Investigation of thermodynamic properties of 4-decyloxybiphenyl-4′-carboxylic acid liquid crystal and preparation of polymer dispersed liquid crystal composite

Accepted Manuscript Investigation of thermodynamic properties 4-decyloxybiphenyl-4′-carboxylic acid liquid crystal preparation of polymer dispersed liquid crystal composite

of and

Emine Öztürk, Hale Ocak, Fatih Cakar, Gürkan Karanlık, Özlem Cankurtaran, Belkis Bilgin-Eran PII: DOI: Reference:

S0167-7322(18)31086-9 doi:10.1016/j.molliq.2018.05.080 MOLLIQ 9135

To appear in:

Journal of Molecular Liquids

Received date: Revised date: Accepted date:

5 March 2018 16 May 2018 19 May 2018

Please cite this article as: Emine Öztürk, Hale Ocak, Fatih Cakar, Gürkan Karanlık, Özlem Cankurtaran, Belkis Bilgin-Eran , Investigation of thermodynamic properties of 4-decyloxybiphenyl-4′-carboxylic acid liquid crystal and preparation of polymer dispersed liquid crystal composite. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Molliq(2017), doi:10.1016/ j.molliq.2018.05.080

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ACCEPTED MANUSCRIPT INVESTIGATION OF THERMODYNAMIC PROPERTIES OF 4DECYLOXYBIPHENYL-4’-CARBOXYLIC ACID LIQUID CRYSTAL AND PREPARATION OF POLYMER DISPERSED LIQUID CRYSTAL COMPOSITE

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Emine Öztürk, Hale Ocak, Fatih Cakar, Gürkan Karanlık, Özlem Cankurtaran*, Belkis Bilgin-Eran

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Department of Chemistry, Yildiz Technical University, Istanbul, Turkey

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ABSTRACT

In this study, firstly, retention behavior of solvents on the liquid crystalline material 4-

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decyloxybiphenyl-4’-carboxylic acid (DBCA) have been studied

by inverse gas

chromatography (IGC) technique. Liquid crystal (LC) selectivity was investigated using the

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acetate isomers by the IGC method at temperatures between 333.2 K and 543.2 K. Later on, the interactions of LC with n-octane, n-nonane, n-decane, undecane, dodecane, tridecane, npropyl benzene, isopropyl benzene, ethylbenzene, chlorobenzene and toluene between 518.2

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K and 543.2 K were examined. LC-solvent interaction parameters for Flory-Huggins theory,

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∞ ∗ 𝜒12 , and equation of state theory, 𝜒12 , effective exchange energy parameters, 𝑋𝑒𝑓𝑓 , the weight

fraction activity coefficent, Ω1∞ , the partial molar heat of mixing at infinite dilution of the solvent, ∆𝐻1∞ , molar heat of vaporization of solvent, ∆𝐻𝑉 and the partial molar heat of

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sorption of the solvent, ∆𝐻1,𝑠 were obtained. Secondly, polymer dispersed liquid crystal (PDLC) composite film in composition 20/80

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poly(methyl methacrylate) (PMMA):DBCA by weight was synthesized by solvent-induced phase separation method. The mesomorphic behaviour of DBCA and PDLC composite has been investigated by differential scanning calorimetry (DSC) and optical polarizing microscopy (PM).

Key words: Liquid crystal, Thermodynamic interaction parameters, Inverse gas chromatography, Poly(methyl methacrylate), Polymer dispersed liquid crystal composite

ACCEPTED MANUSCRIPT 1.Introduction Liquid crystals (LCs) are attractive organic functional materials that exhibit both fluidity and molecular alignment. They have a great potential to obtain high performance materials which can be applied for information and communication technologies [1-3]. Shape anisotropy, dipole–dipole interaction, microphase segregation and non-covalent interactions are the most fundamental factors in designing LC materials exhibiting the desired mesophase behaviour and excellent performance in electro-optic display technologies [4]. Among many kinds of LC

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materials with different molecular structures, rod-shape (calamitic LCs) materials are widely used in a flat-panel display, switchable windows, laser and other photonics. For such materials

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smectic phases are observed in most cases. Some characteristics of LCs such as low viscosity,

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high photochemical and thermal stability, high dielectric biaxiality and a wide range of the smectic C phase are required for useful applications [5-7].

