The use of dilute solution viscometry to characterize the network properties of carbopol microgels

Carnali, J. O.; Naser, M.

doi:10.1007/bf00652185

Cited by 92 publications

(73 citation statements)

References 21 publications

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“…The microstructure of Carbopol solutions typically consists of water-swollen microgels (12). Above a critical concentration, these gel particles are closely packed together and form a sample-spanning network structure, characterized by yield stress behavior (12,50).…”

Section: Discussionmentioning

confidence: 99%

Design of an Experimental Viscoelastic Food Model System for Studying Zygosaccharomyces bailii Spoilage in Acidic Sauces

Mertens

Dang

Vermeulen

et al. 2009

Appl Environ Microbiol

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Within the field of predictive microbiology, the number of studies that quantify the effect of food structure on microbial behavior is very limited. This is mainly due to impracticalities related to the use of a nonliquid growth medium. In this study, an experimental food model system for studying yeast spoilage in acid sauces was developed by selecting a suitable thickening/gelling agent. In a first step, a variety of thickening/gelling agents was screened, with respect to the main physicochemical (pH, water activity, and acetic acid and sugar concentrations) and rheological (weak gel viscoelastic behavior and presence of a yield stress) characteristics of acid sauces. Second, the rheological behavior of the selected thickening/gelling agent, Carbopol 980, was extensively studied within the following range of conditions: pH 4.0 to 5.0, acetic acid concentration of 0 to 1.0% (vol/vol), glycerol concentration of 0 to 15% (wt/vol), and Carbopol concentration of 1.0 to 1.5% (wt/vol). Finally, the applicability of the model system was illustrated by performing growth experiments in microtiter plates for Zygosaccharomyces bailii at 0, 0.5, 1.0, and 1.5% (wt/vol) Carbopol, 5% (wt/vol) glycerol, 0% (vol/vol) acetic acid, and pH 5.0. A shift from planktonic growth to growth in colonies was observed when the Carbopol concentration increased from 0.5 to 1.0%. The applicability of the model system was illustrated by estimating max at 0.5% Carbopol from absorbance detection times.Food structure is, next to the chemical composition and storage conditions, one of the key factors that affect microbial behavior in food products. The effects of food structure are mainly related to the mechanical distribution of water, the chemical redistribution of organic acids, and the mobility of microorganisms (55). In the case of a liquid food product, microbial growth is typically planktonic, and transport of nutrients and metabolites occurs by diffusion, resulting in a homogeneous environment. The majority of foods, however, have some degree of structure, causing microorganisms to be immobilized and constrained to grow as colonies. Within the field of predictive microbiology, where mathematical models are developed for describing microbial growth, inactivation, and survival in food (model systems), most models are based on data obtained in liquid broth media. The scarcity of predictive models that incorporate the effect of structure has been recognized as one of the most important shortcomings in this field of research (41).Conducting experiments on a structured culture medium gives rise to several impracticalities due to the nonliquid nature of the culture medium. Starting from a liquid culture medium, a thickening or gelling agent is added to obtain a structured model system that, ideally, mimics the microstructural properties of the target food product. In order to evaluate the effect of structure on a systematic and consistent basis, the experi-

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Section: Discussionmentioning

confidence: 99%

Design of an Experimental Viscoelastic Food Model System for Studying Zygosaccharomyces bailii Spoilage in Acidic Sauces

Mertens

Dang

Vermeulen

et al. 2009

Appl Environ Microbiol

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“…For these reasons, Carbopol microgels serve as very useful model fluids for exploring and quantifying the LAOStress framework. The microstructure of these gels typically consists of highly swollen and compressed sphericalshaped blobs (of characteristic dimension ∼ 5 µm) which, at high enough concentrations, provide the material with its yield stress (Ketz et al, 1988;Carnali and Naser, 1992;Piau, 2007;Mahaut et al, 2008).…”

Section: A Materialsmentioning

confidence: 99%

Describing and prescribing the constitutive response of yield stress fluids using large amplitude oscillatory shear stress (LAOStress)

Dimitriou

Ewoldt²,

McKinley

2013

Journal of Rheology

244

160

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Large Amplitude Oscillatory Shear (LAOS) is used as a tool to probe the nonlinear rheological response of a model elasto-viscoplastic material (a Carbopol microgel). In contrast to most recent studies, these large amplitude measurements are carried out in a stress-controlled manner. We outline a descriptive framework of characterization measures for nonlinear rheology under stress-controlled LAOS, and this is contrasted experimentally to the strain-controlled framework that is more commonly used. We show that this stress-controlled methodology allows for a physically intuitive interpretation of the yielding behavior of elasto-viscoplastic materials. The insight gained into the material behavior through these nonlinear measures is then used to develop two constitutive models that prescribe the rheological response of the Carbopol microgel. We show that these two successively more sophisticated constitutive models, which are based on the idea of strain decomposition, capture in a compact manner the important features of the nonlinear rheology of the microgel. The second constitutive model, which incorporates the concept of kinematic hardening, embodies all of the the essential behaviors exhibited by Carbopol. These include elasto-viscoplastic creep and time-dependent viscosity plateaus below a critical stress, a viscosity bifurcation at the critical stress, and Herschel-Bulkley flow behavior at large stresses.

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“…Rheological studies of Carbopol and similar microgels have shown that properties such as concentration and crosslink density determine where they lie on the spectrum between entangled linear polymers and noninteracting hard spheres, with higher crosslink densities and lower concentrations making the system more like the latter (Steeneken 1989;Carnali and Naser 1992;Naé and Reichert 1992;Borrega et al 1999). In the 1970s, Taylor and Bagley studied the viscosity of Carbopol varieties 940 and 941 and similar microgels over a range of concentration and pH (Taylor and Bagley 1974, 1975, 1977.…”

mentioning

confidence: 96%

“…Based on this work, they argued that Carbopol dispersions consist of highly swollen deformable particles that become spacefilling above a critical concentration. Later work by Carnali and Naser investigated the effect of crosslink density (Carnali and Naser 1992). They found that the less-crosslinked Carbopol 941 became space filling at lower concentrations than the more highly crosslinked Carbopol 940 and estimated the crosslink density from the rheological measurements.…”

mentioning

confidence: 98%

Scaling and mesostructure of Carbopol dispersions

et al. 2012

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Rheological measurements were performed on aqueous dispersions of two commercial crosslinked polymer microgels, Carbopol Ultrez 10 and Carbopol ETD 2050, prepared over a wide range of concentration and pH. For all concentrations studied, both the yield stress and the elastic modulus initially increased dramatically with pH and displayed broad peaks at intermediate pH. This is consistent with the onset of jamming of the Carbopol particles due to a rapid increase in particle size caused by osmotic swelling in the presence of NaOH. Scaling of both yield stress and elasticity with concentration was observed only at higher concentrations, which we believe indicates a change from a percolated structure at low volume fractions to a space filling network of compressed particles at high volume fractions. This model is supported by confocal microscopy of fluorescently dyed Carbopol dispersions.

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The use of dilute solution viscometry to characterize the network properties of carbopol microgels

Cited by 92 publications

References 21 publications

Design of an Experimental Viscoelastic Food Model System for Studying Zygosaccharomyces bailii Spoilage in Acidic Sauces

Design of an Experimental Viscoelastic Food Model System for Studying Zygosaccharomyces bailii Spoilage in Acidic Sauces

Describing and prescribing the constitutive response of yield stress fluids using large amplitude oscillatory shear stress (LAOStress)

Scaling and mesostructure of Carbopol dispersions

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