57 CHAPTER 2 EXPERIMENTAL This chapter deals with the main experimental techniques employed will be briefly discussed. 2.1 MATERIALS Hexane, dichloromethane, chloroform, ethylacetate, ethanol, methanol, tetrahydrofuran, acetone, N,N-dimethylformamide and water were purified by the reported procedure (Perrin and Armarego 1998, Furniss et al 1994). Potassium hydroxide, sodium hydroxide, potassium carbonate, hydrochloric acid (35%), sodium nitrate, were purchased from Merck, India. 4-hydroxybenzaldehyde, 4- hydroxyacetanilide, 2,4-dihydroxybenzaldehyde, 4-methoxyaniline, 4- ethoxyaniline, 4-nitroaniline, 1-bromobutane potassium iodide, phenol, 2,6- dibromohexane, acrylic acid, methacrylic acid, diethylamine, triethylamine, N,Ndicyclohexylcarbodiimide (DCC), 4-(dimethylamino)pyridine (DMAP), isonicotinic acid, were purchased from Aldrich (Bangalore), India. All other reagent and chemicals were used as received. 2.2 PURIFICATION OF SOLVENT 2.2.1 Dichloromethane Dichloromethane (100 ml) was shaken with portion of concentrated sulphuric acid until the acid layer remains colourless and washed with aqueous 5% sodium carbonate solution then with water. Pre-dried with calcium chloride and distilled over phosphoruspentoxide. The fraction boiling at 40 ºC was collected and used (lit.b.p.40 ºC, Perrin and Armarego 1998).
58 2.2.2 Chloroform Chloroform (500 ml) was shaken several times with half of its volume of 10% aqueous sodium bicarbonate and followed by distilled water; the chloroform layer was separated, dried over fused calcium chloride for 48 h and distilled under nitrogen atmosphere. The fraction boiling at 62 ºC was collected and redistilled with P 2 O 5 to get dry chloroform (lit.b.p.62 ºC, Furniss et al 1994). 2.2.3 Ethylacetate Ethylacetate (1L) was washed with aqueous 5% sodium carbonate solution then washed several times with sodium chloride and dried with potassium carbonate. The fraction boiling at 77 ºC was collected (lit.b.p.77.1 ºC, Perrin and Armarego 1998). 2.2.4 Ethanol Rectified spirit (1L) was refluxed with calcium oxide for 6 h, set aside overnight and distilled. The fraction boiling at 80 ºC was collected (lit.b.p.80 ºC, Furniss et al 1994). 2.2.5 Methanol Dried methanol was obtained by distilling the commercial methanol (1L) which was refluxed over anhydrous calcium oxide. The distilled methanol was treated with magnesium metal and re-distilled. The fraction boiling at 65 ºC was collected (lit.b.p.65 ºC, Furniss et al 1994). 2.2.6 Acetone Acetone (1L) was refluxed with successive quantities of potassium permanganate until the violet colour persisted. It was then dried with anhydrous potassium carbonate and distilled. The fraction boiling at 57 ºC was collected (lit.b.p.57 ºC, Furniss et al 1994).
59 2.2.7 N,N-Dimethylformamide To a 100 ml of N,N-dimethylformamide, freshly roasted copper sulphate (20 g) was added and stirred. This was left for 24 h until green colour solution was obtained and filtered. The filtrate was then distilled under reduced pressure and the fraction boiling at 75 ºC/12mm Hg, was collected (lit. b.p. 75-76 ºC/12mm Hg, Furrniss et al 1994). 2.2.8 Water Water (1L) was distilled with 10 g of potassium permanganate and sodium hydroxide. The distilled water was collected and then redistilled to get double distilled water (b.p. 100 ºC, Furniss et al 1994). 2.2.9 Tetrahydrofuran Tetrahydrofuran (500 ml) was pre-dried with fused calcium chloride and filtered. It was then dried with refluxing sodium wire and fractionally distilled at 65.4 ºC (lit.b.p.65.4 ºC, Perrin and Armarego 1998). 2.2.10 Carbon tetrachloride Carbon tetrachloride (500 ml) was shaken with concentrated sulphuric acid (100 ml) until there is no further coloration, then several times with distilled water, dried over fused calcium chloride and distilled. The fraction boiling at 76 ºC was collected (lit.b.p.76.8 ºC, Perrin and Armarego 1998).
