Particulate level, properties

In the present work, such a systematic approach to the physical characterization of pharmaceutical solids is outlined. Techniques available for the study of physical properties are classified as being associated with the molecular level (properties associated with individual molecules), the particulate level (properties pertaining to individual solid particles), and the bulk level (properties associated with an ensemble of particulates). Acquisition of this range of physical information yields a total profile of the pharmaceutical solid in question, whether it is an active drug, an excipient, or a blend of these. The development of a total profile is a requirement for successful manufacture of any solid dosage form. 

The three representations that are referred to in this study are (1) macroscopic representations that describe the bulk observable properties of matter, for example, heat energy, pH and colour changes, and the formation of gases and precipitates, (2) submicroscopic (or molecular) representations that provide explanations at the particulate level in which matter is described as being composed of atoms, molecules and ions, and (3) symbolic (or iconic) representations that involve the use of chemical symbols, formulas and equations, as well as molecular structure drawings, models and computer simulations that symbolise matter (Andersson, 1986 Boo, 1998 Johnstone, 1991, 1993 Nakhleh Krajcik, 1994 Treagust Chittleborough, 2001). 

Homogeneity. The degree to which a property or substance is randomly distributed throughout a material. Homogeneity depends on the size of the units under consideration. Thus a mixture of two minerals may be inhomogeneous at the molecular or atomic level but homogeneous at the particulate level. 

The complexity of the solid state offers not only an analytical challenge but also interesting aspects and opportunities for the dmg development. Thus, a drug can be engineered at the supramolecular and particulate level in order to optimize its physical properties. This requires, of course, a substantial knowledge of its solid-state properties and the proper analytical tools. 

The visualization techniques introduced in this section will help us to develop a particulate level understanding of many concepts we encounter throughout the text. At this point, let s take some time to look at one application where the properties of aluminum metal make it a popular material choice for engineering a consumer product—a bicycle. 

Distinguish between physical and chemical properties at both the particulate level and the macroscopic level. 

When you think about a physical change at the particulate level, do not break apart or change the particles in any way. Also note that the physical properties of a macroscopic sample of a substance do not apply at the particulate level. Any individual molecule does not have color, feel, smell, or any other physical property. 

You are familiar with the fact that ice—solid water—floats on liquid water. Why is this Ice is less dense than liquid water. What does this mean on the particulate level Considering the definition of density, a given volume of ice must have less mass than the same volume of liquid water. In other words, if all water molecules have the same mass and volume, whether liquid or solid, the molecules in liquid water must pack more closely together than molecules in ice. Figure 3.10 shows how solid water forms ice crystals with spaces between the molecules, whereas liquid molecules have fewer and smaller open spaces. So, at the particulate level, the density of a given pure substance in a given state of matter is a measure of how tightly packed the molecules are in that state. Water is an unusual substance, and the fact that its solid phase is less dense than its liquid phase is just one of many of its unusual properties. The solid phase is more dense than the liquid phase of almost all other substances (Fig. 3.11). 

Diamond has a particulate-level arrangement in which each carbon atom is covalently bonded to four other carbon atoms (Fig. 12.12). Look at a single carbon atom ball in the figure and count the number of bonding sticks. Count the number of bonds to another atom. Note how each carbon atom in diamond has four bonds. This arrangement, where each atom is bonded to four atoms, is responsible for the physical properties of diamond. It is one of the hardest natural materials known. 

Figure 12.12 A particulate-level model of diamond. Each carbon atom is bonded to four other carbon atoms. This bonding arrangement leads to the characteristic physical properties of diamond at the macroscopic level. 

Figure 12.14 (a) A particulate-level model of buckminsterfullerene. Each carbon atom is bonded to three other carbon atoms in a cagehke sphere. The physical properties of buckyballs are very different from those of either diamond or graphite, (b) A soccer baU is another model for the particulate-level arrangement of carbon atoms in buckminsterfullerene. A carbon atom hes at the intersection of each set of three seams on the ball. The result is alternating five-membered (black) and six-membered (white) rings. 

Liquid drops adopt a spherical shape because of a macroscopic measurable property known as surface tension. This property can be understood at the particulate level in terms of the strengths of the attractive forces among the particles that make up the liquid. Strong attractive forces lead to high surface tension. 

The ability to imagine the particulate-level reasons for intermolecular attractive forces is a powerful tool in your thinking as a chemist knowledge stockpile. The more you understand this type of particulate-level behavior, the better you will understand the macroscopic properties that result from it. 

Solids can be classified based on their macroscopic properties. The differences on the macroscopic scale, however, result from differences at the particulate level. In particular, we can classify solids based on the forces holding the particles together. We will start by dividing solids into three general classifications based on the way the particles are arranged in the solid. 

Figure 15.22 Macroscopic properties of crystalline and amorphous solids. The presence or absence of a regular structure at the particulate level influences the macroscopic shape of the solid, (a) CrystaUine solids tend to cleave so that the smaller pieces have smooth and flat faces, (b) Amorphous sohds do not break along lines with predictable patterns. 

Figure 15.24 A particulate-level model of an ionic crystal. The gray spheres represent sodium ions and the green spheres are chloride ions. The macroscopic physical properties of ionic crystals result from the strong electrostatic attractions among the ions. 

Intermolecular Forces Solubility, a macroscopic property, depends on intermolecular forces at the particulate level. Generally speaking, if forces between molecules of A are about the same as the forces between molecules of B, A and B will probably dissolve in each other. This is commonly paraphrased as like dissolves like (Fig. 16.8[a]). On the other hand, if the intermolecular forces between molecules of A are quite different from the forces between molecules of B, it is unlikely that they will dissolve in each other (Fig. 16.8[b]). 

Uses Emulsifer for preparing clear d-limonene/terpene microemulsions that can be used for a variety of cleaning and degreasing applications Features Can remove silicone from glass and metal surfaces at 5 - 30 % d-Limonene levels m,icroemulsions remain clear on dilution alkyl phenol ethoxylate free increases detergency for both oily and particulate soils Properties Cl. yel. liq. dens. 8.26 Ib/gal vise. 100 cP cloud pt. >100 C pH (1% aq.) 6.5 90% act. 

The quaHty, ie, level of impurities, of the fats and oils used in the manufacture of soap is important in the production of commercial products. Fats and oils are isolated from various animal and vegetable sources and contain different intrinsic impurities. These impurities may include hydrolysis products of the triglyceride, eg, fatty acid and mono/diglycerides proteinaceous materials and particulate dirt, eg, bone meal and various vitamins, pigments, phosphatides, and sterols, ie, cholesterol and tocopherol as weU as less descript odor and color bodies. These impurities affect the physical properties such as odor and color of the fats and oils and can cause additional degradation of the fats and oils upon storage. For commercial soaps, it is desirable to keep these impurities at the absolute minimum for both storage stabiHty and finished product quaHty considerations. 

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