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Inverse gas chromatography (IGC) is a simple, fast and accurate method for investigating the physicochemical properties such as solubility and thermodynamic interaction parameters of non-volatile materials, including polymers, polymer blends, LCs, etc. [8-11]. The application

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of LCs as stationary phases in gas chromatography was reported by Kelker [8-10], and Dewar and Schroeder [11, 12]. It was known that LCs have shown this particular selectivity and

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sensitivity as stationary phases for the separation of isomers. While the determination of isomeric solvents by ordinary stationary phases offered some difficulties, these isomers have

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similar boiling points and polarities; a search for better stationary phases including highly selective ones was an important trend of gas chromatography (GC) development. The solubility data of a LC in some probes might be required for design of novel applications. The

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interaction between a LC and a probe is generally investigated by the value of Flory-Huggins interaction parameter [13-15].

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Polymer dispersed liquid crystals (PDLCs) have a great interest as advanced functional materials for a wide variety of electrooptic applications ranging from windows shutters to projection displays, optical information storage devices [16]. PDLCs, in which LC droplets are dispersed in a polymer matrix, can be applied in various industrial fields, such as smart windows, light shutters, high resolution displays and projection light valves a so forth [17]. PDLCs have been suggested to avoid the flow of LCs, to increase the mechanical stability and to facilitate the fabrication process. Moreover, their light transmittance is much higher than conventional LC displays due to the absence of a polarizer [18, 19]. Various techniques such as solvent-induced phase separation (SIPS), polymerization-induced phase separation (PIPS) and thermally-induced phase separation (TIPS) method are being used to form droplets of the

ACCEPTED MANUSCRIPT LCs in the polymer matrix and prepare PDLC composite films. Solvent evaporation rate plays an important role in the formulation structure of the PDLC films in SIPS method, where the LC and the polymer are dissolved in a common solvent to obtain a single phase [20]. In this method is generally used transparent thermoplastic polymers such as poly(methyl methacrylate) (PMMA). In this study, firstly we synthesized and characterized a new LC 4-Decyloxybiphenyl-4’carboxylic acid (DBCA). The selectivity of the DBCA was investigated by using n-butyl

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acetate, tert-butyl acetate and iso-butyl acetate at temperatures between 333.2 K and 543.2 K, and then, thermodynamic interactions were determined using n-butyl acetate, iso-butyl

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acetate, n-octane, n-nonane, n-decane, undecane, dodecane, tridecane, n-propyl benzene,

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isopropylbenzene, ethylbenzene, chlorobenzene and toluene at temperatures between 518.2 K and 543.2 K by IGC technique. Subsequently, we synthesized PDLC composite by SIPS

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method. PMMA and DBCA were controlled to be 20/80 wt%.

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2. Theory of thermodynamic characterization by IGC technique IGC at infinite dilution is used to characterize the thermodynamic characteristics of LCs [13-

(1)

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𝑉𝑔0 = 273.2 𝑄(𝑡𝑅 − 𝑡𝐴 )𝐽/(𝑇𝑓 𝑤)

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15]. The specific retention volume 𝑉𝑔0 was calculated from [21-22]

where Q is the carrier gas flow rate measured at room temperature 𝑇𝑓 ; 𝑡𝑅 and 𝑡𝐴 are retention times of the solvent and air, respectively; w is the weight of LC in the column, J is the

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pressure correction factor, which depends on the inlet pressure 𝑃𝑖 , and outlet pressure 𝑃0 , calculated using the following relation,

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3 (𝑃𝑖 ⁄𝑃0 )2 − 1 𝐽= ⌊ ⌋ 2 (𝑃𝑖 ⁄𝑃0 )3 − 1

(2)

The interaction between two components in a mixture can be evaluated by Flory-Huggins ∞ ∗ interaction parameters, 𝜒12 and 𝜒12 from following equations, respectively:

∞ 𝜒12

273.2𝑅𝑣2 𝑉10 𝑝10 (𝐵11 − 𝑉10 ) = 𝑙𝑛 ( 0 0 ∗ ) − (1 − )− 𝑀2 𝑣2 𝑅𝑇 𝑝1 𝑉𝑔 𝑉1

(3)

ACCEPTED MANUSCRIPT 273.2𝑅𝑣2∗ 𝑉1∗ 𝑝10 (𝐵11 − 𝑉10 ) ∗ 𝜒12 = 𝑙𝑛 ( 0 0 ∗ ) − (1 − ) − 𝑀2 𝑣2∗ 𝑅𝑇 𝑝1 𝑉𝑔 𝑉1

(4)

where, R is the universal gas constant, 𝑉10 , 𝐵11 and 𝑝10 are the molar volume, the second virial coefficient and the saturated vapor pressure of the solvent at temperature T, respectively, 𝑉1∗ is the molar hard-core volume of the solvent, 𝑣2 and 𝑣2∗ are specific volume and specific hardcore volume of the liquid crystal, respectively.

