Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session A4: Polymers at Surfaces: Adhesion, Tribology and Patterning |
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Sponsoring Units: DPOLY Chair: Steve Granick, University of Illinois at Urbana-Champaign Room: Morial Convention Center 206 |
Monday, March 10, 2008 8:00AM - 8:36AM |
A4.00001: Interfacial engineering using heteropolymers with adjustable monomer sequences (HAMS) Invited Speaker: Heteropolymers with adjustable monomer sequences (HAMS) represent a new type of functional random copolymers that could play an important role in emerging areas pertaining to interfacial science and polymer assembly. Due to their disordered but tailorable co-monomer sequence distribution HAMS are capable of adsorbing selectively at interfaces and recognizing patterns on chemical targets (i.e., chemically patterned substrates). HAMS are synthesized in a laboratory by `coloring' the segments of a collapsed homopolymer, A, with a functionalizing agent, B, and then unraveling the resultant polymer to yield a random sequence of A and B blocks, which `remembers' its original collapsed conformation and hence prefers some conformations over others. In the presentation, we will provide details pertaining to the experimental formation of HAMS and studying their physico-chemical characteristics. We will also provide examples of a few case studies that unravel the tailorable interfacial and self-assembly character of HAMS made of poly(styrene-co-4-bromostyrene) and its derivatives. In addition, we present results of computer simulation studies providing molecular insight into forming HAMS. [Preview Abstract] |
Monday, March 10, 2008 8:36AM - 9:12AM |
A4.00002: Carbon Nanotube-Based Synthetic Gecko Tapes Invited Speaker: Wall-climbing geckos have unique ability to attach to different surfaces without the use of any viscoelastic glues. On coming in contact with any surface, the micron-size gecko foot-hairs deform, enabling molecular contact over large areas, thus translating weak van der Waals (vdW) interactions into enormous shear forces. We will present our recent results on the development of synthetic gecko tape using aligned carbon nanotubes to mimic the keratin hairs found on gecko feet. The patterned carbon nanotube-based gecko tape can support a shear stress (36 N/cm$^{2})$ nearly four times higher than the gecko foot and sticks to a variety of surfaces, including Teflon. Both the micron-size setae (replicated by nanotube bundles) and nanometer-size spatulas (individual nanotubes) are necessary to achieve macroscopic shear adhesion and to translate the weak vdW interactions into high shear forces. The carbon nanotube based tape offers an excellent synthetic option as a dry conductive reversible adhesive in microelectronics, robotics and space applications. The mechanism behind these large shear forces and self-cleaning properties of these carbon nanotube based synthetic gecko tapes will be discussed. This work was performed in collaboration with graduate students Liehui Ge, and Sunny Sethi, and collaborators from RPI; Lijie Ci and Professor Pulickel Ajayan. [Preview Abstract] |
Monday, March 10, 2008 9:12AM - 9:48AM |
A4.00003: Polymer adhesion at surfaces: biological adhesive proteins and their synthetic mimics Invited Speaker: Mussels are famous for their ability to permanently adhere to a wide variety of wet surfaces, such as rocks, metal and polymer ship hulls, and wood structures. They accomplish this through specialized proteins collectively referred to as mussel adhesive proteins (MAPs). The biophysical aspects of MAP adhesion is being revealed through the use of single molecule force measurements. The results provide insight into the adhesive roles of key amino acids found in these proteins, including the magnitude of adhesive forces, cooperative effects, and their self-healing properties. This molecular-level information is being incorporated into designs of biomimetic polymer coatings for a variety of applications. Our biomimetic approach to polymer design will be illustrated by a few examples where adhesive constituents found in MAPs are exploited to make wet-adhesive polymer coatings. In addition, small molecule analogs of MAPs can be used to apply thin functional films onto virtually any material surface using a facile approach. These coatings have a variety of potential uses in microelectronics, water treatment, prevention of environmental biofouling, and for control of biointerfacial phenomena at the surfaces of medical/diagnostic devices. [Preview Abstract] |
Monday, March 10, 2008 9:48AM - 10:24AM |
A4.00004: Patterning inorganic nanoparticles in Polymer Films Invited Speaker: |
Monday, March 10, 2008 10:24AM - 11:00AM |
A4.00005: Wrinkling, Crumpling and Snapping for Surface Property Control Invited Speaker: Upon the development of a critical stress, many materials and geometries experience a mechanical instability, which produces significant changes in geometry with very small changes in stress. In nature, mechanical instabilities are ubiquitous with the definition of shape, morphology, and function. Examples range from wrinkles on human skin to the snapping of Venus Flytrap leaflets. Inspired by these examples and others, we use elastic instabilities to control the morphology and function of soft polymer surfaces. We present three strategies. The first is a novel approach for the development of surface wrinkles on a top-constrained elastomer surface. We demonstrate and understand the control of kinetically-trapped and equilibrium wrinkle morphologies associated with changes in the materials properties and geometric constraint. These structures are stabilized to create surfaces with enhanced adhesion and advantageous optical properties. A second strategy is based on the controlled buckling of surface attached sheets. This method allows the fabrication of responsive surface structures that are prone to snap-through instabilities and the fabrication of pattern features that are difficult, if not impossible, to achieve with any other method. The third strategy brings the bio-inspired surface control full circle with the use of mechanical instabilities to control and characterize monolayer sheets of biological cells. [Preview Abstract] |
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