General Conclusion

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Chapter 6

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polyimide is not big enough. In this regard, research work on polyimide alignment thin film by optical SHG needs a development for improving the performances of LCDs device. Therefore, I would like to contribute to developing the research work on polyimide alignment thin film by optical SHG.

In this study, in collaboration with JSR Co. Ltd., a novel rubbed and unrubbed PI with steroidal structure side chain diamine A (PAA-1) were synthesized. The PI film was rubbed by a rubbing machine using nylon cloth. The rotational speed of the roller and the translational speed were 400 rpm and 30 mm/sec, respectively. The thickness of the PI film was 100 nm. So far as I know, there has been no SHG measurement of polyimide polymers with steroidal structures. This study is the first report to find the molecular orientation of side chain of diamine A (PAA-1) by applying SHG measurement. In this regard, I observed the rotational and polarization dependence of SHG intensity from the both unrubbed and rubbed PI thin films with steroidal structure side chains diamine A. The SHG patterns from the unrubbed PI films is isotropic. In this case, the molecular distribution is polar with respect to the surface normal and the chains are oriented in random directions. Οn the other hand, the characteristic anisotropic patterns of the rubbed PI thin film samples are observed due to the rubbing.

In order to find the molecular orientation of the rubbed polymer chains, I assumed that polymer units have one dominant component _{𝛽𝛽𝜉𝜉𝜉𝜉𝜉𝜉}⁽²⁾ along the molecular axis 𝜉𝜉. The individual components of the nonlinear susceptibility _χijk⁽²⁾ of PI film surface can be calculated via _{𝛽𝛽𝜉𝜉𝜉𝜉𝜉𝜉}⁽²⁾ and give the information about the orientation and arrangement of the molecules of the rubbed polyimide layer. Previously, in most reports, the

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amplitude of second order nonlinear susceptibility components, _{|𝜒𝜒𝑖𝑖𝑖𝑖𝑖𝑖}⁽²⁾_| were considered as real values for the determination of the molecular orientation of rubbed polyimide. However, 𝜒𝜒_{𝑖𝑖𝑖𝑖𝑖𝑖}⁽²⁾has not only a real part but also imaginary part (Imχ_ijk⁽²⁾)

because 𝜒𝜒_{𝑖𝑖𝑖𝑖𝑖𝑖} is a complex number, and it is given by χ_ijk= |𝜒𝜒_{𝑖𝑖𝑖𝑖𝑖𝑖}|exp (𝑖𝑖𝜑𝜑_{𝑖𝑖𝑖𝑖𝑖𝑖}), where 𝜑𝜑_{𝑖𝑖𝑖𝑖𝑖𝑖} is the phase of the 𝜒𝜒 component, which appears as a phase shift between

SHG field and fundamental field. Therefore, 𝜒𝜒_{𝑖𝑖𝑖𝑖𝑖𝑖} has no longer a real number only but with the imaginary part due to the phase shift. The imaginary terms,(Imχ_ijk⁽²⁾) associated with the fluctuation dielectric property of material. This fluctuation field will create inhomogeneous molecular orientation in the surface. Therefore, in reality, it is necessary to consider the 𝜒𝜒 component in the complex plane. In this regard, I analyzed the SHG patterns with the second order nonlinear susceptibility components

𝜒𝜒_{𝑖𝑖𝑖𝑖𝑖𝑖}⁽²⁾ in complex plane, which is the first report in my thesis. I took the magnitude of

the absolute value from _{𝜒𝜒𝑥𝑥𝑥𝑥𝑥𝑥}⁽²⁾ and 𝜒𝜒_{𝑧𝑧𝑥𝑥𝑥𝑥}⁽²⁾ components, and finally I determined the average tilt angle of the polymer main chain toward the rubbing direction as _{𝜃𝜃𝑎𝑎𝑎𝑎𝑎𝑎}= 15.7^o ± 1.8⁰. The strong point in this analysis is that I considered the values of _χijk⁽²⁾ elements in the complex plane.

Before the rubbing treatment, the polymer chains are oriented randomly with respect to the surface normal. After the rubbing treatment, the side chains are thought to be pulled on the surface. The main zigzag chains lying perpendicular to the rubbing direction are pulled and in average tilt in the rubbing direction. This happened due to the flexibility of the zigzag chains, which permits the change of the structure by the rubbing treatment.

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This study established the first step to the development and application of polyimide films with steroidal side chains using SHG spectroscopy in the liquid crystal device technology.

