Observance of Multiple Melting and Nematic Phase Transitions in A Next Generation “Quaternary Liquid Crystal System” (QLCS)

Seide M and Sharma D

Published on: 2023-05-31

Abstract

This paper explores the details of a Liquid Crystal (LC) system made by mixing four liquid crystals from the Alkyl Cyanobiphenyl (nCB) family with different molecular weights with different sizes of different sizes CH tails. These four nCB liquid crystals are 4CB, 5CB, 6CB, and 7CB, and they are added in a 3:2:1:3 ratio. We call this liquid crystal system a “Quaternary Liquid Crystal System” (QLCS). After preparing this system, they are used for study using the Differential Scanning Calorimetry (DSC) technique. This QLCS is heated from - 40 °C to 80 °C with a 20 °C/min ramp rate and then cooled from 80 °C to -40 °C in DSC with the same ramp rate. This experimental method brings some unique phase transitional behavior in this QLCS that is not observed in its parent LCs as a single LC. The QLCS shows double melting and double nematic phase transitions in heating and double phase transitions in cooling in nematic. It does not show any crystallization in cooling. This unique result draws our attention toward detailed research and makes this sample significant in the research and science field. This study may bring some significant possibilities for the use of mixed LCs in the Liquid Crystal Display (LCD) world.

Keywords

Liquid crystal; Phase transition; Melting; Nematic; Heating; Cooling; Heat capacity; Heat flow; DSC, Thermodynamics; Gaussian law

Introduction

A liquid crystal (LC) is a substance that combines the properties of two different solid states, liquid and crystalline solid states. For instance, while liquids can flow, they cannot flow through solid bodies. The crystalline solid state of LCs has a unique symmetry, making them different from other types of solids. As the temperature increases, ordinary solid materials like ice can melt into liquid water or vapor. However, some solid materials can melt more than two times, as ice typically would not. At high temperatures, the liquid crystal is an intermediate state between the ordinary state and the crystalline solid called the Nematic State. Although they share similar properties, the symmetries of the crystalline solid state are exhibited by the liquid crystal [1-8].

A Researcher, George Gray, created a type of LCD known as the 5CB LC, which is based on the nCB family. This achievement is a significant discovery in the field of LCD technology. The 5CB LC can function well inside the room temperature range, as they can exhibit a nematic phase between 22 to 35 °C. Although the nCB LCs are similar in terms of their nematic phase. The other nCB LCs have a nematic state occurring around that range [8-15].

Based on that, our interest has increased in studying LCs from the Alkyl Cyanobiphenyl (nCB) family but have different molecular weights from lower to higher weights. Their functional groups are the same, but they are different in their size of C-H tail. The 5CB that is mentioned above is also from nCB group. To study in detail how LCs behave with temperature when they are heated or cooled in the form of a mixture, four different types of LCs are used in this study [13-18].

Mostly, researchers studied mono LCs, a single LC using various methods including Differential Scanning Calorimetry (DSC) to see their thermal behavior and find how many states they have. Following their studies on mono LCs, researchers have taken to combining multiple types of LCs and analyzing their thermal behavior. Binary liquid crystals can be formed by combining two different types of liquid crystals at a certain proportion. A study on binary liquid crystals showed that when 5CB is mixed with 7CB, it goes through crystallization before transitioning to an isotropic state. On the other hand, when it's cooled, it goes back to nematic. Tertiary liquid crystals can be formed by combining three different types of liquid crystals at a certain proportion. A study on tertiary liquid crystals showed that when 5CB, 6CB, and 7CB are mixed together, it was unable to return to its crystalline state during cooling. LCs are very useful in LCDs and smart devices due to their applications in various fields, such as electronic display technology [16-25].

Understanding the phases of these materials is essential for their optimization and development. The goal of this study is to provide an extensive analysis of the properties of quaternary liquid crystals and their importance in the development of electronic devices. In addition, it explores the phase transition of these materials. The LCs used in this study are four LCs from nCB groups. More details are shown in the Material, Method and Result section of the paper.

