Platelet aspect ratio

FIG. 13 Reduction of the relative permeability coefficient is dependent on the clay platelet aspect ratio in the system of polyimide-clay hybrid with water vapor as the permeate. Each hybrid contains 2 wt% clay. The aspect ratios for hectorite, saponite, montmorillonite, and synthetic mica are 46, 165, 218, and 1230, respectively. (From Ref. 71.)... 

Figure 20.2. Effects of platelet orientation relative to the direction of deformation, predicted by using the model of Brune and Bicerano [11]. The orientation angle is defined as the angle between the symmetry axis of the platelets and the direction of deformation, so that it is 90° if the platelets are aligned perfectly along the direction of deformation while it is 0° if the platelets are aligned completely perpendicular to the direction of deformation. The curves are labeled by the platelet aspect ratio Af. The platelet volume fraction was =0.025, the platelets were assumed to have a Young s modulus of 100 times that of the matrix, and a Poisson s ratio of 0.4 was assumed for both the matrix polymer and the platelets in these calculations.

The fiber or platelet aspect ratio has to be above the critical value for an efficient utilization of the reinforcing properties of the filler. In addition to the aspect ratio. 

Table 8. Effect of Platelet Size and Aspect Ratio on Toughness ...

Platelet size, p.m Aspect ratio Bend Strength, MPa Fracture toughness, MPayTn... 

During a steady-state capillary flow, several shear-induced effects emerge on blend morphology [4-6]. It is, for instance, frequently observed that TLCP domains form a fibrillar structure. The higher the shear rate, the higher the aspect ratio of the TLCP fibrils [7]. It is even possible that fibers coalesce to form platelet or interlayers. 

Hence, the addition of inorganic impermeable nanoplatelets improves the barrier properties of polymers. This is attributed mostly to the lengthening of the diffusion path of the permeating gas molecules due to the increase of the tortuosity. Increasing the aspect ratio of the platelets and their volume fraction improves these... 

Under appropriate reaction conditions, regular hexagonal platelets (ca. 50 nm thick and 20 pm in diameter) can be obtained. The high refractive index (n — 2.0), high aspect ratio (> 200), and the extremely even surface of basic lead carbonate make it an optical match to natural pearl essence. 

Dispersion of high luster quality (aspect ratio 1 20 to 1 40) consisting of square or octagonal platelets in nitro-cellulose lacquers (nail polish) or castor oil (lipsticks)... 

Dispersion of very high luster quality (aspect ratio > 1 50) consisting of lens-shaped platelets in nitro-cellulose lacquer, castor oil, or butyl acetate... 

Other platelet crystals with a high aspect ratio are reported for phtalocyanine [5.245], graphite [5.246] and 1,4-diketopyrrolopyrroles [5.247],... 

Talc is a hydrated magnesium silicate that is composed of thin platelets primarily white in color. Talc is useful for lowering the cost of the formulation with minimal effect on physical properties. Because of its platy structure and aspect ratio, these extenders are considered reinforcement. Polymers filled with platy talc exhibit higher stiffness, tensile strength, and creep resistance, at ambient as well as elevated temperatures, than do polymers filled with particulate fillers. Talc is inert to most chemical reagents and acids. The actual chemical composition for commercial talc varies and is highly dependent on the location of its mining site. 

Talcs are either platy or acicular in particle shape. Thin platelet particles have aspect ratios varying from 20 1 to 5 1. Coarse particle sizes (10 to 75 im) are commonly used in these applications at loading levels of 5 to 30 percent. Fine talcs (1 to 10 im) are more expensive and require intensive dispersion processes. Platy grades enhance barrier properties and air, water, and chemical resistance. 

---