Appendix I:

Synopsis of Minor Research

In cellular and molecular biology, cell culture is a significant method, which provided a model systems for studying of the physiology and biochemistry of cells. HEK293 cells and HeLa cells were cultured through Dulbecco's Modified Eagle Medium (DMEM) containing 10% fetal bovine serum (FBS) in a standard CO2 incubator, where CO2incubators allow to better control of culture conditions. Cell passages were performed using standard trypsin/EDTA method. Cell density was estimated by using an erythrocytometer (Thoma-type). Cell suspension at the concentration of 10⁷ cells / ml was then prepared. The number of cells were counted by a cell counter in this process. At the last stage of cell culture, the reporter gene plasmid, EGFP/pcs4+, was added to the suspension at the concentration of 0.1 𝜇𝜇g/𝜇𝜇l. On the other hand, a well established technique , electroporation or electropermeabilization was used in which the application of an external electric field pulse leads to an increase in the permeability of cellular membranes. Home-made electrodes were used in this measurement, where the carbon rods with diameter of 2mm was vertically positioned in this instrument. The voltage waveforms were generated by using AWG-50 (Elmos), an arbitral waveform generator with an aid of supplied software. To find optimal condition of electroporation, FPs (first pulse) and SPs (second pulse) were attenuated by a certain factor and different combinations of these pulses were applied and evaluated GFP expression. In this regard,EGFP was investigate in the nucleus and in the cytoplasm of HeLa and HEK293 cells by optical microscope. Transmission image and fluorescence image were taken at different combinations of these pulses, (FPs+SPs) for both type of cells. Finally, the loading efficiency of all cell were found by the fluorescence image in this study.

Appendix II:

Monochromator Sensitivity (1F pico second laser lab)

Due to calibration our experimental data of wavelength 532 nm, I checked the monochromator sensitivity in terms of SHG intensity and both horizontal (p-polarized) and verical(s-polarized) output polarization. For this purpose, I kept the experimental setup according to the following figure:

Figure 1: Optical setup for monochromator sensitivity check

Figure 1. shows that the incident light of wavelenght 532 nm was irradiated on the GaAs (100) sample. The reflected light was passesd through lens, ω-cut filter, 45^o polarizer, horizontal or vertical polarizer to obtain the SHG signal due to compare the SHG intensity difference for horizontal and vertical output polarization in order to check the sensitivity of monochromator.

Table 1: Monochromator Sensitivity

Symbols: P= Horizontal polarization: 0, S= Vertical polarization: 1 Polarization Intensity

(a.u.)

Average Intensity (a.u.)

Ratio: S/P Average (S/P)

0 25.424

0 27.514 26.47

1 28.617 1.07

1 28.176 28.34

0 20.449

0 21.949 21.20

1 22.726 1.19

1 27.977 25.35

0 21.434

0 20.291 20.86

1 28.213 1.23

1 23.453 25.82

0 18.681 1.17

0 16.02 17.35

1 20.86 1.26

1 23.047 21.95

0 18.593

0 18.104 18.34

1 20.976 1.08

1 18.648 19.812

0 20.938

0 17.779 19.35

1 21.73 1.19

1 24.583 23.156

Appendix III:

List of publication/conference proceedings

1. Muhammad Samir Ullah, Shohei Asai, Yousuke Inomata, Khuat Thi Thu Hien, Goro Mizutani, Yoshitaka Murakami and Takashi Okada, “Optical second harmonic generation study of a rubbed polyimide film containing steroidal structure side chains ” e-J. Surf. Sci. Nanotech. Vol. 15 (2017) 7-12.

Conference Proceedings:

1. Muhammad Samir Ullah, Siti Zulaikha Ngah Demon, Kazuki Matsumoto, Yoshihiro Miyauchi, Khuat Thi Thu Hien, Goro Mizutani and Harvey Rutt ; “Nonlinear optical interferometry study at the interface of organic thin films with indium tin oxide”. The 26th Symposium of Association for Condensed Matter Photophysics, Japan, 11-12 December, 2015.

2. Muhammad Samir Ullah, Siti Zulaikha Ngah Demon, Kazuki Matsumoto, Khuat Thi Thu Hien, Goro Mizutani and Harvey Rutt ; “New Method for Analyzing the Second Harmonic Generation Phase from the Interface between Indium Tin Oxide and Organic Layer”. 10th International Symposium on Atomic Level Characterizations for New Materials and Devices ’15, 25-30 October, 2015, in Matsue, Shimane, Japan 3. Kazuki Matsumoto, Siti Zulaikha Ngah Demon, Muhammad Samir Ullah, Goro Mizutani, Khuat Thi Thu Hien; “Detection of the phase shift from dipole layer of the organic semiconductor by Second Harmonic Generation”, The 25th Symposium of Association for Condensed Matter Photophysics, Japan, 12-13 December, 2014.

4. Shohei Asai, Muhammad Samir Ullah, Yousuke Inomata, Khuat Thi Thu Hien, Goro Mizutani, Yoshitaka Murakami and Takashi Okada, “Surface anisotropy characteristics of polyimide alignment film by nonlinear optical method” The 27th Symposium of Association for Condensed Matter Photophysics, Japan, 2-3 December, 2016.