Material, Methods and Theory

Four liquid crystals from nCB family were used for this study. These are four pure, bulk samples of 4-Butyl-4'-cyanobiphenyl (4CB), 4-pentyl-4-cyanobiphenyl (5CB), 4-Hexyl-4'-cyanobiphenyl (6CB), and 4'-Heptyl-4-cyanobiphenyl (7CB) liquid crystals. These LCs are mixed in a ratio of 3:2:1:3. The chemical structure of these LCs can be seen in Figure 1. The molecular weight of these LCs is 235.33, 249.36, 263.38, and 277.41 g/mol respectively. These four LCs were mixed at room temperature and then heated to their full melting state and kept there for an hour, stirred, then cooled back to room temperature, then this mixture is ready to use for experiments. This mixture is called “Quaternary Liquid Crystal System” QLCS for this study. The molecular sizes of these four LCs can be seen in Figure 2.

Once this QLCS is ready, it is taken to a Differential Scanning Calorimeter (DSC) model DSC 214 instrument from the NETZSCH that is located at WPI’s chemistry and biochemistry department, Worcester, MA, USA. The QLCS is taken into a small pan with a very small amount of it and then placed in this DSC with an empty pan. Then DSC instrument is used to heat the sample from -40 °C to 80 °C and then cooled from 80 °C to -40 °C with a 20 °C/min ramp rate. The results found from the DSC instrument were taken to the Logger Pro for further data analysis.

Figure 1: Skeletal chemical structure of LCs (a) 4CB, (b) 5CB, (c) 6CB, (d) 7CB.

Figure 2: Molecular sizes of 4CB, 5CB, 6CB, and 7CB.

DSC Theory

These experiments involve the thermodynamics of DSC, and this theory can be seen in our recently published papers in detail [25]. Here, we are writing this DSC theory in brief as is used for QLCS. Equation 1 shows heat, Q is equal to the mass, m, specific heat capacity, Cp, and change in temperature, 

The specific heat capacity of the sample can be found by equation 2,

The Enthalpy ( ) of the transition can be found from equation 3.

The heat flow going in the sample can be written as equation 4.

To understand further thermal emchanics of the QLCS, derivatives can be taken to the heat flow where the 1st, 2nd, 3rd derivatives are taken of heat flow and they are shown in the equations 5, 6, 7 respectively.

The QLCS shows multiple peaks including in their melting, nematic transitions. According to Gaussian Law, if there is more than one peak appears, that can be the combination of more than one thing going on in the sample. To study the details of multi peaks, Gaussian Analysis is done for these melting and nematic transitions.

Gaussian Theory

To analyze double peaks observed in QLCS, Gaussian theory is applied to QLCS data. The Gaussian equation is shown below as equation 8 [24,25].

The Gaussian Equation can be written as

Where a, b, c, d are parameters. The a, b, c, and d represent the height of the peak, the center of the peak position or peak value, the width of the peak, and the Asymptotic value respectively. The effect of variation in a, b, c, d in peak can be seen below in Figure 3 which is taken from publication [24,25].

Figure 3: The effect of a, b, c, d parameters on peak according to the Gaussian theory shown in this figure, taken from reference [24,25].

Result

Detailed results of QLCS using DSC can be seen below. The heating and cooling of the QLCS are shown as heat flow versus temperature, and then results are plotted as specific heat capacity versus temperature. To see more clear results of QLCS, some zoomed in plots are also shown for each phase transition observed in QLCS using, taken DSC technique. All of these graphs are plotted in Logger Pro.

Figure 4: Heat Flow (HF) vs. Temperature (T) plot of the Crystalline (K), Nematic (N), and Isotropic (I) phase transitions of QLCS for the heating and cooling.

Figure 4 shows the HF vs. T of the QLCS. The melting peak transition is at 12.0252°C the QLCS. It shows the QLCS crystalline (K) to nematic (N) phase transition. The nematic transition peak is at 38.29°C, which shows the heating nematic (N) to isotropic (I) phase transition. The QLCS transitioned from the isotropic to the nematic state at 29.91°C on the downward peak. The transition temperatures are recorded in Table 1.

Figure 5: Specific Heat Capacity (Cp) Vs. Temperature plot of QLCS. The shaded area represents the change in internal energy of the QLCS.

Figure 5 Cp vs. T, shows how much internal energy was used by the QLCS during the heating and cooling process. The green shaded area shows the integral of the plot, which is the total energy consumed and released during the heating and cooling. The internal energy used in the cycle is 467.2 J/g°C.

