Molecular Motions in Chitosan Studied by Dielectric Relaxation Spectroscopy

Viciosa, María Teresa; Dionı́sio, Madalena; Silva, Rmp da; Reis, Rui L.; Mano, João F.

doi:10.1021/bm049685b

Cited by 50 publications

(65 citation statements)

References 20 publications

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“…7 Due to water losses of the sample by evaporation, the conductivity is reduced in the following runs.…”

Section: Resultsmentioning

confidence: 99%

“…7 The dielectric measurements were carried out using a Hewlett-Packard impedance analyzer HP 4284A, covering a frequency range from 20 Hz to 1 MHz, under an applied electric field of 1 V rms . The temperature control was assured by the Quatro Cryosystem from Novocontrol GmbH (Hundsangen, Germany).…”

Section: Methodsmentioning

confidence: 99%

“…7 In nonneutralized chitosan, the low secondary process becomes more intense as the water decreases. See curves represented by stars and asteriks relative to losanges in Figure 3b.…”

Section: Low Temperature Regionmentioning

confidence: 99%

“…5 For the particular case of the neutralized membrane used in this work, the typical semicrystalline character of chitosan was identified by X-ray diffraction. 6 In a previous publication, 7 wet (13% of water content) and annealed samples of both nonneutralized and neutralized (subject to a further neutralization with alkaline solution) forms of chitosan were studied by dielectric relaxation spectroscopy, which probes the molecular mobility through the reorientation of permanent dipoles under the influence of an applied electrical field. Its detailed dielectric characterization was performed only in samples after being annealed for 20 min at 1508C.…”

Section: Introductionmentioning

confidence: 99%

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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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“…7 Due to water losses of the sample by evaporation, the conductivity is reduced in the following runs.…”

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…7 In nonneutralized chitosan, the low secondary process becomes more intense as the water decreases. See curves represented by stars and asteriks relative to losanges in Figure 3b.…”

Section: Low Temperature Regionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dielectric characterization of neutralized and nonneutralized chitosan upon drying

2005

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“…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. The first process (located at temperature between À100 C and 0 C) has the characteristic of a secondary relaxation process which was related to local chain dynamics, and the second process located at higher temperatures which were related to conductivity.…”

Section: Introductionmentioning

confidence: 99%

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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