Amorphous Solid Structure
Amorphous solid structure refers to the arrangement of atoms or molecules in a non-crystalline, disordered manner. Unlike crystalline solids, amorphous solids lack a regular, repeating pattern in their atomic structure. This results in unique physical properties, such as lack of a distinct melting point and isotropic behavior, making them important in various applications like glass and plastics.
5 Key excerpts on "Amorphous Solid Structure"
eBook - ePubDeveloping Solid Oral Dosage Forms
Pharmaceutical Theory and Practice
- Yihong Qiu, Yisheng Chen, Geoff G.Z. Zhang, Lawrence Yu, Rao V. Mantri(Authors)
- 2016(Publication Date)
- Academic Press(Publisher)
...Amorphous phases are those solids that do not exhibit long-range order in any of the three physical dimensions. However, short-range order could exist for amorphous solids. Because of the importance of this class of solids to pharmaceutical development, it is discussed in detail in Section 2.7 of this chapter. If materials have long-range order in only one or two dimensions, they are liquid crystalline in nature. Liquid crystalline materials can be further categorized based on the number of components contained therein, as is the case for crystalline solids. Since liquid crystals, with properties intermediate to conventional liquids and three-dimensional solids, are not frequently encountered, they will not be discussed in detail. The vast majority of pharmaceutical solids fall into the category of crystalline solids because they exhibit long-range order in all three dimensions. Crystalline solids can be further categorized into various subtypes based on the number of components that make up the solid internally, in a homogeneous fashion. The solid could be composed of the drug alone, or as adducts with one (binary), two (ternary), three (quaternary), other chemical species. Although the number of other chemical species, apart from the drug itself, can increase without limit, it usually is a relatively low integer. When the overall chemical composition of solids is the same, they can be different in internal structures. The ability of a substance to exist as two or more crystalline phases that have different arrangements or conformations of the molecules in a crystalline lattice is called polymorphism, and these different solids are termed polymorphs. One point to emphasize is that, according to the strict definition of this term, different polymorphs are only different physically, not chemically. When these solids are melted or dissolved in solutions, they are exactly the same, both physically and chemically...
eBook - ePubX-Ray Diffraction Imaging
Technology and Applications
- Joel Greenberg, Joel Greenberg(Authors)
- 2018(Publication Date)
- CRC Press(Publisher)
...In this discussion, it is important to first acknowledge a distinction among materials types for amorphous solids. Based on thermodynamic criteria, two types of amorphous solids are definable, those that are non-crystallizable and those that are crystallizable [ 25 ]. The former defines ideal amorphous solids that are unable to crystallize under certain time-temperature-transformation conditions. The latter involves metastable materials that have large defect populations and a corresponding lack of crystallinity. It is noted that meta-stable phases may exist, a consequence of materials processing and chemical kinetics considerations. In fact, many times metastable materials are sought based on their desired properties. Nevertheless, diffraction phenomena from these various forms of amorphous solids and liquids are fundamentally the same. Were it not for short-range order in amorphous materials with particle (a generalized term representing atoms or molecules in amorphous materials) spacing on the order of X-ray wavelengths, structural characterization, and substance classification in X-ray diffraction imaging systems would not be possible. The reproducible XRD features from amorphous solids and liquids give way to the means of determining spatial distributions of particles and, for purposes of threat detection, materials identification. Since short-range order dictates the structure of liquids and glasses, probabilistic atomic distribution functions are used to describe particle configuration [ 24 ]. The association of particles in liquids and amorphous solids is defined by the radial pair distribution function (RDF or, pair distribution function). RDF is used to determine bonding topology and the population of atoms in coordination spheres [ 26 ]—whereby a central particle is surrounded by an array of particles in the configuration of a sphere. Thus, pertinent data related to structure may be obtained from diffraction spectra...
