The cation-controlled and hydrogen bond-mediated shear-thickening behaviour of a tree-fern isolated polysaccharide.
Carbohydr Polym
; 130: 57-68, 2015 Oct 05.
Article
in En
| MEDLINE
| ID: mdl-26076601
ABSTRACT
The shear-thickening rheological behaviour (between 5 and 20s(-1)) of a 5% (w/w) viscoelastic gum extracted from the fronds of the native New Zealand black tree fern or mamaku in Maori was further explored by manipulating the salt content. The freeze-dried mamaku gum contained a high mineral content and sugars which upon removal via dialysis, resulted in the loss of shear thickening. However, this loss was reversible by the addition of salts to the dialysed dispersion. The mechanism of shear-thickening behaviour was therefore hypothesised to be due to shear-induced transition of intra- to intermolecular hydrogen bonding, promoted by the screening effect of cations. Mono-, di- and trivalent salts, i.e. Na(+), K(+), N(CH3)4(+), Ca(2+), Mg(2+), Al(3+) and La(3+) at concentrations between 0.001 and 1.0M were tested to support the hypothesis as well as to demonstrate the sensitivity of the biopolymer to cation valency and concentrations. The cation valency and concentration were crucial factors in determining (i) zero-shear viscosity, (ii) critical shear rate, γËc (or shear rate at the onset of shear-thickening) and (iii) the extent of shear-thickening of the solution. For mono- and divalent cations these parameters were similar at equivalent ionic strengths and fairly independent of the cation type. Trivalent cations (La(3+)) however caused precipitation of the gum in the concentration range of 0.005-0.05 M but clear dispersions were obtained above 0.05 M.
Key words
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Polysaccharides
/
Ferns
Country/Region as subject:
Oceania
Language:
En
Journal:
Carbohydr Polym
Year:
2015
Type:
Article
Affiliation country:
New Zealand