Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session X4: Responsive Gels at Surfaces and in the Bulk |
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Sponsoring Units: DPOLY Chair: Ryan Hayward, University of Massachusetts Room: 306/307 |
Thursday, March 19, 2009 2:30PM - 3:06PM |
X4.00001: Global Signaling of Localized Impact in Chemo-responsive Gels Invited Speaker: A vital function performed by skin is to send a chemical alarm signal throughout the system in response to irritation or damage. Using our recently developed 3D model for chemo-responsive gels, we design a coating that can perform an analogous, biomimetic function. Our system consists of a polymer gel undergoing the Belousov-Zhabotinsky (BZ) reaction. We show that such coatings respond to a spatially localized mechanical force by exhibiting a range of signaling behavior. For example, an initially stationary gel can emit transient waves in response to a sufficiently weak, localized impact. A stronger localized impact, however, can generate a global signal, which encompasses both chemical waves and surface ripples that propagate across the entire sample. This complex dynamical response persists even after the force is lifted. Furthermore, the spatial patterns formed by these oscillating gels reveal the location and magnitude of the applied force. Our findings open up the possibility of harnessing BZ gels for a range of applications, such as creating sensors that transmit a global signal in response to a local mechanical impact. [Preview Abstract] |
Thursday, March 19, 2009 3:06PM - 3:42PM |
X4.00002: Volume-Phase Transitions and Swelling Instabilities in Surface-Tethered Responsive Gels Invited Speaker: Responsive polymer hydrogels have opened exciting opportunities for breathable structures that adopt to environmental cues. Such structures can be designed from a variety of chemical motifs that endow specific response behavior at the material level. Moreover, mechanically pinning a responsive gel to a surface presents further opportunities for designing specific shape- volume transitions due to differential swelling that arises in confined structures. We present a simple technique for fabricating responsive polymer networks based on copolymers comprising the photoactive moiety methacroyloxybenzophenone (MaBP). This approach permits the synthesis of photo-cross- linkable polymers that are easily pattered with thicknesses down to 80 Angstroms. Using a combination of neutron reflection, QCM- D, and ATR-FTIR, we have mapped the volume-phase behavior of ultra-thin layers of responsive networks as a function of chemical functionality, cross-link density, and thickness. Interestingly enough, neutron reflection reveals diffuse interfaces at the periphery of surface-attached networks that grow with the degree of swelling, pointing to surface fluctuations that result from biaxial compression. Finally, confocal microscopy has been used to map three-dimensional swelling in patterned structures revealing swelling instabilities from surface undulations to macroscopic buckling depending on the aspect ratio of the pattern. [Preview Abstract] |
Thursday, March 19, 2009 3:42PM - 4:18PM |
X4.00003: Supramolecular Gels in the Bulk and at Surfaces Invited Speaker: Responsive gels might be broadly classified into two groups: those in which the material response is mediated by a phase transition involving the cooperative behavior of many molecules, or molecule moieties, together, and those in which the material response is dictated by the behavior of individual molecular components acting independently of each other. This talk will discuss the properties of supramolecular gels as a representative of the latter class of responsive materials. In the context of this talk, supramolecular gels are solvent-swollen polymer networks in which the connections between polymer chains that define the network are due to specific, directional, and reversible 1:1 interactions between molecular partners. In such cases, the properties of the network are responsive to the same stimuli that influence the reversible interaction between the molecular partners. The magnitude and sensitivity of stimulus-responsiveness in supramolecular gels is greatest in the vicinity of the gel point, and the characteristics of the sol-gel phase transition will be described for a family of coordinatively cross-linked poly(4-vinylpyridine) (PVP) organogels. It will be shown that the cross-linking interaction can have pround effects on the mechanical properties of similar, surface-bound networks prepared from end-grafted PVP. [Preview Abstract] |
Thursday, March 19, 2009 4:18PM - 4:54PM |
X4.00004: Photoresponsive Polymers: Converting Light to Mechanical Work Invited Speaker: The ability to remotely control the creation of mechanical work, rapidly, with high spatial precision, and over long distances, offers many intriguing possibilities. Whether driving direct conformational changes, initiating reversible chemical reactions to release stored strain, or converting the photon to a local temperature increase, combinations of photoactive units, nanoparticles, ordered mesophases and polymeric networks are providing an expansive array of photo-responsive polymer options. By combining these material responses with kinematic concepts, mechanical devices can be demonstrated that exhibiting tunable and controllable macroscopic deformation, high-frequency oscillation or directional motion. Specifically, we will discuss recent investigation of liquid crystal polymer networks containing main chain and pendent azobenzene moieties (azo-LCN) with modulus $\sim $1.3GPa that are actuated at the absorptive overlap of the cis and trans confirmers (442 nm). Cantilevers and unconstrained beams of these azo-LCNs can be controlled by polarization angle of the source, as well as by a specific optical exposure history (on-off), with responses ranging from lateral motion to oscillations in excess of 30Hz. These phenomena reflect an underlying interaction between the mesophase order, the network architecture and kinematic constraints of the exposed material. In collaboration with Timothy Bunning, Timothy White, Hilmar Koerner, Air Force Research Laboratory; and Nelson Tabiryan, BEAM Co. [Preview Abstract] |
Thursday, March 19, 2009 4:54PM - 5:30PM |
X4.00005: 3D Microfabrication of responsive protein gels Invited Speaker: |
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