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The effective exchange energy parameter, 𝑋𝑒𝑓𝑓 , in the equation of state theory is calculated as

1/3

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follows: 1/3

(5)

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∗ −1 −1 𝑅𝑇𝜒12 = 𝑝1∗ 𝑉1∗ {3𝑇1𝑟 𝑙𝑛[(𝑣1𝑟 − 1)/(𝑣2𝑟 − 1)] + 𝑣1𝑟 − 𝑣2𝑟 + 𝑋𝑒𝑓𝑓 /𝑃1∗ 𝑣2𝑟 }

𝑝1∗ is characteristic pressure, 𝑣1𝑟 and 𝑣2𝑟 are reduced volume of the solvent and LC,

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respectively. 𝑇1𝑟 is reduced temperature of the solvent.

The weight fraction activity coefficent, Ω1∞ has become the most widely used parameter in

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∞ IGC method compared to the 𝜒12 in terms of thermodynamic interactions since it is derived

from the fundamental relations of physical chemistry and consequently does not include any uncertainty coming from the theoretical assumptions and can be calculated from

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chromatographic data using the molar mass of the probe. Ω1∞ is the weight fraction activity coefficient of solvent at infinite dilution is defined by the following equation [23]:

273.2𝑅 𝑝10 (𝐵11 − 𝑉10 ) = 𝑙𝑛 ( 0 0 ) − 𝑅𝑇 𝑉𝑔 𝑝1 𝑀1

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Ω1∞

(6)

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Where 𝑀1 is the molecular weight of solvent. The partial molar heat of mixing, ∆𝐻1∞ , is obtained from equation [24-26]

∆𝐻1∞ = 𝑅 [

𝜕(𝑙𝑛Ω1∞ ) ] 𝜕(1/𝑇)

(7)

The partial molar heat of sorption, ∆𝐻1,𝑠 , of the solvent sorbed by the solute is given as: ∆𝐻1,𝑠

𝜕(𝑙𝑛𝑉𝑔0 ) = −𝑅 [ ] 𝜕(1/𝑇)

(8)

ACCEPTED MANUSCRIPT The molar heat of vaporization, ∆𝐻𝑉 , of the solvent is defined as follows: ∆𝐻𝑉 = ∆𝐻1∞ − ∆𝐻1,𝑠

(9)

3.Experimental

3.1.Materials and Instrumentation

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A Hewlett-Packard 6890 N gas chromatography with a thermal conductivity detector was used to research the retention times of the solvents. The column was made of stainless steel

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tubing with 3.2 mm outside diameter and 1 m in length, was obtained from Alltech Associates, Inc. The LC was coated on the support material by slow evaporation of

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chloroform as stirring the Chromosorb W in the LC solution. 0.1 𝜇L of solvent was injected into the column with a 1 𝜇L Hamilton syringe and flushed into the air. The column was

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conditioned under a helium atmosphere for 24 h at 423.2 K. Compound DBCA was characterized 1H-NMR and

13

C-NMR (Bruker Avance III 500

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spectrometer, in DMSO-d6 solution, with tetramethylsilane as internal standard). The mesomorphic properties of DBCA and PDLC were investigated by using a Mettler FP-82 HT hot stage and control unit in conjunction with a Leica DM2700P polarizing microscope. DSC-

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thermograms of DBCA and PDLC composite films were recorded on a Perkin-Elmer DSC-6,

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heating and cooling rate: 10°C min-1 in a nitrogen atmosphere. The rigid and transparent PMMA was used as a acrylic polymer for PDLC from Alfa Eesar with molecular weight of Mw= 120000 (g/mol). Ethyl 4-hydroxy-4-biphenylcarboxylate (Aldrich), n-decyl bromide

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(Merck), NaOH (Merck) and K2CO3 (Merck) were purchased commercially. Solvents were purchased or distilled. 2-Butanone (Merck) and Ethanol (Merck) were purchased

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commercially and were used without further purification. Solvents (chloroform and ethanol) used in the separation and purification steps were distilled. Analytical thin-layer chromatography (TLC) was carried out on aluminium plates coated with silica gel 60 F254 (Merck). In the IGC method, the probes such as n-butyl acetate, tert-butyl acetate, iso-butyl acetate, noctane,

n-nonane,

n-decane,

undecane,

dodecane,

tridecane,

n-propylbenzene,

isopropylbenzene, ethylbenzene, chlorobenzene and toluene were used without further purification as obtained from Merck AG Inc. The support material, Chromosorb-W (AWDMCS-treated, 80/100 mesh), was also purchased from Merck AG Inc. Silane-treated glass

