Influence of κ-Carrageenan Gel Structures on the Diffusion of Probe Molecules Determined by Transmission Electron Microscopy and NMR Diffusometry

Abstract

The influence of the microstructures of different kappa-carrageenan gels on the self-diffusion behavior of poly(ethylene glycol) (PEG) has been determined by nuclear magnetic resonance (NMR) diffusometry and transmission electron microscopy (TEM). It was found that the diffusion behavior was determined mainly by the void size, which in turn was defined by the state of aggregation of the kappa-carrageenan. The kappa-carrageenan concentration was held constant at 1 w/w%, and the aggregation was controlled by the amount of potassium and/or sodium chloride and, for samples containing potassium, also by the cooling rate. Gels containing potassium formed microstructures where kappa-carrageenan strands are rather evenly distributed over the image size, while sodium gels formed dense biopolymer clusters interspersed with large openings. In a gel with small void sizes, relatively slow diffusion was found for all PEG sizes investigated. Extended studies of the self-diffusion behavior of the 634 g mol(-)(1) PEG showed that there is a strong time dependence in the measured PEG diffusion. An asymptotic lower time limit of the diffusion coefficient was found in all gels when the diffusion observation time was increased. According to the ratio, D/D(0), where D(0) is the diffusion coefficient in D(2)O and D is the diffusion coefficient in the gels, the gels could be divided into three classes: small, medium, and large voids. For quenched kappa-carrageenan solutions with salt concentrations of 20 mM K(+), 100 mM K(+), or 20 mM K(+)/200 mM Na(+) as well as slowly cooled solutions with only 20 mM K(+), D/D(0) ratios between 0.18 and 0.29 were obtained. By quenching a kappa-carrageenan solution with 100 mM K(+), the D/D(0) was 0.5, while D/D(0) ratios between 0.9 and 1 were obtained in a quenched solution with 250 mM Na(+) and slowly cooled samples with 20 mM K(+)/200 mM Na(+) or 250 mM Na(+).

Pore size effects on convective flow and diffusion through nanoporous silica gels

“…It is therefore of utmost importance to determine the relationship between structure and properties in order to design new materials and devices with tailored properties [4]. Previous works have shown a strong correlation between mass transport and structure [4,[10][11][12]. Earlier studies on the transport properties for water of different protein gels as a function of pH, temperature and ionic strength suggests that materials with pore widths in the range from approximately 200 nm and up to 2m are more predisposed to lose moisture compared to materials with pores on an even smaller length scale [13][14][15][16].…”

Molecular mobility and microscopic structure changes in κ-carrageenan solutions studied by gradient NMR

“…Reports on the influence of -carrageenan gel structures on the diffusion of a dendrimer probe (Walther, Lorén, Nydén, & Hermansson, 2006) and a polymer (ethylene glycol) probe (Lorén et al, 2009) have been published, where the gel structures were controlled by varying the salt content and the cooling rate. The diffusion of probe molecules in polymer matrices can be affected by hydrodynamic interactions (Phillips, 2000).…”

Structuring Water by Gelation

“…During slow cooling, time is allowed for aggregation, which results in a considerable coarsening of the network structure and an increase in pore size, as shown in Figure 13.3. The difference in the state of aggregation is reflected both in the rheological properties and in the diffusion rate of macromolecules in the gel structures, as will be discussed later (Walther et al 2006). Kappa-carrageenan has one sulphate group per disaccharide.…”

“…A combination of NMR diffusometry and microscopy has proved useful for the study of probe diffusion in gels and emulsions (Hagslätt et al 2003;Lorén et al 2005;Hermansson et al 2006;Walther et al 2006) For such studies the probe should be much larger than water so that the obstruction can be clearly observed in NMR diffusometry. Small molecules that diffuse in a material with small amounts of obstructing matter having an open structure network structure will not be significantly slowed down.…”

“…Studies have been made of probe diffusion of PEG (polyethylene glycol) of different molecular weights in kappa-carrageenan gels in D 2 O, where the network structures have been varied by aggregation induced by cooling and addition of salts (Walther et al 2006). The relation between microstructure and diffusion was qualitatively investigated by comparing the gel microstructure with the corresponding selfdiffusion coefficient, D, and the diffusion quotient, D/D 0 , where D 0 is the diffusion coefficient of PEG in D 2 O.…”