Transfer Method of Carbon Nanotube Film for Embedded Transparent Electrode

We describe new transfer method of carbon nanotube (CNT) film onto the poly-dimethysiloxane (PDMS) based on the poor adhesion between Si wafer and Au layer. To combine the CNT film with the polymer-MEMS field, it is required to transfer CNT film onto the polymer substrates. CNT film was fabricated by vacuum filtration method and was transferred onto the Au-deposited Si wafer. Using photolithography process, CNT film was patterned and PDMS is pouring and curing on the wafer. After peeling off the PDMS, patterned CNT film was transferred which was embedded into the PDMS. The possibility of embedded CNT film in the micro system was demonstrated in the application of electro-thermal actuator.

High Throughput Continuous Fabrication of Large Surface Area Microstructured PDMS

Rapid creation of devices with microscale features is a vital step in the commercialization of a wide variety of technologies, such as microfluidics, fuel cells and self-healing materials. The current standard for creating many of these microstructured devices utilizes the inexpensive, flexible material poly-dimethylsiloxane (PDMS) to replicate microstructured molds. This process is inexpensive and fast for small batches of devices, but lacks scalability and the ability to produce large surface-area materials. The novel fabrication process presented in this paper uses a cylindrical mold with microscale surface patterns to cure liquid PDMS prepolymer into continuous microstructured films. Results show that this process can create continuous sheets of micropatterned devices at a rate of 3.94 in2/sec (100 mm2/sec), almost an order of magnitude faster than soft lithography, while still retaining submicron patterning accuracy.

High Pressure On-Chip Valves for Thermoplastic Microfluidics

A high-pressure microvalve technology based on the integration of discrete elastomeric elements into rigid thermoplastic chips is described. The low-dead-volume valves employ deformable polydimethylsiloxane (PDMS) plugs actuated using a threaded stainless steel needle, allowing exceptionally high pressure resistance to be achieved. The simple fabrication process is made possible through the use of poly(ethylene glycol) (PEG) as a removable blocking material to avoid contamination of PDMS within the flow channel while yielding a smooth contact surface with the PDMS valve surface. Burst pressure tests reveal that the valves can withstand over 24MPa without leakage.

A Compact Nanostructure Integrated Pool Boiler for Microscale Cooling Applications

An efficient cooling system consisting of a plate, on which copper nanorods (nanorods of size ∼100nm) are integrated to copper thin film (which is deposited on Silicon substrate), a heater, an Aluminum base, and a pool was developed. Heat is transferred with high efficiency to the liquid within the pool above the base through the plate by boiling heat transfer. Near the boiling temperature of the fluid, vapor bubbles started to form with the existence of wall superheat. Phase change took place near the nanostructured plate, where the bubbles emerged from. Bubble formation and bubble motion inside the pool created an effective heat transfer from the plate surface to the pool. Nucleate boiling took place on the surface of the nanostructured plate helping the heat removal from the system to the liquid above. The heat transfer from nanostructured plate was studied using the experimental setup. The temperatures were recorded from the readings of thermocouples, which were successfully integrated to the system. The surface temperature at boiling inception was 102.1°C without the nanostructured plate while the surface temperature was successfully decreased to near 100°C with the existence of the nanostructured plate. In this study, it was proved that this device could have the potential to be an extremely useful device for small and excessive heat generating devices such as MEMS or Micro-processors. This device does not require any external energy to assist heat removal which is a great advantage compared to its counterparts.

Experimental Study of Structure-Electrical Transport Correlation in Single Disordered Carbon Nanowires

We present experimental results characterizing the changes in electrical transport of single disordered carbon nanowires (diameter 150–250 nm) to the changes in microstructure within the nanowires induced by synthesis temperature. The material system studied is a nanoporous, semiconducting disordered carbon nanowire obtained from the pyrolysis of a polymeric precursor (polyfurfuryl alcohol). Unlike the other allotropes of carbon such as diamond, graphite (graphenes) and fullerenes (CNT, buckyballs), disordered carbons lack crystalline order and hence can exhibit a range of electronic properties, dependent on the degree of disorder and the local microstructure. Such disordered carbon nanowires are therefore materials whose electronic properties can be engineered to specifications if we understand the structure-property correlations. Using dark DC conductivity tests, measurements were performed from 300K to 450K. The charge transport behavior in the nanowires is found to follow an activation-energy based conduction at high temperatures. The conductivity for nanowires synthesized from 600°C to 2000°C is calculated and is linked to changes in the microstructure using data obtained from SEM, TEM and Raman spectroscopy. The electrical properties of the nanowire are shown to be linked intrinsically to the microstructure and the degree of disorder, which in turn can be controlled to a great extent just by controlling the pyrolysis temperature. This ability to tune the electrical property, specifically conductivity, and map it to the structural changes within the disordered material makes it a candidate material for use in active/passive electronic components, and as versatile transducers for sensors.

