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Akihiko Sugimura 1 and Geoffrey R. Luckhurst 2 1 Osaka Sangyo University, Japan 2 Southampton University, U.K. 1.Background of the investigation 2.Advantages.

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Presentation on theme: "Akihiko Sugimura 1 and Geoffrey R. Luckhurst 2 1 Osaka Sangyo University, Japan 2 Southampton University, U.K. 1.Background of the investigation 2.Advantages."— Presentation transcript:

1 Akihiko Sugimura 1 and Geoffrey R. Luckhurst 2 1 Osaka Sangyo University, Japan 2 Southampton University, U.K. 1.Background of the investigation 2.Advantages of Deuterium NMR spectroscopy 3.General and curious director alignments 4.Discussion on the curious director alignment Layout of the talk Director dynamics for a low molar mass nematic liquid crystal Director dynamics for a low molar mass nematic liquid crystal Int. Conf. on the Hierarchical Structures in Complex Fluids Beijing, 4-8 th of July, 2011 (presented on 7 th of July)

2 Thin nematic liquid crystal cell Glass substrate L.C. bulk Bulk surface Basic interest is in understanding the nature of the spatial director distribution. For this aim the field-induced director alignments are investigated. alignments are investigated. Methodology? Aim of the investigation

3 A sample is low molar mass nematics confined in a thin sandwich cell. How to produce a non-equilibrium state of the director orientation in the strong magnetic field. Spinning as used for polymer nematics Spinning the sample tube Magnetic field Electric field Field-induced director alignment by the electric and magnetic fields Nematic cell B E NMR spectroscopy

4 The quadrupolar splitting ratio, ( )/ 0, gives the angle made by the director with the magnetic field. =0 /kHz =54.7 =90 B n B n 0 Advantages of Deuterium NMR spectroscopy

5 SCM LC cell Ultra Sonic Motor Receiver Coil U.S.M Glass plate TURN-ON TURN-OFF NCCCCCC HD D HHH HHH H H Time-resolved and -averaged measurements during the director relaxation processes are possible. [1] G. R. Luckhurst, T. Miyamoto, A. Sugimura, T. Takashiro, B. A. Timimi, Journal of Chemical Physics, 114, 10493 (2001). Experimental geometry Experimental geometry [1]

6 Static properties of the director alignments Static properties of the director alignments

7 E Bn EBn nE B α=85.1° T=20 C Voltage dependence of the NMR spectra (1) Uniform director alignment

8 E Bn EBn nE B α=89.1° T=20 C Voltage dependence of the NMR spectra (2) Uniform director alignment Broadening of the spectral line-shape Uniform director alignment Broadening of the spectral line-shape

9 Uniform director alignment can be generally described by the continuum theory for < 90. Uniform director alignment can be generally described by the continuum theory for < 90. General understanding

10 Voltage dependence of the static NMR spectra α=89.9° T=20 C EBn EBn E Bnn Voltage dependence of the NMR spectra for 90 Voltage dependence of the NMR spectra for 90 2D powder pattern Non-uniform director alignment

11 What causes a non-uniform static director alignment? What causes a non-uniform static director alignment?

12 The cell used in the measurements has an inhomogeneity of the film thickness with 0.25% No director deformation along the z-axis, No surface anchoring effect for a thicker cell without any surface treatments are a function of x. Linear change of the film thickness along the x-axis causes an electric field gradient. That is, Inhomogeneity of the film thickness causes a spread of the range of the director orientation. Inhomogeneity of the film thickness causes a spread of the range of the director orientation. Inhomogeneity of the film thickness

13 y-axis top middle bottom Measured 90 points of the cell Top line Middle line Bottom line Measurement of the film thickness

14 Gaussian variation for the inhomogeneity of the film thickness is assumed. Profile of the film thickness in the bulk

15 It is clear that the inhomogeneity of the film thickness is a dominant factor to cause uniform and non-uniform director alignments. It is also apparent that there are some other factors influencing the director alignment. As a basic idea, lets return to the continuum theory to understand the curious director distribution.

16 Cell structure Elastic deformation induced by Teflon spacers Cross section of the cell 5CB-d 2

17 Torque balance equations Coordinate system In the bulk at the surface [2] at the middle of the bulk Teflon spacer B n E z e min W y x Glass substrate Sliced piece [2] A. Sugimura, G. R. Luckhurst, and Z. Ou-Yang, Physical Review E, 52, 681 (1995). Torque Balance Equations

18 Conservation of the director density Torque balance equations Director distribution function at the boundary at the middle of the bulk 5CB-d 2 Cross section of the cell Director probability density function is analytically derived for our experimental geometry. Director probability density function is analytically derived for our experimental geometry. Director probability density function

19 (a) (b) =89.1 =89.9 Voltage dependence of the director distribution

20 T=20 C, α=89.1° T=20 C, α=89.9° Comparison of the recorded spectra with those simulated Comparison of the recorded spectra with those simulated

21 1.A preliminary model has been proposed to understand the factors influencing the nature of the director distribution for a low molar mass nematic. 2.It has been found that the director alignment by Teflon surfaces is essential in order to account for some subtle features of the NMR spectra as the angle between the two fields approaches 90. 3.In addition some of the major spectral features are found to result from the inhomogeneity in the cell thickness. 1.A preliminary model has been proposed to understand the factors influencing the nature of the director distribution for a low molar mass nematic. 2.It has been found that the director alignment by Teflon surfaces is essential in order to account for some subtle features of the NMR spectra as the angle between the two fields approaches 90. 3.In addition some of the major spectral features are found to result from the inhomogeneity in the cell thickness. [3] H. Hamasuna, G. R. Luckhurst, A. Sugimura, B. A. Timimi, H. Zimmermann, Phys. Rev. E, in the press. Summary for the static properties Summary for the static properties [3]

22 1.The static and dynamic director distributions of 5CB- d 2 were investigated using a combination of deuterium NMR spectroscopy and the continuum theory. 2.The experimental results can be understood in terms of the intrinsic director distribution affected by the external fields. 3.The challenge now is to see what kinds of features such as director fluctuation or deformation are responsible for the intrinsic distribution and how this is created during the director relaxation process. 1.The static and dynamic director distributions of 5CB- d 2 were investigated using a combination of deuterium NMR spectroscopy and the continuum theory. 2.The experimental results can be understood in terms of the intrinsic director distribution affected by the external fields. 3.The challenge now is to see what kinds of features such as director fluctuation or deformation are responsible for the intrinsic distribution and how this is created during the director relaxation process. CONCLUSIONS OF THE TALK

23 1.Graduate students of my group (Osaka Sangyo University) 2.Dr. Bakir A Timimi (University of Southampton, UK) 3.Dr. Herbert Zimmermann (Max-Planck-Institute, Heidelberg, Germany ) 4.Prof. Edward T. Samulski (University of North Carolina, USA) 5.Prof. Jim W. Emsley (University of Southampton, UK) 6.Dr. Tetsuo Miyamoto (JEOL) 7.Dr. Anu Kantola (University of Oulu, Finland) 8.Dr. Peter J. Le Masurier (Kodak) 9.Dr. Christopher J Dunn (Merck UK) 10.Dr. Mario Cifelli (University of Pisa, Italy) 11.The Ministry of Education, Culture, Sports, Science and Technology of Japan 12.The Japan Society for the Promotion of Science 13.The Royal Society, UK 14.JEOL AcknowledgementsAcknowledgements


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