Quartz crystal microbalance poly

Fig. 6.97. Some techniques used in the study of isotherms (a) Electrochemical quartz crystal microbalance mass change (AW) vs. quantity of electricity (AG) [Au, 0.1 M HCI04 (a), and 0.05 MH2S04 ( )] and anion coverage vs. electrode potential [poly-Au (open symbols), and Au(111) (dark symbols) HS04 (circles) and CI04 (triangles)]. Reprinted from H. Uchida, N. Ideda, and M. Watanabe, J. Electroanal. Chem. 42 , copyright 1997, Figs. 3 and 5, with permission of Elsevier Science.) (b) Specular reflection method reflectivity change vs. potential [Au, HCI04 with Nal (b) and (c) 0...

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]. 

Figure 7. The self development of a thin film ( 0.2 /Ltm) of poly(p-t-butylphenyl methylsilane) upon irradiation at 248 nm (KrF excimer laser). Mass loss is proportional to the frequency change (Af) of the quartz crystal microbalance.

A potentially important development for the future of biomimetic research was published recently. Using a procedure developed by Whitesides, nucleophiles micropattemed on a gold surface were used as initiators to prepare poly(Y-benzyl-L-glutamate). Thus, an array of poly(amino acid) layers covalently attached to the surface was obtained. These would potentially act as mediators of biomimetic reactions. German workers have described the production of protein-DNA double and triple layers adsorbed on smfaces. Adhesion between layers was provided by biotin-streptavadin interactions and binding was detected by a quartz crystal microbalance. These studies may have some relevance to the understanding of protein DNA interactions at interfaces in biological systems. 

P. Su, Y. Sun, C. Lin, Novel low humidity sensor made of Ti02 nanowires/poly(2-acrylamido-2-methylpropane sulfonate) composite material film combined with quartz crystal microbalance , Talanta, 69, 946-951, (2006). 

Quartz crystal microbalance (QCM)-based SO2 gas sensors were fabricated using amino-functionalized poly(styrene-co-chloromethyl styrene) derivatives [110]. SO2 can be absorbed by the polymer s amine groups, which causes the mass to change such that it can be detected by the QCM. The sensor reaches equilibrium within 50 min in 50 ppm SO2. The sensors exhibit complete... 

The u.v.-visible spectra, in the linear absorption regime, would also yield a linear dependence of the absorbance as a function of the number of layers, provided the structural correlation from layer to layer is maintained. The results of the quartz-crystal microbalance and the u.v.-visible spectral studies for L-B films of a macrocycle, tetrakis-butyl-phenoxy-phthalocyanine show a linear relation in each case,indicating a uniform transfer from layer to layer with the same molecular structure. In contrast, the results on the L-B films of poly-(3 dodecyl-thiophene) reveal a uniform mass transfer (linear relation between the frequency change and the number of layers), but the structural correlation from layer-to-layer changes around the tenth layer, as evidenced by the change of the slope of the absorbance curve, as a function of the number deposited layers. 

Yamashita K, Yamada M, Numata K, Taguchi S (2006) Nonspecific hydrophobic interactions of a repressor protein, PhaR, with poly[(/()-3-hydroxybutyrate] film studied with a quartz crystal microbalance. Macromolecules 7 2449-2454... 

Electrolytes and solvents. The electropolymerization reaction may be sensitive to the nucleophilic nature of the solvent and electrolyte. For this reason, many of the films are prepared in aprotic solvents, such as acetonitrile, which are poor nucleophiles. Electro-oxidative polymerization in the presence of small anions simultaneously incorporates the anions which render the polymer film conductive. Upon reduction, the anions are released from the film. Cycling the film through oxidation and reduction leads to insertion and release in the respective parts of the cycle. Simultaneous incorporation or removal of the solvent and/or cations may also occur, as shown by measurements on the quartz crystal microbalance [51-52]. Polymerization in the presence of large anions such as poly(vinylsulphonate) and poly(4-styrene sulphonate) (PSS") also incorporates the anion during growth [53-56]. Subsequent cycling, however, does not release the anions which are trapped because of their... 

Polymerization of pyrrole has also been carried out chemically by mixing the monomer with a homogeneous oxidant (Fe ) in solution. Mermillod et al [61] found that poly(pyrrole) synthesized in water by action of Fe ( 104)3 produces particles in solution as well as films on the reactor walls. The material was electrochemically identical with electropolymerized product. Gregory et al [62] chemically deposited very uniform films of poly(pyrrole) on textile fibres and woven glass cloth. Gottesfeld et al [63] found that chemically deposited films were uniform and could serve as a conducting substrate for metallization structures for microelectronic circuitry. Hillman et al [64] studied the electrodeposition of poly(vinylfer-rocene) with the quartz crystal microbalance. 

Other polymer systems that have been studied with the electrochemical quartz crystal microbalance are poly(tetracycaoquinyldimethane) [91], poly(3-methylthiophene) [92], diheptylviologen bromide [93], polyani-line/Nafion composite films [94] and polypyrrole/3-(pyrrol-l-yl) propane sulphonate composites [95], and poly(pyrrole) composites with several anions [96-97]. 

Summary Films of polyacrylic acid hydrogels were produced on a conducting substrate by means of electrochemically Initiated polymerization (EIP). An electrochemical quartz crystal microbalance was used to monitor film growth In situ. Homopolymer and copolymer films of polyacrylic acid and poly-N-isopropyl-acrylamide were characterized by FTIR spectroscopy. The degree of swelling of these films could be tuned via the pH. 

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