eBook - ePub- Leslie H. Sperling(Author)
- 2015(Publication Date)
- Wiley-Interscience(Publisher)
...CHAPTER 5 THE AMORPHOUS STATE The bulk state, sometimes called the condensed or solid state, includes both amorphous and crystalline polymers. As opposed to polymer solutions, generally there is no solvent present. This state comprises polymers as ordinarily observed, such as plastics, elastomers, fibers, adhesives, and coatings. While amorphous polymers do not contain any crystalline regions, “crystalline” polymers generally are only semicrystalline, containing appreciable amounts of amorphous material. When a crystalline polymer is melted, the melt is amorphous. In treating the kinetics and thermodynamics of crystallization, the transformation from the amorphous state to the crystalline state and back again is constantly being considered. The subjects of amorphous and crystalline polymers are treated in the next two chapters. This will be followed by a discussion of liquid crystalline polymers, Chapter 7. Although polymers in the bulk state may contain plasticizers, fillers, and other components, this chapter emphasizes the polymer molecular organization itself. A few definitions are in order. Depending on temperature and structure, amorphous polymers exhibit widely different physical and mechanical behavior patterns. At low temperatures, amorphous polymers are glassy, hard, and brittle. As the temperature is raised, they go through the glass–rubber transition. The glass transition temperature (T g) is defined as the temperature at which the polymer softens because of the onset of long-range coordinated molecular motion. This is the subject of Chapter 8. Above T g, cross-linked amorphous polymers exhibit rubber elasticity. An example is styrene–butadiene rubber (SBR), widely used in materials ranging from rubber bands to automotive tires. Rubber elasticity is treated in Chapter 9. Linear amorphous polymers flow above T g. Polymers that cannot crystallize usually have some irregularity in their structure...
eBook - ePubPlastics
Microstructure and Engineering Applications
- Nigel Mills, Mike Jenkins, Stephen Kukureka(Authors)
- 2020(Publication Date)
- Butterworth-Heinemann(Publisher)
...Chapter 3 Amorphous polymers and the glass transition Abstract The consideration of polymers on a molecular level continues in this chapter, the focus of which is amorphous polymers. The three-dimensional shape, motion and glass-to-liquid transition behaviour will be considered in terms of the chemical structure of the polymer, and the measurement of the glass-to-liquid transition temperature (T g) will be introduced using thermomechanical analysis. Knowledge of the T g in polymers is important as it relates to the mechanisms by which the shapes of plastics products are set during processing; noncrystallizable polymers must be cooled to temperatures below T g to stabilize the shape of the part. The effect of molecular mobility and intermolecular forces on the elastic moduli of rubbers and glassy polymers will also be considered. Keywords Amorphous polymers; Bulk modulus; Glass transition; Molecular weight; Rubbers 3.1 Introduction 3.2 Modelling the shape of a polymer molecule 3.2.1 Conformations of the C–C bond 3.2.2 Walks on a diamond lattice 3.2.3 Effect of molecular weight on molecular size 3.2.4 Entanglements in polymer melts 3.2.5 Network chain elasticity 3.2.6 Rubbers 3.3 The glass transition temperature 3.3.1 Rotational and translational motions in the liquid state 3.3.2 Sub- T g motion 3.3.3 Control of the T g 3.3.4 Free volume 3.3.5 Measurement of T g using thermomechanical analysis 3.3.6 Glass microstructure 3.3.7 Elastic moduli of glasses 3.1. Introduction The consideration of polymers on a molecular level continues in this chapter, the focus of which is amorphous polymers. The three-dimensional shape, motion and glass-to-liquid transition behaviour will be considered in terms of the chemical structure of the polymer, and the measurement of the glass-to-liquid transition temperature (T g) will be introduced using thermomechanical analysis...
eBook - ePubUnderneath the Bragg Peaks
Structural Analysis of Complex Materials
- Takeshi Egami, Simon J.L. Billinge(Authors)
- 2012(Publication Date)
- Pergamon(Publisher)
...Chapter 12 Structure of Amorphous Materials Egami Takeshi Simon J.L. Billinge Abstract In this chapter we describe the reapplication of modern PDF methods developed for the study of crystalline and nanocrystalline materials, back to glasses and amorphous materials. Some recent studies are described on compositionally resolved PDFs of glasses, structural relaxation in glasses from the PDF, elastic and anelastic deformation and plasticity of glasses. Keywords glasses; amorphous materials; elastic deformation; anelastic deformation; structural relaxation 12.1 PDF Analysis of Amorphous Materials Historically, the PDF technique was used predominantly for the structural study of amorphous materials, as briefly mentioned in Section 3.1.4. However, the advent of synchrotron-based radiation sources which enabled the application of the PDF technique to crystalline materials has also impacted the study of amorphous materials. Termination errors, which have been a major source of uncertainty for the PDF analysis of liquids and glasses for a long time, are now minimized because of the use of high-energy X-rays and neutrons which greatly extended the Q range. High intensities of the sources and the use of 2D X-ray and neutron detectors very significantly reduce statistical noise. Consequently, more detailed studies are now done routinely, including the analysis of anisotropic amorphous structures, making PDF measurements more relevant to the understanding of the complex physical phenomena of glasses and liquids. In earlier days, the only quantities that could be reliably deduced from the PDF data of amorphous materials were the average distance to the nearest neighbors (position of the first peak of the PDF) and the coordination number (area of the first peak of the RDF)...
