We have grown layered assemblies of poly[4-(N-maleimido)azobenzene-co-diisopropyl (2-vinyloxy)ethylphosphonate], (poly(MAB-VEP)), where interlayer connections are made using zirconium bisphosphonate (ZP) ionic complexation chemistry. The linear optical response of the azobenzene chromophore side group shows constant layer density but a layer-dependent ratio of trans-to-cis isomers. Optical null ellipsometry data show a constant average layer thickness despite the change in conformer ratio. The change in conformer ratio with the growth of multiple polymer layers results from the steric constraints imposed on the polymer side groups by the formation of the ZP interlayer linkage. The driving force for metal ion complexation is greater than the isomerization barrier of S 0 azobenzene. Once the layers are formed, the side-groups do not exhibit any changes in conformer ratio, even when exposed to UV for a prolonged period.
We report on the growth of interfacial multilayer structures formed from maleimidevinyl ether alternating copolymers. The thickness and density of these polymer layers can be controlled by adding acid to the interlayer cross-linking reaction. We have demonstrated this control for several different interlayer cross-linking strategies, where amide, ester, urea, and urethane interlayer covalent bonds are formed. For all reactions, the addition of concentrated acid during polymer layer deposition resulted in a 2-to 4-fold increase in the loading density of the polymer relative to the acid-free reaction, depending on the acid used and its concentration. These findings are consistent with acid catalysis (HCl) and/or dehydration (H 2 SO 4 ).
We report on the achievement of differential control over adsorption and desorption kinetics of selected vapor phase molecules at ultrathin polymer bilayer interfaces. We synthesize and deposit maleimide−vinyl ether alternating copolymer layers, where each polymer layer contains different pendant side group functionalities and the order of layer deposition is controlled. The adsorption isotherm behavior of these interfacial structures, when exposed to methanol and hexane vapor, shows that the identity of the adsorbates and the order of polymer adlayer deposition both influence the interfacial adsorption characteristics. The absence of hysteresis in the isotherm data indicates that our measurements are made under equilibrium conditions, indicating the achievement of chemical and structural control over the thermodynamics of adsorption at these interfaces.
Recent developments in (MEMS) fabrication techniques have exploited the properties of polymers. Traditional lithographic techniques have been used to create a template in a thick layer of photoresist that can be filled with a heat -0r-UV curable polymer and used to cast numerous replicas of Tesla channels in an elastomeric material-poly (dimethylsioloxane) (PDMS). The surface of this replica, and that of a flat slab of PDMS, is oxidized in oxygen plasma and brought into conformal contact to seal tightly. N-isopropylacrylamide polymers have attracted much interest in the area of scientific research and microfluidic technologies due to their unique thermal response in aqueous medium. To design microactuators of these gels with a high aspect ratio and a strong adhesion to the microchannel, substrates have to be developed. To achieve this, a modification of the simple (NIPA) polymer is needed; therefore, this calls for chemical modification of the (NIPA) material itself and the PDMS. The integration of autonomous microvalves into complex microfluidic Tesla channel networks is presented. Hydrogel directly grown onto vinyl modified PDMS and is in contact with process medium. Thermoelectric element capable of changing the temperature of the system is used to actuate the valve. A distortable diaphragm at the center coupled to a piezoelectric that is connected to the ports of two channels. The other ends are connected to two small water tanks. Valve operation results in an oscillating or a positive net flow depending on valve status.
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