Preparation Of Thermoswitchable Capillary-force Valves Inside Polydimethylsiloxane Microfluidic Channels By Region-selective Surface Modification

Manipulation of microfluids in a microfluidic chip is the key operation for micro fluidic analysis, and micro pumps and valves are the basic devices for fluid manipulation. Thus, development of high-quality micro pumps and valves becoming more and more important in various fields. As the surface-to-volume ratio in the micro channels is greatly increased, the surface tension plays a much more significant role compared with gravity and inertia in the micro-scale. Capillary force micro-valve is a kind of none-mechanical valve that relies on surface tension to manipulate micro fluids on microfluidic chips. Capillary force micro-valve has the advantages of low-cost, small-volume and flexibility in operation, especially suitable for disposable polymer chips.Poly(dimethylsiloxane) (PDMS) is a polymer elastic material featuring cost-effective, easy to be fabricated. It is widely used as a common material for preparation of microfluidic chips. Nowadays, gas-pressure driven micro membrane valves are most often used in PDMS micro fluidic chips for fluid manipulation. However, this type of valves needs complicated off-chip pressured gas source and controlling system that deteriorates the degree of integration of the microfluidic systems. To the best of our knowledge, no reports have been published on the preparation of thermo regulated capillary force micro valves on full PDMS microfluidic chips. This paper is focused on development of thermo-regulated capillary force micro valves on full PDMS micro channels via establishment of in-channel region-selective surface grafting techniques.In Chapter One, references on various types of capillary force valves, methods for manipulation of microfluidis with thermo-sensitive polymer, and techniques used for PDMS surface modification are reviewed.In Chapter Two, the method for preparation of thermo regulated capillary force micro-valve system on full PDMS microfluidic chips has been developed. Based on the studies in tailoring of the hydrophobicity/hydrophilicity of PDMS surface by surface grafting of PAA or PNIPAAm via benzophenone initiated surface photopolymerization, a novel two-step region-selective grafting technique was developed to prepare thermoswitchable capillary force valves inside irreversibly bonded PDMS microchannels. A T-shaped PDMS micro channel integrated with the thermoswitchable capillary force valve has demonstrated the capability of thermo-manipulating of aqueous flow.The major novelty of the present work is that it establishes a two-step method.of UV-photochemistry-based, region-selective grafting PAA and PNIPAAm onto inner wall of PDMS channels for fabrication of integrated thermo-manipulated capillary force valves on PDMS micro fluidic chips.