WG
W.A. Groen
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9 records found
1
Bachelor thesis
(2019)
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D. de Boer, T.I.M. Koning, N.A. Leenders, Y.E. Lo-Fo-Sang, Omar Mauri, Matheus Silva, T.V. Tran, Thomas Tweedy, M.A.F. Verschoor, S. Zalman, W.A. Groen, C.A. Dransfeld, Y. Zhang
Bachelor thesis
(2018)
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M.R. Delgado Gosalvez, J.M. van Ham, S.K.B. Joosten, D.J. Juschus, G. Nieuwerth, T.M. van Pelt, L.O.J. Smit, Michel Takken, Yanbo Wang, T.G.J. Ziere, W.A. Groen, F.K. Leverone
Clear ice formation on aircraft is a large economic and safety problem. The phenomenon, also known as ‘freezing rain’, usually occurs when subcooled rain droplets impact the aircraft while it descends from high altitude to prepare for landing. It can quickly increase the aerodynamic drag by up to 80% and reduce the lift force by 50%. Inefficient heating methods or toxic or corrosive chemicals are used to keep flying safe. In this thesis, infrared imaging (IRI) and laser speckle imaging (LSI) are used to observe freezing of water on surfaces with different material properties. A freezing front can be seen to travel through a molecular liquid layer of water (MLL) that covers all surfaces. If this freezing front has passed, impacting droplets freeze much sooner and at unusually high temperatures, which could explain the formation of clear ice on aircraft surfaces.
In the past decade, the interest in anti-icing research has spiked. However, no systematic study has been performed to find out the origin of clear ice. Using the new insight of a freezing molecular liquid layer of water, this thesis is able to explain the origin of clear ice and runback icing. It also suggests that the ongoing conflict in literature on the anti-icing performance of superhydrophobic surfaces might be caused by the presence of the molecular layer of water.
With a systematic study, the surface temperature, contact angle and relative humidity were found to be able to delay freezing of the water layer and the contact angle was able to decrease the velocity of the freezing front. Using this insight, coating architectures and scalable production methods were used to produce hydrophilic-hydrophobic patterns for passive anti-icing coatings. ...
In the past decade, the interest in anti-icing research has spiked. However, no systematic study has been performed to find out the origin of clear ice. Using the new insight of a freezing molecular liquid layer of water, this thesis is able to explain the origin of clear ice and runback icing. It also suggests that the ongoing conflict in literature on the anti-icing performance of superhydrophobic surfaces might be caused by the presence of the molecular layer of water.
With a systematic study, the surface temperature, contact angle and relative humidity were found to be able to delay freezing of the water layer and the contact angle was able to decrease the velocity of the freezing front. Using this insight, coating architectures and scalable production methods were used to produce hydrophilic-hydrophobic patterns for passive anti-icing coatings. ...
Clear ice formation on aircraft is a large economic and safety problem. The phenomenon, also known as ‘freezing rain’, usually occurs when subcooled rain droplets impact the aircraft while it descends from high altitude to prepare for landing. It can quickly increase the aerodynamic drag by up to 80% and reduce the lift force by 50%. Inefficient heating methods or toxic or corrosive chemicals are used to keep flying safe. In this thesis, infrared imaging (IRI) and laser speckle imaging (LSI) are used to observe freezing of water on surfaces with different material properties. A freezing front can be seen to travel through a molecular liquid layer of water (MLL) that covers all surfaces. If this freezing front has passed, impacting droplets freeze much sooner and at unusually high temperatures, which could explain the formation of clear ice on aircraft surfaces.
In the past decade, the interest in anti-icing research has spiked. However, no systematic study has been performed to find out the origin of clear ice. Using the new insight of a freezing molecular liquid layer of water, this thesis is able to explain the origin of clear ice and runback icing. It also suggests that the ongoing conflict in literature on the anti-icing performance of superhydrophobic surfaces might be caused by the presence of the molecular layer of water.
