Fig. 1

Photographs of some dodecane-in-water emulsions stabilized by（A）0.5% silica particles alone,（B）CTAB alone at different concentrations and（C, D）mixtures of 0.5% silica nanoparticles and CTAB at different concentrations（mmol/L）as shown on top of the vessels, taken 24 h（A, B, C）, and 6 months（D）after preparation"

Fig. 2

Photographs and micrographs of the dodecane-in-water Pickering emulsions stabilized by 0.5% silica nanoparticles in combination with 0.01 mmol/L CTAB, following switching off（by adding 0.01 mmol/L SDS）and switching on（by adding 0.01 mmol/L CTABfollowed by homogenization）cycles taken 24 h after emulsification and demulsification, and change of the Zeta potential（black points, 25 ℃）of the silica nanoparticles in corresponding systems. The CTAB-SDS ion pair concentrations in the systems are 0.01 mmol/L（cycle 1）, 0.05 mmol/L（cycle 5）and 0.1 mmol/L（cycle 10）, respectively"

Fig. 3

Zeta potential of 0.5% silica nanoparticles dispersed in aqueous CTAB solutions and in equimolar CTAB-SDS solutions as a function of initial CTAB concentration; adsorption amount of CTAB at the silica particle/water interface as a function of equilibrium CTAB concentration"

Fig. 4

Contact angles of the aqueous solution of CTAB and the equimolar mixture of CTAB-SDS on hydrophilic glass slides in air at 25 ℃ as a function of initial CTAB concentration. The unfilled circle was measured by adding a drop of SDS solution into a drop of CTAB solution already on a slide both at a concentration of 0.3 mmol/L"

Fig. 5

Photographs of dodecane-in-water emulsions stabilized by silica nanoparticles + CTAB which were demulsified by adding an equimolar amount of SDS followed by either shaking or sonication for 5 min, taken 2 h after operation. The concentrations of particle（%）and CTAB（mmol/L）are shown on the vessels"

Fig. 6

Demulsification of dodecane-in-water Pickering emulsions stabilized by 0.5% silica + 0.1 mmol/L DTAB（A）or by 0.5% silica + 0.01 mmol/L CTAB（B）by adding an equimolar amount of sodium alkylsulfate of different chain lengths（given）followed by hand shaking, taken 2 h after shaking"

Fig. 7

Digital photographs of aqueous foams stabilized by 0.5% silica nanoparticles in combination with CTAB at different concentrations as shown on top of the figure, taken immediately（A）and 30 min（B）after shaking 10 mL concentration of dispersion in cylindrical graduated flasks. CTAB（mmol/L）are shown on top of the figure"

Fig. 8

Photographs of cycles between foaming and defoaming of a dispersion（10 mL）of 0.3 mmol/L CTAB aqueous solution containing 0.5% silica nanoparticles（foaming）by adding equal moles of SDS（0.1 g solution of 30 mmol/L, defoaming）, and another amount of free CTAB（0.1 g solution of 30 mmol/L）（foaming again）alternately. The photographs were taken 10 min after shaking, and the total CTAB/SDS concentrations（mmol/L）are shown on top of the figure"

Fig. 9

Illustration of the principles of construction of stimuli-responsive Pickering emulsions and Pickering foams using ordinary inorganic nanoparticles and ionic surfactants by means of ion pair formation trigger"

Fig. 10

Illustration of the pH-responsive principles of the Pickering emulsions stabilized by silica nanoparticles in combination with sodium N-dodecyl-β-aminopropionate（DAP）"

Fig. 11

Photographs and micrographs of the n-decane-in-water emulsions stabilized by a mixture of 0.5% silica nanoparticles in combination with 0.06 mmol/L DAP following pH alternation cycling, taken 24 h（cycle 1-6）and 2 months（cycle 6 only）after homogenization（for stable emulsions）and 20 min after adding dropwise NaOH solution with agitation（for unstable emulsions）"

Fig. 12

Zeta potential of silica nanoparticles（0.1%）dispersed in DAP aqueous solution at different pH as a function of initial DAP concentration（25 ℃）"

Fig. 13

Photographs and micrographs（low pH only）of n-decane-in-water emulsions stabilized by a mixture of 0.5% silica nanoparticles and 0.06 mmol/L C12B following pH alternation by adding 0.1 mol/L HCl or 0.1 mol/L NaOH, taken 24 h and 2 months（cycle 7 only）after preparation"

Fig. 14

Photographs showing cycles between foaming and defoaming of a 10 mL dispersion of 0.5% silica nanoparticles in aqueous C12B solution（0.6 mmol/L）at room temperature（20-25 ℃）, taken immediately after shaking（foaming）and gentle mixing （defoaming）following adding dropwise HCl and NaOH aqueous solutions, respectively"

Fig. 15

Digital photographs of n-decane-in-water Pickering emulsions stabilized by 0.5% alumina nanoparticles in combination with 0.3 mmol/L SDS（A）, and then 0.3 mmol/L DDAA was added, which was transformed between demulsified state（B, D and F）and emulsified state（C and E）by alternately switching on（bubbling with CO2 at a flow rate of 160 mL/min at 0-5 ℃ for 80 min）and switching off（bubbling with N2 at a flow rate of 160 mL/min at 65 ℃ for 80 min）the CO2/N2 switchable surfactant followed by homogenization（H）. Micrographs of the corresponding stable emulsions are also given（a, c and e）"