Fundamental study of emulsions stabilized by soft and rigid. particles

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1 Supporting information Fundamental study of emulsions stabilized by soft and rigid particles Zifu Li, 1 David Harbottle, 1,2 Erica Pensini, 1 To Ngai, 3 Walter Richtering, 4 Zhenghe Xu 1,5* 1, Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4, Canada 2, School of Chemical and Process Engineering, University of Leeds, Leeds, LS2 9JT, UK 3, Department of Chemistry, the Chinese University of Hong Kong, Shatin, N. T., Hong Kong 4, Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, D Aachen, Germany 5, Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing , China * To whom correspondence should be addressed. Phone: ; Fax: ; zhenghe.xu@ualberta.ca 1

2 The adsorption model developed by Ward and Tordai has been commonly used to describe surfactant adsorption onto the interface by considering both adsorption and desorption processes. 1 This model has also be applied to describing adsorption of quantum dots or particles into the interface. 2 For the biwettable S/N 1 and S/N 8 particles of larger sizes at initial adsorption stage, the desorption process can be neglected in the adsorption model derived by Ward and Tordai, 1 leading to the following initial adsorption rate equation Γ =2 1 where is the interfacial particle concentration, D ads is the adsorption coefficient and is the microgel bulk concentration. It should be noted that D ads here is referred to as the adsorption of the particles from boundary layer in water near the oil-water interface into the oil-water interface, which is different from the two-dimensional diffusion of the particles in the oil-water interface plane as reported by Fuller et al 3 and Dai et al 4. Moreover, the interfacial concentration can be correlated to the surface pressure via the Gibb s equation given by 5 = =Γ 2 Combining Eq. (1) and (2), Eq. (3) can be obtained as: =2RT 3 Figures S1 and S2 show π versus for S/N 1 and S/N 8 at 25 at four different concentrations. The four dotted lines shown in Figures S1 and S2 were fitted with Eq. 3 with the slope, being given by: 2

3 =2 4 Figure S3 shows a clear linear relationship between and microgel particle concentration,, with R 2 of the linear fit around The adsorption coefficient, D ads of S/N 1 and S/N 8 particles can be obtained from the slope of the linear fit in Figure S3 using Eq. 4. The D ads values of S/N 1 and S/N 8 particles are given in Table 2. Note that only the initial adsorption stage, when particles first adsorb to the heptane-water interface with a low particle coverage, 2 is used for extracting the adsorption coefficient, D ads. With a low interfacial coverage, particles can freely adsorb to the interface and this adsorption behavior is governed by the excess energy released upon partition of the particles to the interface. 3 The linear relation as shown in Figure S3 verifies that D ads is a constant for a given particle/oil-water interface system as anticipated. As interfacial coverage increases, the adsorbed particles repel new particles from adsorbing to the interface. 2 As a result, particles adsorption to the oil-water interface is reduced. The interaction between the particles at the oil-water interface and adsorbing particles from aqueous solutions makes the Ward-Tordai equation no longer valid, as shown by the deviation from the linear plot in Figures S1 and S2. 3

4 Figure S1. Effect of S/N 1 particle concentration on the evolution of dynamic surface pressure as a function of t 1/2 at 25. The dotted lines are linear fitting lines according to equation 3. 4

5 Figure S2. Effect of S/N 8 particle concentration on the evolution of dynamic surface pressure as a function of t 1/2 at 25. The dotted lines are linear fitting lines according to equation 3. 5

6 Figure S3. Plots of k i vs. particle concentration, at 25. The fitting parameters R 2 are around 0.99, indicating the excellence of these fits. 6

7 Figure S4. Appearances of (A) homogenizer, (B) hand shaking, and (C) self-assembly emulsions stabilized by S/N 1 particles at seven different concentrations; optical microscope images of (D)(F) homogenizer and (G)-(I) hand shaking emulsions stabilized by S/N 1 particles at three different particle concentrations. D-I have the same scale bar 50 µm. 7

8 Figure S5. Appearance of (A) homogenizer and (B) hand shaking emulsions one day after preparation, (C) homogenizer and (D) hand shaking emulsions one year after preparation, stabilized by S/N 1 particles at 1.25 ( 10*+ g/ml. Figure S6. Optical microscope images of (A) homogenizer and (B) hand shaking emulsions stabilized by S/N 8 particles at 1.25 ( 10*+ g/ml. The scale bar is 50 µm. 8

9 Compression isotherm experiments were conducted at the heptane-water interface using a computer controlled Langmuir-Blodgett trough (KSV NIMA), with a trough area of 17,010 mm 2. 6 The interfacial pressure was monitored by a paper Wilhelmy plate. When films form at the interface, the interfacial pressure (P interfacial ) represents the change in the interfacial tension (γ) relative to the clean interface (γ 0 ) and is given by: P γ γ (5) int erfacial = 0 Prior to each measurement, the trough was carefully cleaned with toluene, acetone and Milli-Q water. The lower part of the trough was filled with 120 ml of Milli-Q water as the sub-phase. The trough was considered clean with a pressure sensor reading 0.1 mn/m when the water phase was compressed to an area of 12.5 mm 2. Once cleaned, Milli-Q water was substituted with microgel solution, having a concentration of 5 10 g/ml. After setting the interfacial pressure to zero at the air-water interface, 100 ml of HPLC-grade heptane was added as the top phase. Films were equilibrated for 40 min, during which the interfacial pressure (π) was recorded as a function of time. After the films were equilibrated they were compressed by moving these two symmetric barriers at 10 mm/min. All experiments were conducted at 25. 9

10 Figure S7. Compression isotherms of S/N 1 and S/N 8 particles covered heptane-water interface. References 1. Ward, A. F. H.; Tordai, L., TIME-DEPENDENCE OF BOUNDARY TENSIONS OF SOLUTIONS.1. THE ROLE OF DIFFUSION IN TIME-EFFECTS. Journal of Chemical Physics 1946, 14 (7), Kutuzov, S.; He, J.; Tangirala, R.; Emrick, T.; Russell, T. P.; Boker, A., On the kinetics of nanoparticle self-assembly at liquid/liquid interfaces. Physical Chemistry Chemical Physics 2007, 9 (48),

11 3. Cohin, Y.; Fisson, M.; Jourde, K.; Fuller, G. G.; Sanson, N.; Talini, L.; Monteux, C., Tracking the interfacial dynamics of PNiPAM soft microgels particles adsorbed at the air-water interface and in thin liquid films. Rheologica Acta 2013, 52 (5), Tarimala, S.; Ranabothu, S. R.; Vernetti, J. P.; Dai, L. L., Mobility and in situ aggregation of charged microparticles at oil-water interfaces. Langmuir 2004, 20 (13), Dukhin, S. S.; Kretzschmar, G.; Miller, R., Dynamics of Adsorption at Liquid Interfaces. Elsevier: The Netherlands, Fuller, G. G.; Vermant, J., Complex Fluid-Fluid Interfaces: Rheology and Structure. Annual Review of Chemical and Biomolecular Engineering, Vol , 3,

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