Poly(N-isopropylacrylamide) microgels at the oil–water interface: adsorption kinetics

Li, Zifu; Geisel, Karen; Richtering, Walter; Ngai, To

doi:10.1039/c3sm52168k

Cited by 101 publications

(133 citation statements)

References 59 publications

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“…This result shows that the negative charge density of S/N 1 and S/N 8 is greater compared to that of PNIPAM microgel particles, with a nominal zeta potential -20 mV at a temperature below the VPTT. 18,28 The significantly more negative charge density of S/N 1 and S/N 8 particles is possibly due to residual sulfate groups, originating from the decomposition of initiator KPS. It is well documented that below the VPTT, PNIPAM particles adopt a core-corona structure.…”

Section: Resultsmentioning

confidence: 99%

“…attributed to the addition of styrene to NIPAM. 33 Because PNIPAM is amphiphilic, even at temperatures above PNIPAM's VPTT, 24 S/N 1 particle can be described as a particle with PSrich dense core and PNIPAM-rich loose shell in water, 28 while S/N 8 particle is PS-rich core with a negligible thin PNIPAM periphery layer at the particle surface, as shown in Fig. 2.…”

Section: Resultsmentioning

confidence: 99%

“…34 It is well documented that both PNIPAM chains 35 and microgels 28 spontaneously adsorb onto oil-water interfaces because of the amphiphilicity of PNIPAM, which includes both hydrophobic isopropyl and hydrophilic amide groups. 36 For S/N 8 particles, also at 10 -3 g/mL, the heptane-water interfacial tension does not significantly decrease even after 6000 sec.…”

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confidence: 99%

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Fundamental Study of Emulsions Stabilized by Soft and Rigid Particles

Harbottle

Pensini

et al. 2015

Langmuir

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Two distinct uniform hybrid particles, with similar hydrodynamic diameters and comparable zeta potentials, were prepared by copolymerizing N-isopropyl acrylamide (NIPAM) and styrene.These particles differed in their styrene to NIPAM (S/N) ratios of 1 and 8, and were referred to as S/N 1 and S/N 8. Particle S/N 1 exhibited typical behavior of soft particles, i.e., the particles shrank in bulk aqueous solutions when the temperature was increased. As a result, S/N 1 particles were interfacially active. In contrast, particle S/N 8 appeared to be rigid in response to temperature changes. In this case, the particles showed negligible interfacial activity. Interfacial shear rheology tests revealed the increased rigidity of the particle-stabilized film formed at the heptane-water interface by S/N 1 than S/N 8 particles. As a result, S/N 1 particles were shown to be better emulsion stabilizers and emulsify a larger amount of heptane compared to S/N 8 particles. The current investigation confirmed a better performance of emulsion stabilization by soft particles (S/N 1) than by rigid particles (S/N 8), reinforcing the importance of controlling softness or deformability of particles for the purpose of stabilizing emulsions.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Fundamental Study of Emulsions Stabilized by Soft and Rigid Particles

Harbottle

Pensini

et al. 2015

Langmuir

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“…Upon pH induced protonation of charged groups inside the microgels, particles became more dense as well as less connected, their performance as interfacial stabilizer deteriorated [37,44,45]. Upon protonation of charged groups, also the elastic response of the interface as probed by dilational rheology decreased [39]. In accordance with the latter observations, Destribats et al…”

Section: Viscoelastic Properties Of Interfaces Stabilized By Soft Parmentioning

confidence: 70%

“…These soft particles are found to be excellent stabilizer for various types of oil-in-water emulsion [37]. There are some literature reports on water-in-oil emulsions stabilized by microgels, however, the microgels were found to be swollen by the oil phase [38,39]. It was concluded that alteration of the interfacial properties of the microgels by solvent uptake was responsible for the microgels ability to stabilize water-in-oil emulsions [37,38].…”

Section: Structure Of Emulsion Droplets Stabilized By Soft Particlesmentioning

confidence: 99%

Core-shell particles at fluid interfaces : performance as interfacial stabilizers

