Polymer transducers fabrication

Fortunately, PVDF and its copolymers are compatible with silicon integrated circuit (1C) fabrication and lend themselves to microelectromechanical systems (MEMS) techniques to provide transducers in close physical proximity to electronics through the integration of transducers directly on the IC chip. Previous efforts have integrated polymer ultrasonic transducers with electronics [77, 78]. Silicon has been micromachined to improve transducer performance, air backed and epoxy backed transducers fabricated on sihcon have been demonstrated [79, 80]. 

The techniques and results presented in this paper prove the feasibility of a CMOS compatible fabrication of focused polymer transducers for minimally invasive ultrasonic imaging. The success of this approach justifies investment into additional development towards the integration of CMOS microelectronics with focused polymeric transducers. 

Newbury K-M, Leo D-J (2003) Linear electromechanical model of ionic polymer transducers - part I model development J Intell Mater Syst Struct 14 333-342 Nguyen XT, Goo NS, Nguyen VK, Yoo Y, Park S (2008) Design, fabrication, and experimental characterization of a flap valve IPMC micropump with a flexibly supported diaphragm. Sens Actuators A 141 640-648... 

Akle BJ, Bennett MD, Leo DJ, Wiles KB, McGrath JE (2007) Direct assembly process a novel fabrication technique for large strain ionic polymer transducers. J Mater Sci 42 7031-7041 Arruda TM, et al (2013) In situ tracking of the nanoscale expansion of porous carbon electrodes. Energy Environ Sci 6 225... 

Chemical and biological specificity may also be conferred by the fabrication of a secondary, semipermeable, specificity-conferring membrane over the electroconductive polymer transducer. Thus, a cellulose acetate... 

One of the most promising applications of MIPs is the fabrication of chips with microarrays containing several selective polymers against different targets. Fabrication of such platforms will extend the application and the commercial impact of such materials to many different areas where multianalyte capability is a must. Nevertheless, further efforts are still needed to optimize fabrication of localized polymer structures, avoiding problems related to long term stability of the biomi-metic material, MIP deposition, and transducer coupling. 

In situ polymerization, and electrochemical polymerization in particular [22], is an elegant procedure to form an ultra thin MIP film directly on the transducer surface. Electrochemical polymerization involves redox monomers that can be polymerized under galvanostatic, potentiostatic or potentiodynamic conditions that allow control of the properties of the MIP film being prepared. That is, the polymer thickness and its porosity can easily be adjusted with the amount of charge transferred as well as by selection of solvent and counter ions of suitable sizes, respectively. Except for template removal, this polymerization does not require any further film treatment and, in fact, the film can be applied directly. Formation of an ultrathin film of MIP is one of the attractive ways of chemosensor fabrication that avoids introduction of an excessive diffusion barrier for the analyte, thus improving chemosensor performance. This type of MIP is used to fabricate not only electrochemical [114] but also optical [59] and PZ [28] chemosensors. 

MIP beads or microspheres are also widely used for sensing purposes [166]. They are prepared by precipitation polymerization and then they are embedded in a dedicated matrix, which is immobilized on the transducer surface. Moreover, the MIP beads are used to serve as stationary phases in HPLC [167] and for catalytic purposes. Other systems, such as self-assembled monolayers, SAMs [168], sol-gel matrices [169] and preformed polymers [170] have also been utilized for fabrication of MIP constructs. 

Integration of MIPs with the transducer surface (immobilization) is a foremost and arduous step of chemosensor fabrication. The polymer material must perfectly adhere to this surface, neither dispersing away nor peeling off in aggressive solvent solutions, under extreme pH or ionic strength conditions, or under analytical flow conditions. A range of methods is being used for immobilization of imprinted... 

Solid-state ion sensors with conducting polymers as ion-to-electron transducers (and sensing membranes) offer some advantages over conventional liquid-contact ISEs. Solid-state ISEs without internal filling solution are more durable, require less maintenance, are easier to miniaturize, and allow great flexibility in electrode design and fabrication. 

Composite piezoelectric transducers made from poled Pb-Ti-Zr (PZT) ceramics and epoxy polymers form an interesting family of materials which highlight the advantages of composite structures in improving coupled properties in soilds for transduction applications A number of different connection patterns have been fabricated with the piezoelectric ceramic in the form of spheres, fibers, layered, or three-dimensional skeletons Adding a polymer phase lowers the density, the dielectric constant, and the mechanical stiffness of the composite, thereby altering electric field and concentrating mechanical stresses on the piezoelectric ceramic phase. 

Ion-selective electrodes (ISEs) are relatively simple membrane-based po-tentiometric devices which are capable of accurately measuring the activity of ions in solution. Selectivity of these transducers for one ion over another is determined by the nature and composition of the membrane materials used to fabricate the electrode. While many scientists are quite familiar with the glass membrane pH electrode first described by Cremer (CIO), most are for less aware of the other types of ISEs which may be prepared with crystalline, liquid, and polymer membranes and which allow for the selective measurement of a wide variety of cations and anions (e.g., Na" ", K" ", Ca ", Ag" ", Cl, Br , F , and organic ions). Moreover, in recent years, the range of measurable species has been further extended to include dissolved gases and... 

In general, adsorption is achieved by applying a solution of the molecule to be immobilized to a membrane or him on the sensor transducer and allowing the molecule to adsorb to the transducer over a specified time period. The membrane or film may be hydrophilic or hydrophobic or may contain ionic groups depending on the molecule to be immobilized. Various support/surface materials have been used for adsorption but the most used are silica, cellulose acetate membranes, and polymers such as PVC and polystyrene. As shown in table 8.5, adsorption is still used in the fabrication of many chemical sensors and biosensors. 

Depositing polymer membranes from solution is probably the oldest and simplest method for polymer deposition. Typically a solution of the polymer is deposited onto the transducer surface and allowed to dry. Although this technique is simple to practice, it is a fine art to perfect. Polymer concentration, solvent composition, amount of solution deposited, and solvent evaporation rate are all crucial parameters to control in order to obtain films that adhere well to the substrate, are uniform in thickness, and are free from defects. Gregg and Heller have solution cast redox-functional hydrogels containing glucose oxidase on an electrode to fabricate a glucose sensor [19]. 

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