Browsing by Author "Viitanen, Leevi"
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Item Cellulose foams as scalable templates for phase change materials(Elsevier BV, 2023-12-10) Miranda-Valdez, Isaac Y.; Yazdani, Maryam Roza; Mäkinen, Tero; Coffeng, Sebastian; Viitanen, Leevi; Koivisto, Juha; Alava, Mikko J.; Department of Applied Physics; Department of Mechanical Engineering; Complex Systems and Materials; Energy Conversion and Systems; Department of Applied PhysicsCellulose foams produced by wet-templating fibers and surfactants offer an unlimited creative space for the design of green functional materials with a wide range of energy-related applications. Aiming to reduce plastic pollution, cellulose foams promise to replace plastic foams after tailoring physical functionalities into their structures. Here, this work demonstrates that cellulose foams made of methylcellulose and cellulose fibers can exhibit a solid–liquid phase change functionality by adding a phase change material (PCM) during the foam-forming process. The resulting foam composites, termed cellulose phase change foams (PCFs), exhibit a tenth of cellulose's density (134.7 kg m−3) yet a high Young's modulus (0.42MPa). They are also dimensionally stable over a wide range of temperatures while absorbing up to 108 kJ kg−1 as latent heat when the PCM confined to the foam experiences a solid-to-liquid transition at ∼60 °C, and releasing 108 kJ kg−1 as latent heat when changing from liquid to solid at ∼40 °C. Such phase change transition opens up broad applications for the PCFs as thermal insulators. For example, by further tuning the transition temperature, the PCFs can exploit their phase change and reduce the heat flow rate through their radial direction at specified temperatures. This article showcases the versatility of the foam-forming process of cellulose to accommodate physical functionalities in materials with complex architectures. Furthermore, thanks to the advances in cellulose foam-forming, such foams are recyclable, industrially scalable, and can be exploited as heat storage materials.Item Chlamydomonas reinhardtii swimming in the Plateau borders of 2D foams(ROYAL SOC CHEMISTRY, 2021-01-07) Tainio, Oskar; Sohrabi, Fereshteh; Janarek, Nikodem; Koivisto, Juha; Puisto, Antti; Viitanen, Leevi; Timonen, Jaakko; Alava, Mikko; Department of Applied Physics; Active Matter; Complex Systems and MaterialsUnicellular Chlamydomonas reinhardtii micro-algae cells were inserted into a quasi-2D Hele-Shaw chamber filled with saponin foam. The movement of the algae along the bubble borders was then manipulated and tracked. These self-propelled particles generate flow and stresses in their surrounding matter. In addition, the algae possess the capability of exerting forces that alter bubble boundaries while maintaining an imminent phototactic movement. We find that by controlling the gas fraction of the foam we can change the interaction of the algae and bubbles. Specifically, our data expose three distinct swimming regimes for the algae with respect to the level of confinement due to the Plateau border cross-section: unlimited bulk, transition, and overdamped regimes. At the transition regime we find the speed of the algae to be modeled by a simple force balance equation emerging from the shear inside the Plateau border. Thus, we have shown that it is possible to create an algae-friendly foam while controlling the algae motion. This opens doors to multiple applications where the flow of nutrients, oxygen and recirculation of living organisms is essential.Item Constriction Flow of Cellulose Laden Air-Aqueous Foam(NORTH CAROLINA STATE UNIV DEPT WOOD & PAPER SCI, 2019) Viitanen, Leevi; Halonen, Alisa; Fristrom, Eira; Koivisto, Juha; Korhonen, Marko; Puisto, Antti; Alava, Mikko; Department of Applied Physics; Department of Computer Science; Complex Systems and Materials; Department of Applied Physics; Department of Computer ScienceFoams are encountered in everyday life across wide applications, e.g., in foods and cleaning products. They have also been widely used in different industries in processes such as flotation and oil recovery. The application of bio-based materials is a novel interest, and foam forming enables these materials to be used more flexibly. For efficient industrial usage, the flow of such materials must be well understood and characterized. This work measured the velocity field of nanocellulose laden foam in a two-dimensional Hele-Shaw cell with a constriction, using optical imaging and particle image velocimetry. The measurements showed that the addition of cellulose increased the effective viscosity of the liquid films. In a numerical simulation using