Surface-Induced Crystallization of Sodium Dodecyl Sulfate (SDS) Micellar Solutions in Confinement

Abstract

We investigate the role of confinement on the onset of crystallization in subcooled micellar solutions of sodium dodecyl sulfate (SDS), examining the impact of sample volume, substrate surface energy, and surface roughness. Using small angle neutron scattering (SANS) and dynamic light scattering (DLS), we measure the crystallization temperature upon cooling and the metastable zone width (MSZW) for bulk 10−30 wt% SDS solutions. We then introduce a microdroplet approach to quantify the impact of surface free energy (18−65 mN/m) and substrate roughness (R α ≃ 0−60 μm) on the kinetics of surface-induced crystallization through measurements of induction time (t i ) under isothermal conditions. While t i is found to decrease exponentially with decreasing temperature (increasing subcooling) for all tested surfaces, increasing the surface energy could cause a significant further reduction of up to ∼40 fold. For substrates with the lowest surface energy and longest t i , microscale surface roughness is found to enhance crystal nucleation, in particular for R α ≥ 10 μm. Finally, we demonstrate that tuning the surface energy and microscopic roughness can be effective routes to promote or delay nucleation in bulk-like volumes, thus greatly impacting the stability of surfactant solutions at lower temperatures.

A Novel Hydrate Form of Sodium Dodecyl Sulfate and Its Crystallization Process

“…Oftentimes, a short evaporation time like this makes it difficult to have a good control over the crystalline form of its product to be specific. SDS is highly soluble in water and forms micelles in aqueous solution above 8.2 mM, which is its CMC at 25 °C. , As the solute concentration of SDS in aqueous solution increases by reducing its water content, the SDS solution will pass through several complex phases of micelles, liquid crystals, and coagels toward the formation of a very thick slurry, causing poor mixing, and heat and mass transfer . The strong affinity to water of those structures often makes the removal of water from the slurry with high viscosity very difficult and energy-consuming.…”

“…As the phase diagram of the SDS–water binary system had been well-established using differential scanning calorimetry (DSC), optical microscopy, nuclear magnetic resonance (NMR), and XRD, − the crystallization of SDS from aqueous solutions has also been investigated for several decades. ,− A weak dependence of cooling rate from 20 to 8 °C on the metastable zone width (MZW) was observed using optical microscopy and turbidimetry for the SDS crystallization in aqueous solutions of 5–20% SDS. , It implied that such SDS crystallization is dependent on solute exchange between the micelles and the monomers of SDS (i.e., the nucleating phase) particularly at a lower concentration. An unequivocal relationship between crystallization kinetics, morphologies, and polymorphs of SDS was interpreted using optical microscopy, DSC, and attenuated total reflection (ATR)-FTIR spectroscopy under isothermal conditions over a wide range of temperatures from 20 to −6 °C and concentrations of 10 to 30% SDS .…”

“…36 However, such understanding of those SDS crystallization subjects was constrained to the "cooling" method, in aqueous solutions, and on a small scale, such as sealed capillary tubes, 19,35,36 or sample cells for various instruments, FTIR, 32 DSC, 35,36 dynamic light scattering (DLS) and small angle neutron scattering (SANS). 37 More recently, we have developed a controllable SDS crystallization process, which integrates evaporation, antisolvent addition, and cooling methods, to produce stable SDS•1/8 hydrate-specific solids. 25 The aims of the present study were to screen pseudopolymorphs with the use of organic solvents, and to further develop the crystallization process directly following from the synthesis of SDS.…”

Interface-Templated Crystal Growth in Sodium Dodecyl Sulfate Solutions with NaCl

“…In the bulk, the crystallization of SDS has been studied, and it is known that a number of crystal structures can be formed, depending on the degree of hydration. − However, as recently as in 2021, a novel hydrate form of SDS crystal was discovered . Recently, Khodaparast et al explored the impacts of confinement and surfaces on the crystallization of SDS . The use of microvolumes allowed them to study the impacts of surface roughness and surface energy on crystallization.…”

Study on SO42−/Cl− Erosion Resistance and Mechanism of Recycled Concrete Containing Municipal Solid Waste Incineration (MSWI) Powder

“…Sodium sulfate was the most widely distributed sulfate solution in nature and had the most serious erosion to concrete [ 6 , 7 ]. According to experimental studies [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ], the crystallization of sodium sulfate consists of three compounds, which were Na 2 SO 4 -Thenardite, Na 2 SO 4 ·10H 2 O-Mirabilite, and Na 2 SO 4 ·7H 2 O-Sodium sulfite heptahydrate. Among them, Na 2 SO 4 ·10H 2 O was difficult to maintain at a stable state and was easily decomposed into Na 2 SO 4 and Na 2 SO 4 ·7H 2 O.…”