chemart / self-propelled-droplets

{"species": [{"id": "oleic_anhydride", "structure": "oleic anhydride, the precursor (fuel) dissolved in the nitrobenzene oil phase"}, {"id": "H2O", "structure": "bulk aqueous phase"}, {"id": "oleic_acid", "structure": "oleic acid, the protonated surfactant"}, {"id": "oleate", "structure": "oleate, the surfactant anion that lowers interfacial tension"}, {"id": "H", "structure": "proton released at the interface; it is the local drop in pH that raises the tension and drives the Marangoni flow"}, {"id": "nitrobenzene", "structure": "the oil solvent; it carries the precursor and does not react"}], "reactions": [{"reactants": {"oleic_anhydride": 1, "H2O": 1}, "products": {"oleic_acid": 2}, "rate": null, "count": null}, {"reactants": {"oleic_acid": 1}, "products": {"oleate": 1, "H": 1}, "rate": null, "count": null}], "status": "complete", "initial_state": {"oleic_anhydride": 500.0, "oleate": 10.0, "H": 1e-08}, "inflow": null, "outflow": null, "extras": {"interaction_law": {"name": "Marangoni flow driven by interfacial hydrolysis (onboard fuel)", "configuration": "onboard fuel: the droplet carries its own precursor and moves for minutes to hours, until the fuel runs out or waste accumulates", "steps": ["oleic anhydride meets water at the oil-water interface and hydrolyses to two oleic acids, which deprotonate to oleate and protons", "the reaction is not even over the surface, so the local pH is not even", "interfacial tension rises as local pH falls (maximum at pH 9), so the tension is not even either", "the tension gradient is a Marangoni force tangential to the surface, which drives Marangoni flow; once the initial symmetry breaks by fluctuation a pair of convective vortices organises inside the droplet", "the convective flow brings fresh precursor to one pole and releases product at the other, which sustains the imbalance instead of equilibrating it", "the droplet moves along the axis of the convection, leaving a low-pH trail of expelled surfactant behind it"], "sensor": "the oil-water interface itself", "motor": "the convective flow structure inside the droplet", "chemotaxis": {"stimulus": "pH gradient, self-generated or externally imposed", "direction": "up the gradient, toward the highest pH", "source": "Banzhaf & Yamamoto (2015) section 19.2.5; Hanczyc & Ikegami (2010) section 3.1"}, "tension": {"source": "Hanczyc & Ikegami, Artificial Life 16(3):233-243 (2010), figure 2 and section 3.1; pendant-drop tensiometry, each point in triplicate", "bare_nitrobenzene_mN_per_m": 27.0, "maximum_at_pH": 9.0, "bulk_pH": 11.0, "local_pH_minimum": 7.0, "oleate_mM": 10.0, "relation": "interfacial tension increases as pH decreases from the bulk pH 11, reaching a maximum at pH 9; at pH 11 the tension is already low, so producing more oleate has little further effect and it is the local drop in pH, not the extra surfactant, that moves the droplet"}, "refs": ["[365]", "[364]", "[363]"]}, "analysis": {"system": "oleic-anhydride", "droplet": {"volume_uL": 20.0, "radius_mm": 1.6838903009606296, "diameter_mm": 3.3677806019212593, "surface_area_mm2": 35.631774804909234, "surface_to_volume_per_mm": 1.781588740245462}, "concentration_units": "mM", "pH": 11.0, "surfactant_mM": 10.0, "reactive": true, "motion_is_simulated": false, "why_no_trajectory": "the propulsion mechanism is published qualitatively (a Marangoni force set by the interfacial-tension gradient) but no accessible source gives the force law or a droplet speed, so Chemart records the mechanism and the measured behaviour instead of integrating a trajectory", "fuel_budget": {"precursor_mol": 9.999999999999999e-06, "precursor_umol": 10.0, "surfactant_per_precursor": 2, "surfactant_mol": 