Quartz crystal microbalance , polymer

In the case of Ni(OH)2 and conductive polymer electrodes, solvent and anions intercalate into the electrode at anodic potentials. Electrochemical quartz crystal microbalance (EQCM) is a useful technique for monitoring the ingress and egress of solvent and anions in these materials. 

Mechanism of Polymer Photoablation Explored with a Quartz Crystal Microbalance... 

We first experimented with the Quartz Crystal Microbalance (QCM) in order to measure the ablation rate in 1987 (12). The only technique used before was the stylus profilometer which revealed enough accuracy for etch rate of the order of 0.1 pm, but was unable to probe the region of the ablation threshold where the etch rate is expressed in a few A/pulse. Polymer surfaces are easily damaged by the probe tip and the meaning of these measurements are often questionable. Scanning electron microscopy (21) and more recently interferometry (22) were also used. The principle of the QCM was demonstrated in 1957 by Sauerbrey (22) and the technique was developed in thin film chemistiy. analytical and physical chemistry (24). The equipment used in this work is described in previous publications (25). When connected to an appropriate oscillating circuit, the basic vibration frequency (FQ) of the crystal is 5 MHz. When a film covers one of the electrodes, a negative shift <5F, proportional to its mass, is induced ... 

The photoablation behaviour of a number of polymers has been described with the aid of the moving interface model. The kinetics of ablation is characterized by the rate constant k and a laser beam attenuation by the desorbing products is quantified by the screening coefficient 6. The polymer structure strongly influences the ablation parameters and some general trends are inferred. The deposition rates and yields of the ablation products can also be precisely measured with the quartz crystal microbalance. The yields usually depend on fluence, wavelength, polymer structure and background pressure. 

Figure 15.7 Response of the molecular imprinted polymer quartz crystal microbalance (MIP-QCM) sensor to monoterpene analogues ( ) L-menthol, (A) D-menthol, ( ) citronel-lol, (A) citronellal, and (O) menthone. Reprinted from Percival et al. (2001). Copyright 2001 American Chemical Society.

Percival CJ, Stanley S, Galle TM, Braithwaite A, Newton MI, McHale G, Hayes W. Molecular-imprinted, polymer-coated quartz crystal microbalances for the detection of terpenes. Anal Chem 2001 73 4225-4228. 

Piacham T, Josell A, Arwin H, Prachayasittikul V, Ye L. Molecularly imprinted polymer thin films on quartz crystal microbalance using a surface bound photo-radical initiator. Anal Chim Acta 2005 536 191-196. 

A variety of surface-sensitive spectroscopic and microscopic methods were critical in the investigation of these systems. In the work by Advincula et al, the composition, thickness, physical and thermal properties, and morphology of the tethered polymer brushes were carefully analyzed [72]. A variety of surface-sensitive techniques such as ellipsometry, contact angle measurements, AFM, quartz crystal microbalance (QCM), FT-IR grazing incidence... 

MOS metal oxide sensor, MOSFET metal oxide semiconductor field-effect transistor, IR infrared, CP conducting polymer, QMS quartz crystal microbalance, IMS ion mobility spectrometry, BAW bulk acoustic wave, MS mass spectrometry, SAW siuface acoustic wave, REMPI-TOFMS resonance-enhanced multiphoton ionisation time-of-flight mass spectrometry... 

Table 5 Comparison of performance of quartz crystal microbalance chemosensors using molecularly imprinted polymer for determination of caffeine... 

Exchange of species between a solution and a polymer film is an established means of probing solution composition. The quartz crystal microbalance can monitor such exchange processes with high sensitivity. When combined with selectivity via electrochemical control and appropriate choice of polymer, the EQCM becomes an attractive sensor. In order that the potential advantages of the EQCM can be realised, certain criteria must be met. 

As with all supramolecular structures, one of the most important issues is whether a direct relationship between the structure of a material and its function or properties can be established. In the following, some examples of polymer systems which show such a correlation will be discussed. The materials addressed will include block copolymers, polyalkylthiophenes and a multilayer system based on the self-assembly of polyelectrolytes. Detailed studies on the electrochemical properties of redox-active polymers, based on poly(vinyl pyridine) modified with pendent osmium polypyridyl moieties, have shown that electrochemical, neutron reflectivity and electrochemical quartz crystal microbalance measurements can yield detailed information about the structural aspects of thin layers of these materials. 

Endres et al. [82] have demonstrated the suitability of an air- and water-stable ionic liquid for the electropolymerization of benzene. This synthesis is normally restricted to media such as concentrated sulfuric acid, liquid SO2 or liquid HF as the solution must be completely anhydrous. The ionic liquid used, l-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, can be dried to below 3 ppm water, and this ionic liquid is also exceptionally stable, particularly in the anodic regime. Using this ionic liquid, poly(para-phenylene) was successfully deposited onto platinum as a coherent, electroactive film. Electrochemical quartz crystal microbalance techniques were also used to study the deposition and redox behavior of the polymer from this ionic liquid (Section 7.4.1) [83]. 

A variety of chemical gas sensors are or could be used in electronic nose instruments. So far, successful results have been reached with conductive polymer (CP) sensors, metal oxide semiconductor (MOS) sensors, metal oxide semiconductor field effect transistor (MOSFET) sensors, quartz crystal microbalance (QCM) sensors, and infrared sensors. 

Buttry [47] measured the admittance around resonance of a quartz crystal coated with polynitrostyrene and related those measurements to the rheological changes due to film swelling. Muramatsu et al. used the resonant resistance in addition to the resonant frequency of the electrochemical quartz crystal microbalance (EQCM) as a criterion to evaluate the film non-rigidity for several electroactive polymer systems [6], including... 

Our approach to this problem involves a detailed mechanistic study of model systems, in order to identify the (electro)chemical parameters and the physicochemical processes of importance. This approach takes advantage of one of the major developments in electrochemical science over the last two decades, namely the simultaneous application of /ton-electrochemical techniques to study interfaces maintained under electrochemical control [3-5]. In general terms, spectroscopic methods have provided insight into the detailed structure at a variety of levels, from atomic to morphological, of surface-bound films. Other in situ methods, such as ellipsometry [6], neutron reflectivity [7] and the electrochemical quartz crystal microbalance (EQCM) [8-10], have provided insight into the overall penetration of mobile species (ions, solvent and other small molecules) into polymer films, along with spatial distributions of these mobile species and of the polymer itself. Of these techniques, the one upon which we rely directly here is the EQCM, whose operation and capability we now briefly review. 

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