60 2.3 Synthesis of 4-Formylphenylisonicotinate (1) Figure 2.1 Synthesis of compound 1 4-Formylphenylisonicotinate (1) was synthesized by the following method: A mixture of isonicotinic acid (10 g, 0.08 mol), 4-hydroxybenzaldehyde (9.9 g, 0.08 mol), DCC (17.8 g, 0.085 mol), and DMAP (5% w/w) were dissolved in DCM (200 ml), and the resulting mixture was stirred for 12 h at room temperature under nitrogen atmosphere. Precipitated byproduct urea was filtered from the reaction mixture and the filtrate was concentrated by vacuum distillation. The crude product was purified by repeated (three times) recrystallization from n- hexane. The product 4-formylphenylisonicotinate (Yield 85%) was obtained as a white powder. 2.4 Synthesis of 4-Butyloxyacetanilide (2) Figure 2.2 Synthesis of compound 2 The representative synthetic procedure for the compound 4- butoxyacetanilide (2) is as follows: A mixture of 4-hydroxyacetanilide (6 g, 0.04
61 mol), anhydrous potassium carbonate (10.8 g, 0.08 mol), 1-bromobutane (5.8 g, 0.045 mol) and pinch of potassium iodide in 200 ml of acetone were stirred at 70 ºC for 48 h. Then the reaction mixture was cooled to room temperature, filtered washed with excess of acetone. The solvent was removed under vacuum to give white solid. The solid obtained was dissolved in diethyl ether and washed with water (3 300 ml) to remove unreacted 4-hydroxyacetanilide. The organic layer was dried over anhydrous sodium sulphate, solvent was removed under vacuum and recrystallized from n-hexane to get bright-white crystals of 4- butyloxyacetaniline (Yield 68%). 2.5 Synthesis of 4-Butyloxyaniline (3) Figure 2.3 Synthesis of compound 3 4-Butyloxyaniline (3) was synthesized by the following method: The compound 4-butyloxyacetanilide (5 g, 0.024 mol) was dissolved in ethanol (150 ml), 20 ml of concentrated HCl in ethanol (25 ml) was added dropwise to the reaction mixture. The reaction mixture was heated to reflux for 12 h, cooled and poured into ice-water mixture. The dark brown liquid obtained was extracted by diethyl ether and washed with water (3 300 ml). The organic layer was dried over anhydrous sodium sulphate, solvent was removed under vacuum to give dark brown liquid (Yield 81%).
62 2.6 Synthesis of 4-((4-Alkyloxyphenylimino)methyl)phenylisonicotinate (4a-4b) Figure 2.4 Synthesis of compound 4(a) 4-((4-Alkyloxyphenylimino)methyl)phenylisonicotinate (4a-4b) were synthesised by the following method and as a representative synthetic procedure for the series, the synthesis of compound 4-((4-methoxyphenylimino)methyl) phenylisonicotinate (4a) is as follows: To a mixture of 4-formylphenyl isonicotinate (8 g, 0.057 mol), 4-methoxyaniline (7.1 g, 0.057 mol) were dissolved in methanol (100 ml) and catalytic amount of glacial acetic acid was placed into the reaction mixture. The reaction mixture was refluxed with constant stirring at 70 ºC for 2 h. The resulting product was transferred to crushed ice and the solid formed was filtered, washed with dilute methanol. Then the crude product was recrystallized from dichloromethane to get the desired yellow product (Yield 94%). A similar procedure was adopted for preparation of butyoxy (4b) compound.
