Reversible Wettability of Photoresponsive Pyrimidine-Coated Surfaces

Abbott, Scott; Ralston, John; Reynolds, and Geoffrey; Hayes, Robert A.

doi:10.1021/la990558o

Cited by 160 publications

(135 citation statements)

References 21 publications

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“…One such method is provided by electrowetting (5-8); alternative methods are based on substrate surfaces with grafted molecules that exhibit several isomeric conformations and can be switched by light (16)(17)(18), temperature (19), or electric potential (20). Thus, let us consider a short filament (F ϩ ) with positive Laplace pressure that is in mechanical equilibrium with a larger liquid structure such as a droplet.…”

Section: Resultsmentioning

confidence: 99%

Wetting morphologies at microstructured surfaces

Seemann

Brinkmann

Krämer

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

366

365

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The wetting of microstructured surfaces is studied both experimentally and theoretically. Even relatively simple surface topographies such as grooves with rectangular cross section exhibit a large variety of different wetting morphologies as observed by atomic force microscopy. This polymorphism arises from liquid wedge formation along the groove corners and from contact line pinning along the groove edges. A global morphology diagram is derived that depends only on two system parameters: (i) the aspect ratio of the groove geometry and (ii) The contact angle of the underlying substrate material. For microfluidics, the most interesting shape regimes involve extended liquid filaments, which can grow and shrink in length while their cross section stays essentially constant. Thus, any method by which one can vary the contact angle can be used to switch the length of the filament, as is demonstrated in the context of electrowetting.surface topography ͉ wetting phenomena ͉ microfluidics R apid and efficient handling of relatively small amounts of liquids is a crucial requirement in molecular biology or biomedicine, e.g., for decoding the human genome or for analysis of small blood samples. To do this, one would like to construct labs-on-a-chip on the micrometer scale (see, e.g., ref. 1). An obvious prerequisite for such a lab is appropriate compartments for the confinement of very small amounts of liquids. These microcompartments should have some basic properties: they should have a well defined geometry by which one can measure the precise amount of liquid contained in them; they should be able to confine variable amounts of liquid; and they should be accessible in such a way that one can add and extract liquid in a convenient manner.A variety of concepts has been developed for the construction of such microfluidic systems. In most cases, a solid matrix is used that surrounds micropipes, reservoirs, etc. Here, we explore an alternative system design, namely open microfluidic systems, which contain free liquid͞vapor (or liquid͞liquid) interfaces. One advantage of these open structures is that they are directly accessible and easy to clean.There are two general strategies to construct open microfluidic systems. The first one is to chemically pattern planar substrates and to prepare distinct surface domains that differ in their wettability (2-4). The second strategy, explored here, is to use nonplanar surface topographies that can be fabricated by available photolithographic methods. We find that even relatively simple topographies such as grooves with rectangular cross sections already exhibit a large variety of different liquid morphologies such as droplets, filaments, and wedges. A systematic comparison of experimental observations and theoretical calculations reveals, however, that this polymorphism is primarily determined by only two parameters: (i) the aspect ratio X of the groove geometry, i.e., the ratio of the groove depth to the groove width; and (ii) the contact angle of the underlying substrate material. For...

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Section: Resultsmentioning

confidence: 99%

Wetting morphologies at microstructured surfaces

Seemann

Brinkmann

Krämer

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

366

365

View full text Add to dashboard Cite

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“…19(d)] Light can drive droplet motion when the surface is coated with a photosensitive material. Static optowetting, i.e., a change in contact angle change due to uniform light irradiation, has been reported ͑Wang et al, 1997; Abbott et al, 1999;Shin and Abbott, 1999;Miyauchi et al, 2002;Huang et al, 2003͒. Furthermore, droplet motion has been driven using gradients in light intensity ͑Ichimura et Oh et al, 2002͒.…”

Section: B Surfaces With Wettability Gradientsmentioning

confidence: 98%

Microfluidics: Fluid physics at the nanoliter scale

2005

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Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes ͑nanoliters͒ of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Péclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world. CONTENTS

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“…For example, micro-fluidic is becoming a hot field and obtaining wide applications, people has developed various methods to realize liquid self-transportatoin. [1][2][3][4][5][6][7][8][9][10] So understanding how topology of substrates influence the dynamic behaviors of droplets is essential to clarify the underlying mechanism and practical application.…”

Section: Introductionmentioning

confidence: 99%

Driving Droplet by Scale Effect on Microstructured Hydrophobic Surfaces

Hao

2012

Langmuir

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Abstract:A new type of water droplet transportation on microstructured hydrophobic surface is proposed and investigated experimentally and theoretically -water droplet could be driven by scale effect which is different from the traditional methods. Gradient microstructured hydrophobic surface is fabricated in which the area fraction is kept constant, but the scales of the micro-pillars are monotonic changed. When additional water or horizontal vibration is applied, the original water droplet could move unidirectionally to the direction from the small scale to the large scale to decrease its total surface energy. A new mechanism based on line tension model could be used to explain this phenomenon. It is also found that dynamic contact angle decreases with increasing the scale of the micro-pillars along the moving direction. These new findings will deepen our understanding of the relationship between topology and wetting properties, and could be very helpful to design liquid droplet transportation device in microfluidic systems.

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Reversible Wettability of Photoresponsive Pyrimidine-Coated Surfaces

Cited by 160 publications

References 21 publications

Wetting morphologies at microstructured surfaces

Wetting morphologies at microstructured surfaces

Microfluidics: Fluid physics at the nanoliter scale

Driving Droplet by Scale Effect on Microstructured Hydrophobic Surfaces

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