ACCEPTED MANUSCRIPT wool used to plug the ends of the column was supplied from Alltech Associates, Inc. Purity of reagents and purification method of solvents are given in Table 1. Table 1. Purity of reagents and purification method

none

-

-

Merck Merck Merck Merck Merck Tekkim Merck Merck Merck Merck Merck Merck Merck Merck Merck Merck Merck

<=1.000 <=1.000 ≥ 0.990 ≥ 0.990 ≥ 0.999 ≥ 0.999 ≥ 0.999 ≥ 0.999 ≥ 0.990 ≥ 0.990 ≥ 0.990 ≥ 0.999 ≥ 0.999 ≥ 0.999 ≥ 0.999 ≥ 0.999

none none none none none distilation distilation none none none none none none none none none none none

0.960 0.999 -

GC* GC* -

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= 0.980

*Gas-liquid chromatography

Purification Final Mole method FractionPurity

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chloroform n-octane n-nonane n-decane undecane dodecane tridecane n-propylbenzene isopropylbenzene ethylbenzene chlorobenzene toluene

Aldrich

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ethanol

Initial Mole FractionPurity

D

ethyl 4-hydroxy-4biphenylcarboxylate n-decyl bromide sodium hydroxide potassium carbonate 2-butanone

Source

Analysis Method

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Chemical Name

3.2 Synthesis and Characterization of DBCA The synthesis of DBCA was carried out according to procedures described in the literature

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[27]. Firstly, the mixture of Ethyl 4-hydroxy-4-biphenylcarboxylate (6.7 mmol), n-decyl bromide (10 mmol) and K2CO3 (10 mmol) in 2-Butanone (70 mL) was refluxed under argon

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atmosphere for 5 h, and the end of the reaction was monitored by TLC (chloroform). The resulting mixture was filtered on silica gel and washed with chloroform. The solvent was removed under reduced pressure. The resulting product Ethyl 4-(n-decyloxy)biphenyl-4′carboxylate (EDBC) was purified by crystallization from ethanol. Yield: 92%; colorless crystals. 1H-NMR: (500 MHz, DMSO-d6): δ (ppm) = 8.11 (d, J ≈ 8.4 Hz; 2H, 2 Ar-H), 7.64 (d, J ≈ 8.4 Hz; 2H, 2 Ar-H), 7.59 (d, J ≈ 8.7 Hz; 2H, 2 Ar-H), 7.01 (d, J ≈ 8.7 Hz; 2H, 2 ArH), 4.42 (q, J ≈ 7.1 Hz; 2H, COOCH2), 4.03 (t, J ≈ 6.6 Hz; 2H, OCH2), 1.86-1.81 (m; 2H, CH2), 1.53-1.47 (m; 2H, CH2), 1.39-1.28 (2m; 12H, 6 CH2), 1.44 (t, J ≈ 7.1 Hz; 3H, OCH2CH3), 0.91 (t, J ≈ 6.8 Hz; 3H, CH3).

13

C-NMR (125 MHz, DMSO-d6): δ (ppm) =

166.66 (COOCH2CH3), 159.47, 145.24, 132.26, 128.58 (Ar-C), 130.09, 128.35, 126.43,

ACCEPTED MANUSCRIPT 114.98 (Ar-CH), 68.20 (OCH2), 60.93 (COOCH2CH3), 31.95, 29.63, 29.61, 29.45, 29.37, 29.31, 26.10, 22.73 (CH2), 14.42 (COOCH2CH3), 14.16 (CH3). After the etherification reaction of ethyl 4-hydroxy-4-biphenylcarboxylate with the n-decyl bromide, the hydrolysis was realized to obtain 4-Decyloxybiphenyl-4’-carboxylic acid (DBCA) [28, 29]. 7.8 mmol of EDBC was dissolved in 60 mL of EtOH and added 15.6 mmol of NaOH solution to this mixture. The mixture was heated under the reflux for 12 h. The

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result of the reaction was monitored by TLC (chloroform). Then, the hot solution was poured into the water and the pH adjusted between 1-2 by adding 1 N HCl. The resulting crude

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product was filtered and crystallized from ethanol. Yield: 72%; colorless crystals. 1H-NMR: (500 MHz, DMSO-d6): δ (ppm) = 7.97 (d, J ≈ 8.3 Hz; 2H, 2 Ar-H), 7.72 (d, J ≈ 8.3 Hz; 2H, 2

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Ar-H), 7.67 (d, J ≈ 8.7 Hz; 2H, 2 Ar-H), 7.04 (d, J ≈ 8.7 Hz; 2H, 2 Ar-H), 4.02 (t, J ≈ 6.5 Hz; 2H, OCH2), 1.76-1.71, 1.48-1.39, 1.35-1.25 (3m; 16H, 8 CH2), 0.86 (t, J ≈ 6.8 Hz; 3H, CH3). C-NMR (125 MHz, DMSO-d6): δ (ppm) = 167.20 (COOH), 158.96, 143.83, 131.08, 129.05

