Salt Tolerance of an Aqueous Solution of a Novel Amphiphilic Polysaccharide Derivative

Abstract

An aqueous solution of an amphiphilic polysaccharide derivative, hydrophobically (stearyl alkyl group) and hydrophilically (sulfonic-acid salt group) modified hydroxyethylcellulose (HHM-HEC), showed increased viscosity, elasticity, and thixotropic properties in response to the addition of monovalent and divalent salts. Furthermore, the HHM-HEC solution had a transparent appearance at a NaCl concentration of 7 wt %. Since it showed superior salt tolerance to HEC, we focused attention on the two substituents of HHM-HEC and prepared HEC derivatives, namely, hydrophobically modified hydroxyethylcellulose (R-HEC), hydrophilically modified hydroxyethylcellulose (S-HEC), and nonmodified hydroxyethylcellulose (HEC). In addition, we used oscillatory, thixotropic, and fluorometric methods to compare the rheological properties of HHM-HEC with those of other derivatives in the presence of NaCl and ZnCl2, and attempted to elucidate the respective roles of the two substituents of HHM-HEC solution in the salt-tolerance mechanism. As the NaCl concentration in the HHM-HEC solution increased, the values of the elastic modulus G' and the viscous modulus G'' increased, and, moreover, the relative intensities of the first (I1 = 372 nm) and the third (I3 = 383 nm) vibronic bands of the pyrene monomer emission spectrum (the I1/I3 ratio) decreased. These results suggested that the added salt strengthened the three-dimensional network structure of the HHM-HEC polymer by the formation of cross-linkages through the association of hydrophobic substituents. This hydrophobic substituent was therefore essential in allowing HHM-HEC to exhibit a high viscosity in a salt solution. Although the R-HEC solution showed a higher viscosity than did the HHM-HEC solution in the absence of added salts, it became cloudy and lost its viscosity at high NaCl concentrations, apparently because of the shrinkage of its network structure. This signified that the hydrophilic substituent was essential for the sufficient solubility of HHM-HEC to show its rheological properties in a salt-rich solution. We propose to explain how the viscosity of HHM-HEC increases in the presence of salts as follows: Added salts weaken the electrostatic repulsion between the hydrophilic substituents, thereby enhancing the interactions of hydrophobic substituents and consequently increasing the rigidity of the HHM-HEC solution.

Rheological evaluation of synthesized template‐hydrophobically modified acrylamide based copolymers in brine

“…The effect of sodium salt (NaCl) concentration on the viscosity of TCHPA‐24 solution is shown in Figure . Adding salt has an electric‐shielding effect on the electrostatic resistance of the polymer ions, causing the polymer chains to coil up . This decreases the viscosity of the polymer solution while increasing the salt concentration.…”

Xylan‐Based Nanoparticles: Prodrugs for Ibuprofen Release

“…[31][32][33] For the fluorescence spectra suspensions of sample 4 (DS Ibu ¼ 1.04; particle mean diameter ¼ 342 nm) and the additionally sulfated sample 8 (DS Ibu ¼ 1.04, DS Sulfate ¼ 0.25, particle mean diameter ¼ 162 nm) were used (Figure 8). Pyrene concentration amounted 6 Â 10 À7 molÁL À1 , which is sufficiently low to avoid excimer formation.…”

Thickening properties and emulsification mechanisms of new derivatives of polysaccharide in aqueous solution

“…4). Kawakami et al [22] have already reported the thickening mechanisms of HHM-HEC by the addition of salts. They concluded that when NaCl is added to the HHM-HEC solution, electrostatic repulsion by the sulfonate groups is weakened due to a charge-screening effect, which facilitates the aggregation of hydrophobic moieties and the viscosity increases HEC (A) and (B) highly expand in water due to the electrostatic repulsion between the sulfonate groups, the aggregation of alkyl chains is inhibited and a stronger hydrophobicity of the hydrophobic microdomains less than I 1 /I 3 = ∼1.4 cannot be formed.…”

“…Several studies have been reported on HHM-HEC properties in terms of thickening properties, emulsification mechanisms [19], salt tolerance properties [22], and minimization of emulsified particles by lipophilic surfactant [20]. However, the effects of the substitution degree of the hydrophobic and hydrophilic moieties of HHM-HEC have not been examined yet.…”