Figure 6: The phase traditions that occur during the endothermic process of the QLCS.

Figure 7: The phase transition that occurs during the exothermic period of the QLCS.

Figure 6 shows the Cp vs. T, plot for the endothermic melting and nematic transition peaks whereas Figure 7 shows the Cp vs. T, plot for the exothermic nematic transition peak.

Figure 8: The Cp vs. Temperature (T) for the endothermic melting peak of the TLC mixture.

Figure 9: The Cp vs. Temperature (T) for the first endothermic nematic peak of the QLCS.

Figure 8 shows the enlarged melting phase transition peak of the QLCS. It identifies the location of the starting and ending temperatures and their corresponding specific heat capacity value. The Cp peak, wing jump, temperature change, and specific heat capacity of the melting phase transition are identified. The pink shaded area represents the peak integral, which calculates the energy used for the melting transition. The amount of thermal energy required for the melting transition was 49.94 J/g. The variables used are recorded in Table 2.

Figure 10: The Cp vs. Temperature (T) for the second endothermic nematic peak of the QLCS mixture.

Figure 9 shows the QLC’s enlarged first endothermic nematic phase transition peak. It highlights the starting and ending temperatures and their corresponding specific heat capacity value. The Cp peak, wing jump, temperature change, and specific heat capacity of the melting phase transition are labeled. The pink shaded area represents the peak integral, the calculated energy used for the nematic transition. The amount of thermal energy required for the nematic transition was 0.71 J/g. The symbols used are recorded in Table 2.

Figure 10 shows the QLCS's enlarged second endothermic nematic phase transition peak. It highlights the starting and ending temperatures and their corresponding specific heat capacity value. The Cp peak, wing jump, temperature change, and specific heat capacity of the melting phase transition are labeled. The pink shaded area represents the peak integral, the calculated energy used for the nematic transition. The amount of thermal energy required for the nematic transition was 0.95 J/g. The symbols used are recorded in Table 2.

Figure 11: The Cp vs. Temperature (T) for the exothermic nematic peak of the QLCS.

Figure 12: Compared HF vs. T phase transitions during the endothermic process against its first, second, and third derivatives.

Figure 13: Comparing first, second, and third derivative of HF vs T for melting transition.

Figure 11 shows the QLCS's enlarged exothermic nematic phase transition peak(s). It highlights the starting and ending temperatures and their corresponding specific heat capacity value. The Cp peak, wing jump, temperature change, and specific heat capacity of the melting phase transition are identified. The blue shaded area represents the peak integral, the calculated energy used for the nematic transition. The amount of thermal energy required for the melting transition was 4.79 J/g. The symbols used are recorded in Table 2.

Figure 14: Compared HF vs T nematic transition during the endothermic process against its first, second, and third derivatives.

Figure 12 shows the first, second, and third derivatives of the endothermic phase transition peaks of the QLCS. The top left plot has the HF vs. T of the endothermic phase transition peaks. The top right shows the 1st derivative of the endothermic phase transitions, the bottom left shows the 2nd derivative, and the bottom right shows the 3rd derivative plots.

Figure 13 displays the first, second, and third derivatives of the melting phase transition of QLCS. Figure 14 shows the first, second, and third derivatives of the QLCS endothermic nematic phase transition peaks. The top left plot has the HF vs. T of the endothermic phase transition peak. The top right shows the 1st derivative, the bottom left shows the 2nd derivative, and the bottom right shows the 3rd derivative plots of the endothermic nematic phase transition.

Figure 15: Compared HF vs. T nematic transition during the exothermic process against its first, second, and third derivatives.

Figure 16: HF Vs Time (t) plot for the heating and cooling of a QLCS.

Figure 17: The first derivative of heat flow vs time (min) for heating and cooling of QLCS.

Figure 15 shows the first, second, and third derivatives of the exothermic nematic phase transition peak of the QLCS. The top left plot has the HF vs. T of the endothermic nematic phase transition peak. The top right shows the 1st derivative, the bottom left shows the 2nd derivative, and the bottom right shows the 3rd derivative plots of the exothermic nematic phase transition. Figure 16 presents the change of heat flow through time. Figure 17 shows the first derivative of Figure 16. As shown, there are sharp, steep peaks within the range of the phase transition peaks in Figure 16. The y-axis has the first derivative of the heat flow, and the x-axis has the time.

