Viscosity response curves

Figure 4, Viscosity response curve of isoprene-capped polybutadiene (B BI ),...

Viscosity response curve of styrene-capped (in eight increments) polybutadiene (B BS BS),... 

Viscosity response curve of polybutadiene coupled with silicone tetrachloride. 

Figure 3.22. Influence of viscosity of the injected sample on the response curves obtained when injecting a glucose sample (200 mg glucose/100 mL) into an FIA system using immobilized enzyme (glucose oxidase) and chemiluminiscence detection. Curves a-f 0, 10, 20, 30, 40, and 50 v/v% of glycerol. Note the presence of the isoresponse point. (By courtesy of Bo Petersson.)...

Hou et al. [42] studied the effect of AA in pressure-sensitive adhesives composed of a terpolymer of 2-ethylhexyl acrylate, VAc and AA. Like Gajria et al. they noticed a dependence of latex swelling with polymerization procedure. Hou et al. noted that batch polymerized latexes produced greater viscosity responses with pH adjustments. They demonstrated that addition of sodium chloride effectively reduced the pH-thickening response curve. Hnally, Kries and Sheiman [43] studied the influence of polymerizing various fimctional monomers on the wet adhesion of VAc/B A latexes. A number of monomer types were studied, such as polymoizable monomers containing amines, amides and acetoacetates, alone and in combination with each other. The ureido functional monomras exhibited supoior wet adhesion. 

On the other hand, to make a proper viscosity/shear-rate measurement on-line requires that the liquid be introduced into, and then removed from, a carefully controlled measuring volume which is part of a well-designed viscometer. As we have said, this can take time to carry out, and usually leads to a delay in responding to current viscosity changes in the flow line. What kind of viscometer one chooses depends on one s need for instant information or otherwise. However, data handling systems such as Connoisseur (Predictive Control Ltd., Northwich, UK) exist that can make up for slow instrument response because the form of the response curve is known and reproducible. This means for instance that if we know the response after say 30 seconds, we can predict where the viscosity wfll end up. Figure 2 shows a typical response of this kind. 

As mentioned earlier, hydrotropes can reduce viscosity. This is also a property of SMEs. In Figure 13 the viscosity versus sodium chloride response curve of a test formulation is shown. Different commercial grade anionic surfactants are evaluated for their viscosity response. The NaLAS was a Cl 1.4 high-2-phenyl, high-tetralin sodium linear alkylbenzenesulfonate NaAES was a sodium 3-mole ethoxylaurylsulfate Na SME was a blend of C13.6 SME/sulfonated fatty acid and the NaAOS was a sodium C14,16 alpha-olefinsulfonate. 

Due to dieir compact, branched structure and to die resulting lack of chain entanglement, dendritic polymers exhibit much lower melt and solution viscosity dian their lineal" counterparts. Low a-values in die Mark-Houwink-Sakurada intrinsic viscosity-molar mass equation have been reported for hyperbranched polyesters.198 199 Dendrimers do not obey diis equation, a maximum being observed in die corresponding log-log viscosity-molar mass curves.200 The lack of chain entanglements, which are responsible for most of the polymer mechanical properties, also explains why hyperbranched polymers cannot be used as diermoplastics for structural applications. Aldiough some crystalline or liquid... 

Most characterisation of non-linear responses of materials with De < 1 have concerned the application of a shear rate and the shear stress has been monitored. The ratio at any particular rate has defined the apparent viscosity. When these values are plotted against one another we produce flow curves. The reason for the popularity of this approach is partly historic and is related to the type of characterisation tool that was available when rheology was developing as a subject. As a consequence there are many expressions relating shear stress, viscosity and shear rate. There is also a plethora of interpretations for meaning behind the parameters in the modelling equations. There are a number that are commonly used as phenomenological descriptions of the flow behaviour. 

Fig. 3.14. The data is for a very broad range of times and temperatures. The superposition principle is based on the observation that time (rate of change of strain, or strain rate) is inversely proportional to the temperature effect in most polymers. That is, an equivalent viscoelastic response occurs at a high temperature and normal measurement times and at a lower temperature and longer times. The individual responses can be shifted using the WLF equation to produce a modulus-time master curve at a specified temperature, as shown in Fig. 3.15. The WLF equation is as shown by Eq. 3.31 for shifting the viscosity. The method works for semicrystalline polymers. It works for amorphous polymers at temperatures (T) greater than Tg + 100 °C. Shifting the stress relaxation modulus using the shift factor a, works in a similar manner.

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