Homogeneous nudeation

W [Stefan flow], movement in a temperature gradient [thermophoresis j, and sprays), (. i steam condensation onto aerosols, and (4) homogeneous nudeation of water droplets. 

The critical radius given by Eq. 19.92 is equal to the critical radius for homogeneous nudeation in the bulk liquid. This is the expected result because 7LM = ySM (so that the liquid/solid interface makes an angle of 90° with the mold) and the inward pressure on the interface due to curvature, AP = 2-yLS/R (Eq. 12.4), is then exactly balanced by the change in bulk free energy across the interface, jjphase trans — gB (Eq. 12.1). Substitution of Eq. 19.92 into Eq. 19.91 yields the critical free energy for nudeation ... 

Rasmussen, D., Luyet, B. Contribution to the establishment of the temperature concentration curves of homogeneous nudeation in solutions of some cryopro-tective agents. Biodynamica 11, No. 225, 33—44,1970... 

Homogeneous nudeation occurs in the absence of a solid interface heterogeneous nudeation occurs in the presence of a solid interface of a foreign seed and secondary nudeation occurs in the presence of a solute particle interface. The mechanisms governing the various types of primary and secondary nudeation are different and result in different rate expressions. The relative importance of each type of nudeation varies with the precipitation conditions. 

Crystallization begins from a nucleus that may derive from surfaces of adventitious impurities (heterogeneous nudeation) or from the aggregation of polymer segments at temperatures below (homogeneous nudeation). The latter process is reversible up to the point where a critical size is reached, beyond which further growth results in a net decrease of free energy of the system. Another... 

It also appears from Table II that the probability of homogeneous nudeation decreases markedly as the monomer droplet radins decreases. In considering the number of new particles that may be formed below CMC, the stahility and the growth of the new particles must also be taken into account. The reduction in most probably is lower than would be expected from the decrease m P . 

S. Toshev in Homogeneous Nudeation in Crystal Growth An introduction, (Ed. M, Hartman), North-Holland, Amsterdam, 1973, p. 1. 

The cloud chamber experiments of Wilson (summarized in his 1927 Nobel Lecture) qualitatively demonstrated two nudeation mechanisms (1) condensation on ions at relatively low saturation ratios and (2) condensation on uncharged molecular dusters at much higher saturation ratios. Wilson s studies of condensation on ions are discussed briefly in this chapter. His resulLs on nudeation by molecular dusters which served as a starting point for development of the theory of homogeneous nudeation are discussed in the next chapter. Wil.son .s principal interest was in condensation on ions and its application to the measurement of high-energy nuclear particles,... 

Heterogeneous nudeation. Nncleation induced by foreign matter in a supersaturated liquid. Homogeneous nudeation. Spontaneous nuclemion caused by supersaturation only. 

Homogeneous formation of nuclei has not yet beoi established with certainty in macromolecular solutions. If it does in fact exist, then h is more probable that folded-chain nuclei will be formed in this way than micellar nuclei. In contrast to folded chain nuclei in micellar nuclei several molecules must come together in order to form a stable nucleus. Micellar nuclei thus lead to a greater entropy loss. A homogeneous nudeation is more probable in melts than in solutions, since the concentration of centers is potentially greater in the former. Even in melts, however, it is uncertain... 

In the case of heterogeneous nudeation with strong interactions, on the other hand, the number of spherulites remains constant with time. In addition, all the spherulites are of equal size. In purely homogeneous nudeation, the number of nuclei is constantly increasing, and a spherulite size distribution is observed. 

Keywords nudeation, primary nudeation, nudeation rate, heterogeneous nudeation, supercooling, homogeneous nudeation, aimeal-ing, self-nudeation, nucleating agents, epitaxy, nudeation in blends, nudeation in copolymers, spherulite, lamellae, p-crystal form, secondary nudeation, nudeation rate. 

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