Figure 18: The second derivative of heat flow vs. time (min) for heating and cooling of QLCS.

Figure 19: The third derivative of heat flow vs time (min) for heating and cooling of QLCS.

Figure 18 shows the second derivative of Figure 16. As shown, there are sharp peaks in the areas of the phase transition peaks in Figure 16. The y-axis has the second derivative for the heat flow, and the x-axis has the time.

Figure 20: Comparison of HF vs. t the endothermic phase transitions against their first, second, and third derivative.

Figure 19 shows the third derivative of Figure 16. As shown, there are sharp peaks in the areas of the phase transition peaks in Figure 16. The y-axis has the third derivative for the heat flow, and the x-axis has the time.

Figure 20 shows the first, second, and third derivatives of the endothermic phase transition peaks of the QLCS. The top left plot has the HF vs. Time of the melting phase transition peak. The heat phase transitions plots for the 1st derivative is at the top right, the 2nd derivative is at the bottom left and the 3rd derivative is at the bottom right.

Figure 21 shows the first, second, and third derivatives of the melting phase transition peaks of the QLCS. The top left plot has the HF vs. Time of the melting phase transition peak. The heat nematic phase transition plots for the 1st derivative is at the top right, the 2nd derivative is at the bottom left and the 3rd derivative is at the bottom right.

Figure 22 shows the first, second, and third derivatives of the heat nematic phase transition peaks of the QLCS. The top left plot has the HF vs. t of the melting phase transition peak. The heat nematic phase transition plots for the 1st derivative is at the top right, the 2nd derivative is at the bottom left and the 3rd derivative is at the bottom right.

Figure 21: Comparison of HF vs. t the melting phase transitions against their first, second, and third derivative.

Figure 22: Comparison of HF vs. t the endothermic nematic phase transitions against their first, second, and third derivative.

Figure 23: Comparison of HF vs. t the exothermic nematic phase transitions against their first, second, and third derivative.

Figure 23 shows the first, second, and third derivatives of the exothermic nematic phase transition peaks of the QLCS. The top left plot has the HF vs. t of the melting phase transition peak. The cool nematic phase transition plots for the 1st derivative is at the top right, the 2nd derivative is at the bottom left and the 3rd derivative is at the bottom right.

Discussion

The thermal details found in QLCS using DSC technique are shown in the Result section. The multi-peaks observed for Melting and Nematic phase transitions can be analyzed further using Gaussian Law of Peak Analysis. The Gaussian Analysis is shown below where each phase transition of QLCS is used as a single and then double peak analysis using Gaussian Theory. The details of the peaks found by Gaussian Theory for each peak are shown in the Table section of the paper.

Figure 24: Gaussian Analysis of two peaks of Melting and Nematic as a single peak in heating.

Figure 25: Gaussian Analysis of double peaks of Melting and Nematic as two peaks in heating.

Figures 24 and 25 display the Gaussian analysis of the heating peak transitions. Figure 24 shows how the two transition peaks formed for the melting and nematic transitions were used to form a one peak Gaussian analysis. Figure 25 shows how each transition peak had the Gaussian analysis performed. Table 4 and 5 presents data details from the Gaussian analysis. The Gaussian analysis of the QLCS was performed to gained additional information on each transition peak.

Figure 26: Gaussian Analysis of Cool Nematic peak as a one peak in cooling.

Figure 27: Gaussian Analysis of cool Nematic peak as double peak in cooling.

Figures 26 and 27 display the Gaussian analysis of the cooling peak transitions. Figure 26 shows how the two transition peaks formed for the cooling nematic transition were used to form a one peak Gaussian analysis. Figure 27 shows how each transition peak had the Gaussian analysis performed. Table 6 and 7 presents data details from the Gaussian analysis. The Gaussian analysis of the QLCS was performed to gain additional information on each transition peak.

Figure 28: Melting and Nematic phase transition temperatures of the QLCS, TLCS, BLCS and pure LCs of 4CB, 5CB, 6CB, and 7CB.