the Giesekus polymer model, the experimental trend was reproduced through increasing the fluid's viscosity. Adding highly viscoelastic nanofibrillated cellulose suspension to foam affected only the viscous component of the foam. The delayed elastic response did not change.Item Design and development of a flow optimization module for liquid foam(2024) Vuorilehto, Akseli; Viitanen, Leevi; Insinööritieteiden korkeakoulu; Ekman, KaleviBiobased foams have the potential to replace its polluting plastic counterpart. Developing and building the production process around these new biomaterials brings up challenges. The purpose of this master’s thesis is to study the options of flow controlling and monitoring a non-Newtonian liquid foam. The gained knowledge is applied, following a product development path to achieve an affordable flow controlling unit for a bio-foam production process used by Woamy oy. In this study, the properties of the non-Newtonian fluids are considered in relation to the different controlling methods involving valves, actuators, and flow monitoring solutions. The small-scale trials revealed that the foam produced by Woamy exhibits shear thinning behaviour. The gained background knowledge in combination with the trials helped making the decision for control method. The choice was made to use a 60-degree v-profiled ball valve for flow control in addition with a correctly sized digital servo motor. For the flow speed measuring method options, pressure and optical methods were considered and tested. The optical approach was chosen for multiple advantages, which included affordability, accuracy, and compatibility. The individually chosen components come together to form four affordable flow control unit prototypes. The prototyped flow control units are controlled from a single Raspberry pi computer, which reads the process foam flow speeds and logs necessary parameters for later evaluation. The Raspberry commands an Arduino based on the received flow speeds values to actuate the process flow control valves for optimal flow conditions. The tested hardware in combination with an automation logic is reliably capable of stabilizing and controlling the flow to a desired degree with no human assistance, and thus is deemed worthy for broader use in Woamy’s production process. The developed control unit works as intended, however some key areas can be further improved in the future.Item Enhancing water resistivity of bio-based foam with organic polymers(2022-11-07) Lejon, Juha; Viitanen, Leevi; Perustieteiden korkeakoulu; Alava, MikkoItem Erratum: Chlamydomonas reinhardtii swimming in the Plateau borders of 2D foams (Soft Matter (2021) 17 (145–152) DOI: 10.1039/D0SM01206H)(ROYAL SOC CHEMISTRY, 2021-07-21) Tainio, Oskar; Sohrabi, Fereshteh; Janarek, Nikodem; Koivisto, Juha; Puisto, Antti; Viitanen, Leevi; Timonen, Jaakko V.I.; Alava, Mikko; Department of Applied Physics; Complex Systems and Materials; Active Matter; Department of Applied PhysicsThe authors regret that two of the concentrations in section 2.1 of the Methods section of the original article were incorrect. The first error is in the number concentrations of cells in the cultures used in the experiments. In the original article, the authors stated: ‘‘The number density of cells in the cultures used for experiments was around 106 cells per ml.’’ However, the correct concentration was 106 cells per ml, so the unit in the original sentence is wrong. The second error is in the concentration of saponin. The authors stated: "The solution consisted of high salt medium, active C. reinhardtii cells and saponin (c = 0.5 g ml-1)." The original article is missing one zero in the saponin concentration and the correct concentration here should be c = 0.05 g ml-1)." . The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.Item The flow of foam around an obstacle in Hele-Shaw cell(2017-11-07) Viitanen, Leevi; Koivisto, Juha; Puisto, Antti; Perustieteiden korkeakoulu; Alava, MikkoThis study investigates the flow of a two-dimensional foam between two parallel plates. The project includes building the appropriate experimental apparatus, which would allow studying the flow field around a circular obstacle by filming the bubbles with a regular camera. Furthermore, it has the required flexibility to study the effect of boundary conditions, induced by the cell, to the foam rheology are studied by varying the flow driving. The experiments show that the driving of the flow, whether it is by pressure or moving the obstacle, has a significant effect to the flow field and thus to the foam rheology. The distinct values of static and dynamic friction between the bubbles and the top and bottom plate