Morphology and Rheology of Immiscible Polymer Blends under Electric Fields

Transcription

1 Morphology and Rheology of Immiscible Polymer Blends under Electric Fields H. Orihara 1, Y. Nishimoto 1, K. Aida 1, Y. H. Na 1, T. Nagaya 2 1 Hokkaido University, 2 Oita University

2 Immiscible polymer blends Rheology Morphology Close relationship Doi and Ohta, 1991 Constitutive equations Interface tensor Interface area density Excess stress from Interfacial tension(batchelor, Doi, Onuki) Experimental tests (Takahashi et al.)

3 Effect of electric fields Immiscible polymer blend electro-rheological (ER) fluid Inoue et al LCP OIL CH 3 CH 3 SiO (CH 2 ) 3 m CH 3 SiO CH 3 n CH 3 PDMS PIB OCH 2 CH 2 O COO CN MPS ER effect is due to morphological change. Tajiri, K., K. Ohta, T. Nagaya, H. Orihara, Y. Ishibashi, M. Doi and M. Inoue, J. Rheol. 41, (1997). Kimura, H., K. Aikawa, Y. Masubuchi, J. Takimoto, K. Koyama and K. Minagawa, Rheol. Acta (1998). 3D observations!

4 System combining CLSM and rheometer CSU22, YOKOGAWA MCR301, Anton Paar

5 Outline Subjected to a step electric field without shear flow 1. Coalescence of droplets 2. Shear modulus of columnar structure Subjected to a step electric field with shear flow 3. Interface tensor 4. Separation of viscous, interfacial and electric stresses 5. Relationship between excess stress and interface tensor

6 Experiment Rheometer Shear flow CSLM Glass Plate with ITO Sample Objective Lens Gap: 200mm, Diameter: 35 mm Focal plane z y x Piezo-actuator 5Hz Frame rate 500 f/s 400x390x50 pixels 163x163x56 µm 3 Electric field Blend of LCP and PIB(Polyisobutylene)

7 Coalescence of droplets and column formation without shear flow

8 Blend: LCP(65 Pa s)/pib(7.8 Pa s) at 25 Preshear of 200 s-1 for 20 min Application of ac electric field (512 Hz) without shear flow LCP:PIB=1:6 (φ =0.14) 113mm E Coalescence 0s 168mm 20 s 35 s 100 s (a) 2 kvamp/mm Elongation 0s 20 s 35 s (b) 4 kvamp/mm 100 s

9 Movies (8 times as fast) 2 kv amp /mm 5 kv amp /mm

10 3D spatial correlation function Average lenghts of semi-axes Spheroid

11 Scaling property Assuming that all the droplets keep spherical shape, Scaling property holds? Yes? No!

12 Growth kinetics on the basis of hierarchical model E t=0 Viscous friction Dipole-dipole interaction Exponential growth

13 Volume fraction dependence

14 5/3

15 Sphere Spheroid Deformation t (Torza et al, 1971)

16 Numerical calculation

17 Storage Shear Modulus of Columnar Structure 75µm E 200µm 100 sec later after applying an ac electric field with an amplitude of 5kV/mm and a frequency of 2Hz.

18 Emergence of elasticity LCP:DMS=1:6 Oscillatory measurement f=2 Hz

19 Dependence of G on electric field strength

20 Electric stress on slant column Interfacial stress Electric stress

21 Interfacial tension E dependence f dependence

22 Transient process subjected to a step electric field with shear flow

23 Transient shear stress Blend with the same viscosity LCP:PIB=1:6 (η=33.5 Pa s at 28 ) E amp =6 kv/mm (1000Hz) E on

24 3D images in the transient process E z 163µm 56µm y 163µm x Flow 0 s 1 s 2 s 3 s 4 s

25 Movie in the transient process E 163µm z 56µm y 163µm x Flow Real time speed

26 Interface tensor Symmetrical and traceless Sphere Ellipsoid Slant ellipsoid

27 Time evolution of interface tensor diagonal spheroid

28 Off-diagonal elements shear stress close relation -q zx

29 Mapping from structure to ellipsoid Structure Ellipsoid

30 c a b

31 z E y Flow x Real time speed

32 (Batchelor 1970, Doi 1987, Onuki 1987) Maxwell stress tensor

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35 c?

36 Electric stress Electric torque on ellipsoid Shear flow Electric stress (Halsey et al., 1992)

37 240 Pa approximation

38 200 Pa (theory 240 Pa)

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40 Relaxation process to droplets after removing E From columnar structure E off E on

41 Real time speed

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44 From network structure E off E on

45 Real time speed

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48 Removal of both electric field and shear flow From columnar structure E on

49 Real time speed

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51 From network structure E on

52 Real time speed

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54 Summary Subjected to a step electric field without shear flow 1. Coalescence of droplets in electric filed Hierarchical model is applicable Exponential growth Sphere Non-exponential growth Spheroid 2. Shear modulus of columnar structure Emergence of elasticity under electric fields Dependences of field strength and frequency

55 Subjected to a step electric field under shear flow 3. 3D images 4. Separation of viscous, interfacial and electric stresses 5. Interface tensor

56 Future subject Structure Can Doi-Ohta theory describe the change from droplet-dispersed structure to network one? Topology changes!

57 Different viscosities (Batchelor, 1970)

58 Calculation of interface tensor