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Nanocellular Polymers
Published in S. T. Lee, Polymeric Foams, 2022
Victoria Bernardo, Judith Martin-de Leon, Miguel Angel Rodriguez-Perez
When talking about nucleation, two different approaches can be considered, homogeneous or heterogeneous nucleation. This discrimination is not so easy to be established, but in general terms, homogeneous materials are defined as those in which a second phase is not intentionally included to promote nucleation. On the contrary, heterogeneous materials are considered when a second phase is included to control the nucleation process.
Mechanisms of Heterophase Polymerization
Published in Hugo Hernandez, Klaus Tauer, Heterophase Polymerization, 2021
In a typical heterophase polymerization, the conditions are favorable for heterogeneous nucleation [2]. Before the polymerization is started, the reaction system consists of at least monomer droplets, single surfactant molecules, and surfactant aggregates with aggregation numbers smaller than the critical micelle concentration (CMC). All colloidal objects that have a different chemical composition than the molecules going to be nucleated can be considered foreign objects. Within the frame of CNT, the interaction of the nucleating molecules with the foreign objects is crucial, determining how strong the activation free energy of nucleation will be reduced (cf. Fig. 2.3). Heterogeneous nucleation is a situation where at least three different components participate: the continuous phase (or mother phase in crystallization experiments), the aggregates of the nucleating species, and the foreign particle (or substrate). In any case, the nucleation happens at lower supersaturation and takes place at the interface of the foreign objects. The interaction between the three components is described by the contact angle between the aggregate of the nucleating species and the foreign particle, which is determined by the interfacial tensions between the three components.
Suspension Growth
Published in Gerard F. Arkenbout, Melt Crystallization Technology, 2021
Figure 7.11 shows the flow diagram of the countercurrent option. Now the crystal growth is started at the composition of the waste. Control of nucleation rate may be difficult. In between every two sections, a crystal-melt separator like a hydrocyclone, a filter or a forced bed column (see Section 8.4) is needed to realize the countercurrent transport between crystals and melt. The crystals are taken off at the highest temperature and the lowest impurity concentration. A well-known example is the TSK CCCC Process (see Subsection 12.2.3).
Experimental and numerical investigation of the mechanical properties of low cement thin boards reinforced by polypropylene and fiberglass mesh
Published in European Journal of Environmental and Civil Engineering, 2023
Ali Younesian, Mahmoud Nili, Alireza Azarioon, Sajad Shahriaripour
The hydration acceleration is the most apparent chemical effect of replacing cement with LP to promote nucleation. Finer LP particle size and its corresponding larger specific area improve the nucleation procedure. These impacts play a crucial role in the early stage of cement matrix hydration. By replacing cement with LP, accelerated production of the calcium silicate hydrates (C-S-H) organizes a large part of the fully hydrated cement paste, structuring a comprehensive connection between cement and LP particles to develop strength and decrease the setting time (Ehsani et al., 2017). Similar to SF, the CRV level of LP is the most effective factor that may change the hydration process (Zongjin, 2011). The replacement of cement with fillers like LP means that more space is available to form hydrates. The hydration process is, therefore, accelerated. This effect relies on the fineness of the LP particles since the nucleation is more probable if the CRV increases (Zongjin, 2011). Homogeneous and heterogeneous nucleation are two well-known types of nucleation. Heterogeneous nucleation occurs when cement replacements are present in a phase and accelerate the nucleation process. C-S-H nucleation on the LP surface is heterogeneous (Bentz et al., 2017). On the one hand, due to its nucleation effect, the presence of LP improved the C-S-H production and enhanced the cement hydration. On the other hand, the increase in replacement level might reduce FCB bleeding, thus promoting the bond strength of the interfacial transition zones. Therefore, incorporating LP to replace cement could increase flexural strength.
Heteroepitaxy of diamond semiconductor on iridium: a review
Published in Functional Diamond, 2022
Weihua Wang, Benjian Liu, Leining Zhang, Jiecai Han, Kang Liu, Bing Dai, Jiaqi Zhu
According to the classical nucleation theory, nucleation on a hetero-substrate is called heterogeneous nucleation. As illustrated in Figure 1 (right), the rate of heterogeneous nucleation is then studied in Equation (1) [74, 75], where θ is the contact angle between the nucleus and substrate, N is the atom number per volume in gas, kB is the Boltzmann constant, h is the Planck constant, R is the molar gas constant, P is the actual vapor pressure, P0 is the standard vapor pressure, σf-s is the interface energy between the film and substrate, and T denotes the substrate temperature: where and can be obtained from Equations (2)–(4),
Band-gap-tailoring in Liquid Crystals: Organizing Metal Atoms and Nanoclusters in LC Media
Published in Liquid Crystals, 2022
Archana Kumari Singh, Satya Pal Singh
In the nucleation process, an atom may act as a seed, also referred to as nuclei, which results in crystal growth [25–28]. This process is of two types, namely the homogeneous nucleation and the heterogeneous nucleation. The homogeneous type nucleation is one in which the growth process uniformly takes over the nuclei. The heterogeneous nuclei are formed by structural inhomogeneities like impurities, grain boundaries, dislocations, container surfaces, etc. There are different theories for the nucleation and growth of nanoparticles from seed atoms, molecules or particles as LaMer Mechanism, Ostwald Ripening and Digestive Ripening, Finke-Watzky Two Step Mechanism, Coalescence and Orientated Attachment and Interaparticle Growth [25]. In the LaMer mechanism, first, the concentration of monomers in the solution increases rapidly. Then it undergoes nucleation burst, and as a result of that, the concentration of free monomers decreases in the solution following which, further nucleation is seized. Ostwald Ripening growth mechanism occurs by the change in the solubility of nanoparticles depending on their sizes. Smaller particles have a higher solubility and have large surface energy within the solution. So, these particles redissolve and allow larger particles to grow more. In digestive ripening, smaller particles grow expansively at the cost of the larger ones. It is just the inverse of the Ostwald ripening. In this process, larger particles redissolve and allow the smaller particles to grow more. In the Finke-Watzky two-step mechanism, two steps occur simultaneously, as shown below