are expected to be the cause of the difference in the data obtained with different boundary conditions. Also the foam flow around the obstacle is found to be influenced by the foam’s liquid-gas ratio. Finally, the velocity field is compared to the changes in the bubble contacts. Despite the difficulties in the analysis, the results indicate that bubbles rearrange more frequently at the parts of the device where the spatial variation of the velocity is rapid.Item Foam-formed biocomposites based on cellulose products and lignin(SPRINGER, 2023-03) Miranda-Valdez, Isaac Y.; Coffeng, Sebastian; Zhou, Yu; Viitanen, Leevi; Hu, Xiang; Jannuzzi, Luisa; Puisto, Antti; Kostiainen, Mauri A.; Mäkinen, Tero; Koivisto, Juha; Alava, Mikko J.; Department of Applied Physics; Department of Bioproducts and Biosystems; Complex Systems and Materials; Biohybrid Materials; Department of Applied Physics; Complex Systems and Materials; VTT Technical Research Centre of FinlandAbstract: Foam-formed cellulose biocomposites are a promising technology for developing lightweight and sustainable packaging materials. In this work, we produce and characterize biocomposite foams based on methylcellulose (MC), cellulose fibers (CF), and lignin (LN). The results indicate that adding organosolv lignin to a foam prepared using MC and CF moderately increases Young’s modulus, protects the foam from the growth of Escherichia coli bacteria, and improves the hydrophobicity of the foam surface. This article concludes that organosolv lignin enhances many properties of cellulose biocomposite foams that are required in applications such as insulation, packaging, and cushioning. The optimization of the foam composition offers research directions toward the upscaling of the material solution to the industrial scale. Graphical abstract: [Figure not available: see fulltext.].Item Influence of geometry and density on the compressive behavior of cellulose based foam(2024-06-10) Ghaemi, Aref; Koivisto, Juha; Viitanen, Leevi; Insinööritieteiden korkeakoulu; Freund, JouniFoam materials have become integral in various industries in recent decades due to their lightweight nature and unique mechanical properties. Despite their versatility, challenges persist especially in their shift from being a fossil-fuel-based to bio-based material, particularly in mechanical behavior such as shape recovery capacity. This thesis aims to advance the understanding and optimization of compression properties of bio-based foam materials developed by Woamy Oy, crucial for sustainability and broader application potential. The experimental approach taken in this study revolves around exploiting various foam orientation, density, shapes, and Origami patterns in a compression loading scenario with the goal of identifying the most promising configuration for future development and to provide a more quantitative understanding of the material. It is established that increasing the density by introducing permanent compressive damage to foam sheets in a zero-degree orientation stacking scenario could result in higher specific compressive stress at various strain values with a 42.2 percent increase at peak values as a results of efforts in this work. In addition, optical microscopy technique is used to investigate the effect of pre-compression on the microstructure of the material before and after compressing the samples to 70 percent of their original height. The results show that the microstructure of the samples with higher density are packed with microfibers more than it is in the ones with lower density. Deformation is also observed in the cells of the samples with higher density as a result of pre-compression. Cells and voids in the microstructure of the material show recovery of shape even after testing, with more recovery in the samples with lower density.Item Local time-dependent microstructure of aging TEMPO nanofibrillated cellulose gel(SPRINGER, 2023-01) Koochi, Hakimeh; Mac Intyre, Jonatan; Viitanen, Leevi; Puisto, Antti; Maleki-Jirsaraei, Nahid; Alava, Mikko; Department of Applied Physics; Complex Systems and Materials; VTT Technical Research Centre of Finland; Alzahra UniversityThe aging behavior of TEMPO-CNF suspensions is investigated using rheological measurements and experiments involving the free-falling solid sphere. The properties of CNF suspensions, which are formed of water and cellulose fibers with a large aspect ratio, are fundamentally different from those commonly known as model low-density gels. We characterize their aging utilizing SAOS rheometry following a period of shear rejuvenation, measuring the effect of aging time on the observed stress overshoot, and additionally measure the