Nucleation rheological studies

Viscoelastic and viscosimetic measurements have been performed on model systems and on commercial products [29]. Water-in-silicone emulsions have been prepared, in which the oil phase consisted of decamethylcyclopentasiloxane (cyclomethicone, D5) and the surfactant used was a branched type silicone copolymer. The interfacial rheology study of such surfactants revealed that the ability of these eopolymers to effectively stabilize water-in-D5 emulsions is a result of a process involving the nucleation, growth, and accumulation of surfactant-rich particulates at the D5/water interface [55]. 

The kinetics and mechanisms of the C —> G transition in a concentrated solution of PS-fr-PI in the PS-selective solvent di-n-butyl phthalate was studied [137,149]. An epitaxially transformation of the shear-oriented C phase to G, as previously established in melts [13,50,150], was observed. For shallow quenches into G, the transition proceeds directly by a nucleation and growth process. For deeper quenches, a metastable intermediate structure appears, with scattering and rheological features consistent with the hexag-onally perforated layer (PL) state. The C -> G transition follows the same pathways, and at approximately the same rates, even when the initial C phase is not shear-oriented. 

SEM studies contribute to an understanding of a major obstacle to residual solvent removal. Figure 16.1.2 shows two photographs of polyethylene strands extraded from a melt which initially contained 4000 ppm hexane. After a short period of time following the extrusion, blisters form which remain in the material and become enlarged until they break and release solvent. This blistering mechanism, determines die rate of residual solvent removal from the material. The rate of removal depends on bubble nucleation, temperature, and polymer rheological properties. ... 

Rheological experiments were used by Wittmar et al. (2012) for the stability analysis of functionalised nanoparticles in ionic liquid. The authors examined viscosity curves (i.e. viscosity vs. shear rate) as well as viscoelastic properties for suspensions of varying particle concentration but identical preparation history. The qualitative criterion for destabilisation was whether the suspensions did gel, i.e. whether the storage modulus G was smaller the loss modulus G". A different approach was proposed by Vogelsberger et al. (2000), who studied the nucleation and aggregation kinetics of silica, synthesised via TEOS (tetraethyl-orthosilicate) condensation and precipitation. For that purpose, the viscosity and the viscoelastic moduli were continuously monitored. The latter data were i. a. used to derive the rate of aggregation. 

In semicrystalline thermoplastic matrix composites, the nucleation and growth of a transcrystalline interface around the reinforcing fiber is thought to have a critical influence on the improvement of the stiffness and tensile strength [63-65]. The rheological behavior of in situ microfibrillar HDPE/PET and HDPE/polycarbonate (PC) polymer blends was investigated in a recent study [66,67]. For both HDPE/PET and HDPE/PC microfibrillar blends, the viscosity increased with PET and PC microfibrils concentration. In another study, Xu et al [68] reported that the flexible microfibrils of PET reduced the melt elasticity and viscosity of HDPE/PET microfibrillar blends. 

In this study, with the help of a tandem foam extrasion system, we present the first part of our investigation of the extrasion rheology of foams, both with and without cell nucleation and growth. The pressirre data obtained serve as the basis of evaluating existing cell growth models, and can facilitate die design. 

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