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(Ar-C), 129.89, 128.06, 126.01, 114.96 (Ar-CH), 67.52 (OCH2), 31.26, 28.97, 28.92, 28.73,

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28.66, 28.62, 25.46, 22.06 (CH2), 13.92 (CH3). 3.3. Preparation of PDLC Composite

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In this study, PDLC composite of PMMA and DBCA were prepared by SIPS method. We

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mixed appropriate amounts of PMMA and DBCA in a common solvent (DMSO), this solution was stirred mechanically until glass transition temperature for 30 minutes and then mixture was dried at 50 °C under vacuum in order to induce the phase separation of LC

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droplets from the polymer matrix. PDLC composite (PMMA:DBCA) were controlled to be

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20:80 wt% [17-20].

4.Result and Discussion 4.1.Liquid Crystalline Properties The mesomorphic properties of the DBCA were investigated by using PM and DSC. The phase transition temperatures, corresponding enthalpy values and mesophase type observed for DBCA are given in Figure 1.

ACCEPTED MANUSCRIPT Figure 1. The chemical structure, mesophase type and phase transition temperatures of the DBCA.

O H21C10O

OH T/K [ΔH kJ/mol]a

Compound DBCAb

Heating: Cr1 363.7 [5.2] Cr2 437.9 [7.1] Cr3 443.9 [23.8] SmC 515.6 [38.0] Iso

a

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Cooling: Iso 511.8 [28.6] SmC 437.2 [20.3] Cr3 425.6 [1.4] Cr2 352.9 [4.3] Cr1 Perkin-Elmer DSC-6; enthalpy values in italics in brackets taken from the 2nd heating and

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cooling scans at a rate of 10°C min-1; Abbrevations: Cr = crystalline, Sm = smectic, Iso =

In ref. 29 for compound DBCA: Cr 445.7 SmX 529.7 N 530.2 Iso.

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b

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isotropic liquid phase.

DBCA shows an enantiotropic SmC phase with a Schlieren texture at high temperature as shown in Figure 2. Transition temperatures were detected by calorimetric peaks of the DSC

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D

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heating-cooling scans (see Figure 6 and 7).

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Figure 2. The Schlieren texture obtained between crossed polarizers as observed for SmC phase of DBCA at T= 493.2 K on cooling.

4.2 Thermodynamic interaction results The specific retention volume data is necessary in the determination of the thermodynamic properties of a LC by IGC. The specific retention volumes, 𝑉𝑔0 , of the isomeric solvents such as nBAc, iBAc, tBAc on the DBCA were obtained from IGC measurements between 333.2 K and 543.2 K. The percent error in 𝑉𝑔0 was calculated as less than ±0.5 by using four or five

ACCEPTED MANUSCRIPT successive measurements of each datum. Retention diagrams are plotted in Figure 3 for acetates of DBCA in terms of a plot of 𝑙𝑛𝑉𝑔0 calculated from Equation (1) versus temperature. According to the retention diagram in Figure 3, Cr 1-Cr 2, Cr 2-SmC and SmC-Iso transitions for DBCA were found to be 358.2 K, 449.2 K and 505.2 K, respectively, in terms of the maximum points indicated in the majority of the plots. The Cr 1-Cr 2, Cr 2-SmC and SmC-Iso transition temperatures obtained by IGC technique are in good agreement with the ones

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obtained by DSC (Figure 1). As shown in Figure 3, a good separation can be obtained

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between isomers in the studied temperature ranges.

4.5

3.5

2.5

(3)

2.0

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lnVg0

(2)

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3.0

1.5

D

1.0

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0.5 0.0

0.0020

0.0022

0.0024 0.0026 -1 1/T (K )

0.0028

0.0030

0.0032

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-0.5 0.0018

(1)

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4.0

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Figure 3. The specific retention volume diagrams, 𝑉𝑔0 , of n-butyl acetate (1), iso-butyl acetate (2) and tert-butyl acetate (3) on DBCA.

Thermodynamic properties of DBCA in liquid state can be studied at thermodynamic equilibrium region. Linearity is observed when the stationary phase remains in the same thermodynamic state. Thermodynamic interactions of DBCA were determined at the temperatures between 518.2 K and 543.2 K because it was found out from Figures 4 and 5 that the thermodynamically equilibrium occurred at this temperature range.

