Activity measurements at the microfluidic scale: towards osmotic pressure measurements

GDR CNRS AMC2 October 20-22, Sète Activity measurements at the microfluidic scale: towards osmotic pressure measurements ZIANE Nadia Supervisors: J. Lengand JB. Salmon

Introduction • Dialysisprocess: • Perfect control of the environment • Concentration of non-volatile solutes in aqueous solutions • Towards phase diagrams • Microfluidicsinterests: • Lineargeometry • Easy observations of confinedvolume • Easyanalysis and fastexperiments

Microfluidic chip L0 PDMS h PDMS membrane e = 30 – 40 µm rectangularchannel w = 50 – 60 µm h = 30 – 40 µm L0 = 1,5 – 3 cm nL glass slide Randall and al., 2005 Salmon and Leng, 2010

Water pervaporation

Channel geometry: confined drop Step 1 Filldead-end microchannels Step 2 Injection of a fluorinatedoil or air Step 3 Evaporation of confineddroplets 60 µm L0 = 1,5-3 cm Noblin and al., 2008

Simple model for solutions and dispersions Continuousand uniformconcentration  (t) = 0 L0 /L(t) Evaporation rate controlled by activity  • Hypotheses: • No initial gradients • Pe = hV/D < 1  no vertical gradients • Pervaporation rate uniformalong x • Quasi steadyregime for water pervaporation

Absorbance measurements Bleu brillantFCF at 0,1 mM (10x) 200 µm  No gradients for molecular solutions

Fluorescence meausurements Fluorescent latex (40x) Diameter = 20 nm 50 µm • Gradients at x=0 : • evidence of « leakage » velocity x=Lg x=0 J. Angly and al., 2012

Fluorescence meausurements Fluorescent latex (40x) Diameter = 200 nm 50 µm • Gradients at x=0 : • evidence of « leakage » velocity • Gradients at x=Lg: • is not true < 1 x=Lg x=0 h T = h/V TD = h²/D

Pure water Image analysis Time ~ 1h30

Pure water Vf ~ 0,52 µm/s Te ~ 1500 s  Accurate estimation of humidyusing 1D model

Binary water/glycerol mixture Ninni and al., 2000 Water/glycerol2% v/v Room humidity = 60% h = 26 µm, time ~ 2 hr

Binary water/glycerol mixture Te ~ 2200 s

Binary water/glycerol mixture

Conclusion & outlooks • Robust measurements of the activity of aqueous solutions at the nanoliterscale • New chip design

Conclusion & outlooks Estimation of liquid-liquidtransition of ternary system PEG/water/ammonium sulfate PEG: 5% w/w Ammonium sulfate: 5% w/w Time ~ 1h20

Conclusion & outlooks Microdialysisprocess Hsieh, 2007 Jensen and al., 2008 • Development and characterization of new microfluidic devices including dialysis membranes • Control of osmotic exchanges at a nanoliter scale • Quantitative measurements of thermodynamic properties of complex fluids

Thankyou Questions ?

Activity measurements at the microfluidic scale: towards osmotic pressure measurements