63 2.7 Synthesis of 4-(4-Methoxyphenyliminomethyl)benzene-1,3-diol (5) Figure 2.5 Synthesis of compound 5 4-(4-Methoxyphenyliminomethyl)benzene-1,3-diol (5) was synthesised by the following method. To a mixture of 2,4-dihydroxybenzaldehyde (8 g, 0.057 mol), 4-methoxyaniline (7.1 g, 0.057 mol) were dissolved in methanol (100 ml) and catalytic amount of glacial acetic acid was placed into the reaction mixture. The reaction mixture was refluxed with constant stirring at 70 ºC for 2 h. The resulting product was transferred to crushed ice and the solid formed was filtered, washed with dilute methanol. Then the crude product was recrystallized from dichloromethane to get the desired yellow product (Yield 94%). 2.8 Synthesis of 1-Bromo-6-(4-methoxyphenylimino-2-hydroxy-4 - oxy)hexane (6) Figure 2.6 Synthesis of compound 6
64 1-Bromo-6-(4-methoxyphenylimino-2-hydroxy-4'-oxy)hexane (6) was synthesized by the following method: The compound 4-(4-methoxyphenyliminomethyl)benzene-1,3-diol (5) (6 g, 0.025 mol), K 2 CO 3, (3.4 g, 0.050 mol) and catalytic amount of KI were dissolved in 100 ml of acetone. The mixture was refluxed for 10 minutes then 1,6-dibromohexane (6 g, 0.025 mol) in 20 ml of acetone was added drop by drop to this reaction mixture while continuously stirring. The reaction mixture was further refluxed with constant stirring at 70 ºC for 24 h. The salt formed was filtered, washed with 100 ml of acetone and the solvent was evaporated under reduced pressure. The crude product was purified by column chromatography (ethylacetate/hexane (1/9) used as eluent) to get pale yellow solid (Yield 65%). 2.9 Synthesis of 6-((4-Methoxyphenylimino-2-hydroxy)phenyl-4'- oxy)hexyl methacrylate (7) Figure 2.7 Synthesis of compound 7 6-(4-Methoxyphenylimino-2-hydroxyphenyl-4'-oxy)hexyl methacrylate (7) was synthesized by the following method: Methacrylic acid (0.25 mol) was added drop by drop to K 2 CO 3 (0.50 mol) and stirred at room temperature for 5 minutes and allowed for the formation of potassium methacrylate. A solution of 1-bromo-6-(4-methoxyphenyl- imino-2-hydroxy-4 -oxy)hexane (6) (0.25 mol) and hydroquinone 0.05 gm in N N-dimethylformamide (50 ml) was added to the potassium methacrylate and the resulting mixture was stirred at 90 ºC for 12 h.
65 The reaction mixture was allowed to cool and transferred to distilled water. The precipitate was collected and dissolved in dichloromethane. The organic layer was separated and evaporated under reduced pressure. The crude product was collected and purified by column chromatography (Ethylacetate/hexane (1/9) as the eluent) to get pale yellow solid (Yield 74%). 2.10 Synthesis of 4-(6-Hydroxyalkyloxy)benzoic acid (8a-8b) Figure 2.8 Synthesis of compound 8a 4-(6-Hydroxyalkyloxy)benzoic acid (8a-8b) were synthesized by the following method and as a representative synthetic procedure for the series, the synthesis of compound 4-(6-hydroxyhexyloxy)benzoic acid (8a) is as follows: To a mixture of 4-hydroxybenzoic acid (8 g, 0.057 mol), 6-bromohexan-1-ol (10.4 g, 0.06 mol), potassium carbonate (16.4 g, 0.114 mol) and catalytic amount of KI were dissolved in 100 ml of acetone. The mixture was refluxed with constant stirring at 70 ºC for 24 h. The salt formed was filtered, washed with 100 ml acetone and the solvent was evaporated under reduced pressure. The formed crude product was used for further step reaction (Yield 66%). A similar procedure was adopted for preparation of octyloxy (8b) compound.
