han water- immiscible solvents like dichloromethane and chloroform, (2) in this method, nanoparticles are formed spontaneously with high shear , (3) Further purification is not required because of the surfactant and solvent and (4) it is a simple, fast and reproducible method which is commonly used for the preparation of both nanocapsules and nanospheres.
The solvent displacement technique can be used to formulate nanocapsules by incorporating a small amount of nontoxic oil in the organic phase. Considering the oil-based central cavities of the nanocapsules, high loading efficiencies are usually obtained for lipophilic drugs when nanocapsules are prepared.
The major drawbacks of this preparation method include that: (1) the use of this simple method [176] is restricted to water-miscible solvents, in which the diffusion rate is sufficient to produce spontaneous emulsification. In some cases, spontaneous emulsification is not observed when the coalescence rate of the formed droplets is sufficiently high and this usually occurs with some water-miscible solvents that produce a certain instability when mixed with water [177] and (2) the nanoprecipitation technique possesses poor encapsulation efficacy in the case of hydrophilic drugs, because the drug can diffuse to the aqueous outer phase during polymer precipitation [151]. The encapsulation efficiency has been increased through modifying the drug solubility by changes in pH [178-180].So that, this technique is mostly appropriate for lipophilic drugs due to the miscibility of the organic solvent with the aqueous phase.
Although, a surfactant is not necessary to ensure the formation of PNP by nanoprecipitation method, the particle size is affected by the surfactant nature and concentration [160, 164]. Furthermore, the addition of surfactants helps to maintain the stability of nanoparticle suspensions and prevents agglomeration over long storage periods [143].

Tween 80 Poloxamer 407
Chemical name Polyoxyethylene 20 Sorbitan
Monooleate [181]
α-Hydro-ω- hydroxypoly (oxyethylene) poly (oxypropylene) poly (oxyethylene) block copolymers [182]

Physical form Yellow oily liquid [181]