Measuring semi-solid materials such as gels, pastes, creams and ointments

Measuring rheological properties of semi-solid materials is important in many industries including pharmaceutical, foods, cosmetics and consumer products.

Semi-solid materials exhibit liquid and solid like properties depending on temperature, as well as on being subjected to stress and strain over time. Rheological instrumentation is used for various reasons, for example, to determine yield stress (stress that must be exceeded for flow to occur) to help predict shelf-life and strain sweeps to determine the critical strain (minimum energy needed to disrupt structure, where the higher the critical strain the better the systems is dispersed).

Since the materials act like elastic solids under some conditions and viscous liquids under others, they are viscoelastic materials. If one is interested in influencing consumer perception by having a product appear solid under "at rest” conditions, rheological testing should be carried out at low stress and long time periods (low frequencies) to simulate this. If predicting the pumping of a material for proper sizing of the pump is of interest, rheological tests should be carried out under similar shear rate and stress conditions.

Some of the commonly used tests for characterizing rheological properties of semi-solid materials are:

• flow behavior of non-Newtonian materials (to determine yield stress, shear thinning and/or thixotropic flow behavior)
• strain sweep (to determine linear viscoelastic range and critical strain, to determine how stable a system is)
• creep/recovery (to determine relaxation times, zero shear viscosity and viscoelastic properties to determine strength of bonds)
  

Available products:

	Bohlin Gemini II
	Bohlin CVO
	Bohlin V88
	Rosand RH7/10-D
	Rosand RH2000