rheological hysteresis under continuous shear. In addition to such tests, which probe the sample at the bulk level, we study their local aging behavior via the Stokes' experiment. During SAOS, the aging of the material results in a logarithmic growth of the elastic modulus over the first 50 minutes. In the Stokes' experiment, depending on the sphere size, we find a systematic decrease in the sphere velocity with aging times up to 16 days and identify a range of intermittent particle motion. Based on our experimental evidence, we propose that the aging effect within the TEMPO-CNFs occurs due to the restructuring of fibrous elements by Brownian diffusion and that the aging of the system does not develop homogeneously across the whole sample as a consequence of the wide size distribution of CNFs. Finally, we note that this may be one of the primary reasons why the rheological data on even the same batch of CNFs show a large scatter.Item Machine learning and predicting the time dependent dynamics of local yielding in dry foams(American Physical Society, 2020-06) Viitanen, Leevi; Mac Intyre, Jonatan; Koivisto, Juha; Puisto, Antti; Alava, Mikko; Department of Applied Physics; Complex Systems and MaterialsThe yielding of dry foams is enabled by small elementary yield events on the bubble scale, “T1”s. We study the large-scale detection of these in an expanding two-dimensional (2D) flow geometry using artificial intelligence (AI) and nearest neighbor analysis. A good level of accuracy is reached by the AI approach using only a single frame, with the maximum score for vertex centered images highlighting the important role the vertices play in the local yielding of foams. We study the predictability of T1s ahead of time and show that this is possible on a timescale related to the waiting time statistics of T1s in local neighborhoods. The local T1 event predictability development is asymmetric in time, and measures the variation of the local property to yielding and similarly the existence of a relaxation timescale after local yielding.Item Measuring biofoam anisotropy using optical coherence tomography(SPRINGER, 2022-05-27) Mac Intyre, Jonatan; Raka, Doruntina; Aydin, Mehmet; Viitanen, Leevi; Koivisto, Juha; Department of Applied Physics; Complex Systems and Materials; Department of Applied PhysicsOptical coherence tomography enables quick scans of translucent objects in a simple environment. Here, we apply this technique to wood-based biofoam. We measure the geometrical properties of the foam, such as bubble eccentricity and density fluctuations, in addition to characterising the possible orientation of fibres. We find that the wood-based foams are extremely suitable for optical coherence tomography due to their translucent nature and large changes of optical density between air-filled bubbles and solid films. Measurement of bubble eccentricity revealed a reasonably high aspect ratio of 1:2, enabling the orientation of long cellulose fibres if added to the mixture. The results demonstrate an effective method to characterise foamlike metamaterials. Furthermore, focusing on eccentricity enables the adjustment of the foam’s manufacturing method and, in turn, helps to produce anisotropic structures.Item Predicting and following T1 events in dry foams from geometric features(American Physical Society, 2021-07-15) Tainio, Oskar; Viitanen, Leevi; Mac Intyre, Jonatan; Aydin, Mehmet; Koivisto, Juha; Puisto, Antti; Alava, Mikko; Department of Applied Physics; Complex Systems and Materials; Department of Applied PhysicsMachine learning techniques have been recently applied in predicting deformation in amorphous materials. In this study, we extract structural features around liquid film vertices from images of flowing 2D foam and apply a multilayer perceptron to predict local yielding. We evaluate their importance in the description of the T1 events and show that a high level of predictability may be achieved using well-chosen combinations of features as the prediction data. The most relevant features are extracted by performing the predictions separately for isolated sets of features, and these findings are verified using principal component analysis. Using this approach, we determine which properties of the images are most important with regard to the physics of the processes. Our findings indicate that film lengths and angles between the liquid films joining at the vertex are the most important features that predict the local yield events. These two features describe 83% of the yield events. As an application, we extract the statistics of event waiting times from the experiment.Item Predicting avalanches in fracture(2016-09-06) Viitanen, Leevi; Ovaska, Markus; Perustieteiden