Probing the dynamics of water in chitosan polymer films by dielectric spectroscopy

Abstract

Chitosan biopolymers are increasingly being used in advanced biomedical applications, where aqueous interactions profoundly influence their physical properties and also their in vivo biomolecular and cellular activity. Here, hydration of chitosan films is studied by dielectric spectroscopy in a conventional constraining plate configuration and compared with free standing films. Film hydration proceeds by an initial water uptake followed by a spontaneous dehydration (deswelling) even in saturated atmospheres. At water contents above a critical value, $ 9.5 wt % a dielectric loss resonance peak (b wet ) arises from relaxation of evolving chitosan-water complexes, below this value insufficient interchain space for oscillation of these complexes prevents b wet appearing. The b wet frequency was related to water content by a power law with the frequency changing by $ 3 orders of magnitude.Importantly the scaling exponents (slopes) differed significantly for unconstrained (free standing) and volume constrained films indicating the effect of internal stresses in constrained films. Both dielectric and conductivity behavior were influenced by internal constraining stresses affecting both oscillatory motion and charge mobility. In biomedical devices, biopolymers may be free standing, surface adhered, or enclosed structures imposing different internal stresses on polymer chains and the mobility of their segments. Dielectric spectroscopy can examine these influences on dielectric and electrical characteristics, which play a critical role in biomolecular interactions.

Structure and dynamics of polypyrrole/chitosan nanocomposites

“…The sustained augmentation in the dielectric loss in the low‐frequency range with increasing temperature authenticates the occurrence of Maxwell–Wagner–Sillars (MWS) polarization which results from the separation of charges at the inner dielectric boundary layers . This MWS polarization process has been observed in inhomogeneous materials, such as biopolymers and polysaccharides,including Cs . Both electrode polarization and MWS polarization are of macroscopic nature, directly connected with the DC conductivity of a material, and can mask the dielectric response of a sample in the low‐frequency region.…”

“…43 This MWS polarization process has been observed in inhomogeneous materials, such as biopolymers and polysaccharides, 82,84 including Cs. 34,38,85,86 Both electrode polarization and MWS polarization are of macroscopic nature, directly connected with the DC conductivity of a material, and can mask the dielectric response of a sample in the low-frequency region.…”

Origin and influence of water‐induced chain relaxation phenomena in chitosan biopolymers

“…Dielectric spectroscopic measurements were made on the free standing films which were provided with silver epoxy electrodes (10 × 10 mm 2 ) and multistrand copper wire leads in a condenser mode configuration since we have previously shown that conventional parallel plate configurations, which constrain the biopolymer film during hydration, influenced their dielectric response 23. Data was collected over the frequency range 10 1 –10 6 Hz to probe the water induced relaxation behavior of these samples using a HP 4192A low frequency impedance analyzer (Hewlett‐Packard) on samples within a chamber under controlled relative humidity conditions at a constant temperature of 300 K. The signal amplitude was maintained at 1 V rms throughout the measurements, providing an accuracy of measured capacitance ±0.01 pF for low water content samples and ±1 pF for high water contents.…”

“…Subsequently, the dielectric loss, ε″ was corrected for conductivity. The procedure adopted for simultaneous measurement of water uptake and dielectric properties of the chitosan films has been detailed previously 23…”

Switching of optical‐resolution selectivity through the Onsager's reaction field: Chiral recognition of dl‐amino acids by hydrophilic/hydrophobic chitosans

“…The relative permittivity of chitosan is approximately 5.0, that of poly‐HEMA is about 9.0 and that of polystyrene about 2.2 (similar to that of benzene or toluene). From these static permittivities, the above change in selectivity is well explained by the change in the sign of the reaction field.…”