A MEMS Knudsen pump for high gas flow applications.

The Knudsen pump works on the principle of thermal transpiration. As a result of requiring a thermal gradient, channel hydraulic diameter smaller than the mean free path of the gas being pumped, and having no moving parts, the Knudsen pump features a simple and attractive design. The focus of this thesis is to develop a general relation for the ideal pump efficiency as well as to quantify thermal losses in the efficiency equation to predict the efficiency of fabricated pumps. Understanding the efficiency will enable a better understanding of the practical limits of the pump\u27s ability to transfer energy from a heat gradient to kinetic energy, in terms of flow rate, potential energy, and pressure gradient, generating a greater understanding of the applications for which the pump is best suited. Test method and results for a MEMS fabricated pump are provided. Thermal simulations of two designs are presented

Fabrication of Polymer and Nanocomposite Microstructures and Microactuators by Capillary Infiltration and Replica Molding.

Addition of micro- and/or nanoscale textures to surfaces can enable engineering of a wide range of properties. Passive surfaces (using fixed microstructures) can manipulate cell adhesion, liquid drag, and thermal and electrical contact resistance. Active surfaces (using shape-changing microstructures) can enable modulation of liquid wetting, adhesion, and optical properties. Nevertheless, it remains a challenge to fabricate the mechanically and environmentally robust microstructures and microactuators in large arrays. This thesis presents new fabrication methods for microstructured polymer and nanocomposite surfaces. Two approaches are pursued: capillary driven infiltration of fabricated carbon nanotube (CNT) microstructures and replica molding (REM) of master templates in liquid crystal networks (LCNs). First, it is demonstrated that CNT-polymer microstructures can function as robust large-area master molds. The fabricated microstructures include pins, tubes, re-entrant microwells, bent pillars, and high-aspect-ratio honeycombs (thickness of 400nm, aspect ratio 50:1). All are used as master structures for replica molding. A 25-fold replication sequence is shown with no physical degradation of the master or the replicas. Further, the increased stiffness and toughness of CNT-SU-8 microstructures is quantified. Second, active surfaces were created by capillary infiltration of paraffin into CNT forests. Large stroke sheet actuators, exhibiting up to 20% thermal strain at 175°C are shown. Third, thermally and optically active LCN microstructure replicas were created. Their generated strains were measured to be 6% and 0.25%, respectively. In situ monitoring of the LCN phase and order was also performed. Although having low strains, optically active microstructures are attractive for future work because they can be actuated individually and remotely. These scalable methods of fabricating microstructured surfaces, both with robust mechanical properties and active geometries, indicate promise for enhancement of liquid wetting, adhesion, optical properties, and thermal conductivity of surfaces and interfaces. However, further increases in the thermally and optically generated strains are needed to make useful active surfaces. This could be accomplished by either material reformulation, improvements in material processing, or strain amplification via design of microstructure geometry.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102390/1/copicd_1.pd

Hierarchical Assemblies of Carbon Nanotubes for Ultraflexible Li-Ion Batteries.

The flexible batteries that are needed to power flexible circuits and displays remain challenging, despite considerable progress in the fabrication of such devices. Here, it is shown that flexible batteries can be fabricated using arrays of carbon nanotube microstructures, which decouple stress from the energy-storage material. It is found that this battery architecture imparts exceptional flexibility (radius ≈ 300 μm), high rate (20 A g(-1) ), and excellent cycling stability.Engineering and Physical Sciences Research Council (Grant ID: EP/L025531/1)This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1002/adma.20160091

Anisotropic Carbon Nanotube Structures with High Aspect Ratio Nanopores for Li-Ion Battery Anodes.

Technological advances in membrane technology, catalysis, and electrochemical energy storage require the fabrication of controlled pore structures at ever smaller length scales. It is therefore important to develop processes allowing for the fabrication of materials with controlled submicron porous structures. We propose a combination of colloidal lithography and chemical vapor deposition of carbon nanotubes to create continuous straight pores with diameters down to 100 nm in structures with thicknesses of more than 300 μm. These structures offer unique features, including continuous and parallel pores with aspect ratios in excess of 3000, a low pore tortuosity, good electrical conductivity, and electrochemical stability. We demonstrate that these structures can be used in Li-ion batteries by coating the carbon nanotubes with Si as an active anode material

Resolving protein mixtures using microfluidic diffusional sizing combined with synchrotron radiation circular dichroism

Circular dichroism spectroscopy has become a powerful tool to characterise proteins and other biomolecules. For heterogeneous samples such as those present for interacting proteins, typically only average spectroscopic features can be resolved. Here we overcome this limitation by using free-flow microfluidic size separation in-line with synchrotron radiation circular dichroism to resolve the secondary structure of each component of a model protein mixture containing monomers and fibrils. To enable this objective, we have integrated far-UV compatible measurement chambers into PDMS-based microfluidic devices. Two architectures are proposed so as to accommodate for a wide range of concentrations. The approach, which can be used in combination with other bulk measurement techniques, paves the way to the study of complex mixtures such as the ones associated with protein misfolding and aggregation diseases including Alzheimer’s and Parkinson’s diseases

