New Methodology to Determine Equilibrium Surfactant Adsorption Properties from Experimental Dynamic Surface Tension Data

Moorkanikkara, Srinivas Nageswaran; Blankschtein, Daniel

doi:10.1021/la804324e

Cited by 13 publications

(17 citation statements)

References 47 publications

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“…5f suggests a 4.5 nm thick PVA monolayer which remains after drying. A dynamic equilibrium model with PVA adsorbing and leaving the surface of the microspheres in the aqueous phase could explain the patchy morphology observed in the resultant microspheres [40].…”

Section: Resultsmentioning

confidence: 99%

Chemical and spatial analysis of protein loaded PLGA microspheres for drug delivery applications

Rafati

Boussahel

Shakesheff

et al. 2012

Journal of Controlled Release

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Polymer microspheres for controlled release of therapeutic protein from within an implantable scaffold were produced and analysed using complimentary techniques to probe the surface and bulk chemistry of the microspheres. Time of Flight - Secondary Ion Mass Spectrometry (ToF-SIMS) surface analysis revealed a thin discontinuous film of polyvinyl alcohol (PVA) surfactant (circa 4.5 nm thick) at the surface which was readily removed under sputtering with C(60). Atomic Force Microscopy (AFM) imaging of microspheres before and after sputtering confirmed that the PVA layer was removed after sputtering revealing poly(lactic-co-glycolic) acid(PLGA). Scanning electron microscopy showed the spheres to be smooth with some shallow and generally circular depressions, often with pores in their central region. The occurrence of the protein at the surface was limited to areas surrounding these surface pores. This surface protein distribution is believed to be related to a burst release of the protein on dissolution. Analysis of the bulk properties of the microspheres by confocal Raman mapping revealed the 3D distribution of the protein showing large voids within the pores. Protein was found to be adsorbed at the interface with the PLGA oil phase following deposition on evaporation of the solvent. Protein was also observed concentrated within pores measuring approximately 2 μm across. The presence of protein in large voids and concentrated pores was further scrutinised by ToF-SIMS of sectioned microspheres. This paper demonstrates that important information for optimisation of such complex bioformulations, including an understanding of the release profile can be revealed by complementary surface and bulk analysis allowing optimisation of the therapeutic effect of such formulations.

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Section: Resultsmentioning

confidence: 99%

Chemical and spatial analysis of protein loaded PLGA microspheres for drug delivery applications

Rafati

Boussahel

Shakesheff

et al. 2012

Journal of Controlled Release

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“…These observations also point out the experimental difficulties to quantitatively analyse data from pendant droplet tensiometry. 22,23 Between the two asymptotic behaviours we observe a crossover region where the kinetics is not signicantly affected by the surfactant concentration. These results indicate that micelles contribute to the decrease of surface tension, provided that they have sufficient time to diffuse to the interface from the bulk and that the dissociation of micelles is not the limiting step as observed for other micelles.…”

Section: Dynamics Of Surfactant Adsorption: Pendant Dropmentioning

confidence: 88%

“…15,20 Tensiometry is widely used for both equilibrium and dynamic measurements but provides limited information on adsorption-desorption processes due to the predominance of diffusion at large scales. 13,[21][22][23] Deviations of the experimental data from the minimal diffusive-limited model introduced by Ward and Tordai are almost systematically observed, and attributed to curvature effects, [24][25][26][27] convective currents, 23,28,29 or adsorption barriers. 14,17 These adsorption barriers are revealed in the transfer-limited regimes which dominate at small dimensions 21,30 and in convective systems, 29,31 namely under the conditions relevant to emulsication or foaming.…”

Section: Introductionmentioning

confidence: 94%

Microfluidic Dynamic Interfacial Tensiometry (μDIT)

2014

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We designed, developed and characterized a microfluidic method for the measurement of surfactant adsorption kinetics via interfacial tensiometry on a microfluidic chip. The principle of the measurement is based on the deformability of droplets as a response to hydrodynamic forcing through a series of microfluidic expansions. We focus our analysis on one perfluoro surfactant molecule of practical interest for droplet-based microfluidic applications. We show that although the adsorption kinetics is much faster than the kinetics of the corresponding pendant drop experiment, our droplet-based microfluidic system has a sufficient time resolution to obtain quantitative measurement at the sub-second time-scale on nanoliter droplet volumes, leading to both a gain by a factor of ∼10 in time resolution and a downscaling of the measurement volumes by a factor of ∼1000 compared to standard techniques. Our approach provides new insight into the adsorption of surfactant molecules at liquid-liquid interfaces in a confined environment, relevant to emulsification, encapsulation and foaming, and the ability to measure adsorption and desorption rate constants.