With a systematic study, the surface temperature, contact angle and relative humidity were found to be able to delay freezing of the water layer and the contact angle was able to decrease the velocity of the freezing front. Using this insight, coating architectures and scalable production methods were used to produce hydrophilic-hydrophobic patterns for passive anti-icing coatings.
In the past decade, the interest in anti-icing research has spiked. However, no systematic study has been performed to find out the origin of clear ice. Using the new insight of a freezing molecular liquid layer of water, this thesis is able to explain the origin of clear ice and runback icing. It also suggests that the ongoing conflict in literature on the anti-icing performance of superhydrophobic surfaces might be caused by the presence of the molecular layer of water.
With a systematic study, the surface temperature, contact angle and relative humidity were found to be able to delay freezing of the water layer and the contact angle was able to decrease the velocity of the freezing front. Using this insight, coating architectures and scalable production methods were used to produce hydrophilic-hydrophobic patterns for passive anti-icing coatings.
Master thesis
(2018)
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Jan Jorissen, Pim Groen, Roserio Vieira Valente, Sybrand van der Zwaag, Jos Sinke
Incorporating carbon nanomaterials such as carbon nanotubes into a polymer matrix not only enhances the mechanical properties of the composite, but also induces good electrical properties. This makes carbon nanocomposite interesting for potential electronic applications, such as electromagnetic interference shielding by means of creating housings for electronic devices. One potential option of producing carbon nanocomposites is via injection molding, which is widely used in the plastics industry since it is a fast and cost effective method to mass-produce plastic parts.
Looking at the current state-of-the-art literature a lot of research in this area can be found. It has been identified that injection molding is not beneficial for high electrical properties of the composite and it leads to a non-uniform in-plane distribution of the electrical properties. Moreover treatments such as annealing have been described to enhance the electrical properties of the composites. However some shortcomings in the current research have been identified.
Hence this master thesis research aims at eliminating those shortcomings by characterizing the electrical properties of different injection-molded nanocomposites and their in-plane distribution. Moreover it has been investigated how additional treatments such as below melt temperature annealing and dielectricphoresis enhance the electrical properties and their in-plane distribution.
...
Looking at the current state-of-the-art literature a lot of research in this area can be found. It has been identified that injection molding is not beneficial for high electrical properties of the composite and it leads to a non-uniform in-plane distribution of the electrical properties. Moreover treatments such as annealing have been described to enhance the electrical properties of the composites. However some shortcomings in the current research have been identified.
Hence this master thesis research aims at eliminating those shortcomings by characterizing the electrical properties of different injection-molded nanocomposites and their in-plane distribution. Moreover it has been investigated how additional treatments such as below melt temperature annealing and dielectricphoresis enhance the electrical properties and their in-plane distribution.
...
Incorporating carbon nanomaterials such as carbon nanotubes into a polymer matrix not only enhances the mechanical properties of the composite, but also induces good electrical properties. This makes carbon nanocomposite interesting for potential electronic applications, such as electromagnetic interference shielding by means of creating housings for electronic devices. One potential option of producing carbon nanocomposites is via injection molding, which is widely used in the plastics industry since it is a fast and cost effective method to mass-produce plastic parts.
Looking at the current state-of-the-art literature a lot of research in this area can be found. It has been identified that injection molding is not beneficial for high electrical properties of the composite and it leads to a non-uniform in-plane distribution of the electrical properties. Moreover treatments such as annealing have been described to enhance the electrical properties of the composites. However some shortcomings in the current research have been identified.
Hence this master thesis research aims at eliminating those shortcomings by characterizing the electrical properties of different injection-molded nanocomposites and their in-plane distribution. Moreover it has been investigated how additional treatments such as below melt temperature annealing and dielectricphoresis enhance the electrical properties and their in-plane distribution.
