**USE:** Conditioner is used to give hair "body" - that is, a "thicker" and smoother feel [after shampoo is used for cleaning hair].

**Test Equipment**:

**R/S-CPS Plus Rheometer****Spindle:**75-mm diameter, 1°-angle, DIN cone**Accessory:**(none)**Speed, rpm:**Varies; Controlled Stress mode, linear stress ramp, 0-160 Pa in 80 s, followed by 160-0 Pa in 80 s.

The test may be run at room temperature.

Data for two different conditioners are shown in Figure 1, below:

Figure 1: Shear rate D, s-1, versus shear stress Tau, Pa, for two commercial conditioners.

The first or increasing-stress ramp data are shown, without the second or decreasing-stress ramp data, for clarity. Conditioner 2 achieves higher shear rates than conditioner 1 at all stresses tested, indicating that 2 has lower viscosity at each stress. The dramatic increase in the slope of 2's shear rate-vs.-shear stress curve, above 76 Pa, may indicate an even faster structural breakdown or experimental artifact. Please note that conditioners tested in Controlled Rate mode are typically tested to only a few *hundred* s^{-1} - corresponding to estimated application rates and significantly below the rates reached in the above test. Thus, our Controlled *Stress* test could reasonably be run to about 80 Pa, to acquire sufficient data, in this case. The viscosity, Pa·s, versus shear stress, Pa, curve, for both products, is shown in Figure 2, below:

Figure 2: Viscosity, Eta, Pa·s, versus shear stress Tau, Pa, for conditioners 1 and 2.

Conditioner 1 is significantly more viscous at each given stress, compared to Conditioner 2. Therefore, Conditioner 1 feels like it has more "richness" or "body", to the consumer. Data were fitted using RHEO2000 Version 2.7's software models. The Herschel-Bulkley or "H-B" model curve-fit was selected. This equation fits data in which there is a yield stress and then power-law shear-thinning behavior:

*where:*

- is the shear stress (Pa);
- is the yield stress (Pa);
- is the plastic viscosity (Paosn+1);
- is the shear rate, s-1;
- is the dimensionless yield exponent

Typical results are shown in Figure 3, below, for Conditioner 1's increasing stress ramp data set:

Figure 3: Herschel-Bulkley model fit to Conditioner 1 data.

The calculated values for the H-B model fit are: = 0.0000 Pa, = 42.7184 Pa·s^{n+1}, and = 0.2195. The calculated correlation coefficient is 0.99467, indicating a reasonably good fit. Although the calculated yield stress is zero, this conditioner has and maintains significant "body" (viscosity) during flow - as reflected in the moderate plastic viscosity and yield exponent values.