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Description
Project Summary
Intellectual merit: Friction is an unusually persistent issue dating back to the 1600s and still
ongoing today. One of the key challenges is a universal understanding of how the many
changeable parameters, such as viscoelasticity, loading conditions, or size scale, govern relative
motion between two surfaces. The proposed project will provide new fundamental insight into
small scale friction of soft polymeric surfaces. Over the last several decades, friction behavior of
soft materials, mainly rubbers, have been studied; however, it is not well understood on a single
microscale level. It is known that at small scales, with small being defined by the ratio of surface
tension to elastic modulus known as the elastocapillary length, liquid-like characteristics play a
critical role in the interfacial mechanics and large out-of-plane deformations are observed.
However, whether these can be described by classical rubber friction (e.g. elasticity) or by fluid
characteristics (e.g. contact angles) is unclear. A lateral force microscopy method combined with
confocal microscopy will be employed to investigate the friction behavior of a small spherical
probe in contact with a soft model material. Crosslinked polydimethylsiloxane networks having
different crosslinking densities, and hence moduli, will be investigated. These will provide the
ability to systematically control the elastocapillary length to below, near and above the
microparticle radius to determine if and when a transition occurs from elastic to viscoelastic to
liquid-like friction. The proposed work is a step towards a comprehensive understanding soft
material friction by tuning and quantifying the (visco)elasticity, loading conditions, and size scale.
Broader impacts: The proposed project will have significant impact on our understanding of
fundamental friction behavior of soft surfaces on small length scales. The expected outcomes will
guide the development of organogels, biomaterials, coatings, seals, and adhesives, all of which
are important for a broad range of important applications including tissue engineering, cosmetics,
corrosion protection, water filtration, and commodity products. Moreover, the proposed project will
validate a high precision method for investigating microscale lateral force and displacement
measurements. This work will also offer a route to educate and train graduate and undergraduate
students on not only soft materials, but also small scale experimental techniques – both of which
are important skills for the current science and engineering industry. The PI has a record of
mentoring women in science and aims to provide an equal opportunity for success of diverse and
underrepresented groups. The emphasis on both fundamental science and practical application
of this work will ensure the success of students joining the workforce, whether government,
industry or academia.
Status | Finished |
---|---|
Effective start/end date | 8/15/18 → 12/31/22 |
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Projects
- 1 Finished
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Supplement: Soft Materials Friction at Smaller Length Scales
Pham, J. (PI)
8/15/18 → 7/31/22
Project: Research project