Looking at the current state-of-the-art literature a lot of research in this area can be found. It has been identified that injection molding is not beneficial for high electrical properties of the composite and it leads to a non-uniform in-plane distribution of the electrical properties. Moreover treatments such as annealing have been described to enhance the electrical properties of the composites. However some shortcomings in the current research have been identified.
Hence this master thesis research aims at eliminating those shortcomings by characterizing the electrical properties of different injection-molded nanocomposites and their in-plane distribution. Moreover it has been investigated how additional treatments such as below melt temperature annealing and dielectricphoresis enhance the electrical properties and their in-plane distribution.
Piezoelectric materials have found application in wide range of devices from accelerometers to energy harvesters. They have proven their potential and versatility in aerospace, automotive, electronics and biomedical industry. Piezoelectric ceramics are not suitable for energy harvesting applications due to its brittleness and low strain levels, although having a high piezoelectric charge constant (d33). The polymer based piezoelectric composites offers high flexibility with low dielectric constant, hence having potential application in energy harvesting systems. Currently quasi-structured and fiber based piezoelectric composites offer the highest piezoelectric properties having the required flexibility for energy harvesting application. The polling processes of these composites though, are not so efficient due to the dielectric mismatch between the ceramic filer and surrounding polymer matrix. This leads to low piezoelectric charge constant than theoretically possible. To avoid this dielectric mismatch, dielectric constant cermic filler is added to get the required chain like particle structuring. The decrease in dielectric mismatch would lead to better poling due to increase in the active electric field experienced by the ceramic filler. The work here majorly focuses on development of a 3 phase piezoelectric composites having two different types of ceramic filers. Barium Titanate (BT) nanoparticles were added into a two phase Lead Zirconate Titanate (PZT)/Epoxy composite and were characterized to evaluate piezoelectric properties and particle structuring. The particle size effects of BT nanoparticles were also investigated.
...
Piezoelectric materials have found application in wide range of devices from accelerometers to energy harvesters. They have proven their potential and versatility in aerospace, automotive, electronics and biomedical industry. Piezoelectric ceramics are not suitable for energy harvesting applications due to its brittleness and low strain levels, although having a high piezoelectric charge constant (d33). The polymer based piezoelectric composites offers high flexibility with low dielectric constant, hence having potential application in energy harvesting systems. Currently quasi-structured and fiber based piezoelectric composites offer the highest piezoelectric properties having the required flexibility for energy harvesting application. The polling processes of these composites though, are not so efficient due to the dielectric mismatch between the ceramic filer and surrounding polymer matrix. This leads to low piezoelectric charge constant than theoretically possible. To avoid this dielectric mismatch, dielectric constant cermic filler is added to get the required chain like particle structuring. The decrease in dielectric mismatch would lead to better poling due to increase in the active electric field experienced by the ceramic filler. The work here majorly focuses on development of a 3 phase piezoelectric composites having two different types of ceramic filers. Barium Titanate (BT) nanoparticles were added into a two phase Lead Zirconate Titanate (PZT)/Epoxy composite and were characterized to evaluate piezoelectric properties and particle structuring. The particle size effects of BT nanoparticles were also investigated.
