Development of the partial exposure method on SU-8 for double-reentrant hydrophobic structures
|關鍵字:||數位微流體;疏水;超疏水;雙反摺結構;部分曝光;Digital microfluidic;Hydrophobic;Superhydrophobic;Double-reentrant;Partial exposure|
Digital microfluidic chips have demonstrated many advantages in biomedical applications in recent years. It can be used in operating biological specimen in microns, including gas, cells, serum samples and so on. And it can also be automatically manipulated by computer programs so as to reduce testing time. In these days, most of the hydrophobic layer of the digital microfluidic chips are fabricated by coating hydrophobic material. But there are several disadvantages. For example, the hydrophobic material is easy to fall off and uneven, the biological samples may cause protein adsorption and it is expensive. These demerits affect the quality of the chip, and even make the chip lose the hydrophobic properties. Therefore, coating hydrophobic material may not suitable for microfluidic chips. In our study of hydrophobic layer, we found the hydrophobic structure could substitute for hydrophobic material. Thus, we summarized the presently known hydrophobic structure types, we concluded that to apply double-reentrant structure in microfluidic chip has many advantages. One is it can rise contact angle to over 150 degrees through the structure. Another is it has good applicability for liquid with different surface tension. The other is that the hydrophobicity is less effected by protein adsorption. Up until now, there are still some goals for manufacturing procedure of double-reentrant structures like simplifying procedure, improving the physical and chemical properties of material. And on application, we expect the material has better transmittance and applicability for different substrates In this research, we developed the front-side partial exposure method on SU-8 for double-reentrant hydrophobic structures. Compared to the currently existing manufacturing processes of double-reentrant structure, front-side partial exposure method has the advantage of simple procedures, unrestricted substrates, great transmittance and high stability of physical and chemical properties simultaneously. We succeeded in making double-reentrant structures by this manufacturing procedure, and made the contact angle of silicon oil with low surface tension rise from 0 degree to 146 degrees, which showed the oleophobic ability. In addition, there is no paper discussing the height of double-reentrant structures so far. In our study, we discussed the sagging height between double-reentrant structures, and deduced the theory of the corelation between structure height and hydrophobic stability. By contact angle measuring, we found that the results of droplet state are in accordance with theoretical predictions. Take SU-8 double-reentrant structure as an example, when structure angle is about vertical, and the spacing of double-reentrant array is 180um, the structure height must be higher than 90um, which is half of the spacing, so as to make silicon oil, whose initial contact angle is close to 0 degree, stay oleophobic. In this research, we made three structures of different height, which are 20um, 60um and 100um separately and tested them with oil droplet. Consequently, only the 100um double-reentrant structure successfully made oil oleophobic,as we predicted. We believe that the model deduced in this research can provide practical assistance in hydrophobic structure design in the future.
|Appears in Collections:||Thesis|