66 2.11 Synthesis of 4-(6-Acryloyloxyalkyloxy)benzoic acid (9a-9b) Figure 2.9 Synthesis of compound 9a 4-(6-Acryloyloxyalkyloxy)benzoic acid (9a-9b) were synthesized by the following method and as a representative synthetic procedure for the series, the synthesis of compound 4-(6-acryloyloxyhexyloxy)benzoic acid (9a) is as follows: Acrylic acid (0.21 mol) was dissolved in chloroform (150 ml), and then thionyl chloride (50 ml, 0.62 mol) was added drop by drop to the reaction mixture. The resultant mixture was refluxed with constant stirring at 80 ºC for 6 h. The chloroform and excess thionyl chloride were removed under vacuum distillation to get acid chloride as colourless liquid (Yield 92%) (Petersen 1953). The acryloyl chloride (0.1 mol) dissolved with 100 ml dry tetrahydrofuran (THF) and 4-(6-hydroxyhexyloxy)benzoic acid (0.1 mol) followed by dry triethylamine (0.12 mol) were added and stirred at 5 to 15 ºC for 12 h under nitrogen atmosphere. The precipitated triethylamine hydrochloride salt was removed and the product is dissolved in THF and filtered. The filtrate was removed under vacuum distillation to get crude product, then recrystallized from ethanol to get white crystals (Yield 90%). A similar procedure was adopted for preparation of octyloxy compound.
67 2.12 Synthesis of 4-Hydroxy-4 -methoxyazobenzene (10a-10b) Figure 2.10 Synthesis of compound 10a The representative synthetic procedure for the compound 4-hydrox-4ʹmethoxy azobenzene (10a) is as follows: 4-methoxyaniline (6.16 g, 0.05 mol,) was dissolved in 3 mol/l hydrochloric acid (50 ml). After complete dissolution, the solution was cooled with an ice-salt mixture to a temperature below 5 C. With vigorous stirring, to this cold solution was added slowly a solution of sodium nitrite (3.5 g, 0.05 mol) in 10 ml of water. The resulting diazonium solution, kept below 5 C, was subsequently added drop wise to a cold solution of phenol (4.7 g, 0.05 mol) in 25 ml of 10% aqueous sodium hydroxide. The dark brown suspension was acidified, and the precipitate was collected. The crude product was washed with water and dried under vacuum. The crude product was washed with CCl 4 to get the product (Yield 82%). A similar procedure was adopted for the preparation of 4-Hydroxy-4 -nitroazobenzene (10b).
68 2.13 Synthesis of 1-Bromo-4-(4-methoxyazobenzene-4 -oxy)alkane (11a-11d) Figure 2.11 Synthesis of compound 11a 1-Bromo-4-(4-methoxyazobenzene-4 -oxy)alkane (11a-11d) were synthesised by the following method and as a representative synthetic procedure for the series, the synthesis of compound 1-bromo-4-(4-methoxyazobenzene-4 - oxy)hexane (11a) is as follows: A mixture of 4-hydroxy-4ʹ-methoxyazobenzene (6.85 g, 0.03 mol), 1,6-dibromohexane (13 g, 0.06 mol), potassium carbonate (4.2 g, 0.03 mol) and acetone were refluxed with constant stirring at 70 ºC for 24 h. The reaction mixture was filtered at hot condition and the residue was washed with acetone. The acetone was removed under reduced pressure and petroleum ether (30-60 C) was added to the concentrated organic extracts. The resulting precipitate was collected and dried. The crude product was recrystallized with hot filtration from ethanol to get desired product (Yield 64%). A similar procedure was adopted for the preparation of 11b-11d compounds.
69 2.14 Synthesis of Triethylammonium-Functionalized 1-Bromo-4-(4- methoxyazobenzene-4 -oxy)alkane (12a-12d) Figure 2.12 Synthesis of compound 12a Triethylammonium-Functionalized 1-Bromo-4-(4-methoxyazobenzene- 4 -oxy)alkane (12a-12d) were synthesized by following method and as a representative synthetic procedure for the series, the synthesis of compound triethylammonium-functionalized 1-bromo-4-(4-methoxyazobenzene-4 -oxy) hexane (12a) is as follows: 1-bromo-4-(4-methoxy- azobenzene-4 -oxy)hexane (3.5 g (0.01 mol) was dissolved in 25 ml of absolute ethanol. To the warm solution, 5 ml of triethylamine in alcohol (10 ml) was added drop by drop and the resulting mixture was refluxed with constant stirring at 95 ºC for 24 h. Ethanol was removed by evaporation. The crude product was purified by recrystallization from ethanol to get yellow crystals (Yield 86%). A similar procedure was adopted for the preparation of 12b-12d compounds.