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“…The first analysis of surfactant layers dates back to the 18th century with Franklin's experiments (1) and the first comprehensive studies on adsorption kinetics by Ward and Tordai (18) and Langmuir (19). From this point, a wide variety of models describe the adsorption dynamics, accounting for all kinds of molecular effects at interfaces (20)(21)(22)(23)(24)(25)(26). We expect two limiting cases: (i) the adsorption is limited by the bulk transport toward the interface, leading to a local equilibrium between the surfactant interfacial concentration and the bulk concentration in the vicinity of the interface at all times; and (ii) the adsorption is limited by the adsorption/desorption rate constants at the interface, and the bulk concentration is homogeneous at all time.…”

mentioning

confidence: 99%

Surfactant adsorption kinetics in microfluidics

Riechers

Maes

Akoury

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Emulsions are metastable dispersions. Their lifetimes are directly related to the dynamics of surfactants. We design a microfluidic method to measure the kinetics of adsorption of surfactants to the droplet interface, a key process involved in foaming, emulsification, and droplet coarsening. The method is based on the pH decay in the droplet as a direct measurement of the adsorption of a carboxylic acid surfactant to the interface. From the kinetic measurement of the bulk equilibration of the pH, we fully determine the adsorption process of the surfactant. The small droplet size and the convection during the droplet flow ensure that the transport of surfactant through the bulk is not limiting the kinetics of adsorption. To validate our measurements, we show that the adsorption process determines the timescale required to stabilize droplets against coalescence, and we show that the interface should be covered at more than 90% to prevent coalescence. We therefore quantitatively link the process of adsorption/desorption, the stabilization of emulsions, and the kinetics of solute partitioning-here through ion exchange-unraveling the timescales governing these processes. Our method can be further generalized to other surfactants, including nonionic surfactants, by making use of fluorophore-surfactant interactions.droplet | interfaces | surfactant | emulsion | microfluidics S urface active compounds are ubiquitous in our daily life, be it in living systems or in industrial and technological products (1-3). The compounds are used widely for the stabilization of foams and emulsions for food and cosmetic products, painting materials, and industrial coatings (3). Emulsions are nowadays also used in combination with microfluidic systems for applications in biotechnology (3-11). An emulsion is a dispersion of one liquid phase into another, stabilized by surfactants in a metastable state. The kinetic stabilization of emulsions occurs through several mechanisms, involving electrostatic or steric repulsion and the buildup of Marangoni stresses to improve the lifetime of emulsions against coalescence (12, 13). On the other hand, surfactants are involved in transport processes such as Ostwald ripening or solute transport, which mediates the chemical equilibration of the system (14-17): in general, all processes affecting the lifetime of emulsions (coalescence, rupture, exchange, and loss of molecules) are directly related to the physics and dynamics of the surfactant molecules at interfaces (3,4,6,10,11,15,16). The first analysis of surfactant layers dates back to the 18th century with Franklin's experiments (1) and the first comprehensive studies on adsorption kinetics by Ward and Tordai (18) and Langmuir (19). From this point, a wide variety of models describe the adsorption dynamics, accounting for all kinds of molecular effects at interfaces (20-26). We expect two limiting cases: (i) the adsorption is limited by the bulk transport toward the interface, leading to a local equilibrium between the surfactant interfacial concen...

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New Methodology to Determine Equilibrium Surfactant Adsorption Properties from Experimental Dynamic Surface Tension Data

Cited by 13 publications

References 47 publications

Chemical and spatial analysis of protein loaded PLGA microspheres for drug delivery applications

Chemical and spatial analysis of protein loaded PLGA microspheres for drug delivery applications

Microfluidic Dynamic Interfacial Tensiometry (μDIT)

Surfactant adsorption kinetics in microfluidics

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