1.9999999999999998e-05, "surfactant_umol": 20.0}, "tension": {"source": "Hanczyc & Ikegami, Artificial Life 16(3):233-243 (2010), figure 2 and section 3.1; pendant-drop tensiometry, each point in triplicate", "bare_nitrobenzene_mN_per_m": 27.0, "maximum_at_pH": 9.0, "bulk_pH": 11.0, "local_pH_minimum": 7.0, "oleate_mM": 10.0, "relation": "interfacial tension increases as pH decreases from the bulk pH 11, reaching a maximum at pH 9; at pH 11 the tension is already low, so producing more oleate has little further effect and it is the local drop in pH, not the extra surfactant, that moves the droplet"}, "above_tension_maximum": true, "overall_reaction": "oleic_anhydride + H2O -> 2 oleate + 2 H (hydrolysis followed by deprotonation of both oleic acids)", "measured_behaviour": {"source": "Horibe, Hanczyc & Ikegami, Entropy 13(3):709-719 (2011), doi:10.3390/e13030709 (open access)", "oil": "fresh oleic anhydride mixed with nitrobenzene at 1:1 v/v", "aqueous": "10 mM oleate micelles at pH 11", "volumes_uL": [1.0, 3.0, 10.0, 20.0, 30.0, 50.0], "modes": ["directional", "circular", "fluctuating", "vibrating"], "modes_by_volume_uL": {"1": ["circular", "fluctuating"], "20": ["directional", "circular", "fluctuating"], "50": ["vibrating", "circular", "fluctuating"]}, "vibrating_only_at_uL": [50.0], "collective_attraction_uL": [3.0, 20.0], "no_collective_attraction_uL": [50.0], "observation_minutes": 60.0, "window_minutes": 20.0, "sampling_interval_s": 1.0, "binning_interval_s": 20.0, "mean_coefficient_of_restitution": 1.0, "findings": ["velocity falls and turning angle rises as the droplet ages", "turning angle is negatively correlated with velocity: droplets change direction while stopped", "the reaction happens at the surface, so the reaction rate is set by droplet size, and it weakens as the oil volume is consumed", "spontaneous (non-collision) events give a coefficient of restitution with mean around 1, and values above 1 when the reaction is re-activated", "two droplets of 3 or 20 uL stay closer together than two droplets in separate dishes, and the attraction weakens over time; 50 uL droplets, whose convective flow is unstable, show no attraction"]}, "sizes_and_timings": {"source": "Hanczyc & Ikegami, Artificial Life 16(3):233-243 (2010)", "oil": "oleic anhydride in nitrobenzene at 0.5 M (appendix A.2)", "aqueous": "oleate micelles at pH 11, NaOH-adjusted (appendix A.1)", "diameter_range": "a few hundred microns to a few centimetres", "convective_droplet_diameter_mm": 0.1, "no_shape_fluctuation_below_um": 100.0, "shape_fluctuation_up_to_cm": 0.5, "shape_series_uL": [1.0, 5.0, 10.0, 30.0], "frame_interval_s": 8.0, "onset": "the droplet starts moving within seconds of the oil meeting the water", "without_precursor": "droplets still move chemotactically in a pH gradient, but the motion is not sustained and stops within a few seconds once the tension imbalance is equilibrated", "mechanism_shift": "above a few hundred microns self-movement shifts from convection-driven to shape-driven, and a horseshoe shape best supports straight directional motion"}, "modes_at_this_volume": ["directional", "circular", "fluctuating"], "size_series": [{"volume_uL": 1.0, "radius_mm": 0.6203504908994001, "diameter_mm": 1.2407009817988002, "surface_area_mm2": 4.83597586204941, "surface_to_volume_per_mm": 4.835975862049408, "modes": ["circular", "fluctuating"], "collective_attraction": null, "precursor_mol": 5e-07, "precursor_umol": 0.5, "surfactant_per_precursor": 2, "surfactant_mol": 1e-06, "surfactant_umol": 1.0}, {"volume_uL": 3.0, "radius_mm": 0.8947002289396495, "diameter_mm": 1.789400457879299, "surface_area_mm2": 10.059235159318462, "surface_to_volume_per_mm": 