Soft Materials Friction at Smaller Length Scales

  • Pham, Jonathan (PI)

Grants and Contracts Details


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.
Effective start/end date8/15/1812/31/22


Explore the research topics touched on by this project. These labels are generated based on the underlying awards/grants. Together they form a unique fingerprint.