In fact, fulfilling consumer expectations has measurements were performed with an AG2 model TA become imperative in the food and personal care industry. Concentric cylinders 25 mm Proper assessment of features related to human perception diameter and parallel plates 25 mm diameter were used; the merits great attention for both scientific and practical reasons. The The rheological properties of emulsions are influenced by geometries were selected depending on the viscosity of the their colloidal structure and therefore can be related to physical emulsion.
The former was that application and acceptance of semisolid products are carried out by using a unidirectional steady-shear flow ranging greatly dependent on the flow properties of the final product. All tests were carried out in triplicate This work focuses on the characterization of a cosmetic to ensure the reproducibility. The emulsions were investigated in terms of the continuous shear images from microscopy were analyzed to obtain information steady stateviscosity and thelinear viscoelastic response, that is, regarding the morphology of the emulsions. Finally, 2. Statistical Analysis.
Statistical analysis was emulsion morphology. Diff erences in the computed parameters were considered significant when the computed probabilitieswere lessthan 0. Emulsions Preparation.
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Emulsions were prepared by 3. Steady-Shear Flow Measurements. Thesteady-state GmbH, Germany asan emulsifier in deionized water; contents rheology experimental results were adjusted to the power law and concentration of this emulsion are presented in Table 1. The parameters n and k are obtained by alinear stirred, the polyacrylate was slowly added to phase A 30 min.
After preparation, the rheological behavior of 3. Concentration Eff ect. As expected, performed with an HCl solution for acidification and a sodium viscosity increases consistently with polyacrylate content in all hydroxide solution for basification.
Eff ect of polymer concentration on thesteady-shear viscosity Figure 3. Eff ect of temperature on the steady-shear viscosity of 2. Asthe shear rate increases, the fluid structures become disrupted and the polymer molecules align toward the flow direction, thisreducesthe viscosity, amore stablestructure becomes shear thinning at higher shear rates stronger interactions are produced by a higher interphase area and moredispersed particles.
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Then, all sampleshave essentially the same shear-thinning slope. In Figure 2, a significant increase of viscosity is evident at concentrations from 1 to 1. Wethink that thepolyacrylateis reaching optimum swelling conditions at concentrations near 1. Viscosity is built by the swelling of the dispersed polymer, and this is known to provide an elegant skin feel and sun care in the final emulsion. Figure 4. Eff ect of pH on the steady-shear viscosity of 2. Temperature Eff ect.
It can be observed that the change in viscosity is not a factor that generates macrostructural changes in the flow behavior of the behavior. This result indicates other concentrations studied not shown.
The values of the that there isacritical pH value for structure build up between 4 flow consistency index at diff erent temperatures remain and 6 pH. Above thiscritical pH value, the formation of amore constant all curves are parallel which means that this material stable network is evident and consistent with previous reports. Therefore, the and is then stable up to pH 9. This makes it ideal for the spreading of the product is independent of the temperature at majority of personal care applications. The important fact that application.
Figure 4 shows the viscosity profile of preparation of cosmetic products and increases the potential emulsions with 2. When the pH of the formulation is 4. Oscillatory Flow Measurements. To perform measurements in the linear viscoelastic region, the linear region must be determined first amplitude sweep test.
Linear oscillatory shear flow measurements SAOS are in essence nondestructive tests since only a very small deformation is applied to the fluid at a certain frequency. Figure 5 shows the oscillatory flow curves as a function of polymer concentration maintaining Figure 5. Figure 6. The eff ect of pH on the polymer is shown concentrations above 1.
This behavior does not hold for that the emulsions are temperature independent within the the emulsions of pH 4.
Rheology Essentials of Cosmetic and Food Emulsions by Rüdiger Brummer
Overall rheological A polymer network is formed when an electrical interaction assessment at diff erent temperatures indicates that the between atoms is present van der Waals forces, hydrogen dx. This is an indication that there is a critical pH value below which a network structure is not well formed which is consistent with the rheological results.
From the micrographsit wasevident that the emulsion at pH 4 was the more unstable one and that the emulsions at pH 6. The rheological behavior and morphology results can be attributed to a combination of two factors: The first one is that the lower droplet size results in a reduction of the free energy associated with the strength of the interaction. The second one is that the creation of a larger specific surface area in the fine Figure 7. These interactions are modified the polymer content.
For a polymer results and modeling are used to explain the rheological concentration of 2. This is enough to make final conclusions regarding overall emulsion due to the formation of a polymer network more stable to the characteristics; yet certain diff erentiations between diff erent flow; the nature of this network is pH- and temperature- conditions could be made and used as guidelines at various dependent.
The viscoelastic response of the studied mixtures increasesas 3. Finally, images from optic microscopy the polymer concentration rises, becoming more resistant to analysis of the batches of polyacrylate at diff erent pH values deformation even at high temperatures.
The pH is a investigated are shown in Figure 8. Figure 8a shows a determining factor in the rheological behavior of the emulsions that contain sodium polyacrylate; thisisbecause the rheological properties suff ered evident changes related to the stability of the network formed by the polymer. A critical pH value has been encountered to attain a stable network; below this critical pH, network formation is incomplete. These results help to identify the conditions in which the polymer off ers the best advantages in industrial applications: pH 6.
The results confirmed that rheology can be used to diff erentiate emulsions regarding mechanical properties and the best process conditions can be selected according to the end-use application to obtain tailor-made cosmetics.
Skin feel is an important sensory area for cosmetic products. Fax: Figure 8. For this reason, examples of food rheology are didactically useful to explain the dynamics of other materials we are less familiar with. Ketchup is commonly used an example of Bingham fluid and its flow behavior can be compared to that of a polymer melt. Psychorheology is the sensory judgement of rheological properties. It is a term used in the food industry , to describe how a food "feels" to the mouth.
It is not necessarily straightforward to predict how a food will "feel" based purely on the true rheological properties. The most important factor in food rheology is consumer perception of the product. This perception is affected by how the food looks on the plate as well as how it feels in the mouth, or " mouthfeel ". Mouthfeel is influenced by how food moves or flows once it is in a person's mouth and determines how desirable the food is seen to be.
From Wikipedia, the free encyclopedia. Food portal. McKenna, and J. Lyng Retrieved Herh, Steven M. Colo, Nick Roye, and Kaj Hedman Circle Reader Service.
Rheology of fluid and semisolid foods: principles and applications. Advances in food and nutrition research. Academic Press. Aix-Marseille University - Course of Rheology.