skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Salt and Temperature Effects on Xanthan Gum Polysaccharide in Aqueous Solutions
Xanthan gum (XG) is a carbohydrate polymer with anionic properties that is widely used as a rheology modifier in various applications, including foods and petroleum extraction. The aim was to investigate the effect of Na+, K+, and Ca2+ on the physicochemical properties of XG in an aqueous solution as a function of temperature. Huggins, Kraemer, and Rao models were applied to determine intrinsic viscosity, [η], by fitting the relative viscosity (ηrel) or specific viscosity (ηsp) of XG/water and XG/salt/water solutions. With increasing temperature in water, Rao 1 gave [η] the closest to the Huggins and Kraemer values. In water, [η] was more sensitive to temperature increase (~30% increase in [η], 20–50 °C) compared to salt solutions (~15–25% increase). At a constant temperature, salt counterions screened the XG side-chain-charged groups and decreased [η] by up to 60% over 0.05–100 mM salt. Overall, Ca2+ was much more effective than the monovalent cations in screening charge. As the salt valency and concentration increased, the XG coil radius decreased, making evident the effect of shielding the intramolecular and intermolecular XG anionic charge. The reduction in repulsive forces caused XG structural contraction. Further, higher temperatures led to chain expansion that facilitated increased intermolecular interactions, which worked against the salt effect.  more » « less
Award ID(s):
1953428
PAR ID:
10490961
Author(s) / Creator(s):
; ;
Publisher / Repository:
MDPI
Date Published:
Journal Name:
International Journal of Molecular Sciences
Volume:
25
Issue:
1
ISSN:
1422-0067
Page Range / eLocation ID:
490
Subject(s) / Keyword(s):
xanthan gum viscosity carbohydrate viscosity enhancement polymer aqueous solution salt effect
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; (, Langmuir)
    In many commercial applications, polymer–dye interactions are frequently encountered from food to wastewater treatment, and while shear rheology has been well characterized, the extensional properties are not well known. The extensional viscosity ηE and relaxation time λE are the extensional rheological parameters that provide valuable insights into how aqueous polymers respond during deformation, and this study investigated the effect of dyes on the extensional rheology of three different aqueous polymer solutions (e.g., anionic, cationic, and neutral) paired with two different dye salts (e.g., anionic and cationic) using drop pinch-off experiments. We have found that the influence of dyes on the pinch-off dynamics is complex but generally leads to a decrease in, for example, the apparent extensional relaxation time. We have utilized the dripping-onto-substrate method to probe the uniaxial deformation of widely used polymers such as xanthan gum (XG), poly(diallyldimethylammonium chloride) (PDADMAC), and poly(ethylene oxide) (PEO) as the anionic, cationic, and neutral polymers, respectively, paired with either fluorescein (Fl) or methylene blue (MB) as the anionic and cationic dyes, respectively. Polymer–dye pairs with opposite charges (e.g., XG–MB and PDADMAC–Fl) displayed a pronounced decrease in pinch-off times, but even PEO, which is a neutral polymer, resulted in decreased pinch-off times, which was restored by the addition of NaCl. The pinch-off times for the Boger fluid (mixture of poly(ethylene glycol) and PEO), however, were surprisingly uninfluenced by dyes. These results showed that not only did the small addition of dyes strongly decrease the polymer relaxation times, but the relative importance of the dye salts on the polymer pinch-off dynamics was also different from that of pure salts such as NaCl. 
    more » « less
  2. ; ; (, Food Hydrocolloids)
    The anionic hydrocolloid polysaccharide xanthan gum is widely used in the food and petroleum industries (among others) as a viscosity enhancement polymer due to its high viscosity at low concentrations and moderate temperatures. The physical properties of microbial polysaccharide xanthan gum aqueous solutions were investigated using temperature dependent viscosity measurements. Specifically, the effect of thermal history on the solution viscosity was investigated. Heating and cooling cycles were assessed in two ways, by using a “sawtooth” and “triangle” pattern, which essentially differed in the rates of cooling. The sawtooth method used a cooling rate of 2.0 ◦C min􀀀 1 whereas the triangle pattern had a cooling rate of 0.20 ◦C min􀀀 1. The sawtooth cooling rate was controlled by the speed at which the Peltier device could cool the sample, and the triangle rate was governed by the time required to measure the viscosity at each temperature on return to the initial value. Cycles measured using the sawtooth pattern for 16 mg/kg xanthan gum in water showed an 8–10% overall decrease in the viscosity over four complete cycles. Comparatively, at 320 mg/kg the xanthan gum solution showed a 25% decrease in viscosity over four cycles. The observed temperature dependent viscosity variation suggested minor modifications in the physical network structure of xanthan gum. When using a triangle heating/cooling pattern, the overall decrease in the xanthan gum solution viscosity was 5–7% for 16 mg/kg and only 10% change for 320 mg/ kg solutions. The activation energy of viscous flow for the aqueous xanthan gum solutions by either method was ~15.0 kJ/mol under all conditions. The data showed that temperature and heating cycles influence xanthan gum viscosity and thermal history, which depends more strongly on xanthan gum concentration than solution temperature. 