ACCEPTED MANUSCRIPT

3.0 2.5

(1)

2.0

(2) (3)

1.5

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lnVg0

(4)

1.0

(6)

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0.5

(5)

-0.5 0.00183

0.00185

0.00187

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0.0

0.00189 1/T (K-1)

0.00191

0.00193

0.00195

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Figure 4. The specific retention volume diagrams, 𝑉𝑔0 , of tridecane (1), dodecane (2),

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undecane (3), n-decane (4), n-nonane (5) and n-octane (6) on DBCA

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2.0

(5)

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lnVg0

1.0

(1) (2) (3) (4)

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1.5

0.5

0.0

-0.5 0.00183

0.00185

0.00187

0.00189 1/T (K-1)

0.00191

0.00193

0.00195

Figure 5. The specific retention volume diagrams, 𝑉𝑔0 , of n-propyl benzene (1), isopropyl benzene (2), ethylbenzene (3), chlorobenzene (4) and toluene (5) on DBCA

ACCEPTED MANUSCRIPT ∞ ∗ The LC-solvent interaction parameters, 𝜒12 and 𝜒12 determined from Equations (3) and (4)

the values were given in Tables 2 and 3, respectively. ∞ The 𝜒12 higher than 0.5 indicates unfavorable LC-solvent interactions whereas the values

lower than 0.5 remarks favorable interactions in dilute LC solutions. The values of the obtained parameters are higher than 0.5 and show an increase in the interaction parameter as ∞ ∗ the temperature is increased. The values of 𝜒12 and 𝜒12 suggest that all the studied solvents

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are poor for DBCA. All of the parameters decrease with temperature indicating exothermic solubility.

518.2 523.2 528.2 533.2 538.2 543.2

n-octane

1.22

1.32

1.46

1.58

1.70

1.76

n-nonane

1.38

1.45

1.61

1.71

1.79

1.90

n-decane

1.47

1.56

1.67

1.77

1.87

1.98

undecane

1.57

1.66

1.77

1.87

2.00

2.09

dodecane

1.60

1.69

1.79

1.90

1.98

2.05

tridecane

1.67

1.78

1.88

1.98

2.08

2.14

n-propylbenzene

1.33

1.52

1.65

1.88

2.01

1.33

1.54

1.77

1.95

2.11

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1.14

ethylbenzene

1.08

1.24

1.42

1.65

1.82

1.98

chlorobenzene

1.08

1.28

1.50

1.74

2.04

2.25

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isopropylbenzene 1.13

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Solvent

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∞ Table 2. Flory-Huggins LC-solvent interaction parameters, 𝜒12 , of DBCA

0.60

0.80

1.03

1.27

1.58

1.80

toluene

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∞) Standard uncertainty 𝑢 is 𝑢(𝜒12 =0.01

ACCEPTED MANUSCRIPT ∗ Table 3. The equation of state LC-solvent interaction parameters, 𝜒12 , of DBCA

518.2 523.2 528.2 533.2 538.2 543.2

n-octane

1.40

1.51

1.66

1.78

1.91

1.97

n-nonane

1.53

1.60

1.76

1.87

1.95

2.06

n-decane

1.59

1.68

1.79

1.89

2.00

2.11

undecane

1.67

1.75

1.88

1.98

2.10

2.19

dodecane

1.68

1.77

1.87

1.98

2.06

2.13

tridecane

1.73

1.84

1.95

2.04

2.14

2.20

n-propylbenzene

1.29

1.48

1.67

1.81

2.05

2.19

isopropylbenzene 1.29

1.50

1.71

1.95

2.13

2.30

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Solvent

1.27

1.43

1.62

1.85

2.02

2.20

chlorobenzene

1.28

1.48

1.71

1.94

2.25

2.47

toluene

0.83

1.04

1.27

1.52

1.84

2.06

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ethylbenzene

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∞) Standard uncertainty 𝑢 is 𝑢(𝜒12 =0.01

In this study, the effective exchange energy parameters, 𝑋𝑒𝑓𝑓 , in the equation of state theory were obtained from Equation (5), and the values were tabulated in Table 4. Small values of

D

𝑋𝑒𝑓𝑓 indicate that there are specific interactions between solvents and LC; the higher values

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of 𝑋𝑒𝑓𝑓 define poor solubility. It was seen that the 𝑋𝑒𝑓𝑓 results of DBCA in all solvents increased with temperature. It was determined that the values are high and approve the

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∞ discussion concerning 𝜒12 .

