| Polydimethylsiloxane (PDMS) continues to be a very popular material for the microfluidic chips, due to its numerous advantages, including its elastomeric properties, biocompatibility, optical transparency, chemical inertia, gas permeability, low cost of manufacturing and easy of bonding to other material, such as glass. However, the hydrophobicity of native PDMS makes it difficult to applied in many microfluidic devices. Herein, this paper studied the surface modification of PDMS, combining with micromanufacturing technology, simplified the microfluidic chip process. Making it get more extensive application in the field of microfluidic.First we studied the structure, fundamental characteristic and molding technology of PDMS, investigated the different nitrogen plasma modifications. By measuring the water contact angle, the influences to PDMS surface modification had been studied, such as pressure, treatment time and RF power. Increasing power and pressure, or decreasing treatment time can get the smaller water contact angle and surface roughness, delayed the hydrophobicity recovery. The power can’t been too high, otherwise it would produce the cracking, making the surface roughness increase quickly.Then Fourier Transform Infrared Spectroscopy (FTIR) was used to analyze the surface of native PDMS and different nitrogen plasma modified PDMS. It is to be found that the amine group was introduced onto the PDMS surface after nitrogen plasma modification, and the nitrogen atom of the amine group was connected on the carbon atom of PDMS. With the increase of treatment time, the number of amine group will increase too. The X-ray Photoelectron Spectroscopy (XPS) was also used to analyze the surface of native PDMS and nitrogen plasma modified PDMS. The results showed that the PDMS surface content of carbon and silicon would decrease after the modification, duo to introduce the amine group.At last, the PDMS-based microfluidic chip had been designed and then fabricated. The SU-8 photoresist was used for microchannel through photolithography. The microfluidic chip was sealed by the nitrogen plasma modified PDMS and SU-8. The mechanism of PDMS bonding with SU-8 had been investigated. Pull-off tests were used for estimating the bonding effect of interface between nitrogen plasma modified PDMS and SU-8. Combining with the results of contact angle and pull-off test, it can be found that 70W/30s/50Pa was the best nitrogen plasma modification process. |
