Thermodynamic and Kinetic Pathways to Agitated and Spontaneous Emulsification

Kullappan, Monicka; Chaudhury, Manoj K.

doi:10.1021/acs.langmuir.0c01707

Cited by 6 publications

(18 citation statements)

References 107 publications

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“…The more plausible scenario is that the oil is injected into the aqueous phase as droplet via transient or persistent shake up events due to instabilities occurring at the interface. Such a picture was presented in our earlier publication 26 , where we conjectured that the inverted (water-in-oil) emulsions first fuse with the interfacial monolayer following which a curvature reversal (an instability) develops at the interface, thus triggering the phase inversion. Because of the difference of the interfacial tensions between the flat interface and the water-in-oil emulsion, we surmise that local heterogeneous Marangoni instability to play an important role in the explosive phase inversions as depicted in Figure 9 (A and B).…”

Section: Bathochromic and Hypsochromic Shifts: The Polybasic Characte...mentioning

confidence: 53%

“…While a tightly packed hydrocarbon chain occupies an area of about 0.2 𝑛𝑚 2 , one would expect that the average area per molecule in an emulsion or in a vesicle would be higher than this value as they would be more disordered. On the other hand, the average area occupied by the ethylene glycol group of the non-ionic surfactant should be greater than (0.6 𝑛𝑚 2 ), as obtained 26 from the surface pressure-area isotherm. The average area per molecule, as estimated on the basis of the number of hydrocarbon chains) range from 0.34 𝑛𝑚 2 𝑡𝑜 0.4 𝑛𝑚 2 for the emulsions and vesicles (Table 2 and S4).…”

Section: Bathochromic and Hypsochromic Shifts: The Polybasic Characte...mentioning

confidence: 90%

“…In our previous publication, we primarily focused on emulsification under agitated conditions that lead to hydrodynamic turbulence 26 . Here, we pay our attention to what happens without any external agitation.…”

Section: Background Motivation and Objectivementioning

confidence: 99%

“…The chemical potential gradients across the interface lead to mass transfer and a concomitant hydrodynamic instability 3 , whereas an in-plane gradient of concentration can lead to Marangoni force induced hydrodynamic flow. Due to a resurgent interest in this field of research, new insightful papers have continued to be published even recently 17,[22][23][24][25][26][27][28] , whereas detailed accounts of the earlier research have been reviewed 16,18 . As this particular article is not meant to be a review, here we summarize only the salient features of the related literatures.…”

Section: Introductionmentioning

confidence: 99%

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Spontaneous Emulsification: Elucidation of the Local Processes

Kullappan

Patel

Chaudhury

2023

Preprint

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Micro and/or Nano sized emulsions are formed when an organic liquid gently comes in contact with water in the presence of a surfactant, where no external agitation is required. Many years of research made it clear that the driving force for spontaneous emulsification arises from the differences of the chemical potentials of various components in the organic and aqueous phases, which triggers diffusion coupled hydrodynamic fluctuation. While extraordinary theoretical developments have taken place that attempted to describe these processes within the scopes of equilibrium and non-equilibrium thermodynamics, the local processes underlying the spontaneous emulsification, however, still remain elusive. In this research, we investigate the local processes that involve the transfer of surfactant as well as water from one phase to another (i.e. water to oil), which results in the formation of water-in-oil emulsion in the organic phase and, subsequently. Thes emulsions invert into oil-in-water emulsion, rather abruptly, as they cross the phase boundary. Studies based on UV spectroscopy and molecular dynamics indicate that these processes may involve explosive events and subsequent assembly of the fragments to other organized structures which are reminiscent of cusp catastrophe proposed earlier by Dickinson. These processes lead to either to a strong or a weak fluctuation of the component concentrations below the interface that also becomes evident in the fast (athermal) diffusion of the emulsion droplets from the interfacial region farther into the bulk water. These events can be arrested suitably with polymeric additives.

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Section: Bathochromic and Hypsochromic Shifts: The Polybasic Characte...mentioning

confidence: 53%

Section: Bathochromic and Hypsochromic Shifts: The Polybasic Characte...mentioning

confidence: 90%

Section: Background Motivation and Objectivementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Spontaneous Emulsification: Elucidation of the Local Processes

Kullappan

Patel

Chaudhury

2023

Preprint

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“…Hexadecane is soluble in TPM but insoluble in both water and methanol. 54 Therefore, hexadecane acted as a tracer molecule 55 dissolved in the TPM phase to identify droplet pinch-off from the interface. We found that mixtures of TPM and C16 emulsified spontaneously but that residual oil remained at the air−water interface (Figure 3a).…”

Section: Resultsmentioning

confidence: 99%

Droplet Formation and Growth Mechanisms in Reaction-Induced Spontaneous Emulsification of 3-(Trimethoxysilyl) Propyl Methacrylate

2021

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Spontaneous emulsification of 3-(trimethoxysilyl) propyl methacrylate (TPM) can produce complex and active colloids, nanoparticles, or monodisperse Pickering emulsions. Despite the applicability of TPM in particle synthesis, the nucleation and growth mechanisms of TPM emulsions are still poorly understood. We investigate droplet formation and growth of TPM in aqueous solutions under quiescent conditions. Our results show that in the absence of stirring the mechanisms of diffusion and stranding likely drive the spontaneous emulsification of TPM through the formation of co-soluble species during hydrolysis. In addition, turbidity and dynamic light scattering experiments show that the pH modulates the growth mechanism. At pH 10.1, the droplets grow via Ostwald ripening, while at pH 11.5, the droplets grow via monomer addition. Adding surfactants [Tween, sodium dodecyl sulfate (SDS), or cetyltrimethylammonium bromide] leads to <100 nm droplets that are kinetically stable. The growth of Tween droplets occurs through addition of TPM species while the number density of droplets is kept constant. In addition, in the presence of the ionic surfactant SDS, electrostatic repulsion between the solubilized TPM species and SDS leads to a significant increase in the number density of droplets as well as additional nucleation events. Finally, imaging of the solubilization of TPM in capillaries shows that in the absence of a surfactant, TPM hydrolysis is likely the rate-limiting step for emulsification, whereas the presence of silica particles in the aqueous phase likely acts as a catalyst of TPM hydrolysis. Our experiments highlight the importance of diffusion and solubilization of TPM species in the aqueous phase in the nucleation and growth of droplets.

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