Crystallization rate enhancement

Therefore, what is known about the crystallization rate enhancement resulting from the use of seed crystals at the current time is that a) nanometer-sized... 

A rate enhancement effect due to secondary nucleation has been identified in the solution-mediated transformation of the 7-phase of (i)-glutamic acid to its / -phase [82]. In this study, the kinetics of the polymorphic transition were studied using optical microscopy combined with Fourier transform infrared, Raman, and ultraviolet absorption spectroscopies. The crystallization process of n-hexatriacontane was investigated using micro-IR methodology, where it was confirmed that single... 

Also, Chin s dihydroxy-bridged dicobalt(III) complex 10 provides one of the largest rate enhancements ever observed for phosphodiester hydrolysis [36]. Reaction with the activated phosphodiester methyl(p-nitrophenyl)phosphate (MNPP) yields 11. A crystal structure is available for the analogous dimethylphosphate complex in which the Co ions are 2.9 A apart. At pH 7 and 45 °C 11 releases p-nitrophenolate with k = 0.1 s 1 which corresponds to a nearly 10I2-fold rate enhancement over spontaneous hydrolysis of the substrate. The product of the reaction is a methylphosphate-bridged complex. Based on the pH rate profile and on... 

Let us now And out how the system works. Assume that it starts at a large reduced flow-rate (point A) and reduce the input slowly. Up to the point C, any deviation from the equilibrium curve will die out rapidly. At C, concentration fluctuations become unstable and the system evolves quite rapidly towards D (p is fixed) where it finds a stable steady-state. The system has become unstable because reducing the flow-rate enhances crystallization which through the kinetic factor enhances the rate of precipitation and thereby depletes the residual liquid. The system quenches. Upon reducing the flow-rate further, the stable evolution continues towards point E. 

At this time of writing, isophthalic acid has become the most widely accepted modifier for packaging applications, due to its relatively minor effect on the PET Tg, considerable reduction in crystallization rate but not in ultimate level of crystallinity (at <5mol% modification levels), slight enhancement in oxygen and carbon dioxide barrier properties, and relatively low monomer cost. 

The ligation of Ln3+ by DTPA, DTPA-BPA, DTPA-BGLUCA, and DTPA-BEN-GALAA has been derived from Nd3+-C distances as evaluated from Nd3+-induced 13C relaxation rate enhancements [5-8]. The distances obtained are in agreement with those observed in crystal structures of this class of compounds. H NMR studies on various paramagnetic [Ln(DTPA)]2 complexes [9,10] and 13C relaxation rate measurements on the diamagnetic [La(DTPA)] 2 confirm this mode of coordination [11]. A detailed X-ray absorption spectroscopy study of [Gd(DTPA)2-] also showed that the local structure around the Gd3+ ion in aqueous solution is similar to that in crystals [12]. 

Scherer and Willig (65) have studied the rate enhancement, due to cations and protons, of electron transfer from the surface of an organic insulator crystal, such as perylene, to oxidized ions, such as [Fe(CN)g] and fMo(CN)g] ", in solution. In an electrochemical method such as this, the saturation current directly renders the rate constant for electron transfer at the crystal surface. Furthermore, electron transfer on [Fe(CN)6l or [Mo(CN)g] can be studied in the absence of reduced forms, whereas the salt effect can be measured up to the solubility limit. They found that for the same concentration of added electrolyte, rate constants increased with the increased charge of the cation. Up to s 1M rate enhancement was of the order Li < Na < Cs but at salt concentrations >3.5 M a reversal that could be explained by different hydrations of the cations took place. They also found a good linear correlation in the shift to higher redox potentials (simultaneously increasing rate constants) with higher salt concentrations. 

The crystallization process of PDHS film was monitored. The spincast films of PDHS on a 6AzlG-PVA monolayer were first heated to 100°C and then cooled. The enhancement of 370 nm band with concomitant decrease of 320 nm band reflects formation of the all-fm s-zigzag Si chain conformation upon crystallization. The crystallization rate strongly depended on the initial isomerization state of the Az of the surface layer (see Figure 15.8). The crystallization process was accelerated on the Z-Az monolayer in comparison... 

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