Flexible electronics have become the subject of industry focus, generating a market desire for fully flexible temperature sensors. To the best of our knowledge, there are no current systems that can adequately satisfy both the mechanical flexibility and sensing performance demanded for commercial applications. This work focused on a design for a flexible temperature sensor by designing a thermistor using functional granular composites using ceramic NTC fibre particles and a resistive polymer matrix. The objective was to achieve good thermistor performance (high sensitivity: B-value > 3000 K, and low resistivity: rho ˜ 10^1 - 10^2 Ocm) while being mechanically flexible (surviving bending radii = 1 cm over 100 cycles). To achieve this objective this thesis work was organised into 5 major phases. Due to the high commercial value of NTC ceramic thermistors, no reference composition with its exact processing conditions are available in literature that produce a thermistor with commercially desirable properties. Phase 1 was therefore to select a NTC ceramic composition and Phase 2 was to investigate the necessary processing conditions to be able to produce bulk ceramics with adequate temperature sensing performance. Phase 3 involved making NTC ceramic fibres by wet fibre spinning and modifying the processing conditions developed in Phase 2. Phase 4 involved the selection of an appropriate polymer matrix and to attempt to create thermistor composites. Phase 5 involved creating more optimal composite thermistors using stencil printing and to test its thermistor and bending performance. Using an isotropic mixture of Mn2.4 Ni0.5 Cu0.1 O4 NTC ceramic fibre particles in an Electrodag matrix, composite thermistors were created by stencil printing onto thin-film substrates of polyethylene terephthalate that have silver inkjet printed interdigitate electrodes. A percolated network is formed with as little as 10 wt% of fibres (˜ 2.86 vol%). The composite with 10 wt% of fibres has good thermistor performance at a low fibre content. The average resistivity at 25°C (rho_25) is low around 920 · 10^3 Ocm (with a standard deviation of 220 · 10^3 Ocm) and the sensitivity is high with a B-value = 3290 K and alpha = -3.7 %/K. The overall composite resistance and sensitivity can be tailored and customised by changing the gap width of the interdigitate electrodes. At an electrode gap width of 0.13 mm, with our interdigitate electrodes, R_25 = 280 kO and R_85 = 45 kO. The composite with 10 wt% fibre particle content and an electrode gap of 0.13 mm can survive 300 bends cycles (100 cycles with bending radius 10 mm (strain ˜ 0.621%), 100 cycles with bending radius 5 mm (strain ˜ 1.23%), 100 cycles with bending radius 2.5 mm (strain ˜ 2.44%) without any observable, aesthetic damage. The relative resistance (R/R0) does increase with bending, but after 20 bend cycles it appears to stabilise for every bending radius. In comparison to other flexible temperature sensors in recent literature, this thermistor composite is found to deliver a superior combination of thermistor performance and mechanical flexibility.
...
Flexible electronics have become the subject of industry focus, generating a market desire for fully flexible temperature sensors. To the best of our knowledge, there are no current systems that can adequately satisfy both the mechanical flexibility and sensing performance demanded for commercial applications. This work focused on a design for a flexible temperature sensor by designing a thermistor using functional granular composites using ceramic NTC fibre particles and a resistive polymer matrix. The objective was to achieve good thermistor performance (high sensitivity: B-value > 3000 K, and low resistivity: rho ˜ 10^1 - 10^2 Ocm) while being mechanically flexible (surviving bending radii = 1 cm over 100 cycles). To achieve this objective this thesis work was organised into 5 major phases. Due to the high commercial value of NTC ceramic thermistors, no reference composition with its exact processing conditions are available in literature that produce a thermistor with commercially desirable properties. Phase 1 was therefore to select a NTC ceramic composition and Phase 2 was to investigate the necessary processing conditions to be able to produce bulk ceramics with adequate temperature sensing performance. Phase 3 involved making NTC ceramic fibres by wet fibre spinning and modifying the processing conditions developed in Phase 2. Phase 4 involved the selection of an appropriate polymer matrix and to attempt to create thermistor composites. Phase 5 involved creating more optimal composite thermistors using stencil printing and to test its thermistor and bending performance. Using an isotropic mixture of Mn2.4 Ni0.5 Cu0.1 O4 NTC ceramic fibre particles in an Electrodag matrix, composite thermistors were created by stencil printing onto thin-film substrates of polyethylene terephthalate that have silver inkjet printed interdigitate electrodes. A percolated network is formed with as little as 10 wt% of fibres (˜ 2.86 vol%). The composite with 10 wt% of fibres has good thermistor performance at a low fibre content. The average resistivity at 25°C (rho_25) is low around 920 · 10^3 Ocm (with a standard deviation of 220 · 10^3 Ocm) and the sensitivity is high with a B-value = 3290 K and alpha = -3.7 %/K. The overall composite resistance and sensitivity can be tailored and customised by changing the gap width of the interdigitate electrodes. At an electrode gap width of 0.13 mm, with our interdigitate electrodes, R_25 = 280 kO and R_85 = 45 kO. The composite with 10 wt% fibre particle content and an electrode gap of 0.13 mm can survive 300 bends cycles (100 cycles with bending radius 10 mm (strain ˜ 0.621%), 100 cycles with bending radius 5 mm (strain ˜ 1.23%), 100 cycles with bending radius 2.5 mm (strain ˜ 2.44%) without any observable, aesthetic damage. The relative resistance (R/R0) does increase with bending, but after 20 bend cycles it appears to stabilise for every bending radius. In comparison to other flexible temperature sensors in recent literature, this thermistor composite is found to deliver a superior combination of thermistor performance and mechanical flexibility.