70 2.15 Synthesis of poly[4-(6-acryloyloxyalkyloxy)benzoic acid] (13a-13b) Figure 2.13 Synthesis of compound 13a Side-chain polymer was synthesised by free radical polymerization using AIBN as free radical initiator in THF. Poly[4-(6-acryloyloxyalkyloxy)benzoic acid (13a-13b) were synthesized by the following method and as a representative synthetic procedure for the compound poly[4-(6-acryloyloxyhexyloxy)benzoic acid] (13a) is as follows: 4-(6-acryloyloxyhexyloxy)benzoic acid (9a) (1 g) and AIBN (2 mol %) were dissolved in dry THF. Then dry nitrogen gas was purged for 15 minutes. The polymerization tube was closed and kept in oil bath at 60 ºC for 48 h. The resulting polymer solution was cooled and poured into excess of n- hexane to precipitate the polymer. The polymer was purified by precipitating twice using chloroform and n-hexane. The purified polymer was dried under vacuum at 40 ºC for 48 h. A similar procedure was adopted for preparation of other polymers such as poly[4-(6-acryloyloxyoctyloxy)benzoic acid] (13b), poly(acrylic acid) (PAA) (14), poly(methacrylic acid) (PMA) (15) and poly[6-((4- methoxyphenylimino-2-hydroxy)phenyl-4'-oxy)hexyl methacrylate] (poly (6M2HM)) (16).
71 2.16 Synthesis of target self-assembled compounds 2.16.1 Synthesis of poly[6-((4-methoxyphenylimino-2-hydroxy)phenyl-4'- oxy)hexyl methacrylate] 4-((4-alkyloxyphenylimino)methyl)phenyl isonicotinate hydrogen bonding complexes (Ia-Ib) Figure 2.14 Synthesis of compounds Ia-Ib A typical procedure for the synthesis of Ia-Ib is as follows: To a mixture of equimolar amount of poly[6-((4-methoxyphenylimino-2-hydroxy)phenyl-4'- oxy)hexyl methacrylate] (16) and 4-((4-methoxyphenylimino)methyl)phenyl isonicotinate (4a) in chloroform/thf (1:1 vol) and heated slowly to 50 ºC until complete solubilisation of compounds. The solvent was evaporated slowly under atmospheric pressure. The obtained powder complex (Ia) was dried under vacuum at 40 ºC for 3 days. The above synthetic procedure was adopted for the preparation of Ib complex.
72 2.16.2 Synthesis of poly[4-(6-acryloyloxyalkyloxy)benzoic acid] 4-((4- alkyloxyphenylimino)methyl)phenylisonicotinate hydrogen bonding complexes (IIa-IId) Figure 2.15 Synthesis of compounds IIa-IId A typical procedure for the synthesis of IIa-IId is as follows: To a mixture of equimolar amount of poly[4-(6-acryloyloxyhexyloxy)benzoic acid] (13a) and 4-((4-methoxyphenylimino)methyl)phenylisonicotinate (4a) in chloroform/thf (1:1 vol) and heated slowly to 50 ºC until complete solubilisation of compounds. The solvent was evaporated slowly under atmospheric pressure. The obtained powder complex (IIa) was dried under vacuum at 40 ºC for 3 days. The above synthetic procedure was adopted for the preparation of other (IIb, IIc, and IId) complexes.
73 2.16.3 Synthesis of poly(acrylic/methacrylic acid) 4-((4-alkyloxy phenylimino)methyl)phenylisonicotinate hydrogen bonding complexes (IIIa-IIId) Figure 2.16 Synthesis of compounds IIIa-IIId A typical procedure for the synthesis of IIIa-IIId is as follows: To a mixture of equimolar amount of poly(acrylic acid) (14) and 4-((4- methoxyphenylimino)methyl)phenylisonicotinate (4a) in chloroform/thf (1:1 vol) and heated slowly to 50 ºC until complete solubilisation of compounds. The solvent was evaporated slowly under atmospheric pressure. The obtained powder complex (IIIa) was dried under vacuum at 40 ºC for 3 days. The above synthetic procedure was adopted for the preparation of other (IIIb-IIId) complexes.
