Characterization of highly substituted, cationic amphiphilic starch derivatives: Dynamic surface tension and intrinsic viscosity

Abstract

The surface activity and viscometric behavior of highly substituted, amphiphilic polysaccharides, derived from potato starch by modification with benzyl‐ and hydroxypropyl‐trimethylammonium groups, are studied in salt‐free and 0.05 M NaCl aqueous solution. For the first time dynamic surface tension measurements of amphiphilic starch derivatives have been effected using the pendant drop method and it was possible to correlate them with particle sizes and apparent charge density. Rheological investigation of large concentration ranges (0.01–20 g/L) is used to discuss Huggins plots and typical polyelectrolyte (PEL) behavior for all starch derivative samples could be found. The determination of overlap concentration and, in dilute aqueous solution, of intrinsic viscosity was possible. For the latter one the semi‐empirical equation of Rao was used, making it possible to get insights to PEL conformation in dependence on the degrees of substitution (DS) of both substituents. It is shown that for intrinsic viscosity an inversion of the impact of both substituents takes place, with hydrophobic benzyl groups on the one hand and cationic hydroxypropyl‐trimethylammonium groups on the other. Data evaluation via the ratio of both DS values had been successfully utilized and thus, the applied method has been identified as being a promising tool to compare a multitude of starch derivatives with substituents of different polarity in various DS to get tendencies regarding overall hydrophobicity.

Non‐invasive high throughput approach for protein hydrophobicity determination based on surface tension

“…From our stalagmometric measurements we observed a stronger decrease of surface tension with increasing molecular weight and thus conclude that this is caused by the increase of hydrophobicity. This is in agreement with the findings of Genest et al () on hydrophobically modified polyelectrolytes that also exhibited lower surface tension values the more hydrophobic they were. Thus, the presented stalagmometric method is capable of deducing an analytes’ hydrophobicity from its influence on the surface tension.…”

“…The more hydrophobic the protein, the greater the depression in the interfacial tension. Recently Genest et al () found a correlation between the depression of the surface tension and the polymer hydrophobicity.…”

Insight into the Interaction Between Carbopol® 940 and Ionic/Nonionic Surfactant

“…The intrinsic viscosity of pure Carbopol Ò 940 in water was calculated to be 6.24 (dL/g). This value is influenced by hydrodynamic volume, size and conformation of a single Carbopol Ò 940 polymer chain [25]. Appropriate linearity of the Huggins plot, which is a characteristic of neutral polymers, indicated that the dissociation of carboxyl groups of Carbopol Ò polymer chain was negligible in diluted solution at a certain pH value (pH ca.…”

Flocculation Efficiency of Novel Amphiphilic Starch Derivatives: A Comparative Study

“…Despite hydrophobic modification, the cationic starch derivatives studied retain good solubility in water with CDs virtually independent of the pH value owing to the presence of quaternary ammonium groups. Our systematic study of solution properties of these amphiphilic starches revealed that for derivatives with DS N 0.25–1.0 hydrophobic substitution at the level DS Bn 0.30 does not significantly affect CD compared to the purely cationic starch, while further increase of DS Bn results in decrease of apparent CD due to intramolecular hydrophobic aggregation …”

“…In agreement with this concept, one can see from the data listed in Table that hydrophobic substitution up to DS Bn 0.50 only slightly influences apparent CD of the cationic starch with medium DS N of 0.39, whereas increase of DS Bn up to 0.70 leads to much more significant changes in apparent CD and hydrodynamic radius of starch in solution. Previously, we have identified thresholds of DS, which involve property changes of this amphiphilic starches in solution besides CD, such as dynamic surface tension and intrinsic viscosity, when passing over the ratio DS Bn /DS N of 1.0 . Owing to the electrostatic repulsion between charged fragments highly cationic starch (HPMAS‐1.54) exists in the solution in extended conformation and, consequently, has the highest hydrodynamic radius.…”