korkeakoulu; Alava, MikkoItem Predicting Creep Failure from Cracks in a Heterogeneous Material using Acoustic Emission and Speckle Imaging(American Physical Society, 2019-02-06) Viitanen, Leevi; Ovaska, Markus; Ram, Sumit Kumar; Alava, Mikko J.; Karppinen, Pasi; Department of Applied Physics; Complex Systems and MaterialsFinding out when cracks become unstable is at the heart of fracture mechanics. Cracks often grow by avalanches and when a sample fails depends on its past avalanche history. We study the prediction of sample failure in creep fracture under a constant applied stress and induced by initial flaws. Individual samples exhibit fluctuations around a typical rheological response or creep curve. Predictions using the acoustic emission from the intermittent crack growth are not feasible until well beyond the sample-dependent minimum strain rate. Using an optical speckle analysis technique, we show that predictability is possible later because of the growth of the fracture process zone.Item Predicting effect of fibers on thermal gelation of methylcellulose using Bayesian optimization(Elsevier Science Ltd., 2022) Miranda Valdez, Isaac; Viitanen, Leevi; Mac Intyre, Jonatan; Puisto, Antti; Koivisto, Juha; Alava, Mikko; Department of Applied Physics; Complex Systems and MaterialsUnderstanding of the viscoelastic behavior of a polymer is a prerequisite for its thermomechanical processing beyond laboratory scale. Utilizing rheological characterization is a powerful tool to comprehend the complex nature and time-dependent properties of macromolecular materials. Nevertheless, it consumes time as rheometry involves iterating experiments under several conditions to visualize the non-linear behavior of materials under varying conditions. The work hereunder examines the rheology of cellulosic aqueous suspensions prepared using cellulose fibers as the dispersed phase (Refcell and Storacell) and methylcellulose (MC) as the polymeric matrix. Interfacial phenomena between MC and cellulose fibers arise in particle laden systems with supramolecular structures formed by non-covalent interactions. Therefore, this study elucidates the rheological evolution of these interactions as a function of temperature and fiber concentration. This study displays how researchers may reduce the number of rheological experiments and save time utilizing a novel method based on a Bayesian optimization with Gaussian processes.Item Probing the local response of a two-dimensional liquid foam(SPRINGER, 2019-02-01) Viitanen, Leevi; Koivisto, Juha; Puisto, Antti; Alava, Mikko; Santucci, Stephane; Department of Applied Physics; Complex Systems and Materials; École normale supérieure de LyonAqueous foams are viscoelastic yield stress fluids. Due to their complex rheology, foam flow around an obstacle embedded in a 2D Hele-Shaw cell has been widely studied. Typically, in such geometry in the moving flow reference frame the flow field of viscoelastic fluids exhibit a quadrupolar structure characterized by a negative wake. Here, we introduce a measuring geometry, new in this context, whereby instead of flowing the foam around the obstacle, we move the obstacle as an intruder inside the foam. The proposed setup makes it possible to independently control the driving velocity and the liquid foam properties, such as the gas fraction and polydispersity. We show that the liquid foam velocity field around the intruder is similar to the one observed in viscoelastic fluids, in particular the emergence of a negative wake, e.g. a velocity overshoot downstream side of the obstacle. However, surprisingly, the intensity of this velocity overshoot decreases with the number of intruder passes, probably related to the evolution of the local disordered structure of the liquid foam.Item Rheological properties of structured complex fluids(Aalto University, 2022) Viitanen, Leevi; Koivisto, Juha, Dr., Aalto University, Finland; Teknillisen fysiikan laitos; Department of Applied Physics; Complex systems and materials; Perustieteiden korkeakoulu; School of Science; Alava, Mikko, Prof., Aalto University, Department of Applied Physics, FinlandFoams are present in many applications of modern-day life, however, one seldom stops to admire their beautiful structure and fascinating dynamics. These properties make foams a subject of extensive scientific research ranging from elementary dynamics of amorphous materials to applications in industry and consumer products. The present article dissertation addresses the deformation, yielding and flow of foams using experimental methods. The emphasis is on predicting the deformation and yielding, and modifying the flow properties of foam