Chemical surface modification of thin film polymers

Polymers have been used recently in a wide variety of applications including many that require specific chemical and physical properties. The advent of polymers being used in semiconductor devices and implantable electronic devices has created a need to understand and control the surface properties of polymers without destroying their bulk properties. This research focused on modifying the surfaces of several polymers that have been considered for use as biomaterials or as coatings for implantable electronic devices. A two-pronged approach was employed. Photooxidation was studied with the goal of attaching oxygen-containing groups, and downstream microwave ammonia plasma treatment was studied with the goal of attaching primary amine groups. Photooxidation was studied for parylene-N and parylene-C at doses up 10,000 mJ/cm2. Exposure to short-wavelength ultraviolet (UV) light in the presence of air caused aldehydes and carboxylic acids to form in the top 25% of the films. Increasing the UV dose or temperature increased the extent to which this reaction occurred. In order to understand and optimize this reaction, a first-principles model was developed which showed qualitative agreement with photooxidation data obtained for parylene-N and parylene-C. Downstream microwave ammonia plasma treatment was studied for parylene-C and polydimethylsiloxane (PDMS). This treatment was studied at microwave powers up to 200 W, treatment times up to 300 s, and sample temperatures up to 200°C. Downstream microwave ammonia plasma treatment of PDMS resulted in the attachment of primary amine groups in addition to a variety of other nitrogen- and oxygen-containing functional groups. In general, the amount and type of oxygen-containing groups increased as a function of wattage, treatment time, and temperature. Downstream microwave ammonia plasma treatment of parylene-C resulted in an ammonium chloride complex, which passivated the surface and prevented further reaction between the polymer and ammonia plasma. Overall, the results of this study may be used to tailor the surface modification of any of the polymers studied so that desired functional groups can be attached while minimizing undesired physical or chemical effects.