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RHEOLOGY-4

RHEOLOGY-4

PHARMAROCKS
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RHEOLOGY-4

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  1. RHEOLOGY • Thixotrophy • Negative thixotrophy

  2. RHEOLOGY Rheology is the science which deals with flow of liquid and deformation of solid.

  3. RHEOLOGY Rheology is a Greek word Rheo Means “Flow” & Logia, “study of” THUS RHEOLOGY MEANS STUDY OF FLOW Rheology is the science/physics that concerns with the flow of liquids and the deformation of solids.

  4. THIXOTROPHY The property of becoming less viscous when subjected to an applied stress, shown for example by some gels which become temporarily fluid when shaken or stirred. Thixotropy is a rheological property whereby the viscosity of a liquid decreases when it is agitated

  5. THIXOTROPHY Thixotropy is a time-dependent shear thinning property. Certain gels or fluids that are thick (viscous) under static conditions will flow (become thin, less viscous) over time when shaken, agitated, or otherwise stressed (time dependent viscosity).

  6. THIXOTROPHY They then take a fixed time to return to a more viscous state. In more technical language: some non-Newtonian pseudoplastic fluids show a time-dependent change in viscosity; the longer the fluid undergoes shear stress, the lower its viscosity.

  7. THIXOTROPY The property of becoming less viscous when subjected to an applied stress, shown for example by some gels which become temporarily fluid when shaken or stirred. Decrease in viscosity when shearing stress is applied

  8. THIXOTROPY Some Non-Newtonian pseudoplastic fluids show a time-dependent change in viscosity; the longer the fluid undergoes shear stress, the lower its viscosity 1. Tragacanth in water 2. Sod. Alginate in water 3. Methyl cellulose in water 4. Sodium CMC in water

  9. Thixotropy in Formulation In suspension, particles will not settle down in the container (gel form), will become fluid (sol) on shaking for a dose to dispense. At rest, it will retain its consistency to maintain the particles suspended. This is also applied to emulsions, lotions and creams. Parenteral suspensions used for intramuscular depot therapy, e.g. procaine penicilline G 40- 70% w/v in water

  10. THIXOTROPY “Change by touch” Thixotropy is defined as an isothermal & comparatively slow recovery process on standing of a material of a consistency lost through shearing. This is applied for plastic & pseudoplastic system This is also called as gel to sol to gel transformation.

  11. ANTITHIXOTROPY This is also called as Negative thixotropy, this represents an increase in consistency on the down curve. The down curve shifts to the right of the up curve. This is also called as sol to gel to sol transformation

  12. ANTITHIXOTROPY Negative thixotropy, also called antithixotropy, is the effect of a flow-induced increase in viscosity that has been observed for many polymer solutions. Occur in flocculated system with low solid content 1-10% Solid content of suspension. Solid form gel more readily in resting state than sheared state

  13. THIXOTROPY EVALUATIONS Thixotropy can be quantitatively measured using a rotational rheometer. Cup and bob viscometer Cone and plate viscometer Brook field viscometer

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