Influence of Additives on Nucleation of Vanillin:  Experiments and Introductory Molecular Simulations

Abstract

Nucleation of vanillin (VAN) in 2-propanol/water in the presence of additives, viz., acetovanillone (AVA), ethyl vanillin (EVA), guaiacol (GUA), guaethol (GUE), 4-hydroxyacetophenone (HAP), 4-hydroxybenzaldehyde (HBA), and vanillic acid (VAC) is investigated experimentally and by molecular simulations. In the experimental work, the induction time for nucleation is measured at different temperatures and levels of supersaturation using a multicell apparatus. A large variation in the experimental data is observed, and this variation is analyzed by statistical methods. By classical nucleation theory, the induction time data are used to estimate the solid-liquid interfacial energy of vanillin for each VAN-additive system. At 1 mol %, the interfacial energy becomes lower in the presence of AVA, EVA, HAP, and VAC, while it becomes higher in the presence of the other additives. As the additive concentration increases from 1 to 10 mol %, the interfacial energy also increases. The interfacial energy ranges from 6.9 to 10.1 mJ m -2 . Molecular modeling, implemented in the program Cerius2, is used to simulate and examine the surface chemistry of the likely crystal growth faces of VAN (i.e., {0 0 1} and {1 0 0}). To evaluate the additivecrystal face interaction energy, two approaches are used: the surface adsorption method and the lattice integration method. Both experimental and molecular simulation results indicate that the additives studied are potential modifiers of the nucleation of VAN. However, a simple and clear relationship between the experimental values of interfacial energy and the calculated interaction energies for the most important crystal faces of VAN cannot be identified. The modeling does not concern the actual nucleation but rather the conditions of a growing surface and are based on several severe simplifications. Obviously, this simplistic approach does not sufficiently capture the influence of additives on the nucleation of vanillin.

Modelling the stochastic behaviour of primary nucleation

“…[4][5][6][7][8][9][10][11][12][13][14] The second category encompasses the experiments where a macroscopic system property (such as transmittivity or turbidity), which is related to the volume fraction of the crystals, is measured. 2,[15][16][17][18][19][20][21][22][23][24] Crystals are detected, and hence the detection time is measured, when such volume fraction exceeds a specic threshold value. This latter technique suffers from two weaknesses: rst, the quantitative relationship between the solid volume fraction and, for instance, turbidity is difficult to calibrate; secondly, the threshold value is extremely difficult to estimate and might well be dependent on a series of factors, e.g.…”

The magic of aqueous solutions of ionic liquids: ionic liquids as a powerful class of catanionic hydrotropes

“…28,35 These biomolecules are present at high concentrations in a variety of biomass sources, such as fruits, vegetables and wood, and also in many residues from industrial or agricultural activities. 25,36–38 Their extraction from natural sources is usually carried out with mildly polar solvents such as alcohols, 39,40 due to their low solubility in water (the solubility of vanillin in water is 12.78 g L −1 and that of gallic acid is 12.14 g L −1 at room temperature). 41 Although no previous studies on the hydrotropic solubilization of gallic acid have been reported, the solubility of vanillin in aqueous solutions is already recognized to increase in the presence of typical hydrotropes, such as nicotinamide, sodium salicylate, resorcinol and citric acid.…”

Comparison of the interfacial energy and pre-exponential factor calculated from the induction time and metastable zone width data based on classical nucleation theory

“…As the induction time can be experimentally determined by the isothermal method at a constant supersaturation level, the induction time data are frequently used as a measure of the nucleation event to calculate the interfacial energy of the crystallized substance in the literature [5][6][7][8][9][10][11][12][13].…”