Formation of co-amorphous is either by thermodynamic or kinetics pathways. In thermodynamic pathway, thermally stable binary crystalline physical mixture converted to non crystalline amorphous from by direct melting the physical mixture and followed by rapid cooling. While kinetic approach carried out by direct conversion of the components by milling / grinding techniques. Typically co-amorphous can be form either by rapid cooling of the melt (melt-quench, HME), evaporation from the solution (slow solvent evaporation/ rotary solvent evaporation), rapid precipitation from the solution (spray drying), and mechanical activation (grinding/milling). Typically when the crystal is heated beyond to its melting point (Tm), it becomes a liquid. In the schematic figure 2, the vertical line demonstrates the melting process of the specific volume V or the enthalpy (H).
The phase conversion of crystal to liquid is a first order phase transition and maintain equilibrium liquid state. After melt components can easily recrystallize at different phenomenon, two crystal lines indicate polymorphisms. Notably below the melting point compound either by recrystalize or without nucleation remains liquid from, this liquid form termed as supercooled liquid. However, rapid cooling molecules moved to non-equilibrium state and molecular movement slowing down, so it is impossible to rearrangement of the component lattice structure, this is so-called glass or amorphous. A critical temperature between equilibrium and non-equilibrium state is termed as glass transition temperature (Tg). In co-amorphous system, this Tg is an important characteristic to identify either binary component form co-amorphous (single Tg) or not.
Furthermore, when the viscosity of the components increases, molecules can dissolve each other and maintain a non-equilibrium liquid state condition. Followed by fast cooling, components have no change to rearrange themselves and maintain a glassy state. The above discussion can give the overall scenario of the co-amorphous formation either by MQ or HME