Vilkova Natal'ya Georgievna, Doctor of chemical sciences, professor, sub-department of physics and chemistry, Penza State University of Architecture and Construction (28 G. Titov street, Penza, Russia), email@example.com
Volkova Nataliya Valentinovna, Candidate of biological sciences, associate professor, head of sub-department of chemistry and theory and methods of teaching chemistry, Penza State University (40 Krasnaya street, Penza, Russia), firstname.lastname@example.org
Kozlova Elena Pavlovna, Student, Penza State University (40 Krasnaya street, Penza, Russia), email@example.com
Background. Foam firmness, stabilized by solid particles, may be explained by formation of the structure as far back as at the stage of obtaining initial suspensions. The work is aimed at examining the changes in shear stress in suspensions composed of Ludox HS-40 silica, hydrophobizated by hexylamine, and at analyzing the changes of properties of foams, produced from the stated disperse systems.
Materials and methods. To prepare the foams, stabilized by silica particles, cationic SAS (surface active substance) hexylamine was used. To stabilize the foams and foam films the researchers used silica of two types: Aerosil-380 and Ludox HS-40. The shear stress was determined by the method of lamina tangential displacement. Multiplication of the foams was determined by the method based on electrical conduction measurement. To examine the stability of foam’s thin layers external pressure was applied. To characterize the stability the researchers used the percentage (D, %) of disruption of a certain area of a foam layer during 30 minutes.
Results. In makeup suspensions the shear stress is zero, however in 30 minutes after preparation one may observe a dependency of deformation changes on the imposed load. Addition of the electrolyte (5 millimole/litre NaCl) into the suspension leads to shear stress decrease. Shear stress increase in the suspensions leads to stability increase of foam, produced on the basis thereof. Provided equal degree of hydrophobization, larger particles of silica create more stable gel structures already in the initial suspension. Decrease of hydrophobization degree, provided equal mass content of the solid phase, increase of the size of solid particles decreases gel strength. In foams, produced from suspensions with high mass content of ludox, one may observe syneresis deceleration caused by effective viscosity increase in suspensions provided increased concentration of the solid phase.
Conclusions. The observed dependence of deformation changes on the imposed load, obtained in 30 minutes after the suspension formation, indicates the structuring process advancing in the suspensions. Provided changes of hexylamine concentration in all suspensions under analysis there is an area with maximum value of shear stress. The foams produced from suspensions with high shear stress are characterized by syneresis deceleration and high stability. High values of shear stress in the initial suspensions, caused, to the great degree, by the concentration of solid particles, but not by hydrophobization thereof, appear to be an insufficient condition for the stable foam obtainment.
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