Influence of water on the dielectric behaviour of chitosan films

Nogales, Aurora; Ezquerra, Tiberio A.; Rueda, Daniel R.; Martínez, Francisco; Retuert, Jaime

doi:10.1007/s003960050099

Cited by 40 publications

(33 citation statements)

References 13 publications

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“…Our results compared with the work of Nogales et al 13 for neutralized chitosan films containing 11% water show that these authors characterized a low-temperature process compatible with the -wet process here described. They found an activation energy of 71 kJmol -1 in agreement with the activation energy values found for wet polysaccharides as mentioned above and a strong reduction of intensity upon drying.…”

Section: Figuresupporting

confidence: 81%

“…This could be the reason why some authors report a disappearance of the high temperature process upon annealing. 13 Finally, a separated Maxwell Wagner Sillars (MWS) process located in the low frequency side of the process was additionally found at higher temperatures in all runs. The strong low frequency increase of "@ could be incorrectly assumed to be of pure electronic origin, but the low frequency tail detected in the permittivity (shown in the inset of Figure 7) dismantles that hypothesis.…”

Section: à18mentioning

confidence: 98%

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Dielectric characterization of neutralized and nonneutralized chitosan upon drying

2005

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Isothermal dielectric loss spectra of neutralized and nonneutralized chitosan were acquired in successive runs from -130 degrees C up to increasing final temperatures, in a frequency range between 20 Hz and 1 MHz. Essentially, three relaxation processes were detected in the temperature range covered: (i) a beta-wet process, detected when the sample has a higher water content that vanishes after heating to 150 degrees C; (ii) a beta process, which is located at temperatures below 0 degrees C, becoming better defined and maintaining its location after annealing at 150 degrees C independently of the protonation state of the amino side group; and (iii) a sigma process that deviates to higher temperatures with drying, being more mobile in the nonneutralized form. Moreover, in dried neutralized chitosan, a fourth process was detected in the low frequency side of the secondary beta process that diminishes after annealing. Whether this process is a distinct relaxation of the dried polymer or a deviated beta-wet process due to the loss of water residues achieved by annealing is not straightforward. Only beta and sigma processes persist after annealing at 150 degrees C. The changes in molecular mobility upon drying of these two relaxation processes were evaluated.

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Section: Figuresupporting

confidence: 81%

Section: à18mentioning

confidence: 98%

Dielectric characterization of neutralized and nonneutralized chitosan upon drying

2005

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“…This relaxation process is related to a local main chain motion of CMCs coupled with adsorbed water. As previously mentioned, (see the Introduction) Einfeldt et al 25,26 and Nogales et al 28 reported the same relaxation process in Cs. The origin of the former finding (Einfeldt et al) was attributed to the motion of a mixed phase of both polysaccharide and water, whereas the later (Nogales et al) was attributed to hydrogenbonded water.…”

Section: Molecular Dynamics Investigationsupporting

confidence: 61%

“…In case of Cs, Nogales et al 28 described two relaxation processes: (i) b-relaxation, with characteristics similar to the b-relaxation reported by Einfeldt et al, 25,26 but was attributed to hydrogen-bonded water, and (ii) a conduction process related to adsorbed water molecules upon heating at T > 80 C which disappeared after water desorption at high temperatures. By using dielectric spectroscopy, Viciosa et al 29 reported two relaxation processes with an Arrhenius temperature dependence for wet (13% of water content) and annealed (for 20 min at 150 C) non-neutralized and neutralized forms of Cs.…”

Section: Introductionmentioning

confidence: 64%

Preparation, characterization, structure, and dynamics of carboxymethyl chitosan grafted with acrylic acid sodium salt

El‐Sherbiny

Elmahdy

2010

J of Applied Polymer Sci

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Graft copolymerization of different vinyl monomers onto chitosan (Cs) and its derivatives can alter their properties and consequently expands their potential applications. In this study, carboxymethyl chitosan (CMCs) was prepared and characterized. Graft copolymerization of acrylic acid sodium salt (AAs) onto CMCs was accomplished by using ammonium persulphate (APS)-induced free radical polymerization in aqueous medium under nitrogen atmosphere. Occurrence of grafting was confirmed and the effects of [AAs], [APS], reaction time, and temperature on the extent of grafting were studied. The influence of grafting yield on the structure and dynamics was also investigated by using differential scanning calorimetry (DSC), two-dimensional wide-angle X-ray scattering (2D-WAXS), scanning electron microscopy (SEM), and dielectric spectroscopy. Preliminary study, using dielectric spectroscopy, was carried out to the CMCs-g-AAs copolymer with grafting percent $ 2900%, as an example, in a wide range of temperature (from 299 to 473 K) and frequency (from 1 Â 10 À2 to 1 Â 10 5 Hz). One relaxation process with Arrhenius type was detected. This process has the characteristics of a secondary relaxation process related to local chain dynamics with activation energy of 53 6 3 kJ/mol.

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“…10 -7 F/cm 2 was determined at 1 kHz in a drop cast film of chitosan on ITO, though the film thickness was not reported [10]. It should be pointed out that, in view of its highly hygroscopic nature, the dielectric response of the chitosan is dependent on the water content [12] and likely on the deacetylation degree, leading to variable values in different reports. Figure 3 shows the output characteristics and the transfer curve for the pentacene-based TFT.…”

Section: Methodsmentioning

confidence: 99%

Self-standing chitosan films as dielectrics in organic thin-film transistors

Morgado¹,

Pereira²,

Bragança³

et al. 2013

Express Polym. Lett.

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Abstract. Organic thin film transistors, using self-standing 50 !m thick chitosan films as dielectric, are fabricated using sublimed pentacene or two conjugated polymers deposited by spin coating as semiconductors. Field-effect mobilities are found to be similar to values obtained with other dielectrics and, in the case of pentacene, a value (0.13 cm 2 /(V·s) comparable to high performing transistors was determined. In spite of the low On/Off ratios (a maximum value of 600 was obtained for the pentacene-based transistors), these are promising results for the area of sustainable organic electronics in general and for biocompatible electronics in particular.

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Influence of water on the dielectric behaviour of chitosan films

Cited by 40 publications

References 13 publications

Dielectric characterization of neutralized and nonneutralized chitosan upon drying

Dielectric characterization of neutralized and nonneutralized chitosan upon drying

Preparation, characterization, structure, and dynamics of carboxymethyl chitosan grafted with acrylic acid sodium salt

Self-standing chitosan films as dielectrics in organic thin-film transistors

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