Experimental Approach for Developing and Testing Predictive Self-Assembly Models

Testing methods and apparatus for studying capillary self-assembly processes are presented. This system permits the control of key self-assembly process variables so that relationships between process rates and yields and the process variables can be tested. Part arrival energies and angles are controlled by dropping through a fluid at terminal velocity onto fixed substrate binding sites. Using this system, the assembly probability at the low energy limit is shown to match a simple area fraction relationship.

Joint Use of Traveling Wave Dielectrophoresis and AC-Electroosmosis for Particle Manipulation

Joint effect of traveling wave dielectrophoresis and AC electroosmotic fluid flow is used to sort bacteria from other particles and increase the bacteria output concentration in a microfluidic device. The device consists of a thin and long rectangular channel with two interdigitated electrode arrays, one at the bottom and one at the top of the channel, that are used to generate a nonuniform electric field. A four-phase signal at high frequency superposed on a low frequency signal is applied. At the end of the channel, the fluid is collected in two outputs: the bacteria are collected on one side and fluid without bacteria is collected on the other side. We have previously demonstrated a method to optimize cell separation using multiple frequency dielectrophoresis. The device presented here illustrates a novel use of multiple frequencies that permits the combined use of traveling wave dielectrophoresis and AC electroosmotic fluid flow.

Implementation of an Efficient Algorithm for Virtual Prototyping of Dynamics of Molecular Conformation

This paper presents an O(N) algorithm and its preliminary computer simulation results for virtual prototyping of molecular systems with a simple chain structure. The algorithm is based on proper integration between an internal coordinate method (ICM) and a multibody molecular model. ICM method makes the use of recursive relations possible between two adjacent subsets within a molecular system. The multibody molecular model takes the benefits of freezing degrees of freedom of some lightly excited high frequency bonds. Because these high frequency bonds would force the use of very small integration step sizes, which severely limits the time scales for virtual prototyping of dynamics of molecular conformation over long periods of time. Thus a new multiscale model and efficient algorithm is produced to increase computational efficiency for virtual prototyping of dynamical behaviors of molecular confirmation. This paper will be initially directed towards introduction of the new model and algorithm. Then attention will be turned to the implementation of the algorithm at macro scale, which can be used to demonstrate the validity of the procedure and algorithm. Final focus will be turned to the implementation of the algorithm to a simple molecular chain at micro scale. The algorithm gives an O(N) computational performance for formation/solution of equations of motion for a molecular chain system.

Numerical Study on Electrokinetic Interaction Between a Pair of Cylindrical Colloidal Particles

Electrophoresis is the motion of dispersed particles relative to a fluid under the influence of an electric field. Presently this phenomenon of electrokinetics is widely used in biotechnology for the separation of proteins, sequencing of polypeptide chains etc. The separation efficiency of these biomolecules is affected by their aggregation. Thus it is important to study the interaction forces between the molecules. In this study we calculate the electrophoretic motion of a pair of colloidal particles under axial electric field. The hydrodynamic and electric double layer (EDL) interaction forces are calculated numerically. The EDL interaction force is calculated from electric field distribution around the particle using Maxwell stress tensor and the hydrodynamic force is calculated from the flow field obtained from the solution of Stokes equations. The continuous forcing approach of immersed boundary method is used to obtain flow field around the moving particles. The EDL distribution around the particles is obtained by solving Poisson-Nernst-Planck (PNP) equations on a hybrid grid system. The EDL interaction force calculated from numerical solution is compared with the one obtained from surface element integration (SEI) method.

Planar Phospholipid Membrane Formation in Open Well Thermoplastic Chips

A key requirement for the effective study of interactions between analytes and ion channels is the ability to dynamically vary analyte type and concentration to a membrane-bound ion channel within a planar phospholipid membrane (PPM). Here an open well microfluidic PPM apparatus supporting dynamic perfusion is presented. The plastic chip supports the manual formation of bilayer membranes that are resistant to pressure disturbances during perfusion with stability on the order of several hours. Using a chamber volume of 20 μL and a flow rate of 0.5 μL/min, the system enables rapid perfusion without breaking the membrane. The perfusion capability is demonstrated through gramicidin ion channel measurements.