1 / 66

TO MY PRE-PhD PUBLIC SEMINER

TO MY PRE-PhD PUBLIC SEMINER. WELCOME. “Photo Physical Studies of Organized Molecular Assemblies in Langmuir Blodgett Films”. PRESENTED BY: Syed Arshad Hussain Department of Physics Tripura University Suryamaninagar-799 130 Tripura, India . UNDER THE SUPERVISION OF:

idalia
Download Presentation

TO MY PRE-PhD PUBLIC SEMINER

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. TO MY PRE-PhD PUBLIC SEMINER WELCOME

  2. “Photo Physical Studies of Organized Molecular Assemblies in Langmuir Blodgett Films” • PRESENTED BY: Syed Arshad Hussain Department of Physics Tripura University Suryamaninagar-799 130 Tripura, India. UNDER THE SUPERVISION OF: Dr. D. Bhattacharjee Lecturer Department of Physics Tripura University Suryamaninagar-799 130 Tripura, India

  3. 1. “Spectroscopic Characterizations of non-amphiphilic 2-(4- biphenylyl)-6-phenyl benzoxazole molecules at the air-water interface and in Langmuir-Blodgett Films”. Journal of Luminescence(Elsevier science) 114 (2005) 197-206. 2. “Langmuir Blodgett Films of 9-phenyl anthracene molecules incorporated into different matrices”. Spectrochimica Acta Part-A(Elsevier science), 61 (2005) 2448-2454. 3. “Role of microenvironment in the mixed Langmuir-Blodgett films”. Journal of Colloid and Interface Science(Elsevier science) (Accepted for publication, Manuscript no. JCIS-05-1209R1) List of my publications:

  4. Following are the published papers where I have significant contribution: 1.Spectroscopic Characterizations of the mixed Langmuir-Blodgett (LB) films of 2,2'-biquinoline molecules: evidence of dimer formation. S.Deb, S.Biswas, S.A.Hussain and D.Bhattacharjee Chem. Phys. Letts. 405, 323-329 (2005) 2. Ageing effect of mixed Langmuir-Blodgett film of 9-Phenyl anthracene in PMMA and SA matrices. S. Deb, S. Biswas, S. A. Hussain and D. Bhattacharjee Ind. J. Phys. 79 (9) 1027-1031 (2005) 3. Formation of complex films with water-soluble CTAB molecules S. Biswas, S. A. Hussain, S. Deb, R. K. Nath, D. Bhattacharjee Spectrochimica Acta Part-A (accepted for publication) 4. Langmuir-Blodgett films of p-terphenyl in different matrices: Evidence of dimer formation S. Deb, S. A. Hussain, S. Biswas, D. Bhattacharjee Chem Phys. Letts. (Communicated)

  5. Paper presented in national seminar/symposium: 1.“Spectroscopic study of nonamphiphilic buPBD assembled onto Langmuir-Blodgett Films”. Third Regional Conference on Physics Research in North East India. November 09, 2002 Organized by Department of Physics, Dibrugarh University Dibrugarh-786004, Assam, INDIA. 2.“Photophysical characteristics of mixed Langmuir Blodgett films of PBBO molecules”. CMDAYS-04 August 25-27, 2004 Department of Physics, NEHU, Shillong-793022

  6. Contd…. 3.“Time dependent change in mixed Langmuir-Blodgett films of 9-Phenyl Anthracene in PMMA and SA matrices”. National Symposium on Impact of Chemistry on Life and Society (NSICLS) October 1-3, 2004 Department of Chemistry, Tripura University Suryamaninagar-799130, Tripura 4.“Photophysical studies of mixed Langmuir-Blodgett films of molecules mixed with two different matrices”. PANE conference - 2004 November 5 & 6, 2004 Department of Physics, Gurucharan College Silchar-788004, Assam 5.“Pressure effect studies of mixed Langmuir-Blodgett films of 2-2/ biquinoline molecules mixed with SA matrix”. 50th Annual Technical session and National Conference on Current Trends of research in Science and Technology under the auspices of Assam Science Society January 28 & 29, 2005 Department of Physics, Guwahati University, Guwahati

  7. Introduction: • Thin films of thickness of few nanometers (monolayer/ multilayer) are the source of high expectations as being useful components in many practical and commercial applications such as sensors, detectors, optoelectronics devices and molecular electronics devices. • A thin film can be deposited on a solid substrate by various techniques. However Langmuir-Blodgett (LB) technique is one of the most promising techniques for preparing thin films as it offers: • (a) the precise control of the monolayer thickness, (b) homogeneous deposition of the monolayer over large areas (c) the possibility to make multilayer structures with varying layer composition. (d) The crystal parameter & packing of the film can be controlled by changing various LB parameter. Also by LB technique monolayer can be deposited on almost any kind of solid substrates.

