Dynamiczna kontrola separacji ładunków elektrostatycznych w układach miękkiej materii

Transcription

1 Dynamiczna kontrola separacji ładunków elektrostatycznych w układach miękkiej materii Tomasz Szymborski, Natalia Ziębacz, Piotr Korczyk, Jan Tobiś, Olgierd Cybulski, Stefan Wieczorek, Andrzej Żywocioski, Robert Hołyst i Piotr Garstecki Department of Soft Condensed Matter Institute of Physical Chemistry Polish Academy of Sciences Institute of Fundamental Technological Research PAS, 9th December

2 controlling soft matter with electric fields dynamic separation of charge in LC can we see the motion of ions with an optical microscope? electrocoalescence ionic contribution to polarization of droplets phase separation in a blend of LC and PS 1000 fold increase of the rate of phase separation summary 2

3 electrostatic forces 3

4 electrostatic potential 1 R any other behavior? control the electrostatic interactions with electric fields? exp(-r/d) R 4

5 dynamic separation of charge in LC can we see the motion of ions with an optical microscope? electrocoalescence ionic contribution to polarization of droplets phase separation in a blend of LC and PS 1000 fold increase of the rate of phase separation summary 5

6 temperature dynamic separation of charge in LC 6

7 dynamic separation of charge in LC experiment 7

8 dynamic separation of charge in LC needle through DC 8

9 dynamic separation of charge in LC needle below AC, high frequency 9

10 dynamic separation of charge in LC electric field U U? 10

11 frequency dynamic separation of charge in LC electric field 10 2 Hz sharp 10 1 Hz transition at f CR 10 0 Hz 11

12 dynamic separation of charge in LC MHPPHBC ferroelectric LC 12

13 dynamic separation of charge in LC 8CB non-ferroelectric LC 13

14 dynamic separation of charge in LC 14

15 (length of the finger) amplitude [pixels] dynamic separation of charge in LC time [frames] 15

16 dynamic separation of charge in LC t CR = (1/2)(1/f CR ) 16

17 dynamic separation of charge in LC critical frequency (f CR ) is linear in voltage da/dt is linear in voltage f CR does not depend on the diameter of the island Island diameter: f CR does not depend on the thickness of the island (repetitive experiments on new films yield very similar values of f CR ) 17

18 dynamic separation of charge in LC 1. We estimate the EC mobility via literature gives m 2 V -1 s -1 for electrophoretic mobility of ions in LCs. Electrophoretic mobility for different ion diameter and charge q (e) R (Å) µ (m 2 V -1 s -1 ) 1 1 3, , , We estimate the distance d ions traveled by the ions within t = (2f CR ) -1 d ions compares well to the Debye screening length 1 : d ions ranged from d ions = 50 nm for NPOB in SmA phase to d ions = 460 nm for MHPPHBC in the SmC* phase. These values are similar in magnitude to the reported value of the Debye screening length of 0,7 µm 1 in CS1015 SmC* phase. [1] J.-B. Lee, R. A. Pelcovis and R. B. Meyer, Phys. Rev. E, 2007, 75,

19 dynamic separation of charge in LC ~ Debye Length microscopic separation of charges 19

20 dynamic separation of charge in LC high frequencies ions oscillate with amplitude < Debye length low frequencies ions osicillate with amplitudes > Debye length microscopic separation of charges the boundary of the meniscus becomes charged and undergoes an electrohydrodynamic instability macroscopic separation of charges 20

21 (length of the finger) amplitude [pixels] dynamic separation of charge in LC low frequencies ions osicillate with amplitudes > Debye length microscopic separation of charges the boundary of the meniscus becomes charged and undergoes an electrohydrodynamic instability macroscopic separation of charges time [frames] 21

22 dynamic separation of charge in LC we can visualize (indirectly) the motion of ions instability only ensues when ions are separated over distances larger than the Debye length macroscopic separation of charges, slow relaxation dynamically controlled 22

23 dynamic separation of charge in LC can we see the motion of ions with an optical microscope? electrocoalescence ionic contribution to polarization of droplets phase separation in a blend of LC and PS 1000 fold increase of the rate of phase separation summary 23

24 electrocoalescence E U = 2.3 kv DC U = 400 V L. Fidalgo et al. Angew. Chem. Int. Ed. 2008, 47 R. Link et al. Angew. Chem. Int. Ed. 2006, 45 24

25 electrocoalescence Hexadecane + Span80 water 5 mm 25 mm HV 25

26 electrocoalescence 1 mm AC EF Oil phase: hexadecane + 2% SPAN 80 Droplets: water + dye 26

27 1 khz, 100 V 1 khz, 500 V 1 khz, 5000 V 27

28 electrocoalescence coalescence stable 28

29 electrocoalescence NaCl 29

30 electrocoalescence Image analysis number of droplets total contour 30

31 ~ n electrocoalescence influence of voltage 1,0 0,9 0,8 0,7 0,6 0,5 0,4 U=120 V 0,3 U=180 V 0,2 U=240 V U=360 V 0,1 U=600 V 0,0 0,1 0,2 0,3 0,4 0,5 time (s) 31

32 ~ n electrocoalescence influence of voltage 1,00 f=5 khz, U=240 V 0,95 0,90 0,85 0,80 0,75 0,70 0,65 0,0 t 0,1 0,2 0,3 0,95 time (s) 32

33 electrocoalescence influence of voltage AC (nm) distance calculated for Cl - distance calculated for Na + Debye length for 10-4 M NaCl ( D =30,4 nm) C = 10-4 M NaCl /t 0, U (V) U (V) 33

34 electrocoalescence influence of frequency 4,0 3, distance calculated for Cl distance calculated for Na + Debye length for 10-4 M NaCl ( D =30,4 nm) C = 10-4 M NaCl 1/t 0,95 3,0 2,5 2,0 AC (nm) , ,0 f (Hz) 0,5 0, frequency (Hz) 34

35 dynamic separation of charge in LC can we see the motion of ions with an optical microscope? electrocoalescence ionic contribution to polarization of droplets phase separation in a blend of LC and PS 1000 fold increase of the rate of phase separation summary 35

36 phase separation in polymer & liquid crystal blend Polymer-polystyrene H H C C, H n. Liquid crystal-5cb N C CH 3 36

37 phase separation in polymer & liquid crystal blend polymer-dispersed liquid crystals (PDLCs) polymer-stabilized liquid crystals (PSLCs) PDLCs were invented at Kent State University in

38 phase separation in polymer & liquid crystal blend quench one phase region (perfect mixing) binodal curve two phase region (separation) spinodal curve Polymer-rich phase volume fraction Liquid crystal-rich phase 38

39 phase separation in polymer & liquid crystal blend distance mm the sample glass ITO 39

40 phase separation in polymer & liquid crystal blend 80 S(q,t) [a.u.] q max ~ 1/L(t) q [mm -1 ] 100 µm 40

41 phase separation influence of voltage 41

42 time (s) phase separation influence of frequency 10 3 q max = 2 µm -1 E = 3.3 Vµm -1 frequency (Hz) 42

43 dynamic separation of charge in LC can we see the motion of ions with an optical microscope? phase separation in a blend of LC and PS 1000 fold increase of the rate of phase separation electrocoalescence ionic contribution to polarization of droplets summary 43

44 summary dynamic control of the efficiency of screening separation of charges at the microscale possibility of macroscopic separation via other mechanisms uses/applications: electrocoalescence phase separations electrokinetic transport? ordering of colloids? 44

45 Laboratory of Complex Fluids and Microfluidics Institute of Physical Chemistry, Polish Academy of Sciences Thank you! 45