Attended Conferences/Symposium/Workshop

1. Muhammad Samir Ullah, Siti Zulaikha Ngah Demon, Kazuki Matsumoto, Khuat Thi Thu Hien, Goro Mizutani, Heisuke Sakai, Toshinori Matsushima and Hideyuki Murata; “Observation of Optical Second Harmonic Generation Interference Pattern for ITO/MTDATA system”. The 2nd JAIST Poster Challenge, JAIST Festival, Japan, 11 October, 2014.

2. Muhammad Samir Ullah, Siti Zulaikha Ngah Demon, Kazuki Matsumoto, Khuat Thi Thu Hien, Goro Mizutani, Heisuke Sakai, Toshinori Matsushima and Hideyuki Murata; “Optical Second Harmonic Investigation of the ITO/MTDATA/Al OLED Device”, The 7th International Symposium on Surface Science (ISSS-7), Matsui, Shimane, Japan, 2-6 November, 2014.

3. Kazuki Matsumoto, Siti Zulaikha Ngah Demon, Muhammad Samir Ullah, Goro Mizutani, Khuat Thi Thu Hien; “Detection of the Phase Shift from Dipole Layer of the Organic Semiconductor by Second Harmonic Genration”, The 25th Symposium of Association for Condensed Matter Photophysics, Japan, 12-13 December, 2014.

4. Muhammad Samir Ullah, Siti Zulaikha Ngah Demon, Kazuki Matsumoto, Khuat Thi Thu Hien, Goro Mizutani and Harvey Rutt ; “Study of Optical Second Harmonic Interference Pattern at Interface between Iron Phthalocyanine Layer and Indium Tin Oxide” JPS meeting-2015, 16-19 September, 2015 at Kansai University, Japan.

5. Muhammad Samir Ullah, Siti Zulaikha Ngah Demon, Kazuki Matsumoto, Khuat Thi Thu Hien, Goro Mizutani and Harvey Rutt ; “New Method for Analyzing the Second Harmonic Generation Phase from the Interface between Indium Tin Oxide and Organic Layer”. 10th International Symposium on Atomic Level Characterizations for New Materials and Devices ’15, 25-30 October, 2015, in Matsue, Shimane, Japan 6. Muhammad Samir Ullah, Siti Zulaikha Ngah Demon, Kazuki Matsumoto, Khuat Thi Thu Hien, Goro Mizutani and Harvey Rutt;“ Phase of the Second Order Nonlinear Susceptibility at the Interface of Indium Tin Oxide/Organic Semiconductor”. JAIST Symposium on Advanced Science & Technology 2015 (JAIST SAST 2015), 11-12 November, 2015, JAIST, Japan.

7. Muhammad Samir Ullah, Siti Zulaikha Ngah Demon, Kazuki Matsumoto, Yoshihiro Miyauchi, Khuat Thi Thu Hien, Goro Mizutani and Harvey Rutt ;

“Nonlinear optical interferometry study at the interface of organic thin films with indium tin oxide”. The 26th Symposium of Association for Condensed Matter Photophysics, Japan, 11-12 December, 2015.

8. Muhammad Samir Ullah, Siti Zulaikha Ngah Demon, Kazuki Matsumoto, Yoshihiro Miyauchi, Khuat Thi Thu Hien, Goro Mizutani and Harvey Rutt ;“Measurement of the Absolute Phase at the Interface of Organic Semiconductor by Second Harmonic Interference Technique”. II-Sc-JAIST Joint Workshop on Functional Inorganic and Organic Materials, Japan, 7 March, 2016.

9. Muhammad Samir Ullah, Siti Zulaikha Ngah Demon, Kazuki Matsumoto, Yoshihiro Miyauchi, Khuat Thi Thu Hien, Goro Mizutani and Harvey Rutt ;

“Investigation of the Phase Shift at the Interface of the Functional Organic Materials by Nonlinear Optical Method”. JPS meeting-2016, 13-16 September, 2016 at Kanazawa University, Japan.

10. Muhammad Samir Ullah, Siti Zulaikha Ngah Demon, Kazuki Matsumoto, Yoshihiro Miyauchi, Khuat Thi Thu Hien, Goro Mizutani and Harvey Rutt ;

“Theoretical Approach of the Nonlinear Second Harmonic Interferometry Technique:

Case Study for Organic Semiconductor Interface”. Organic and Inorganic Electronics Symposium: O & I Symposium, 15-16 July, 2016

11. Shohei Asai, Muhammad Samir Ullah, Yousuke Inomata, Khuat Thi Thu Hien, Goro Mizutani, Yoshitaka Murakami and Takashi Okada, “Surface anisotropy characteristics of polyimide alignment film by nonlinear optical method” The 27th Symposium of Association for Condensed Matter Photophysics, Japan, 2-3 December, 2016.

12. Yousuke Inomata, Muhammad Samir Ullah, Shohei Asai, Khuat Thi Thu Hien, Goro Mizutani, Yoshitaka Murakamiand Takashi Okada, “Study of the structure of constituent molecules of a liquid crystal panel substrate by SHG spectroscopy” JPS meeting-2017, 17-20 March, 2017 at Osaka, Japan.