1.3. AMORPHOUS STATE
The amorphous state of solids is composed of molecules that have a disordered arrangement, which do not constitute to the characteristic of the crystal grid and, therefore, have zero crystallinity. The distribution of molecules in the solid amorphous form is not entirely random as it is specific to a gaseous state because it has a certain degree of order between neighboring molecules. Due to the lack of regulation and the absence of a crystal grid, compared to the crystal the amorphous form has higher enthalpy, entropy and Gibbs free energy. Therefore, it is thermodynamically unstable and susceptible to spontaneous transition to a more stable crystalline form (14). Differences between the crystal and amorphous states are shown in Figure 3. Figure 3: Crystal (a) and amorphous (b) state (15) …show more content…
This is the temperature interval in which the heating of the substance passes from a solid glassy state into a softened glassy state (16). It is distinguished from a liquid due to mobility of molecules. Glasses are liquids that are frozen in time when their evaluation (experiment) is carried out. Irrespective of their thermodynamic instability, they can be stable from a kinetic point of view, but only as long as applicable in pharmaceuticals (17). Movement of molecules below the glass transition temperature is very limited, whereas amorphous materials are relatively stable below the glass transition temperature, while above it they are vulnerable to mechanical and thermal stresses. Furthermore, molecules are moving slowly below the mentioned temperature, resulting in alteration of properties during aging of an amorphous sample
The amorphous state of solids is composed of molecules that have a disordered arrangement, which do not constitute to the characteristic of the crystal grid and, therefore, have zero crystallinity. The distribution of molecules in the solid amorphous form is not entirely random as it is specific to a gaseous state because it has a certain degree of order between neighboring molecules. Due to the lack of regulation and the absence of a crystal grid, compared to the crystal the amorphous form has higher enthalpy, entropy and Gibbs free energy. Therefore, it is thermodynamically unstable and susceptible to spontaneous transition to a more stable crystalline form (14). Differences between the crystal and amorphous states are shown in Figure 3. Figure 3: Crystal (a) and amorphous (b) state (15) …show more content…
This is the temperature interval in which the heating of the substance passes from a solid glassy state into a softened glassy state (16). It is distinguished from a liquid due to mobility of molecules. Glasses are liquids that are frozen in time when their evaluation (experiment) is carried out. Irrespective of their thermodynamic instability, they can be stable from a kinetic point of view, but only as long as applicable in pharmaceuticals (17). Movement of molecules below the glass transition temperature is very limited, whereas amorphous materials are relatively stable below the glass transition temperature, while above it they are vulnerable to mechanical and thermal stresses. Furthermore, molecules are moving slowly below the mentioned temperature, resulting in alteration of properties during aging of an amorphous sample