with varying experimental parameters. The four articles reveal the importance of the local configuration and dynamics in defining the macroscopic flow response and how tuning the local interactions alters the mechanical deformation of foams. Publications I and II adapt view from amorphous solids where the foam deforms plastically in local topological transformations and these events define the macroscopic dynamics. The center of this view is the ability to predict these events from the past configuration of the foam. Both of the publications apply machine learning tools to large data sets describing foam motion and classify locations with high propensity to yield. Publication I reveals that the vertex, transforming in the yield event, results in the best predictions of the yielding. In addition, Publication I characterizes the essential time scale for predictions to be around 1 second for the used system. Publication II studies the essential features of the yielding vertex in more detail. The analysis reveals the essential predictors for yield events which are the angles of films joining in the vertex and the lengths of the films joining in the vertex. Publication III studies the effect of external mechanical vibration on the flow of foam. An external pressure drives foam flow in an experimental cell which is vibrated. The results showed that the vibration enables flow on small driving pressure below yielding and enhances the flow velocity on small pressures that exceed the yielding. Publication III provides evidence that the vibration increases the probability of yield events which then decreases the effective viscosity. Publication IV modifies the flow properties of foam with fibers in the continuous medium. The fibers decrease the flow velocity of foam. Although, the fibers form a viscoelastic fluid, the fibers in the continuos medium do not enhance the elastic response of the foam indicating that the origin of the elasticity of the foam remains in the bubble matrix. Giesekus model describes well the foam flow, and the addition of the fibers may be incorporated to the model with increasing the ratio of viscous contribution to the elastic contribution.Item Scalable method for bio-based solid foams that mimic wood(Nature Publishing Group, 2021-12-21) Reichler, Mikael; Rabensteiner, Samuel; Törnblom, Ludwig; Coffeng, Sebastian; Viitanen, Leevi; Jannuzzi, Luisa; Mäkinen, Tero; Mac Intyre, Jonatan R.; Koivisto, Juha; Puisto, Antti; Alava, Mikko; Department of Applied Physics; Complex Systems and Materials; Department of Applied Physics; Aalto University; Complex Systems and MaterialsMimicking natural structures allows the exploitation of proven design concepts for advanced material solutions. Here, our inspiration comes from the anisotropic closed cell structure of wood. The bubbles in our fiber reinforced foam are elongated using temperature dependent viscosity of methylcellulose and constricted drying. The oriented structures lead to high yield stress in the primary direction; 64 times larger than compared to the cross direction. The closed cells of the foam also result in excellent thermal insulation. The proposed novel foam manufacturing process is trivial to up-scale from the laboratory trial scale towards production volumes on industrial scales.Item Study of drying technologies on a cellulose based material(2024-03-11) Gil Escribano, Juan; Viitanen, Leevi; Insinööritieteiden korkeakoulu; Partanen, JouniBio foams have been recently proposed as an alternative to single use plastics in order to reduce their enviromental impact. A bottleneck on the production of bio foams has been identified in the drying process. In this study, multiple drying technologies, such as hot-air, air impingement, and infrared radiation, are tested on a cellulose based foam. Drying rates are calculated for each of the technologies tested at different temperature ranges. The resulting foam quality is also evaluated for each of the technologies. It is stablished that air impingement holds the highest drying rates with up to 18.6 kg of H2O per h per m2 at 290ºC. The lowest temperature tested with impingement, with a drying rate of 11.4 kg of H2O per h per m2 at 175ºC, is twice as high as the drying rate obtained with hot air and infrared. The foam quality obtained under hot-air and impingement drying was satisfactory, while the one subject to only infrared ranged from poor to acceptable. Based on theoretical background research a drying process combined the tested technologies is proposed. Additionally, it was found a shift on the foam properties when dried with air at high temperatures, which is likely to happened to the degradation of the methylcellulose.
