"Should I buy a rotational rheometer or a capillary rheometer?" This is the most common selection question asked by polymer material companies. The answer doesn't depend on 'which one is better,' but rather on 'what questions you want to answer' — these two types of rheometers complement each other rather than replace one another.  

The 'comfort zone' of a rotational rheometer is at low to medium shear rates (10⁻⁶ to 10³ s⁻¹). It can measure not only viscosity but also parameters reflecting the viscoelastic nature of materials, such as G' (storage modulus), G'' (loss modulus), yield stress, and thixotropy. A rotational rheometer is best suited to answer questions like: How is the adhesive's workability? Does the paint resist sagging well? What is the gelation temperature of the hydrogel? For R&D personnel, this is a core tool for understanding the rheological behavior of materials.  

The 'battlefield' of a capillary rheometer is at high shear rates (10² to 10⁶ s⁻¹), simulating real processing conditions like injection molding, extrusion, and blow molding. If you need to know the flow behavior of modified PP in an injection molding screw, or the dispersion behavior of color masterbatch during spinning, a capillary rheometer is essential. Moreover, a capillary rheometer can also measure extensional viscosity (calculated from the pressure drop at the inlet), which is critical for film-blowing processes.  

Practical advice: R&D-oriented companies should prioritize a rotational rheometer (for richer information), while companies relying heavily on processing technology should add a capillary rheometer. If the budget allows, having both is ideal, as they complement each other.  

Dehuisci Instruments (www.dehuisci.com) distributes both rotational and capillary rheometers and offers free sample testing. Phone: 0512-67071902.