Fig. 1

Schematic diagram of switching process of CO2/N2switchable surfactant DDMA"

Fig. 2

Digital photos of n-decane-in-water emulsions（7 mL/7 mL）stabilized by（A, C）0.01% and（B, D）0.001% alumina nanoparticles in combination with DDMA-C（cationic）at different concentrations（mmol/L）as shown above the vessels, taken 24 h（A and B）and one month（C and D）after preparation"

Fig. 3

Micrographs of n-decane-in-water emulsions stabilized by 0.01% alumina nanoparticles in combination with DDMA-C at different concentrations（mmol/L）as given taken 24 h after preparation"

Fig. 4

Micrographs of n-decane-in-water emulsions stabilized by 0.001% alumina nanoparticles in combination with DDMA-C at different concentrations（mmol/L）as given taken 24 h after preparation"

Fig. 5

SEM images（A, B）and optical micrographs（C, D）of dried（A, B and D）or half-dried（C）O/W emulsion droplets stabilized by alumina nanoparticles in combination with either DDMA-C（A, B）or SDS（C, D）taken 24 h after preparation.（A）0.01% alumina + 0.01 mmol/L DDMA-C, n-decane,（B）0.01% alumina + 0.01 mmol/L DDMA-C, n-hexane,（C, D）0.5% alumina + 0.1 mmol/L SDS, n-hexane"

Fig. 6

Zeta potential of 0.1% alumina nanoparticles dispersed in aqueous cationic DDMA-C solution（●）as function of initial surfactant concentration and the comparison with that dispersed in aqueous CTAB solution（○）. The dashed line shows the critical Zeta potential which separates stable（above the line）and unstable（below the line）emulsions"

Fig. 7

Digital photographs of gasoline-in-water emulsions stabilized by 0.1% negatively charged silica nanoparticles in combination with SDBS at different concentration using either（A）tap water or（B）DI water as aqueous phase, respectively, taken 24 h after preparation. SDBS concentration in mmol/L for（A）and in μmol/L for（B）is shown on each vessel"

Fig. 8

Digital photographs of diesel oil-in-water emulsions（7 mL diesel oil/7 mL DI water）stabilized solely by silica nanoparticles at different concentration（%）as shown on top of the vessels, taken 24 h（A）and 1 week（B）after emulsification at room temperature（25 ℃）"

Tab. 1

Zeta potential of 0.1% nano-silica dispersed in DI water containing different concentration of NaCl and corresponding droplet size and stability（24 h after preparation）of the diesel oil-in-water emulsions at 25 ℃"

Fig. 9

Appearance（A-E）and micrographs（a, c and e）of n-decane-in-water emulsions stabilized by 0.01% alumina nanoparticles in combination with 0.2 mmol/L DDMA-C upon alternately bubbling N2（30 mL/min at 65 ℃ for 50 min, B and D）and CO2（40 mL/min at 0-5 ℃ for 150 min）followed by homogenization（H）（C and E）"

Fig. 10

Illustration of the demulsification/re-stabilization cycles of a n-decane-in-water emulsion stabilized by positively charged alumina nanoparticles and cationic DDMA-C at very low concentration by bubbling N2 or CO2 followed by homogenization, respectively"

Fig. 11

Appearance（A）and micrographs（a, c and e） of n-decane-in-water emulsions stabilized by 0.5% alumina nanoparticles plus 0.3 mmol/L CTAB, subsequent switching off（B, D and F）via addition of 0.3 mmol/L SDS and switching on（C and E）via addition of 0.3 mmol/L CTAB and homogenization（H）at 25 ℃, taken 24 h after operation"