designed a demonstrator for a proof-of-concept suitable for gripping a soft object with a complex shape, i.e., a strawberry. We show that this composite is entirely biodegradable in soil, enabling more sustainable approaches for soft actuators in robotics applications.
Iron-Catalyzed Laser-Induced Graphitization Enabling Current Collector-Free Electrodes With Spatially Tunable Iron/Iron Oxide Phases
Dreimol, Christopher; Edberg, Jesper; Kürsteiner, Ronny; et al. (2025)
Advanced Materials
Iron-catalyzed laser-induced graphitization (IC-LIG) represents an eco-efficient alternative to traditional carbon electrode manufacturing. Combining a bio-based tannic acid-iron precursor ink with CO₂ laser treatment results in sheet resistance of 23.59 ± 1.2 Ω square⁻¹ on renewable substrates. Varying the tannic-acid-to-iron ratio (TA:Fe), the rheology of the precursor ink can be tuned, enabling versatile application techniques, including spray coating, screen printing, and direct-ink-writing (DIW). Subsequent laser-treatment enables the formation of functional IC-LIG electrodes for all application methods, while even thick DIW-printed layers (260 μm) result in complex, conductive electrode patterns. Laser post-treatment expands design possibilities by locally tuning iron phases, such as converting γ-iron to magnetite. The unidirectional laser-treatment results in a layered arrangement, forming a multilayer electrode with a highly graphitized top layer serving as a current collector substitute, and an underlying composite of iron-rich nanoparticles embedded in a porous graphitic foam, acting as a hybrid electrode. Electrochemical analysis reveals double-layer capacitor behavior at low TA:Fe ratios, while higher ratios demonstrate increased redox activity and pseudo-capacitive characteristics. Achieving stable capacities of 15 mF cm⁻² with a 1 M NaCl electrolyte over 5000 cycles underscores the potential of IC-LIG electrodes as a sustainable solution for advanced energy storage devices and beyond.
Salt-In-Wood Piezoelectric Power Generators with Circular Materials Design for High-Performance Sustainable Energy Harvesting
Garemark, Jonas; Ritter, Maximilian; Dreimol, Christopher; et al. (2025)
Advanced Functional Materials
The nanowatt-level power density of current biobased piezoelectric energy harvesters restricts their applicative potential for the efficient conversion of biomechanical energy. A high-performing, fully renewable piezoelectric device incorporating green piezo-active Rochelle salt in a laser-drilled wood template is demonstrated to form ordered crystal pillar arrays by melt crystallization. Investigating the effect of different crystal pillar configurations on the piezoelectric response, a shearing design (45 degrees-oriented pillars) shows potential of up to 30 V and a current of 4 mu A - corresponding to a 10-fold power increase compared to single-crystalline Rochelle salt. A concept of direct laser graphitization on the crystal surfaces are demonstrated using a fully renewable ink to create electrodes of low resistance (36 Omega sq-1). The entire device can be disassembled, fully recycled, and reused. This nanogenerator outperforms state-of-the-art biobased ones and competes with conventional lead-based devices in power generation while showing a significantly lower environmental footprint, as indicated by life-cycle assessment.
Parameter estimation and model selection for water vapour sorption of welded bond-line of European beech and Scots pine
Vaziri, Mojgan; Dreimol, Christopher; Abrahamsson, Lars; et al. (2023)
Holzforschung
The single exponential kinetics (SEK) and parallel exponential kinetics (PEK) models were fitted to kinetic sorption data of welded and unwelded Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.). Furthermore, diffusion coefficients of water vapour in wood were determined using two different Fickian diffusion solutions. The objective was to identify how well these models could represent the moisture contents of the specimens and to characterize differences between the sorption behaviour of welded and unwelded wood. This knowledge can be used to enhance the moisture resistance of welded wood, develop drying schedules, and improve the quality of timbers. The PEK and SEK models provided the most precise and the second most precise fits to the sorption kinetic data, respectively. The two Fickian models are equivalent when both the infinite series are truncated at n = 10. The Fickian models also exhibited the highest discrepancy with the experimental data. Nevertheless, the Fickian models fit relatively better to the sorption data of the welded wood than to that of the unwelded wood. This behaviour may be due to the rigid and less-swelling structure of the welded bond line.
Passive climate regulation with transpiring wood for buildings with increased energy efficiency
Ding, Yong; Dreimol, Christopher; Zboray, Robert; et al. (2023)
Materials Horizons
Buildings are significant end-users of global energy. About 20% of the energy consumption worldwide is used for maintaining a comfortable indoor climate. Therefore, passive systems for indoor temperature and humidity regulation that can respond to environmental changes are very promising to reduce buildings' energy consumption. We developed a process to improve the responsiveness of wood to humidity changes by laser-drilling microscopic holes and incorporating a hygroscopic salt (calcium chloride). The resulting "transpiring wood" displays superior water adsorption capacity and high moisture exchange rate, allowing regulation of humidity and temperature by the exchange of moisture with the surrounding air. We proved that the hygrothermal performance of transpiring wood can be used to regulate indoor climate, with associated energy savings, for various climate types, thus favoring its application in the building sector. The reduction of temperature fluctuations, thanks to the buffering of temperature peaks, can lead to an indirect energy saving of about 10% for cooling and between 4-27% for heating depending on the climate. Furthermore, our transpiring wood meets different sustainability criteria, from raw materials to the fabrication process, resulting in a product with a low overall environmental impact and that is easy to recycle.
Microfluidic immersion freezing of binary mineral mixtures containing microcline, montmorillonite, or quartz
Shardt, Nadia; Isenrich, Florin N.; Nette, Julia; et al. (2025)
Atmospheric Chemistry and Physics
Mineral dusts are among the most active ice-nucleating particles present in cloud droplets, with their properties influencing radiative properties and precipitation formation. To improve weather predictions and climate projections, it is important to understand under which conditions ice will form on mineral dusts. Laboratory experiments have primarily focused on single minerals, and field samples are complex mixtures that cannot be controlled in their composition or particle size. To fill this gap, a bottom-up investigation of suspensions containing pure or binary mixtures of microcline, montmorillonite, or quartz at concentrations between 0.0001 and 0.1 wt % is presented. Arrays of monodisperse aqueous droplets (diameters of 75 μm) are generated using a microfluidic device and subsequently cooled at a rate of 1 K min^-1. The probability of freezing in the presence of binary mixtures generally follows that of the most ice-active mineral. Each pure mineral's nucleation site density is fit as a function of temperature and used to predict the frozen fraction curves for each binary mixture assuming additivity of mineral surface area. Predictions are also made for Arizona Test Dust from the obtained pure mineral fits, and general agreement with experiments is observed. This work presents a systematic study of ice formation in the presence of pure and binary mixtures of common mineral dusts, providing information for the future design of composition-aware parameterizations for ice nucleation in the atmosphere.

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