Figures 28 - 31 display the summary graphs where the data for the melting and nematic peaks were compared. Figure 28 displays a comparison of the temperature at which a phase transition occurs between the different types of LCs. Since the QLCS has two transition peaks occurring for each phase transition, both temperatures were included. Figure 29 and 30 shows a comparison of WJ, Cpp, and ΔCp between the QLCS, TLCS, BLCS, and pure samples for the heating and cool. Figure 29 shows that the 4CB sample has a significantly high Cpp, and ΔCp in comparison to the other typed of LCs for the heating. Figure 30 shows that 4CB had a significantly higher Cp than the other LCs. Figure 31 compares the nematic phase transition range between the BLCS, TLCS, and QLCS. It found that the nematic range temperature for heating and cooling decreases as the number of different types of LCs in the system increases. The comparative data is shown in tables 1-3.

Figure 29: Comparison of WJ, Cpp, and ΔCp in the heating nematic transition of the QLCS with BLCS, TLCS, and pure LCs of 4CB, 5CB, 6CB, and 7CB.

Figure 30: Comparison of WJ, Cpp, and ΔCp in the cooling nematic transition of the QLCS with BLCS, TLCS, and pure LCs of 4CB, 5CB, 6CB, and 7CB.

Figure 31: The nematic range transitions for the heating and cooling phase transition of QLCS compared to BLCS and TLCS.

Figure 32: The predicted molecular orientation of 4CB, 5CB, 6CB, and 7CB in TLCS during heating.

Figure 33: The predicted molecular orientation of 4CB, 5CB, 6CB, and 7CB in TLCS during cooling.

Figures 32 and 33 display the possible orientation of the LC molecules for the QLCS for the heat and cool phases. The 4CB and 7CB LCs were closer together because their melting point temperatures were closer to each other similarly with 5CB and 6CB. In Figure 32, the 4CB and 7CB molecules were higher in the crystalline state (K) to represent the two melting transition peaks. As Figure 33 shows, once the QLCS transitions to the isotropic state, it’s unable to return to the organized crystalline state shown in Figure 32. So, when it’s cooled, it transitions to the Frozen Nematic (FN) state.

Data Tables

The details of all analyzed data of QLCS are shown in the Data Tables below from the Table 1- 12.

Table 1 shows the comparison between QLCS, TLCS and BLCS of their melting phase transition(s). The QLCS requires more energy than TLCS, but less than BLCS. The melting point temperature for each of the pure compounds were obtained and recorded in Table 8. The QLCS has two melting phase transitions occurring at T_M1= 3.91 and T_M2= 12.03°C. While the BLCS and TLCS have only one melting transition occurring at T_M = -0.79°C and T_M = 6.32°C.

Table 2 and 3 show details of each transition peak when it starts, ends, how tall or deep they are, how wide or shallow they are for heating and cooling for QLCS compared to TLCS, BLCS and their parent LCs.

For the endothermic nematic transition, the QLCS had a lower enthalpy of 0.71 and 0.95 J/g in comparison to the other LCs. While the exothermic nematic transitions of the LCs showed that the QLCS had an enthalpy value of 4.79 J/g. The enthalpy for the cooling process was higher than most of the LC samples except 7CB. Table 2-3 contain the data values to compare the QLCS with the other LC systems. When compared to the other LC systems, QLCS has a higher WJ.

Tables 4-7 present the detailed values of Gaussian Analysis of transition peaks of QLCS for heating and cooling. They show the Gaussian parameters of height (a), center of peak (b), width (c), area (A) for Figure 24-27. Table 8 contains the data values of melting and endothermic and exothermic nematic transition for the LC samples. Table 9 and 10 contains data of WJ, Cpp, and ΔCp for the for the LC systems.

Table 11 shows a comparative study of the nematic range found for QLCS, BLCS and TLCS. QLCS shows shorter nematic range for heating but larger in cooling when compared with LCs. The QLCS has three values recorded for heat and cool. For the heating, the first value is the range between the first peak of the melting and nematic transition. The second value is the range between the second peak of the melting and nematic transition. The third value is the total range from the first melting transition peak and the second nematic transition peak. For cooling, the first value is the range between the first peak of the heating nematic and cool nematic transition. The second value is the range between the second peak of the heating nematic and cool nematic transition. The third value is the total range from the first heating nematic transition peak and the cool second nematic transition peak. The QLCS* shown in Figure 31 is the total nematic range. Table 12 shows the full names of all abbreviations used in the tables.