    more » « less
  3. ; ; ; ; (, RSC Advances)
    Herein we report the synthesis of ternary statistical methacrylate copolymers comprising cationic ammonium (amino-ethyl methacrylate: AEMA), carboxylic acid (propanoic acid methacrylate: PAMA) and hydrophobic (ethyl methacrylate: EMA) side chain monomers, to study the functional role of anionic groups on their antimicrobial and hemolytic activities as well as the conformation of polymer chains. The hydrophobic monomer EMA was maintained at 40 mol% in all the polymers, with different percentages of cationic ammonium (AEMA) and anionic carboxylate (PAMA) side chains, resulting in different total net charge for the polymers. The antimicrobial and hemolytic activities of the copolymer were determined by the net charge of +3 or larger, suggesting that there was no distinct effect of the anionic carboxylate groups on the antimicrobial and hemolytic activities of the copolymers. However, the pH titration and atomic molecular dynamics simulations suggest that anionic groups may play a strong role in controlling the polymer conformation. This was achieved via formation of salt bridges between cationic and anionic groups, transiently crosslinking the polymer chain allowing dynamic switching between compact and extended conformations. These results suggest that inclusion of functional groups in general, other than the canonical hydrophobic and cationic groups in antimicrobial agents, may have broader implications in acquiring functional structures required for adequate antimicrobial activity. In order to explain the implications, we propose a molecular model in which formation of intra-chain, transient salt bridges, due to the presence of both anionic and cationic groups along the polymer, may function as “adhesives” which facilitate compact packing of the polymer chain to enable functional group interaction but without rigidly locking down the overall polymer structure, which may adversely affect their functional roles. 
    more » « less
  4. ; ; (, Geochemistry, Geophysics, Geosystems)
    Abstract The continental crust is produced by the solidification of aluminosilicate‐rich magmas which are sourced from deep below the surface. Migration of the magma depends on the density (ρ) contrast to source rocks and the melt viscosity (η). At the surface, these silica‐rich melts are typically sluggish due to highη > 1,000 Pa s. Yet at their source regions, the melt properties are complexly influenced by pressure (P), temperature (T), and water contents (). In this study, we examined the combinedP‐T‐ effects on the behavior of melts with an albite stoichiometry (NaAlSi3O8). We usedfirst‐principlesmolecular dynamics simulations to examine anhydrous (0 wt % H2O) and hydrous (5 wt % H2O) melts. To constrain thePandTeffects, we exploredP ≤ 25 GPa across several isotherms between 2500 and 4000 K. The melts show anomalousP‐ρrelationships at lowP ∼ 0 GPa and highT ≥ 2500 K, consistent with vaporization. At lithospheric conditions, meltρincreases with compression and is well described by a finite‐strain formalism. Water lowers the melt density (ρhydrous < ρanhydrous) but increases the compressibility, that is, 1/Khydrous>1/KanhydrousorKhydrous < Kanhydrous. We also find that the meltηdecreases with pressure and then increases with further compression. Water decreases the viscosity (ηhydrous < ηanhydrous) by depolymerizing the melt structure. The ionic self‐diffusivities are increased by the presence of water. The decreasedρandηby H2O increase the mobility of magma at crustal conditions, which could explain the rapid eruption and migration timescales for rhyolitic magmas as observed in the Chaitén volcano in Chile. 
    more » « less
  5. ; ; ; (, Soft Matter)
    The effect of net charge of zwitterionic polymers on the phase behavior and viscoelastic properties of hybrid polyampholyte-polyoxometalate (POM) complexes in salted aqueous solutions is investigated with polyampholyte copolymers consisting of both positively and negatively charged monomers. Zwitterionic polyampholytes of varied net charge, abbreviated as PAxMy, are synthesized by varying the feeding molar ratio of negatively charged 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) to positively charged [3-(methacryloylamino) propyl]trimethylammonium chloride (MAPTAC) monomers in aqueous solution. The coacervate formation between PAxMy and inorganic anionic POM, {W12} in LiCl added aqueous solutions can be enhanced by increasing the molar fraction of positively charged MAPTAC monomer and LiCl concentration. The salt-broadened coacervation, clearly distinct from the salt-suppressed one between oppositely charged polyelectrolytes, suggests the account of zwitterion-anion pairing for PAxMy-{W12} coacervate formation due to stronger binding of multivalent {W12} giant ions with PAxMy than simple ions. Importantly, as AMPS or MAPTAC monomer fraction in polyampholytes is varied by merely ±5% from the effective net neutral case, the viscoelasticity of PAxMy-{W12} coacervates can be modified by 4-5 folds, suggesting a new tuning parameter to fine control the macroionic interactions and material properties of biomimetic complex coacervates. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email