Liquid-liquid phase separation (LLPS) occurs when a homogenous solution containing different solutes undergoes phase separation into at least two immiscible liquids. Coacervates form in a specific process of LLPS and are usually described as the dense phase rich in macromolecules such as proteins, polymers, or nucleic acids that condensate out of the dilute phase. LLPS is considered a significant process in biological systems, leading to the formation of various membrane-less organelles in the cells. Many regions and compartments in the cells exhibit liquid phase characteristics, such as the nucleolus and Cajal bodies in the nucleus and stress granules and P-bodies in the cytoplasm. LLPS is involved in different diseases including cancer, infectious diseases, and various neurodegenerative diseases. In several cases a link was found between the formation of coacervates through LLPS, the following liquid-to-solid transition of these coacervates into aggregates and neurodegenerative diseases. Such cases include the microtubule-associated protein Tau in Alzheimer's disease, α-synuclein in Parkinson's disease, and poly-glutamine in Huntington's disease. Coacervates can form in processes of complex or simple coacervation. In complex coacervation, two solutes condensate together due to attractive interactions. An example of complex coacervates can be found in polymers with opposite charges such as poly-aspartic acid or poly-glutamic acid with poly-arginine or poly-lysine. In simple coacervation only one solute is involved, and its attractive intermolecular interactions cause it to condensate at certain conditions, i.e. solute concentration, pH, and ionic strength. Various interactions can contribute to the formation of coacervates depending on the solute, including ionic interactions, hydrogen bonds, π-π stacking, and cation-π interactions. The model of associative polymers can be used to describe the behavior of polymers and proteins in LLPS. This model depicts molecules with functional groups called stickers, separated by spacers. The stickers form reversible bonds with each other that lead to intermolecular clusters and finally to phase separation. The hydrophobicity of the sticker and the polarity of the spacer were shown to influence the ability of the solute to form stable coacervates. For most biological processes, the investigation of LLPS occurs in solution. However, coacervates can form during evaporation of the solution, which increases the concentration of the solute as well as the ionic strength. Evaporation could have been crucial for prebiotic processes and since LLPS was shown to form membrane-less organelles inside cells, coacervates are considered as potential protocell models. During evaporation of a sessile droplet, preferential evaporation of the edge of the droplet causes capillary effects that replenish the liquid. This capillary flow transports the particles to the edges, forming a coffee stain effect. This effect can be suppressed by introducing surface tension gradients that generate inward Marangoni flows. These effects can be used to control the deposition of particles on surfaces, which is important for surface coating and surface patterning applications. The capillary and Marangoni flows can also affect the deposition of coacervates on surfaces.