Buchcic¹

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There is a growing interest in the use of particles as stabilizers for foams and emulsions. Applying hard particles for stabilization of fluid interface is referred to as Pickering stabilization. By using hard particles instead of surfactants and polymers, fluid interfaces can be effectively stabilized against Ostwald ripening and coalescence. A drawback of the use of hard particles as interfacial stabilizers is that they often experience a pronounced energy barrier for interfacial adsorption and that hard particles are very specific with regard to the type of fluid interface they can adsorb to. Soft particles, on the other hand, are known as good stabilizers against coalescence and they spontaneously adsorb to a variety of different fluid interfaces. The aim of this thesis was to investigate core-shell particles comprising a hard core and soft shell with regard to their interfacial behaviour and their ability to act as sole stabilizers for foams and emulsions. We hypothesised that the presence of the soft shell allows for easier interfacial adsorption of core-shell particles compared to the hard core particles only. To test this hypothesis, we prepared core-shell particles comprising a solid polystyrene (PS) core and a soft poly-N-isopropylacrylamide (PNIPAM) shell. To ascertain the effect of shell thickness, we prepared a range of core-shell particles with different shell thicknesses, containing identical core particles. We found that core-shell particles are intrinsically surface active and can generate high surface pressures at the air-water interface and oil-water interfaces, whereas core particles seemed to experience a large energy barrier for interfacial adsorption and did not lower the surface tension. We also confirmed by microscopy that coreshell particles are actually adsorbing to the fluid interface and form densely packed interfacial layers. Further, we found that a certain critical thickness of the soft shell is necessary in order to ensure facile interfacial adsorption. If the PNIPAM shell on top of the core particles is well above 100nm thick, particle adsorption at the air-water interface was found to be diffusion limited.By gentle hand-shaking we were able to produce dispersion of air bubbles and emulsion droplets solely stabilized by core-shell particles. The resulting bubbles still underwent Ostwald ripening, albeit slowly. For oil-in-water emulsions of hexane and toluene, both of which have a relatively high solubility in the continuous phase, we found that core-shell particles can stop Ostwald ripening. The resulting emulsion droplets adopted pronounced non-spherical shapes, indicating a high elasticity of the interface. The high stability and the remarkable non-spherical shape of the emulsion droplets stabilized by core-shell particles were features we also observed for fluid dispersion stabilized by hard particles. This shows that in terms of emulsion stability core-shell particles behave similar to hard particles as interfacial stabilizer.As to why the differences between the st...

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Ultrastrong Anchoring Yet Barrier‐Free Adsorption of Composite Microgels at Liquid Interfaces

Monteillet

Workamp

Appel

et al. 2014

Adv Materials Inter

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conditions inside the particle, for example by changing the solvent quality with temperature, or adjusting the charge density with pH can thus give rise to changes in the particle size. [ 1 ] Similarly, increasing the particle concentration in bulk solutions can induce osmotic compression of the particles and lead to a size reduction. [ 2 ] By contrast, microgel particles display much of the same characteristic phase behavior that solid, dispersed, colloidal suspensions exhibit, such as crystallization, [ 3 ] glass formation [ 4,5 ] and gelation.[ 6 ] Microgels thus display a fascinating polymer-particle duality [ 7,8 ] ; this is refl ected in, for example, the particle-like scaling of rheological data at intermediate concentrations, and the polymer-like behavior in dense systems. [ 9 ] While recent work has established the versatility of microgels in stabilizing fl uid interfaces, [10][11][12][13][14][15][16][17][18][19][20][21][22] the details of their adsorption, conformation and organization remain largely elusive. Moreover, how their compressibility and deformability interplay with the other forces that act on particles at a liquid interface is still largely unknown. Cryo-SEM imaging, upon freeze-fracturing of microgel-stabilized emulsions has shown that signifi cant deformation of the soft particles may occur. [ 13,14,20 ] This suggests a subtle interplay between the forces acting on the particles at the interface, such as capillary forces and the internal elasticity of the microgels. However, due to the thermosensitivity and delicate nature of microgels this information would ideally be obtained from non-invasive methods that do not require extreme temperature changes or phase changes in the two immiscible liquids. Direct and accurate imaging of solvent-swollen microgels is diffi cult as their refractive index is inherently close to that of the aqueous solvent that swells them. Moreover, addition of a fl uorescent dye, even in small amounts, can signifi cantly alter their interfacial properties.Composite microgels effectively stabilize oil-water interfaces. [ 23,24 ] In this paper, we prepare composite microgel particles in which a highly fl uorescent solid core is embedded into a pH and temperature responsive microgel shell; this design allows accurate and in-situ visualization of the structure of microgel-laden fl uid interfaces. Combining direct in-situ observation with tensiometry allows us to estimate the adsorption energy and the particle elasticity. We place our observations Microgel particles display an interesting duality with properties attributed typically both to polymeric and colloidal systems. When adsorbed at a liquidliquid interface, this duality becomes particularly apparent as the various phenomena at play are governed by different aspects of these soft and responsive particles. The introduction of a solid, fl uorescently labeled, polystyrene core into the microgels allows direct and accurate visualization without the necessity of potential perturbing sample preparation techniques. By com...

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Poly(N-isopropylacrylamide) microgels at the oil–water interface: adsorption kinetics

Cited by 101 publications

References 59 publications

Fundamental Study of Emulsions Stabilized by Soft and Rigid Particles

Fundamental Study of Emulsions Stabilized by Soft and Rigid Particles

Core-shell particles at fluid interfaces : performance as interfacial stabilizers

Ultrastrong Anchoring Yet Barrier‐Free Adsorption of Composite Microgels at Liquid Interfaces

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