74 2.16.4 Synthesis of poly(methacrylic acid) Triethylammonium-Functio- nalized 1-bromo-4-(4-ethoxyazobenzene-4 -oxy)alkane Ionic self- assembled complexes (IVa-IVd) Figure 2.17 Synthesis of compounds IVa-IVd A typical procedure for the synthesis of ionic self-assembled complexes (IVa-IVd) is as follows: To a mixture of 10 mg/ml of poly(methacrylic acid) (15) in double distilled water was added drop wise to triethylammoniumfunctionalized 1-bromo-4-(4-ethoxyazobenzene-4 -oxy)hexane (12a) aqueous solution with concentration of 3 mg/ml, in 1:1 molar ratio. The precipitated complex (IVa) was washed with several times with double distilled water to remove residual salts and possible noncomplexed precursors and then dried under vacuum at 50 ºC for 3 days. The above synthetic procedure was adopted for the preparation of other (IVb-IVd) complexes. 2.17 CHARACTERIZATION OF COMPOUNDS In our studies, a combination of different experimental techniques has been used to characterize the structural and phase behaviour of liquid crystalline materials. They include direct space techniques such as FTIR and NMR spectroscopy to ascertain the chemical structure, polarized optical microscopy (POM) for identification of mesophase, X-ray diffraction analysis for
75 conformation of mesophase, thermogravimetric analysis and differential scanning calorimetry (DSC) were employed to study the thermal stability and thermal transition temperature occurring liquid crystalline system, gel-permeation chromatography and viscosity measurements were studied for molecular weight determination of polymers. 2.17.1 Viscosity 1% solutions of the polymer in N,N'-dimethylformamide (DMF) were prepared and filtered through glass filter to remove dust particles. The dust free polymer samples were taken in an Ubbelohde suspended level viscometer with a flow time of 160 seconds for DMF at room temperature. Flow times for the polymer solution and solvent were recorded at the same temperature. Intrinsic viscosities [η] for the polymer solutions were determined using the following set of expressions. Relative viscosity η r = t 2 /t 1 Where t 1 and t 2 are time of flow for solvent and polymer solution respectively. Specific viscosity η sp = η r = 1 The intrinsic viscosity [η] was calculated by plotting η sp /C versus C and extra plotting the straight line to zero concentration. 2.17.2 Gel permeation chromatography The weight average molecular weight (M w ) and number average molecular weight (M n ) of the polymers were determined by Waters 1515 separation module using polystyrene as a standard and THF as an eluent. 2.17.3 Elemental analysis Elemental analysis was carried out on a Heraeus-CHNO rapid elemental analyser with sample weight 2 mg. 2.17.4 Fourier Transform Infrared Spectroscopy Fourier Transform Infrared Spectroscopy (FT-IR) is multidisciplinary analytical tool yields information pertaining to the structural details of a chemical
76 compounds. FT-IR involves the absorption of electromagnetic radiation in the infrared region of the spectrum which results change in the vibrational energy of a molecule. It is a valuable and formidable tool in identifying organic compounds has polar chemical bonds such as OH, NH, CH, etc., with good charge separation. Since every functional group has unique vibrational energy, the IR spectra can be seen as their fingerprint region. FT-IR spectrometer (Shimadzu FTIR 8300/8700) was used to substantiate the formation of products in this study. The spectra recorded for solid samples were made into a thin film using transparent KBr (Merck, IR Grade) pellets. About 10 mg of the samples was grind with about 70 mg of spectral grade KBr to form a mixture, which was then made into a pellet using a hydraulic pressure. All the spectra were recorded in the range of 4000 to 400 cm -1 at a resolution of 4 cm -1 with a maximum of 100 scans. A background spectrum was run before recording the spectra for each sample. The spectral calibration of the instrument was made using a KBr film at regular intervals of time. 2.17.5 Nuclear Magnetic Resonance Spectroscopy Nuclear magnetic resonance spectroscopy (NMR) is a spectroscopic method is even more important to the organic chemist than infrared spectroscopy. Many nuclei may be studied by NMR techniques, but hydrogen and carbon are most commonly investigated. Whereas infrared spectroscopy reveals the types of functional groups present in a molecule, NMR gives information about the number of magnetically distinct atoms of the type being studied. High-resolution 1 H-NMR and 13 C-NMR spectra were recorded using Brucker EX-400 FT-NMR spectrometer. Deuterated chloroform [Aldrich, CDCl 3, 99.8% containing 0.03% V/V tetramethylsilane (TMS)] and DMSO-d 6 were used as solvents for recording NMR spectra. The proton NMR were recorded using broadband inverse probe where the inner coil for the protons and outer coil for X nuclei. Solvent suppression was applied in some cases where the solvent signal is very strong compared to the sample signals.