ACCEPTED MANUSCRIPT Table 4. The effective exchange energy parameters, 𝑋𝑒𝑓𝑓 ( j cm-3), of DBCA 518.2 523.2 528.2 533.2 538.2 543.2

n-octane

35.8

41.0

47.9

53.7

60.1

64.1

n-nonane

34.8

38.1

44.5

48.7

52.8

57.6

n-decane

32.8

36.1

40.3

44.0

48.3

52.5

undecane

32.2

35.1

38.2

42.6

46.9

50.0

dodecane

32.1

34.5

37.6

41.3

tridecane

29.8

33.1

35.7

38.5

n-propyl benzene

36.8

45.6

55.0

61.6

73.4

80.4

isopropylbenzene 38.1

48.4

58.5

70.5

80.3

89.1

75.7

85.9

96.3

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Solvent

46.2

41.4

43.2

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43.8

42.2

51.7

62.5

chlorobenzene

53.7

67.9

83.0 100.0 120.9 136.4

toluene

23.8

37.8

53.1

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ethylbenzene

69.7

90.9 106.3

-3

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Standard uncertainty 𝑢 is 𝑢(𝑋𝑒𝑓𝑓 ) =1.0 ( j cm ) The weight fraction activity coefficients of the studied solvents at infinite dilution, Ω1∞ , were

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detected from Equation (6) and the results were given in Table 5. According to Guillet [30],

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the solvent is good if Ω1∞ < 5 but it is poor if Ω1∞ > 10. The values between 5 and 10 show moderately good solubility. The values of the Ω1∞ parameters suggest that n-alkanes are poor

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however benzenes are slightly poor solvents for DBCA.

ACCEPTED MANUSCRIPT Table 5. The weight fraction activity coefficients at infinite dilution of the solvents, Ω1∞ , of DBCA. Solvent

518.2 523.2 528.2 533.2 538.2 543.2 9.5

10.7

12.4

14.0

15.9

17.0

n-nonane

10.1

10.9

12.9

14.2

15.8

17.4

n-decane

10.2

11.2

12.5

13.8

15.5

17.2

undecane

10.5

11.4

12.8

14.2

16.2

17.7

dodecane

10.0

10.9

12.1

13.6

14.6

15.8

tridecane

10.0

11.2

12.4

13.7

15.1

16.0

n-propyl benzene

7.4

9.0

11.0

12.5

16.0

18.2

isopropylbenzene

7.3

9.0

11.0

14.0

16.9

19.9

ethylbenzene

7.4

8.7

10.6

13.3

15.9

18.8

chlorobenzene

6.1

7.5

9.4

12.0

16.3

20.3

toluene

4.9

6.1

7.8

10.0

13.7

17.2

Standard uncertainty 𝑢 is

𝑢(Ω1∞ )

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n-octane

=0.1

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The values of partial molar heat, ∆𝐻1∞ , of mixing at infinite dilution were calculated from the

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slopes of the plots of 𝑙𝑛Ω1∞ versus 1/T using Equation (7) in the temperature ranges from 518.2 K to 543.2 K and were given in Table 6. According to the values of ∆𝐻1∞ , the solubility of LC in all solvents is exothermic and the obtained values of ∆𝐻1∞ confirm the discussion

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∞ concerning 𝜒12 and 𝑋𝑒𝑓𝑓 . As well as the values of the partial molar heat, ∆𝐻1,𝑠 , of sorption of

the solvents on DBCA were found from the slopes of the straight lines of 𝑙𝑛𝑉𝑔0 versus in the

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same temperature ranges using Equation (8) and results were given in Table 6. The values of ∆𝐻𝑉 for the studied solvents calculated from Equation (9) were also compared to the literature values [31]. The results for all of the studied solvents were given in Table 6. There is a very good agreement between ∆𝐻𝑉 and ∆𝐻𝑉𝐿 values for dodecane (boiling point 487.2 K) and tridecane (boiling point 505.2 K) as reported in Table 6. The boiling points of these two compounds are very close to studied temperatures. However, for other solutes, the calculated values of ∆𝐻𝑉 deviate somewhat at studied temperatures.

ACCEPTED MANUSCRIPT Table 6. The values of the partial molar heat of sorption, ∆𝐻1,𝑠 , (kcal mol−1), the partial molar heat of mixing at infinite dilution, ∆𝐻1∞ (kcal mol−1), the molar heat of vaporization, ∆𝐻𝑉 (kcal mol−1), of the studied solvents, and the literature values of the molar heat of vaporization, ∆𝐻𝑉𝐿 (kcal mol−1) [31]. ∆𝐻1,𝑠 ∆𝐻1∞

∆𝐻𝑉

∆𝐻𝑉𝐿

n-octane

-19.5 -13.4

6.1

8.2

n-nonane

-19.5 -12.3

7.2

8.8

n-decane

-20.0 -11.8

8.2

undecane

-21.2 -12.0

9.2

dodecane

-20.4 -10.4

10.0

tridecane

-21.6 -10.7

10.9

10.9

n-propyl benzene -28.0 -20.2

7.8

9.1

7.4

9.0

7.0

8.5

-28.4 -21.4

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ethylbenzene

9.4 9.9

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isopropylbenzene -30.3 -22.9