Piezoelectric energy harvesting technology is an alternative source for powering low power electronics. The ability of piezoelectric materials to convert ambient vibrational energy into usable electrical energy is seen as a promising battery-free solution to be used in inhospitable areas to self-power electronics for a longer time with little maintenance. The goal of this research is to maximise the mechanical input: elastic strain energy experienced by a lead zirconium titanate (PZT) bilayer piezoelectric buzzer by introducing four different boundary conditions during loading. Investigation of how mechanical input from each of these boundary condition influences the stored electrical output is carried out. The effect of three different static loads on each of the stored electrical output for four boundary conditions are studied. In order to accurately compare the data, the mechanical input (elastic strain energy) is calculated while the electrical output (stored energy) is measured experimentally. Given the brittle nature of ceramics, the maximum load bearing capacity for the PZT ceramic disc is determined by mechanical tests such as the ball-on-the-ring and uniaxial compression tests. This is to ensure that the experiments do not fracture the sample. Results show that, by inducing a bending mode in the buzzer, mechanical input values almost four orders of magnitude higher can be reached when compared to boundary conditions without bending modes. A similar result was found for the stored electrical energy with values for the bending mode of almost three orders of magnitude higher than when no bending is involved. The comparison between the calculated mechanical input and the measured electrical output shows good agreement in the boundary conditions involving bending. The energy conversion is highly efficient for the full range of applied loads for these boundary conditions. In the case of non-bending boundary conditions, the stored electrical energy is one order of magnitude high than predicted for the mechanical input and thus the model is in poor agreement with experiment.
...
Piezoelectric energy harvesting technology is an alternative source for powering low power electronics. The ability of piezoelectric materials to convert ambient vibrational energy into usable electrical energy is seen as a promising battery-free solution to be used in inhospitable areas to self-power electronics for a longer time with little maintenance. The goal of this research is to maximise the mechanical input: elastic strain energy experienced by a lead zirconium titanate (PZT) bilayer piezoelectric buzzer by introducing four different boundary conditions during loading. Investigation of how mechanical input from each of these boundary condition influences the stored electrical output is carried out. The effect of three different static loads on each of the stored electrical output for four boundary conditions are studied. In order to accurately compare the data, the mechanical input (elastic strain energy) is calculated while the electrical output (stored energy) is measured experimentally. Given the brittle nature of ceramics, the maximum load bearing capacity for the PZT ceramic disc is determined by mechanical tests such as the ball-on-the-ring and uniaxial compression tests. This is to ensure that the experiments do not fracture the sample. Results show that, by inducing a bending mode in the buzzer, mechanical input values almost four orders of magnitude higher can be reached when compared to boundary conditions without bending modes. A similar result was found for the stored electrical energy with values for the bending mode of almost three orders of magnitude higher than when no bending is involved. The comparison between the calculated mechanical input and the measured electrical output shows good agreement in the boundary conditions involving bending. The energy conversion is highly efficient for the full range of applied loads for these boundary conditions. In the case of non-bending boundary conditions, the stored electrical energy is one order of magnitude high than predicted for the mechanical input and thus the model is in poor agreement with experiment.