  8. Historical Perspective: • Sir Benjamin Franklin described some experiments on spreading oil films on water surface (1774) • Lord Rayleigh showed that these films are one molecular thick • Agnes Pockel reported that oil film can be controlled by movable barrier • Irving Langmuir developed the theoritical and experimental concept (1920) (Nobel prize) • Katherine Blodgett made sequential transfer of monolayer onto solids. • H. Khun (Late 1960’s) demonstrated LB films with designated properties. • First international conference on LB films was held in 1979.

  9. Scientific interest: After Katherine Blodgett’s successful transfer of a monolayer from water surface to a glass plate in 1934, the scientific interest in LB films have been intensified in recent years. There is much current interest in the ultra thin films fabricated by the LB technique as it offers the simplest yet the most elegant method of obtaining highly organized molecular assemblies which have their potential applications in sensors, optoelectronic, optical signal processing, digital optical switching devices and as models mimicking biological membranes. Extensive studies on LB films have been conducted after the pioneering works of Kuhn and co-workers (late 1960’s) Although these studies have received considerable attention, the role of ultra structure as well as domain structure and also the electrical and optical properties of such films is a topic of fundamental importance. In recent year nanocrystalline films obtained by Langmuir-Blodgett technique which have a great potential towards the formation of nanoscale devices. Detailed investigations of LB films with different molecules are important to understand the basic physics involved in such system.

  10. 1322 in 1998 Figure 1: Number of publications per year with "monolayer" in the title.

  11. Insoluble amphiphilies at the air-water interface:(Ideal LB compatible material) Amphiphilic molecule Hydrophilic part Hydrophobic part Hydrophobic part: Long hydrocarbon / Fluorocarbon chain Hydrophilic part: Polar group ( -OH, -CN, -COOH, -NH3+, -PO4-, (CH2)2NH3+ etc, heavy metal ion )

  12. Langmuir-Blodgett (LB) film deposition instrument ( LB APEX-2000C) Go to LB trough

  13. Formation of monolayer on the subphase: • The Environment The LB trough must be installed in a clean dust – free environment. • The Subphase Water, Mercury, glycerol are most commonly used subphase. • Preparation of Film material Standard solution of the materials of our interest was prepared in highly volatile water -insoluble organic solvent such as chloroform, benzene etc.

  14. Formation of monolayer on the subphase (Contd…) • Monolayer Spreading Known quantity of solution was spread at the air - water interface and sufficient time was given to evaporate the solvent and then the molecule remains at the air-water interface hapazardly.

  15. SURFACE PRESSURE: • Surface tension of pure water is 70 mN/m. • Addition of impurity causes decrease in surface tension. • In LB technique this decrease in surface tension is referred to as an increase in surface pressure i.e., numerically these two are same. The surface tension of pure water is taken as the reference level. • Surface pressure () can be defined as  = o -  Where o = surface tension of clean subphase  = surface tension in presence of impurity. Thus it is possible to monitor the surface pressure as a function of the area occupied by a single molecule provided that the number of molecules deposited on the surface is known.

  16. LANGMUIR-BLODGETT (LB) TECHNIQUE Enlarged form of the LB trough View LB instrument

  17. Solid phase Surface pressure (mN/m) Liquid phase Gas phase Molecular area (nm2/molecule) Monolayer Phases • When the molecules are first spread on the water surface, they are loosely packed and form a so-called gas phase. • Increasing the surface pressure by compressing the barrier causes a transition to a liquid phase. • Further increases in pressure bring about a last compressibility change that is associated to a solid phase transition. Further decrease in area per molecule causes collapse of monolayer.