A Monolithically-Integrated μGC Chemical Sensor System

Gas chromatography (GC) is used for organic and inorganic gas detection with a range of applications including screening for chemical warfare agents (CWA), breath analysis for diagnostics or law enforcement purposes, and air pollutants/indoor air quality monitoring of homes and commercial buildings. A field-portable, light weight, low power, rapid response, micro-gas chromatography (μGC) system is essential for such applications. We describe the design, fabrication and packaging of μGC on monolithically-integrated Si dies, comprised of a preconcentrator (PC), μGC column, detector and coatings for each of these components. An important feature of our system is that the same mechanical micro resonator design is used for the PC and detector. We demonstrate system performance by detecting four different CWA simulants within 2 min. We present theoretical analyses for cost/power comparisons of monolithic versus hybrid μGC systems. We discuss thermal isolation in monolithic systems to improve overall performance. Our monolithically-integrated μGC, relative to its hybrid cousin, will afford equal or slightly lower cost, a footprint that is 1/2 to 1/3 the size and an improved resolution of 4 to 25%

Corrugated Paraffin Nanocomposite Films as Large Stroke Thermal Actuators and Self-Activating Thermal Interfaces

High performance active materials are of rapidly growing interest for applications including soft robotics, microfluidic systems, and morphing composites. In particular, paraffin wax has been used to actuate miniature pumps, solenoid valves, and composite fibers, yet its deployment is typically limited by the need for external volume constraint. We demonstrate that compact, high-performance paraffin actuators can be made by confining paraffin within vertically aligned carbon nanotube (CNT) films. This large-stroke vertical actuation is enabled by strong capillary interaction between paraffin and CNTs and by engineering the CNT morphology by mechanical compression before capillary-driven infiltration of the molten paraffin. The maximum actuation strain of the corrugated CNT-paraffin films (∼0.02−0.2) is comparable to natural muscle, yet the maximum stress is limited to ∼10 kPa by collapse of the CNT network. We also show how a CNT–paraffin film can serve as a self-activating thermal interface that closes a gap when it is heated. These new CNT–paraffin film actuators could be produced by large-area CNT growth, infiltration, and lamination methods, and are attractive for use in miniature systems due to their self-contained design

Corrugated Paraffin Nanocomposite Films as Large Stroke Thermal Actuators and Self-Activating Thermal Interfaces

High performance active materials are of rapidly growing interest for applications including soft robotics, microfluidic systems, and morphing composites. In particular, paraffin wax has been used to actuate miniature pumps, solenoid valves, and composite fibers, yet its deployment is typically limited by the need for external volume constraint. We demonstrate that compact, high-performance paraffin actuators can be made by confining paraffin within vertically aligned carbon nanotube (CNT) films. This large-stroke vertical actuation is enabled by strong capillary interaction between paraffin and CNTs and by engineering the CNT morphology by mechanical compression before capillary-driven infiltration of the molten paraffin. The maximum actuation strain of the corrugated CNT-paraffin films (∼0.02−0.2) is comparable to natural muscle, yet the maximum stress is limited to ∼10 kPa by collapse of the CNT network. We also show how a CNT–paraffin film can serve as a self-activating thermal interface that closes a gap when it is heated. These new CNT–paraffin film actuators could be produced by large-area CNT growth, infiltration, and lamination methods, and are attractive for use in miniature systems due to their self-contained design

Hygroscopic biomimetic transducers made from CNT-hydrogel composites

Plants as well as other biological organisms achieve directed movements by fibres that constraint and direct the isotropic expansion of a matrix material. In order to mimic these actuators, complex arrangements of rigid fibres must be achieved, which is challenging, especially at small scales. In this paper, a new method to organize carbon nanotubes (CNTs) into complex shapes is employed to create a framework for hydrogel infiltration. These CNT frameworks can be realized as iris, needle and bridge architectures, and after hydrogel infiltration, they show directed actuation in response to water uptake. Finally, we show how the latter can be employed as a novel hygroscopic sensor.status: publishe

Hydrothermal Coating of Patterned Carbon Nanotube Forest for Structured Lithium-Ion Battery Electrodes.

Controlling the arrangement and interface of nanoparticles is essential to achieve good transfer of charge, heat, or mechanical load. This is particularly challenging in systems requiring hybrid nanoparticle mixtures such as combinations of organic and inorganic materials. This work presents a process to coat vertically aligned carbon nanotube (CNT) forests with metal oxide nanoparticles using microwave-assisted hydrothermal synthesis. Hydrothermal processes normally damage delicate CNT forests, which is addressed here by a combination of lithographic patterning, transfer printing, and reduction of the synthesis time. This process is applied for the fabrication of structured Li-ion battery (LIB) electrodes where the aligned CNTs provide a straight electron transport path through the electrode and the hydrothermal coating process is used to coat the CNTs with conversion anode materials for LIBs. These nanoparticles are anchored on the surface of the CNTs and batteries fabricated following this process show a fourfold longer cyclability. Finally, this process is used to create thick electrodes (350 µm) with a gravimetric capacity of over 900 mAh g-1 .S.J. and M.D.V. acknowledge the ERC starting grant 337739‐HIENA. D.C. acknowledges the Marie Skłodowska‐Curie Actions MSCA‐IF 660351. S.J. acknowledges the EPSRC Studentship (Hierarchical Carbon nanostructures, 1470335). S.E. acknowledges funding from EPSRC grant EP/L016087/1. S.A. and M.D.V. acknowledge the financial support from DST‐UKIERI (DST/INT/UK/P‐167/2017)