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Surface Film Controls Gas Flow

Reversible adjustment depends on temperature-induced, melting-like transition

by Mitch Jacoby
November 4, 2013 | A version of this story appeared in Volume 91, Issue 44

The push to make lab-on-chip devices, all-in-one microfluidic tools for chemical and clinical analysis, is driven by their projected low cost and portability, as well as by the tiny sample size and short analysis time required to obtain results. Such tools could be used to quickly measure analytes in, for example, hospital, battlefield, and home settings. One challenge impeding faster development is having a means to precisely control gas flow through the devices. Chemical engineers at Virginia Tech may have come up with a simple solution that does not involve moving parts. Dongjin Seo and William A. Ducker report that gas flow rates can be reversibly adjusted by using heat to alter the roughness of an organic film lining the inside of a micrometer-diameter glass tube (Phys. Rev. Lett. 2013, DOI: 10.1103/physrev​lett.111.174502). On the basis of atomic force microscopy and other analyses, the team showed that heating and cooling a monolayer of octadecyltrichlorosilane causes the material to undergo a conformational transition. The film’s roughness at 18 °C, which impedes the flow of nitrogen at 1 atm, can be smoothed by warming to 40 °C, causing flow rates to double.


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