CONTROL OF INTERFACIAL ADHESION BY POLYMER BRUSHES*
Polymers Division, National Institute of Standards and Technology,
Gaithersburg, MD 20899, USA
Mentor: Christopher M. Stafford
Polymer brushes present a versatile and facile route to constructing well-defined interface structures critical to many applications, including precise control over interfacial adhesion. For instance, adhesion of polydimethylsiloxane (PDMS), widely used in microfluidic devices and medical implants, to a majority of solid substrates is weak due to the low surface energy of PDMS. As a result, much attention has been paid to enhance adhesion via generic methods such as oxidization and silanization, whereas limited methods are available to fine-tune the adhesion between contacting surfaces of PDMS and a solid. For example, studies have demonstrated moderate adhesion enhancement between PDMS and a solid substrate by attaching end-functionalized PDMS chains ; however, a full understanding of the role of polymer brushes in adhesion is lacking, particularly when the brush chemistry is different from that of the opposite contacting surface.
At the NIST Combinatorial Methods Center, a high-throughput methodology for fabricating polymer brush libraries would be extremely valuable. These brush libraries having well-defined and spatially varying structures were then integrated with our combinatorial adhesion measurement platforms to unravel the complexity of adhesion between two surfaces. In this poster, we demonstrated that three polymer brush architectures were discussed which impart a wide range of control over the adhesion of PDMS to a substrate. First, regulation of strong adhesion of PDMS to HEMA-grafted rigid substrates was achieved by the chain-extension of PBMA block of various thickness on the top of PHEMA along with the proper solvent treatment of the brush-grafted substrate. Secondly, control over adhesion between PDMS and PDMS was realized by solvent treatment of PDMS on which a PHEMA brush was grafted. Thirdly, the adhesion hysteresis of PDMS to a solid substrate was diminished by grafting a comb-shaped PDMS brush to the surface.