Polymer film swelling

A unique feature of this kind of highly ordered LC networks is their anisotropic swelling [77]. The polymer films swells only perpendicularly to the molecular director (Fig. 2.18) [77]. 

Enomoto K, Takahashi S, Iwase T, Yamashita T, Maekawa Y (2011) Degradation manner of polymer grafts chemically attached on thermally stable polymer films swelling-induced detachment of hydrophilic grafts from hydrophobic polymer substrates in aqueous media. J... 

Oxidation processes induces a significant reorganization of the polymer structure (see below) and in turn of the polymer film (swelling phenomenon due to the transition between a hydrophobic neutral form and a more hydrophilic charged form) upon doping. 

Fig. 3.15 (a) Conductivity responses for three donut-shaped thin-film sensors based on carbon-doped poly 4-vinyl phenol (b, c) conductivity responses of carbon-doped polyvinyl acetate to (b) temperature and (c) air humidity. The polymer films swell in response to the presence of a particular gas which increases the distance between the carbon dopants and changes the resistance of the film. These results were obtained from 3-day experiments in an air ambient where the gas sensors were kept in stagnant air (Data from Buchler and Ryan (1997))... 

In each of these approaches, imaging is confined to the top of a single polymeric film by adjusting optical absorption. The penetration depth of the silylation agent and the attendant swelling of the polymer film must also be controlled to avoid distortion of the silylated image. Resists of this type are capable of very high resolution (Fig. 37). 

The flow of an anodic current oxidizes the conducting polymer and the film swells. At the polypyrrole/tape interface, electrochemically stimulated conformational changes in the polymer promote an expansion that... 

Fukumura, H., Mibuka, N., Eura, S. and Masuhara, H. (1991) Porphyrin-sensitized laser swelling and ablation of polymer films. Appl. Phys. A, 53, 255-259. 

Cross, G. H. Ren, Y. Swann, M. J., Refractometric discrimination of void space filling and swelling during vapour sorption in polymer films, Analyst 2000, 125, 2173 2175... 

Several approaches have been undertaken to construct redox active polymermodified electrodes containing such rhodium complexes as mediators. Beley [70] and Cosnier [71] used the electropolymerization of pyrrole-linked rhodium complexes for their fixation at the electrode surface. An effective system for the formation of 1,4-NADH from NAD+ applied a poly-Rh(terpy-py)2 + (terpy = terpyridine py = pyrrole) modified reticulated vitreous carbon electrode [70]. In the presence of liver alcohol dehydrogenase as production enzyme, cyclohexanone was transformed to cyclohexanol with a turnover number of 113 in 31 h. However, the current efficiency was rather small. The films which are obtained by electropolymerization of the pyrrole-linked rhodium complexes do not swell. Therefore, the reaction between the substrate, for example NAD+, and the reduced redox catalyst mostly takes place at the film/solution interface. To obtain a water-swellable film, which allows the easy penetration of the substrate into the film and thus renders the reaction layer larger, we used a different approach. Water-soluble copolymers of substituted vinylbipyridine rhodium complexes with N-vinylpyrrolidone, like 11 and 12, were synthesized chemically and then fixed to the surface of a graphite electrode by /-irradiation. The polymer films obtained swell very well in aqueous... 

Freger s model treats swelling as a nonaffine inflation of the hydrophobic polymer matrix by small aggregates of water molecules (droplets) separated by polymer films. This model results in a relation. 

Swell Index and Percent Solubles Measurements. Polymer films were cast on polyester film at 25X solids with various post additives. The films were air dried (16-48 h) then cured for 3 and 10 min at 150 C In a converted oven. Small samples (50-100 mg) of film were weighed, soaked In dimethylformamide (DHF) for 1 h, briefly pat-dried and reweighed In an A1 weighing pan. The samples were then redried at 150 C (20 torr) or 170 C, 1 atm for 30 min. 

Table I shows a comparison of free film swell Index results as a function of crosslinker at a constant comonomer level (0.3 moles/kg of polymer). ABDA and AEP gave crosslinking performance Identical to a conventional crosslinker, BNMA. However, derivatives which cannot cycllze, either because the amide has an additional substituent, as In 13, or the chain connecting the amide to the blocked aldehyde Is too short, as In 14, did not exhibit efficient crosslinking. They also showed significant discoloration, presumably due to Increased aldol condensation relative to 1, 2, or BNMA.

Tablets coated with the Eudragit-PEG 400 mixture were made with three different polymer film thicknesses 6, 10 and 15 mg (KET-R, 10 and 15 tablets). For these tablets it was not possible to obtain swelling measurements because this was prevented by the lake coating.

So, we have two possibilities for the case of the ion-exchange polymer film-coated electrode reduction could occur by physical diffusion of the Fe3+ through the film, or reduction could occur via electron hopping through the film. How can we know which process is operative Electrochemists have devoted a considerable amount of research effort to answering this question. The answer clearly depends on the nature of the polymer, the extent of swelling of the... 

Fig. 8 Polymer volume fraction (j) = ho//t,w, where ho is the thickness of the polymer film after spin-coating and hsw is the thickness of a swollen film, measured by in situ spectroscopic ellip-sometry as a function of (a) the relative solvent vapor pressure for thin films of homopolymers PS, PB, and SBS block copolymer. Reprinted from [49], with permission. Copyright 2004 American Institute of Physics, (b) Polymer volume fraction as a function of the swelling time for PS- >-P2VP (SV) block copolymer and for homopolymers PS and P2VP at p/po = 1.0 [118]. The equilibrium degree of swelling indicates that toluene is a selective solvent for the PS block, and that SV block copolymer shows asymmetric swelling under toluene vapor. Reproduced by permission of The Royal Society of Chemistry (RSC) [118]...

In contrast to swollen homopolymer films, only a limited number of studies on thin films of block copolymers have been reported in which the degree of the film swelling has been directly accessed. In situ SE has been used to evaluate the polymer-solvent interaction parameters [144], to construct phase diagrams of surface structures [49, 51], and to control the mechanism of lamella reorientation in thick swollen films [118, 163, 164], Spectroscopic reflectometry combined with real-time GISAXS has been used to follow structural instabilities in swollen lamella films [165], Recently, it was demonstrated that swelling of diblock copolymer films in organic selective and non-selective solvents follows the same physical behavior as in thin films of homopolymers [119]. 

Along with the surface interactions, the chain conformation that is imposed by the confined geometry and by the film preparation strongly affects the swelling behavior of polymer films [119, 169-171]. 

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