Oxygen Diffusion in Cross-Linked, Ethanol-Swollen Poly(vinyl alcohol) Gels: Counter-Intuitive Results Reflect Microscopic Heterogeneities

Abstract

Oxygen diffusion coefficients have been determined in ethanol-swollen poly(vinyl alcohol), PVA, gels using a technique wherein oxygen sorption is optically monitored using singlet oxygen phosphorescence. Data were recorded as a function of the extent to which the PVA chains are chemically cross-linked using glutaraldehyde. Contrary to conventional expectation, the diffusion coefficients obtained increase with an increase in the extent of cross-linking. This observation is interpreted in terms of a cross-link-dependent increase in the microscopic heterogeneity of the polymer wherein dense cross-linked domains coexist with more fluid domains. It is expected that, in the latter domains, segmental motions of the macromolecule that facilitate oxygen diffusion are more readily achieved. This model of cross-link-dependent heterogeneity is supported by the results of small-angle X-ray scattering experiments. Among other things, the data reported herein provide an informative foundation for studies of small molecule diffusion in biological cells, particularly during photoinduced cell death where the hydrogel-like nature of the cell can change due to cross-linking reactions.

Singlet oxygen: there is indeed something new under the sun

“…This latter statement is likewise relevant for recent work in which singlet oxygen phosphorescence experiments were used to quantify oxygen diffusion coefficients in solvent-swollen gels. 238 Data thus recorded indicated that, as the extent of crosslinking in these polymers was increased, these materials became more heterogeneous and were characterized by a combination of dense domains and less-dense open ''channels'' through which oxygen could more readily move. Data such as these certainly appear relevant with respect to light-initiated reactions that alter intracellular morphology (e.g., the collapse of cytoskeletal proteins, Fig.…”

Anion exchange nanofiber materials activated by daylight with a dual antibacterial effect

“…Some recent studies of oxygen permeability in polymers have obtained ambiguous conclusions; one study found that the presence of cross-links in glassy PMMA moderately decreased the oxygen permeability, 33 whereas another study found that the oxygen permeability increased with increased cross-linking in ethanol swollen cross-linked PVA. 34 The formation and kinetics of O 2 ( 1 Δ g ) were monitored by time-resolved phosphorescence at 1270 nm (Fig. 7, panel A) and singlet oxygen sensitized delayed fluorescence (SODF) at 650 nm (Fig.…”

Manipulating the Collective Surface Plasmon Resonances of Aligned Gold Nanorods in Electrospun Composite Nanofibers

“…Strong swelling capabilities of ethanol and toluene to PVA have been well documented in the literature. 65,66 Our results indicated that the swelling of composite nanofibers would become more substantial with the order of acetone, hexane, DCM, chloroform, toluene, and ethanol, and such an order could be related to the polarities and chemical structures of the solvents.…”