Fig. 1

Contact angle of a colloidal particle at oil/water interface and the type of emulsion formed"

Fig. 2

Calculation of adsorption/desorption free energy of a particle based on its contact angle at oil/water interface"

Fig. 3

Desorption free energy of a nanoparticle from hydrocarbon/water interface as a function of its contact angle"

Fig. 4

Adsorption of ionic surfactant at solid/water interface and corresponding change of contact angle. Monolayer adsorption（a）; double layer adsorption（b）; and the contact angle θ of water on solid as a function of surfactant concentration c（c）"

Fig. 5

SEM image of silica nanoparticles（HL-200）（a）and the Zeta potential of the particles in aqueous phase as a function of pH（b）at 25 ℃"

Fig. 6

Zeta potential of silica nanoparticles（HL-200）dispersed in aqueous solutions of different cationic surfactants as a function of surfactant concentration at 25 ℃[22]"

Fig. 7

Digital photographs and micrographs of n-octane-in-water emulsions stabilized by（A）silica nanoparticles solely at different concentrations, （B）CTAB solely at different concentrations, （C）1.0% silica nanoparticles plus CTAB at different concentrations, （a）3.0 mmol/L CTAB alone, （b）1.0% silica nanoparticles plus 0.01 mmol/L CTAB; （c）1.0% silica nanoparticles plus 0.1 mmol/L CTAB, and（d）1.0% silica nanoparticles plus 10 mmol/L CTAB, taken a week after preparation（Scale bar=100 μm）"

Fig. 8

Digital photographs and micrographs of n-octane-water emulsions stabilized by 0.1% silica nanoparticles in combination with diC12DMAB at different concentrations, taken a week after preparation.（a）3.0 mmol/L diC12DMAB;（b）1.0% silica nanoparticles plus 0.01 mmol/L diC12DMAB;（c）1.0% silica nanoparticles plus 2.5 mmol/L diC12DMAB; and（d）1.0% silica nanoparticles plus 30 mmol/L diC12DMAB（Scale bar=100 μm）"

Fig. 9

Contact angle of water on the glass slides adsorbed with different cationic surfactants as a function of surfactant concentration"

Fig. 10

Principles of inorganic nanoparticles stabilizing Pickering emulsions via in situ hydrophobization and inducing phase inversion of emulsions"

Fig. 11

SEM image of calcium carbonate nanoparticles（a）and their Zeta potential in aqueous phase（2.0%）as a function of pH（b）"

Fig. 12

Micrographs of emulsion droplets stabilized solely by CaCO3 nanoparticles taken 24 h after preparation.（a）toluene-in-water, 2% particles;（b）toluene-in-water, 3% particles;（c）n-octane-in-water, 2% particles;（d）n-octane-in-water, 3% particles（Scale bar is 500 μm for（a, b, c）and 50 μm for（d））"

Fig. 13

Digital photographs（A）and micrographs（B）of toluene-water emulsions stabilized by 2 wt.% CaCO3 nanoparticles with SDS at different concentrations taken 24 h after preparation.（a）0.3 mmol/L SDS, O/W（1）;（b）2 mmol/L SDS, W/O;（c）6 mmol/L SDS, O/W（2）;（d）6 mmol/L SDS alone（Scale bar denotes 500 μm for a, b and 20 μm for c, d）"

Fig. 14

Adsorption isotherm of SDS at calcium carbonate nanoparticle/water interface at 25 ℃ and the corresponding SDS concentration range forming different types of toluene- water emulsions"

Fig. 15

Reversible inter-conversion between active form（amidinium/cationic）and inactive form（amidine/nonionic）of a CO2/N2 switchable surfactant, N′-dodecyl-N, N-dimethylacetamidine"

Fig. 16

Digital photographs and optical micrographs of n-octane-in-water Pickering emulsions stabilized by silica nanoparticles（0.5 wt.%）plus CO2/N2 switchable surfactant at different concentrations taken 24 h（（A）and（C））and one week（B）after preparation"

Fig. 17

Digital photographs of n-octane-in-water Pickering emulsions stabilized by 0.5 wt.% silica nanoparticles together with（a~h）0.3 mmol/L switchable surfactant undergoing switching or（i, j）0.1 mmol/L CTAB.（a）Emulsion with amidinium（10 mL：10 mL）;（b）transferred to bubbling device;（c）bubbling N2 at 65 ℃ for 80 min;（d）transferred to vessel;（e）re-homogenized for 2 min, 24 h later;（f）one week later;（g）bubbling CO2 in ice bath for 50 min followed by re-homogenization for 2 min, one week later;（h）emulsion（7 mL∶7 mL）with amidinium kept at 65 ℃ for 24 h without bubbling N2;（i）Emulsion（7 mL∶7 mL）with CTAB, 24 h later;（j）emulsion with CTAB after bubbling N2 at 65 ℃ for 80 min, 24 h later"

Fig. 18

Digital photographs of aqueous foams stabilised by（A）0.5 wt.% silica nanoparticles alone; （B）N′-dodecyl-N, N-dimethylacetamidinium alone at different concentrations, and（C and D）0.5 wt.% silica nanoparticles in combination with N′-dodecyl-N, N-dimethylacetamidinium at different concentrations, taken immediately after shaking（A, B, C）and 24 h later（D）; Surfactant concentrations in B, C, D from left to right are： 0.1, 0.2, 0.3, 0.6, 1, 2, 3 and 6 mmol/L"

Fig. 19

（A）Photograph of the foam stabilized by 0.5 wt.% silica nanoparticles in combination with 0.3 mmol/L N′-dodecyl-N, N- dimethylacetamidinium, taken immediately after bubbling with N2 at room temperature for 5 min;（B）micrograph of the bubbles（produced by shaking）stabilized by 0.5 wt.% silica nanoparticles in combination with 1.0 mmol/L N′-dodecyl-N, N- dimethylacetamidinium;（C）micrograph of the bubbles stabilized by 1.0 mmol/L amidinium solely, taken immediately after shaking"

Fig. 20

Photographs of the dispersion of 0.5 wt.% silica nanoparticles in 0.3 mmol/L N′-dodecyl-N, N-dimethylacetamidinium aqueous solution in a bubbling device following bubbling with N2（160 mL/min）at 65 ℃ initially（A）; bubbling with N2（160 mL/min）at 65 ℃ for 80 min（B）and then bubbling with CO2（160 mL/min）at 0-5 ℃ for 50 min（C）"