  18. Langmuir Film:The two dimensional crystalline arrangement of molecules at the air- water interface is known as Langmuir film.Langmuir-Blodgett (LB) Film:When the mono- or multilayers of Langmuir films were transferred onto a solid substrate it is called Langmuir-Blodgett (LB) film. Deposition of Langmuir film onto solid substrate: There are three deposition schemes commonly used to transfer Langmuir film onto solid substrate to form Langmuir-Blodgett (LB) film. These are: Y-Type deposition X-Type deposition Z-Type deposition

  19. Langmuir-Blodgett Film Deposition • The substrates: • Hydrophilic • Glass and quartz • Metal plates composed of oxides of chromium, aluminium, or tin • Silver and gold (conductive substrates) • Silicon or gallium arsenide plates (semiconductive) • Hydrophobic • Mica, HOPG & teflon coated glass etc. • Y-Type deposition: (up & down strokes) Hydrophilic-hydrophilic or hydrophobic-hydrophobic interaction

  20. X-Type deposition (Down stroke) • Z-Type deposition (Upstroke) Hydrophilic-hydrophobic interaction (X & Z type)

  21. Y, X AND Z-TYPE LANGMUIR-BLODGETT FILMS: Y-type film on a hydrophobic surface

  22. Film Investigation: • Once the films are formed, several techniques can be utilized to characterize them: • Pressure-Area isotherms; provides information on the miscibility of heterogeneous phases. • Spectroscopy; provides information on the chemical composition and nature of the aggregation on the films. • UV-Vis • Steady state fluoresecnce spectroscopy • FTIR • NMR • Raman etc. • X-ray diffraction; provides insights as to the arrangement of heterogeneous films. • Microscopy; enables to get a visual representation of the film surface. • AFM • SEM • TEM • Other parameters include changes in conductivity, pH & Temperature of sub phase, molefraction, pressure of lifting, thickness etc.… SEM image CA-SA mixed LB film.

  23. Recent scientific investigations suggest that certain non-amphiphilic molecules can also form excellent Langmuir monolayer at the air-water interface when they are mixed with long chain fatty acids such as stearic acid (SA), Arachidic acid (AA), or some inert polymer such as Polymethyl methacrylate (PMMA) or polystyrene (PSt). The interesting features of these molecules are: • they are easily available and very easy to synthesize, • their spectroscopic and aggregating properties are very much similar to their amphiphilic counterparts, • these molecules are cheap and • they can form highly stable Langmuir monolayer at the air-water interface when incorporated into suitable supporting matrices. • Their electrical & photophysical characterizations are changed markedly when they are incorporated in to the restricted geometry of LB films

  24. Activities of our Group: • Photophysical characterizations of Langmuir Blodgett (LB) films of various polymeric, organic, metallo organic and other materials having interesting optical and electrical properties. • My research work is mainly concentrated on the photophysical studies of organized molecular assemblies in mono- and multilayer Langmuir-Blodgett films. • Studies of these materials are done by changing various parameters such as molefraction, surface pressure of lifting, thickness of the films, ageing effect etc. • For photophysical characterizations we have used the traditional and convensional spectroscopic instruments such as UV-Vis absorption spectrophotometer (Perkin Elmer, Lambda-25) and Fluorescence spectrophotometer (Perkin Elmer, LS-55). In some cases to visualize the domain structure of the mixed LB films a traditional imaging method namely scanning electron microscopy (SEM) has been employed (model S-415A)

  25. Activities of our Group: (contd….) In my Pre-PhD research work, I have already studied the photophysical characteristics of mixed LB films of the following non-amphiphilic molecules mixed with inert fatty acid (stearic acid) & inert polymer matrix (polymethyl methacrylate). (i) 2-(4-biphenylyl)-6-phenyl benzoxazole (PBBO) (ii) 9-Phenyl Anthracene (PA) (iii) Carbazole (CA) [ Recently work on two more systems have already been completed and are now in the process of communication.]

  26. (i) “Spectroscopic characterizations of non-amphiphilic 2-(4-biphenylyl)-6-phenyl benzoxazole molecules at the air-water interface and in Langmuir-Blodgett films” Published in Journal of Luminescences, Elsevier science 114 (2005) 197-206 • 2-(4-biphenylyl)-6-phenyl benzoxazole abbreviated as PBBO a well-known oxazole derivative have intense fluorescence and are used in- • Light emitting diodes, solar energy concentrators and in thin film electro-luminescent devices [1.1, 1.2]. • Ultra fast optical amplitude limit material and UV-laser dye due to their non-linear transmission property [1.3]. • Photophysical characterization of non-amphiphilic PBBO molecules mixed with SA and PMMA have never been studied in Langmuir Blodgett films. • Figure:1 Molecular structure of PBBO

  27. 2(a) 2(b) Figures 2(a) and 2(b) represent the Isotherm characteristics of PBBO mixed withPMMA and SA respectively along with pure PMMA and SA & PBBO. The numbers denote the molefractions of PBBO in PMMA or SA. The inset shows the area per molecule versus molefraction plot.