3.3530783864394875, "modes": null, "collective_attraction": true, "precursor_mol": 1.5e-06, "precursor_umol": 1.5, "surfactant_per_precursor": 2, "surfactant_mol": 3e-06, "surfactant_umol": 3.0}, {"volume_uL": 10.0, "radius_mm": 1.3365046175719757, "diameter_mm": 2.6730092351439514, "surface_area_mm2": 22.446611560909467, "surface_to_volume_per_mm": 2.244661156090947, "modes": null, "collective_attraction": null, "precursor_mol": 4.9999999999999996e-06, "precursor_umol": 5.0, "surfactant_per_precursor": 2, "surfactant_mol": 9.999999999999999e-06, "surfactant_umol": 10.0}, {"volume_uL": 20.0, "radius_mm": 1.6838903009606296, "diameter_mm": 3.3677806019212593, "surface_area_mm2": 35.631774804909234, "surface_to_volume_per_mm": 1.781588740245462, "modes": ["directional", "circular", "fluctuating"], "collective_attraction": true, "precursor_mol": 9.999999999999999e-06, "precursor_umol": 10.0, "surfactant_per_precursor": 2, "surfactant_mol": 1.9999999999999998e-05, "surfactant_umol": 20.0}, {"volume_uL": 30.0, "radius_mm": 1.927573210407049, "diameter_mm": 3.855146420814098, "surface_area_mm2": 46.690833590177625, "surface_to_volume_per_mm": 1.556361119672588, "modes": null, "collective_attraction": null, "precursor_mol": 1.4999999999999999e-05, "precursor_umol": 14.999999999999998, "surfactant_per_precursor": 2, "surfactant_mol": 2.9999999999999997e-05, "surfactant_umol": 29.999999999999996}, {"volume_uL": 50.0, "radius_mm": 2.285390748670416, "diameter_mm": 4.570781497340832, "surface_area_mm2": 65.63429036687326, "surface_to_volume_per_mm": 1.3126858073374656, "modes": ["vibrating", "circular", "fluctuating"], "collective_attraction": false, "precursor_mol": 2.4999999999999998e-05, "precursor_umol": 24.999999999999996, "surfactant_per_precursor": 2, "surfactant_mol": 4.9999999999999996e-05, "surfactant_umol": 49.99999999999999}]}, "space": {"kind": "continuous", "dimensions": 2, "units": "mm", "droplet": {"volume_uL": 20.0, "radius_mm": 1.6838903009606296, "diameter_mm": 3.3677806019212593, "surface_area_mm2": 35.631774804909234, "surface_to_volume_per_mm": 1.781588740245462}, "vessels": [{"what": "glass slide with a concave depression", "diameter_mm": 15.0, "aqueous_uL": 100.0, "source": "Hanczyc & Ikegami (2010), appendix A.3"}, {"what": "glass dish with a quartz base", "diameter_mm": 35.0, "base_diameter_mm": 27.0, "aqueous_uL": 800.0, "source": "Hanczyc & Ikegami (2010), appendix A.4; the 27 mm base is the 'diameter of the liquid recipient' in the book's figure 19.11"}, {"what": "glass dish, behavioural modes", "diameter_mm": 100.0, "aqueous_uL": 20000.0, "source": "Horibe et al. (2011), experimental"}, {"what": "glass dish with a triangular glass wall, restitution", "diameter_mm": 60.0, "wall_length_mm": 48.0, "aqueous_uL": 5000.0, "source": "Horibe et al. (2011), experimental"}, {"what": "glass dish with a glass base, two-droplet collective behaviour", "diameter_mm": 35.0, "base_diameter_mm": 27.0, "aqueous_uL": 2000.0, "source": "Horibe et al. (2011), experimental"}], "positions": "not simulated: this entry returns the published interfacial chemistry and the published assay geometry, not a droplet trajectory"}, "phases": {"oil": ["nitrobenzene", "oleic_anhydride"], "aqueous": ["H2O", "oleate", "H"], "interface": ["oleic_acid"]}, "buffered": ["H2O"], "units": {"initial_state": "mM; oil-phase and aqueous-phase species are listed together, see extras['phases'] for which is which", "droplet_volume": "uL (1 uL = 1 mm^3)"}, "conservation": [{"name": "oleoyl groups", "vector": {"oleic_anhydride": 2, "oleic_acid": 1, "oleate": 1}}]}, "chemistry": "self-propelled-droplets", "params": {"system": "oleic-anhydride", "droplet_volume_uL": 20.0, "precursor_M": 0.5, "surfactant_mM": 10.0, "pH": 11.0}, "seed": 1}