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Solvent

10.4

-34.2 -27.2

7.0

8.7

toluene

-34.2 -28.4

5.8

7.9

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chlorobenzene

4.3. PDLC Composite Properties

LC:polymer composites have a wide variety of promising applications ranging from LC

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displays to smart windows and projection light valves [32]. Due to their numerous and important properties for a wide variety of applications, we prepared PDLC in the ratio 20/80

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(wt% LC) by SIPS method. The thermotropic behavior of polymer dispersed LC composite was investigated by PM and DSC. Comparison of the mesomorphic properties of the DBCA with the PDLC composite film show that the both LC materials exhibit SmC mesophase in a wide temperature range. The melting and crystallization points of the PDLC composite closely resemble to that of the DBCA. DSC thermograms of DBCA and PDLC on heating and cooling were shown in Figure 6 and 7, respectively.

ACCEPTED MANUSCRIPT

Heat Flow Endo Down

(1) 362.2

380.0 441.6

496.5

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(2) 363.7

515.6

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437.9

350.0

400.0

450.0

500.0

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300.0

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443.9

550.0

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Temperature (K)

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Figure 6. DSC thermograms of PDLC (1) and DBCA (2) during the heating process

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363.9 381.0

479.3 (1)

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354.6

437.2 511.8

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Heat Flow Endo Down

435.1

352.9

300.0

350.0

425.6

400.0 450.0 Temperature (K)

(2)

500.0

550.0

Figure 7. DSC thermograms of PDLC (1) and DBCA (2) during the cooling process

ACCEPTED MANUSCRIPT The phase transition temperatures on second heating of LC and PDLC were observed at 443.9 K, 515.6 K and 441.6 K, 496.5 K, respectively. The phase transition temperatures on second cooling of LC and PDLC were observed at 437.2 K, 511.8 K and 435.1 K, 479.3 K, respectively. In case of the PDLC composite, the clearing temperature (Tc) of the LC phase was shifted to a lower temperature and the sharp peak became broader in the DSC heating and cooling curves

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by PM. The texture of the PDLC sample was given in Figure 8.

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Phase transition temperatures as well as morphology of the PDLC composite was examined

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Figure 8. The mesophase texture of PDLC below 479.2 K on cooling.

The mesophase transition temperatures observed in DSC study of PMMA:DBCA composite

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on heating and cooling were confirmed with polarized optical microscopy. According to the PM results, the birefringent regions of DBCA in the composition PMMA:DBCA (20/80) also

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appear in PMMA-rich domains on heating and cooling. The existence of the smectic phase in PMMA:DBCA composite material was illustrated in Figure 8. The Schlieren texture of SmC mesophase was observed until 434.2 K on cooling and the birefringent texture of mesophase starts decomposing as the temperature is reduced further (Figure 9) and the isotropic-smectic phase transition occurs at lower temperature as compared to pure DBCA. As seen in textures, the LC droplets with spherical shape were not observed on cooling from the isotropic liquid; however DBCA molecules are partially dispersed in the polymer matrix.

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(a)

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K and (b) 386.2 K.

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Figure 9. Optical microscopic images under polarized light for PDLC on cooling (a) at 418.2

Conclusions

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In this study, we reported the synthesis and characterization of DBCA exhibiting an enantiotropic SmC mesophase in a wide temperature range. The phase behaviour of DBCA

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was investigated by PM, DSC and IGC. The phase transition temperatures of DBCA obtained by IGC are good agreement with ones obtained by DSC. The study also suggests that the seperation ability of the DBCA was good enough for acetate isomers in the studied

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temperature ranges. The thermodynamic parameters of DBCA were determined via IGC. The

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results suggest that selected solvents are poor solvent for the DBCA. IGC is a convenient method for the characterisation of the thermodynamic and isomer selectivity of LC compounds.

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The PDLC composite was prepared from PMMA and DBCA by SIPS method. The mesomorphic behavior of PDLC composite has been investigated by DSC and PM. The reduce in the transition temperatures of DBCA molecules as well as PM textures of the PDLC

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composite confirmed that DBCA molecules are partially dispersed in the polymer matrix.

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Graphical abstract

ACCEPTED MANUSCRIPT Highlights  A new chiral calamitic liquid crystal DBCA was studied. We reported thermodynamic properties of DBCA.



PDLC composite film was synthesized by solvent-induced phase separation method.



DBCA selectivity was investigated using the acetate isomers by the IGC method

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