  28. From the Isotherm characteristics of fig 2(a) & 2(b) we observe that: • For pure PBBO isotherm the pressure rises up to 19 mN/m only & repeated attempt to transfer this film onto quartz substrate was failed. • PBBO mixed with PMMA/SA form stable Langmuir monolayer at the air-water interface. • In both the cases, the area per molecules systematically decreases with the rise in surface pressure. • Isotherm studies as well as area per molecule versus mole fraction study of PBBO (inset of 2a & 2b) indicate either ideal mixing or complete demixing of the binary components. • However complete demixing of the binary components was revealed by UV-Vis absorption study of the mixed LB films. view fig 2a & 2b

  29. Figure 3: Schematic representation of molecular organization of PBBO molecules in the mixed LB films.

  30. 4(b) 4(a) The absorption spectra at various molefractions of PBBO in both the matrices are almost similar to the PBBO microcrystal spectrum having identical peak position. However the absorption bands of mixed LB films are red shifted and show broadened spectral profile with respect to the PBBO solution spectrum. The broadening of the absorption bands accompanied with the red shift in the mixed LB films of PBBO, seems to be due to the formation of J-aggregates.

  31. 5(a) 5(b) The fluorescence spectra of PBBO-PMMA mixed LB films show two well resolved vibrational peaks. However the fluorescence spectra of PBBO-SA mixed LB films do not consist of any prominent vibrational structure. In this case the fluorescence spectra have distinct similarity with that of the microcrystal spectrum. Moreover the fluorescence spectra of the mixed LB films of PBBO for both the matrices show a broadened spectral profile. This may be due to the excimeric emission occurring from the microcrystalline aggregates of PBBO, which is later confirmed by excitation spectroscopic studies.

  32. Excitation spectra 6(a) 6(b) 7(a) 7(b) Figure 7(a) & 7(b): Excitation spectra of mixed LB films of PBBO in PMMA & SA respectively; Striking wavelength = 415 Figure 6(a) & 6(b): Excitation spectra of mixed LB films of PBBO in PMMA & SA respectively; Striking wavelength = 380

  33. From the figures it is observed that: • The excitation spectra are almost similar irrespective of the monitoring wavelength. • Moreover the excitation spectra give broadened spectral profile and support the various band positions of absorption spectra. • The close similarity of the excitation spectra monitoring at high energy and longer wavelength band gives the conclusion that the broadened spectral profile of emission spectra originates due to the formation of excimer in the mixed LB films. View Excitation spectra

  34. Conclusion: • Non-amphiphilic PBBO mixed with PMMA or SA form excellent monolayers at the air-water interface. • Isotherm studies as well as area per molecule versus mole fraction study of PBBO indicate either ideal mixing or complete demixing of the binary components. • The UV-Vis absorption study of the mixed LB films of PBBO reveal the nature of complete demixing of the binary components of the sample molecules PBBO and PMMA or SA which leads to the formation of clusters or aggregates. • Fluorescence spectroscopic studies show that excimer emission occurs from the microcrystalline aggregates of PBBO. • Excitation spectroscopic study confirms the formation of only excimeric sites.

  35. References: • 1.1. S. J. Bai, C. C. Wu, T. D. Dang, F.E. Arnold and D. Sakaran, Appl. Phys. Lett. 84 (2004) 1656. • 1.2. Tania M. H. Costa, Vater Stefani, Marcia R. Gallas, Naira M. Balzaretti and Joao A.H. da Jornada, J. Mater. Chem. 11 (2001) 3377. • 1.3. Dong Xiao, Guilan Zhang, Haiyan Wang, Guoqing Tang and Wenju Chen, J. Nonlinear Opt. Phys. Mat. 93 (2000) 309. • 1.4. • (i) Gaines, G. L, Ed. Insoluble Monolayers at Liquid-Gas Interfaces Wiley Interscience, New York, 1966. • (ii). Dorfler, H. D. Adv. Colloid Interface Sci. 31 (1990) 1 • (iii) Barnes, G.T., J. Colloid Interface Sci. 144 (1991) 299.

