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Control of Triboelectricity from Micro to Macro as a Principle ofSticking, Particulate Contamination and ESD Prevention of Micromachines

Periodic Reporting for period 1 - Tribocharge (Control of Triboelectricity from Micro to Macro as a Principle ofSticking, Particulate Contamination and ESD Prevention of Micromachines)

Reporting period: 2016-03-01 to 2018-02-28

Summary:

Contact electrifcation (CE)—charging of surfaces that are contacted and separated, is a common phenomenon, however it is not completely understood yet. Tribocharging is a very common event causing value losses due to electrostatic sticking and electrostatic discharging (ESD) problems in many industrial manufacturing processes such as static cling of powder materials in drug processing, ESD problems in electronics. In this study, I focused on the elimination of static charge that accumulates on polymers that are used to produce MEMS.. Although friction and tribocharging were presented to be mutually related, to what extent tribocharging affects friction-related macroscopic-scale losses was not shown to date. Here I show, for common polymers which are used to manufacture MEMS, friction - which indeed is strongly related with surface charge density- can be significantly reduced by various methods of tribocharge mitigation, namely, corona discharging, solvent treatment, or placing a grounded conductor on the backside of one of the shearing materials. One fourth of the global energy losses result from friction and wear. I show, a remarkable two thirds of energy lost during operation of simple mechanical devices can be saved and wear can be reduced by a factor of ten at macro scale as a first step using polymeric materials. Our simple demonstrations indicate important practical ramifications in mechanical systems with insulating materials that are used in MEMS.

What is the problem/issue being addressed?

The fundamental problem being addressed is a millennia-old problem of how (static) electricity is generated on some surfaces. Known broadly as contact electrification, triboelectrification or frictional electricity, this phenomenon yields many adverse effects in industry, e.g. polymer, electronics, space industries and drug manufacturing. With the recent advancements are promote MEMS devices to replace the conventional ones, the tribocharging during operation of these devices, which hinder and sometimes prevent their operation, is becoming vitally important. For this reason, we start by understanding the fundamentals of the triboelectrification by using the common polymer material used in MEMS and showing the mechanism of charge formation in tribocharging in this study.


Why is it important for society?

Triboelectrification or frictional electricity is a phenomenon that causes billions of dollars of losses in industry, e.g. polymer, electronics, space industries and drug manufacturing. These losses can be the energy lost in stiction, or total malfunction because of electrostatic discharges. The smaller the devices are, the more important is the effect of tribocharging; stiction and electrostatic discharges. Understanding the mechanism of electrification can prevent these losses and can boost the device operation lifetimes.
With this paper, for the first time we have shown that, on contrary to the common belief, triboelectrification of two surfaces that are contacted and separated does not occur only upon contact or separation but happens in both. Also, we could resolve the charge formation events in contact and separation very neatly and saw that upon contact of the surfaces there are two polarities of charge – again undermining the conventional thinking that charge transfers from one surfaces to the other unidirectionally. These findings help us to design better antistatic materials to prevent the negative effects of tribocharging.

What are the overall objectives?

To eliminate the stiction and ESD problems in MEMS (and other) devices, one has to discover a general approach, based on the mechanism of charge formation. The overall objective of this publication is to uncover the mechanism of tribocharge formation on contacted polymer surfaces, resolving the charging event in time to understand the charge formation and transfer during contact and separation events. We use common polymers that are used in MEMS device
On the research part of the project; with the aim to find a general method to prevent tribocharging related problems, e.g. stiction, we first targeted at understanding the tribocharging of all common polymers used in polymeric MEMS devices. Therefore; 1) we performed contact electrification experiments with all common polymers used in these devices with conventional touching and controlled tapping instruments and recorded the charges, 2) we probed the relationships between external parameters such as humidity and the amount of charge formed on polymers, 3) we also probed the relationship between internal parameters such as the thickness of the samples and the mode of charge measurements and the amount of charge formed on polymers, 4) we analyzed the data during tapping of polymers to figure out the mechanism of charging; a fine instrument was build to minimize the mechanical vibrations, to reduce the oscillation during the contact of the surfaces and to resolve the charge data in time with high resolution, 5) obtained results were analyzed and an unprecedented mechanism of charge formation (bipolar contact, unipolar separation electricification) and bidirectional transfer of charges were proposed (Published in Scientific Reports, 2018). 6) I have also worked on the next step to coin down the relation between wear and tribocharging and prepared a manuscript for submission (planned within this month). The main result from this study is that the friction and wear are very related to each other and both can be minimized with removal of tribocharges, depending on the system dimensions.
On the educational part of the project; I have attended national and international workshops on friction and received the trainings for the new methods and instruments I used.
Publications are the main advancements this project and they has provided beyond the state of the art in the field. Our new results on bidirectional bipolar charging is a game- changer in the field, since it refutes the old and conventional mechanism of triboelectrification. These new results can be used not only in charge and stiction prevention in MEMS and other devices, but it can also be used to enhance the triboelectric output in some triboelectric harvesters. For both prevention and enhancement, we have provided fundamentally new way of looking into the billion-dollar industrial problems. As for another important point, revealing the relation between wear and tribocharging; wear and friction were shown to be vitally linked with tribocharge as predicted in the proposal. We presented a new approach to reduce the economical problems associated with wear and friction that causes the malfunction of devices and long downtimes.
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