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Disgrifiad prosiect

Contact angle instrumentation and the measurement of surface free energy

(supervisor: John Tomes)

Nature of project: experimental, experimental

Available to students on full-time physics degree schemes or joint students.

Project description and methodology

The interface between a liquid and the solid that it sits on, is fundamentally influenced by the surface free energy of interaction. This surface free energy can be determined by measuring the ‘contact angle’ at the tri-point between solid, liquid and atmosphere surrounding them. The interaction and balance of forces can be described by Young’s equation, which incorporates the thermodynamic equilibrium present between the three materials.

Understanding the surface free energy of a substrate has many applications, ranging from materials science, such as determining the success of a surface treatment, to commercial printing applications, for example the wettability of a material to printing inks.

This project would seek to design, manufacture and calibrate a low cost tensiometer (a contact angle measuring device), this will probably take the form of a Raspberry Pi camera system and 3D printed elements to align the necessary components. A successful project will review and understand the function and importance of each instrument component. Design schemes should incorporate elements based on cost and availability. Once the chosen design is assembled a full calibration and characterization of the instrument should be conducted.

Corona-Virus: this is primarily a practical 'lab' based project, in the event of additional Corona-Virus restrictions, components could be taken for 'home working' allowing the project to continue. Furthermore, a change of emphasis towards image analysis would generate 'desk based' data for evaluation.

A successful project will develop beyond the above in one/some of the following directions:
There exists significant opportunity for further project development, it is possible to incorporate features within the fluid delivery mechanism that could explore the hysteresis seen in forward and receding contact angle, or potentially capture both static and dynamic droplet measurements. A further potential development would be to review and evaluate popular image analysis methods used to measure the contact angle from captured images. Ideally this will quantify the errors associated with current ‘plugins’ that are available.

When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.

Additional scope or challenge if taken as a Year-4 project: 4th year students can investigate the influence of polar liquids and substrates on contact angle described by Fowkes theory. Possibly extending to the use of Van-Oss theory which seeks to accommodate acid / base materials such as chemical powders and dye pigments.

Please speak to John Tomes (jjt12) if you consider doing this project.

Initial literature for students:

  1. Y. Yuan and T. R. Lee, “Contact angle and wetting properties”, in Surface Science Techniques, B. G., Ed., Springer, 2013, pp. 3–34, ISBN: 9783642342424. DOI: 10.1007/978-3-642-34243-1_1
  2. D. K. Owens and R. C. Wendt, “Estimation of the surface free energy of polymers”, Journal of Applied Polymer Science, vol. 1, no. 19, pp. 1741–1747, 1969, ISSN: 10974628. DOI: 10.1002/app.1969.070130815.
  3. F. Fowkes, “Determination of interfacial tensions, contact angles and dispersion forces in surfaces by assuming additivity of intermolecular interactions in surfaces.”, The Journal of Physical Chemistry, vol. 66, no. 2, p. 382, 1961.

Novelty, degree of difficulty and amount of assistance required

Moderate to high difficulty that requires good practical skills when executing the instrument design and manufacture. Some technical assistance will be required for the fabrication of 3D printed components.

Project milestones and deliverables (including timescale)

milestoneto be completed by
Initial review of understanding and potential project pathsend of October
Finalization of project experimental designChristmas
Confirmation of construction / start of image analysisend of February
Confirmation of data for analysismid-March

Students taking this project will have to submit a full risk assessment form