  36. (ii) “Langmuir-Blodgett films of 9-phenyl anthracene molecules incorporated into different matrices”.(The paper is published in Spectrochimica Acta Part-A , Elsevier science 61 (2005) 2448-2454). • Anthracene and its derivatives have rigid molecular structure and interesting spectroscopic and photo conducting properties as well as also have high fluorescence intensity. • Moreover the properties of these derivatives are highly sensitive to the microenvironment in which they are incorporated. • However detailed study of 9-phenyl anthracene in various matrices have never been done before.

  37. 1(b) 1(a) Figure 1(a) & 1(b): -A isotherm of PA mixed with PMMA & SA respectively, alongwith pure PMMA & SA isotherm. Number denotes corresponding molefraction. Inset shows molecular structure of PA.

  38. The isotherm characteristics (figure 1a & 1b), show that the area per molecule for pure PMMA and SA are 0.11 nm2 and 0.225 nm2 respectively at a surface pressure of 15 mN/m. • Also the area per molecule decreases consistently with the increase in molefraction of PA in both the matrices, which confirms the successful incorporation of PA molecules into the mixed Langmuir-Blodgett films. • The area per molecule vs. molefraction study (figure not given) also confirms that the PA molecules have been successfully in corporated in the mixed films which are consistent with the behaviour of other non-amphiphiles. View fig 1a & 1b

  39. 2(b) 2(a) Figure 2(a) & 2(b): UV-Vis absorption & steady state fluorescence spectra of mixed LB films of PA in PMMA & SA respectively, along with their solution and microcrystal spectra.

  40. From figure 2a & 2b it is observed that: • There is no shifting of band position of the absorption spectra of PA-PMMA mixed LB films w.r.to the solution absorption spectrum. However absorption spectra of PA-SA mixed LB films show a blue shifting for lower molefraction and no shifting for higher molefraction w.r.to the solution spectrum. • Almost identical peak position in case of PMMA matrix may be due to the formation of I-type of aggregates of PA in PA-PMMA mixed LB films. • However in case of SA matrix simultaneous blue shifting as well as no shifting of the high energy band depending on molefraction may lead to the conclusion that there is a competition between two different types of aggregates namely I-type and H-type play their dominant role in the PA-SA mixed LB films. • The fluorescence spectra (figure 2a & 2b) of mixed LB films of PA in both the matrices show distinct similarity with that of solution spectrum. Also the high energy band at 399 nm is considerably reduced in intensity and the band at 417 nm is quite intense. This may be due to the reabsorption effect owing to the closer association of the molecules. view fig 2a & 2b

  41. Ageing Effect: 3(a) 3(b) Figure 3(a) & 3(b): UV-Vis absorption & steady state fluorescence spectra of recent & stable LB films of PA in PMMA & SA respectively at two different molefractions of 0.1M & 0.5M.

  42. From the ageing effect study we observe that: • Once multilayered LB films are deposited onto the quartz substrate, it would take several hours (>200 hours) to get the film in a stable condition. • UV-Vis absorption spectroscopic study of recently fabricated (00 h) and stable (> 200 h) LB films of PA in SA matrix give evidence of the orientational change of molecules from I-type to H-type aggregates. Where as their fluorescence spectra remain almost same, suggesting no translational movement of the molecule in the mixed LB film of PA in SA. • UV-Vis absorption spectra of recently lifted and stable PA- PMMA mixed LB films are identical in nature which suggests no orrientational change of molecules took place. But the fluorescence spectroscopic studies reveal that recently lifted films at higher molefraction of PA (0.5M) in PMMA gives a broad excimeric band whereas stable LB film of the same gives the well structured vibrational bands which may arise due to the presence of monomeric species. That is with increasing time monomeric species gradually increases and excimeric species decreases suggesting a translational movement of molecules take place in the PA-PMMA mixed LB films so that with the passage of time molecules move away from each other to create monomeric sites. Fig 3(a) & 3(b)

  43. 4(a) 4(b) Figure 4(a): UV-Vis absorption and steady state fluorescence spectra of PA-SA mixed LB films lifted at different surface pressure of 15, 20, 25 & 30 mN/m. Figure 4(b): Excitation spectra of PA-SA mixed LB films lifted at surface pressure 15 & 30 mN/m; striking wavelengths are 420, 448 & 480 nm.

