Measurement of cluster formation in aqueous citric acid solutions by photon correlation spectroscopy

Properties of Citric Acid and Its Solutions

“…2.40) considering experimental difficulties to determine them accurately. Measurements in dilute solutions were performed by Muller and Stokes [167] and in a more concentrated solutions by Laguerie et al [15] and by van Drunen et al [24]. These diffusion coefficients at 25 °C (Table 2.18), can roughly be approximated by (2.97) Pa · s Cit) = (7.1 -8.7).10 −6 cm 2 s −1 for the molecular citric acid and for the trivalent ion D(Cit 3− ) = (5.9 -7.6).10 −6 cm 2 s −1 values.…”

Cluster Formation in Precrystalline Solutions

“…The Small Angle Neutron Scattering (SANS) technique gives direct evidence of colloidal structures in precrystalline systems, as shown by Gage-Duport [8] and Niimura [9]. Clusters or colloidal structures have been reported in undersaturated and saturated solutions [7], while in other solutions, there appear to be no structures before the solutions get supersaturated [10], or no structure is found at all as shown by Sontum [11]. The sizes of the reported clusters often increase with time and are a function of the properties that control supersaturation [12,13,5]), but clusters with sizes which are not a function of time, are also reported [7].…”

“…Clusters or colloidal structures have been reported in undersaturated and saturated solutions [7], while in other solutions, there appear to be no structures before the solutions get supersaturated [10], or no structure is found at all as shown by Sontum [11]. The sizes of the reported clusters often increase with time and are a function of the properties that control supersaturation [12,13,5]), but clusters with sizes which are not a function of time, are also reported [7]. The reported structures are always named precrystalline, but the behavior of these structures is not found to be the same in different systems.…”

“…Modern instruments give more directly experimental evidence. Measurements of the diffusivity using Gouy interferometry as shown by Myerson [5] and Photon Correlation Spectroscopy (PCS) by Tanaka [6] and Drunen [7] give experimental evidence of interactions, structures, or clustering in precrystalline liquids. The Small Angle Neutron Scattering (SANS) technique gives direct evidence of colloidal structures in precrystalline systems, as shown by Gage-Duport [8] and Niimura [9].…”

Molecular dynamics simulation of solution structure and dynamics of aqueous sodium chloride solutions from dilute to supersaturated concentration

“…Investigations on concentration gradients in vertical columns [2][3][4], diffusivity studies [5][6][7][8][9][10][11][12][13][14][15], and spectroscopic studies [16][17][18][19][20][21][22][23][24][25] have indirectly demonstrated the existence of clusters. Studies at a molecular level of the structure and dynamics of supersaturated solutions are therefore necessary to understand and elucidate the nucleation and crystallization phenomena.…”