GB2526268A

GB2526268A - Arc discharge assembly of dielectrophoretically aligned conductive particulates

Info

Publication number: GB2526268A
Application number: GB1408659.9A
Authority: GB
Inventors: Richard Stone; Dagou Zeze
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-05-15
Filing date: 2014-05-15
Publication date: 2015-11-25
Also published as: GB201408659D0

Abstract

This invention aligns and adheres conductive particulates 4 together to form a composite material. The process uses the combination of dielectrophoresis for alignment, and plasma dissociation followed by recombination for the adhesion. Particulates 4, e.g. carbon nanotubes, are dispersed in a dielectric fluid between two electrodes 1 & 2 which generate a non-uniform electric field. Dielectrophoresis causes the particulates to align and bridge the gap between the electrodes. When an arc breakdown occurs either between the two electrodes or between the particulates acting as extensions of the electrodes, the particulates adhere together to form a composite material, which may grow larger as the process continues. The process may be automated to control the electrode separation, signal power and frequency.

Description

Title: Arc Discharge Assembly of Dielectrophoretically Aligned Conductive Particulates

Description

An example of the invention will be described with reference to the accompanying figures: Figure 1 A diagram showing an arrangement of the process, with a magnified diagram outlining the mechanism and a projected view for clarity.

Figure 2 An optical microscope image of the process in action.

Figure 3 A scanning electron microscope image of multi-walled carbon nanotubes adhered via this process in oleic acid.

Figurc 4 A scanning electron microscope image of multi-walled carbon nanotubes adhercd within polydimethylsiloxane.

Figure 5 A scanning electron microscope image of multi-walled carbon nanotubes adhered within C-15 perfluorinated carbon.

This invention demonstrates a process for the combination of didectrophoretic alignment with plasma disassociation and recombination to adhere conductive particulates together to create a composite material consisting of the conductive particulates and components of thc fluid in which they are dispersed, providing an effective means for exploiting the combined constituent characteristics ol the materia's involved over a greater length.

The process utilizes dielectrophoresis (DEP) whereby particulates within an insulating medium experience a force in the presence a non-uniform electric field. When in the presence of an attractive DEP force without excessive fluidic motion, these particulates may form dipole chains, which move towards and attach to the source of the non-uniform electric field.

If these particles are conductive they may accumulate and increase the chain in length as the end of the chain becomes the next source of the non-uniform electric field. The particles can then form a connection between the non-uniform electrodes and form a short circuit between them. lithe voltage is sufficiently high, an arc breakdown will occur over the dipole chain, immediately before the short circuit is formed. The phsma formed with this arc initiates disassociation followed by recombination of the surrounding insulating material, as well as causing dissociation within the particulate. The result is the particulates either adhere together, or are adhered to the surrounding medium as it recombines, hi the case when the conductive particulates are adhered together. (hey form a larger conductive particulate, and the process of alignment and arc breakdowns continues around this new thread and the electrodes. The electrodes are gradually separated to allow new gaps in the chains to occur, hut may he brought closer together if the electric fidd becomes too weak, or dipole chains start failing to form. In addition to this, it is possible to separate the electrodes such that an arc discharge occurs continuously. With sufficient dielectrophoretic force the particulates are aligned and adhered to each other with the rate of adhesion extending the physical length of the source of the non-uniform deetrie field compensating for the rate of separation. The typical nano-seale structure caused by adhesion from the plasma is shown in figure 3.

An embodiment of this invention is outlined in figure 1 whereby a tungsten probe (I) with a tip radius less than 100 nm creates the non uniform electric field over a hat, stainless steel counter electrode (2) from a power supply delivering 500 V peak-peak) 200 kHz sine wave signal (3). Both the tungsten probe and counter electrode are immersed in a mixture of 10 ml polydimethylsiloxane (PDMS) and I g ultrasonically dispersed muhi-walled carbon nanotubes (MWNTs) 4) within a 10 ml container (5). The electrodes are initially brought close together at approximately 20 pm such that dipole chains (6) form between them, and arcing (7) between the particulates commences. The MWNTs experience a dielectrophoretic force and move (8) towards the tungsten probe which repknishes the supply of MWNTs for assembly. As the dipole chains are adhered together, the electrodes are separated via an actuator perpendicular to the counter electrode (9) to allow new dipole chains to form, and the process repeats. The process is monitored visually and by measured distortions in the dielectrophoretic signal wave and by induced currents caused by arc discharges in a nearby wire (10) connected to an ammeter (11). This embodiment can be both manually and automatically controlled by adjusting the voltage, current, frequency, separation distance and separation rate.

An example product of the process can be observed from scanning electron micrographs in figure 4 which shows carbon nanotubes adhered to a plasma polynierised PDMS structure.

Further embodiments of the invention may use a variety of mediums ci dielectric liquids and mixtures such as styrene and maleic anhydride. perfluorinated carbons or a PDMS and copper sulphate solution emulsions. It is also possible to use naturally occurring triglyceride plant oils such as oleic or ricinoleic acid. The essential characteristic is that the overall mixture is non-conductive between the 2 electrodes and capable of adhesion after an arc discharge. An example product from perfiuorinated carbons with carbon nanotuhes as a medium via continuous arc discharge is shown in figure 5.

The invention may also include different combinations of particulates such as carbon nanotuhes and semiconducting nanowires, or a variety of carbon nanotubes to different thickness and lengths. The key characteristic is that the particulates are sufficiently conducting to allow the arc discharge to propagate between the electrodes.

The invention may also include methods to adjust the concentration and mixture of the medium during the process such as attached pumps, pipes and reservoirs of new particulates and insulating liquid. Altematively syringes may be used to manually add a new medium or remove the used medium.

Claims

Claims 1. A process in which conductive particulates within an insulating medium are aligned under a dielectrophoretic force between two electrodes with a voliage sufficient to form arc breakdowns between the particifiate chains and electrodes such that the particulates are adhered together to form a composite material.
2. A process as defined in claim 1 wherein the insulating medium is a polymer capable of undergoing plasma polymerisation.
3. A process as defined in claims 1 wherein (he particulates are semiconducting.
4. A process as defined in claims 1 wherein the electrode separation distance is changed during the process.
5. A process as defined in claims I wherein the dielcctrophorctic force is modulated to control the process.
6. A process as defined in claims 1 wherein both of the electrodes exhibit a positive dielectrophoretic force on the particulates.