  44. From the pressure effect study we observed that: • Fluorescence spectra (figure 4a) of LB film lifted at 25 mN/m pressure show that a weak hump is developed at about 480 nm along with a prominent peak at around 450 nm and other vibrational bands at 420 and 397 nm. • Although the high energy band at 397 nm is considerably reduced in intensity. At the higher surface pressure of 30 mN/m, 480 nm band is more prominent along with 450 nm band. Other vibrational energy bands are considerably reduced. View fig 4(a)Contd…..

  45. pressure effect studycontd …….. • The excitation spectra monitoring at 420 nm and 448 nm, in the 300-420 nm region show prominent and distinct vibrational bands system with identical peak position, prototype of absorption spectra. • These bands arise due to the monomeric/excimeric sites present in the LB films. • However, while monitoring the band position at 480 nm, the excitation spectra is somewhat different. The vibrational bands are diffused and only a broadened band appears at longer wavelength sides. • Especially at higher surface pressure of 30 mN/m the broadened band is shifted to 400 nm, a shift of about 11 nm in comparison to longer wavelength vibrational band at 389 nm. • Moreover this band is sufficiently broadened and other vibrational bands are totally absent. This totally different nature of excitation spectra while monitoring at 480 nm, definitely brings us to the conclusion that some higher order n-mers (dimer, trimer, tetramer etc.) species may exist in the LB films. View fig 4(a) & 4(b)

  46. Conclusion: • Non-amphiphilic 9-phenyl anthracene molecule when mixed with SA or PMMA forms stable Langmuir films at air-water interface and can be easily transferred onto solid substrate to form uniform Langmuir-Blodgett films. • I-type aggregate is formed in PMMA matrix where as both I-type and H-type aggregate forms in SA matrix. • It is also observed that molecular movement exist in the recent LB films and it takes about 200 hour to aged the LB films in a stable condition. • Dimmers and n-mers are formed in the mixed LB films of higher mole fraction of PA in SA matrix and which is lifted at higher surface pressure of 30 mN/m.

  47. (iii) “Role of microenvironment in the mixed Langmuir-Blodgett films”.(The paper is accepted by theJournal of Colloid and Interface Sciencefor publication (Manuscript no. JCIS-05-1209)) For this work we have choosen carbazole because- • CA and its derivatives have intense and well characterized absorption and fluorescence spectrum [3.5-3.6]. • Carbazole (CA) and its derivatives are used in the manufacture of organic photoconductors [3.1] and electroluminescent devices [3.2-3.4].

  48. 1(a) 1(b) Figure 1(a) 1(b): Isotherm characteristics of CA mixed with PMMA or SA respectively, along with pure PMMA & SA isotherm. Inset shows the collapse pressure vs. molefraction plot and the molecular structure of CA.

  49. From the isotherm characteristics we observe that: • For CA-PMMA mixed isotherm 0.3 M, the area per molecule of mixed film is larger than that of pure PMMA. • At 0.4 M and above area per molecule is lower than that of PMMA. • The reason may be at lower molefractions the repulsive interaction between unlike components in the mixed films predominates over a greater extent resulted in the phase separation of unlike molecules. • Also the predominance of this repulsive interaction at lower molefractions may occur due to conformational and orientational ordering of molecules. • However for both the matrices the area per molecule gradually decreases with increasing molefractions. • From the collapse pressure vs. molefraction plot it was observed that the collapse pressure for all the molefraction are almost constant and independent of molefractions of CA in both the matrices and do not match with the ideality (solid line) curve. • This indicate that CA molecules and PMMA/SA molecules are totally immiscible in the mixed monolayer. • This immiscibility or complete demixing between CA and PMMA or SA may lead to the formation of crystalline aggregates of CA molecules in the mixed LB films. view fig 1(a) & 1(b)

  50. Scanning Electron Microscopy (SEM) : Figure 2: Scanning Electron Micrograph (SEM) of 10 layers of CA-SA mixed LB films (mole fraction of CA = 0.5 M) at room temperature.

More Related