A two-stage surface treatment for the long-term stability of hydrophilic SU-8

Sobiesierski, Angela, Thomas, Robert, Buckle, Philip Derek ORCID: https://orcid.org/0000-0001-9508-7783, Barrow, David ORCID: https://orcid.org/0000-0003-2096-7262 and Smowton, Peter Michael ORCID: https://orcid.org/0000-0002-9105-4842 2015. A two-stage surface treatment for the long-term stability of hydrophilic SU-8. Surface and Interface Analysis 47 (13) , pp. 1174-1179. 10.1002/sia.5870

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Abstract

The use of SU-8 photoresist as a structuring material for portable capillary-flow cytometry devices has been restricted by the near-hydrophobic nature of the SU-8 surface. In this work, we evaluate the use of chemical and plasma treatments to render the SU-8 surface hydrophilic and characterise the resulting surface utilising a combination of techniques including contact angle goniometry, atomic force microscopy and X-ray photoelectron spectroscopy. In particular, for low-power plasma treatments, we find that the chemistry of the plasma used to modify the SU-8 surface and the incorporation of O2 on that modified surface are paramount for improved surface wettability, whilst plasma-induced surface roughness is not a necessary requirement. We demonstrate a technique to obtain a hydrophilic SU-8 surface with contact angle as low as 7° whilst controlling and significantly reducing the level of surface roughness generated via the applied plasma. An additional chemical treatment step is found to be essential to stabilise the activated SU-8 surface, and incubation of the samples with ethanolamine is demonstrated as an effective second-stage treatment. Application of the optimised two-stage surface treatment to cross-linked SU-8 is shown to result in a smooth hydrophilic surface that remains stable for over 3 months.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Engineering Schools > Physics and Astronomy
Subjects:	Q Science > QC Physics
Publisher:	Wiley
ISSN:	0142-2421
Funders:	EPSRC
Date of First Compliant Deposit:	30 March 2016
Date of Acceptance:	22 September 2015
Last Modified:	17 Jan 2024 07:22
URI:	https://orca.cardiff.ac.uk/id/eprint/84155

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