77 2.17.6 Differential Scanning Calorimetry Differential canning calorimetry (DSC) has become a method of choice for quantitative studies of thermal transition in polymers. Differential scanning calorimetry was performed using the Universal V4.5A DSC Instrument DSC Q20 V24.2 Build-107 calorimeter and Mettler Toledo STAR system thermal analysis unit attached to a DSC module. The experiments were carried out in nitrogen atmosphere at a heating rate of 5 ºC/min from room temperature to ambient 500 ºC with nitrogen flow of 10 ml/min. Generally, DSC measures the power released or absorbed by materials during temperature treatments that can include dynamic (i.e., heating or cooling ramps) or isothermal segments. The measurement is performed by comparing the temperature of the sample and that of the reference materials. The instantaneous heat flux is computed from this temperature difference using instrumental calibration constant. Standard samples like pure indium or zinc with known transition enthalpies and temperatures are used for the calibration. The measuring cell of a calorimeter includes the sample and reference material enclosed in a single furnace. The DSC furnace is made of silver and separated from the DSC sensor by a ceramic plate. The temperature of each of the two containers (pans) is measured by thermocouples connected in series and located around each of them. The measuring of enthalpy variation can allow assigning a given thermal event to a polymorphic crystal to crystal or to a mesophase to mesophase transition in LC systems. This is based on the fact that the enthalpy variation associated with crystal melting by far more important than the one corresponding to the mesophase to mesophase or mesophase to isotropic transitions. The DSC is a convenient tool to measure the temperatures and transition enthalpies to determine the phase diagram of the each self-assembled complexes and to study the kinetics of transition as a function of heating/cooling rates or as a function of time. DSC has become a method of choice for
78 quantitative studies of thermal transition in polymer and its self-assembled complexes. 2.17.7 Polarizing Optical Microscope Polarizing optical microscope (POM) was carried out to find out the LC texture analysis and also determine the phase transition with sensitivity of ± 0.1 ºC. POM studies were performed with a Euromex polarizing microscope attached with a Linkem HFS 91 heating stage and a TP-93 temperature programmer. Samples were placed in between two thin glass cover slips and melted with heating and cooling at the rate of 2 ºC/min. The photographs were taken from Nikon FM10 camera. All the micrographs were taken from the second cooling stage from isotropic transition temperature. 2.17.8 X-Ray Diffraction Measurement X-ray diffraction measurements were carried out to investigate the texture of the mesophase. Powder samples were used to obtain diffraction patterns of liquid crystalline compounds. The powder samples held in sealed capillaries were heated from room temperature to mesophase and irradiated. The X-ray was generated by 800 W Philips (PANANALYTICAL, Netherland) powder diffractometer using anode diffractometer with Cu-Kα radiation. Samples placed on a mettle FP 52 hot stage. 2.17.9 Thermogravimetric analysis Thermal degradation of polymer and its self-assembled complexes were determined by Universal V4.5A TA Instrument SDT Q600 V24.2 Build-107 thermogravimetric analyser. All the TGA data were measured under a nitrogen atmosphere at a heating rate 10 ºC/min, and the thermal degradation temperature was determined at the point of 95 wt% of the original weight. 2.17.10 Ultraviolet-Visible (UV-vis) Spectroscopy UV-visible spectra were obtained at Hewlett-Packard 8435 UV-visible spectrophotometer. Samples were prepared in the form of solution or thin films.