Based on Figure 31 the QLCS has a lower nematic range for heat and cool compared to BLCS and TLCS. This may be due to the addition of 4CB, which makes the sample heavier than the BLCS and TLCS. As the molecular weight increases, then the nematic range would decrease. For future, it be better to combine LCs with melting point that are closer to each other.

Table 1: Melting Transition data of the QLCS sample compared to TLCS and BLCS.

Melting Transition peak

Sample

Ts (?)

Te (?)

ΔT(?)

Cps (J/g?)

Cpe (J/g?)

Cpp (J/g?)

ΔCp (J/g?)

ΔH (J/g)

WJ (J/g?)

QLCS

-13.87

32.08

45.95

2.12

2.78

4.12

1.99

35.71

0.66

TLCS [22]

-13.497

34.7651

48.2621

1.3031

1.6298

3.079

34.05

34.05

0.3267

BLCS [19]

-26.33

34.24

60.57

-0.05

2.28

3.6

93.38

93.38

2.33

Table 2: Endothermic Nematic Transition data of the QLCS sample compared to TLCs, BLCs mixtures and pure LCs.

Endothermic Nematic Transition Peak

Sample

Ts (?)

Te (?)

ΔT(?)

Cps (J/g?)

Cpe (J/g?)

Cpp (J/g?)

ΔCp(J/g?)

ΔH(J/g)

WJ (J/g?)

QLCS - 1

32.15

42.52

10.36

2.78

2.75

2.96

0.1791

0.71

-0.03

QLCS - 2

42.59

51.79

9.20

2.75

2.35

2.79

0.04

0.95

-0.40

TLCS[22]

34.84

80.72

45.88

1.629

1.312

2.031

0.4011

2.48

-0.3177

BLCS [19]

36.42

63.71

27.29

2.27

2.02

2.68

0.66

3.39

-0.25

4CB [23]

46.32

55.81

9.49

0.51

0.71

32.93

32.44

106.6

0.20

5CB[14]

30.12

40.59

10.45

2.98

3.22

-2.12

1.10

221.8

0.24

6CB [14]

25.55

39.79

14.23

1.52

1.61

-0.53

1.08

158.4

0.09

7CB [14]

38.71

46.71

7.94

1.47

1.27

-3.28

2.00

99.46

0.20

Table 3: Exothermic Nematic Transition Temperatures of the QLCS sample compared to TLCs, BLCs mixtures and pure LCs.

Exothermic Nematic Transition Peak

Sample

Ts (?)

Te (?)

ΔT(?)

Cps (J/g?)

Cpe (J/g?)

Cpp (J/g?)

ΔCp(J/g?)

ΔH(J/g)

WJ (J/g?)

 

QLCS

45.29

2.272

-43.02

-1.922

-1.997

-2.342

-0.4192

4.79

-0.0749

 

TLCS[22]

50.07

13.20

-36.86

-1.149

-1.173

-1.678

-0.5286

4.36

-0.0233

 

BLCS [19]

42.34

20.68

63.02

-1.90

-1.97

-2.46

0.56

4.57

-0.07

 

4CB [23]

15.99

8.97

7.02

0.41

0.47

1.26

0.86

9.02

0.06

 

5CB[14]

39.26

23.77

15.50

2.93

2.96

-1.960

1.00

1.62

0.03

 

6CB [14]

36.85

21.02

15.80

1.40

1.10

-0.5760

0.859

1.20

0.30

 

7CB [14]

45.61

30.28

15.33

0.80

0.88

-2.640

1.84

8.33

0.08

 

Based on detailed analysis discussed above and show data in the tables, it can be seen that QLCS has lowest Nematic Range in heating when compared with BLCS and TLCS whereas the total Nematic Range for QLCS is higher in cooling when compared with TLCS and its parent LCs but lower than BLCS. Having higher Nematic range in cooling makes it more useful for LCDs to be used for higher temperature ranges. This behavior of QLCS can be explained in terms of size of nCB tails those are present as its parent LCs in QLCS. The 4CB is the smallest member in QLCS with smallest tail size that pushes the entire LC system of QLCS towards lower values of the Nematic range. If the proportion of 4CB is decreased and the proportion of 5CB, 6CB, and 7CB are increased in QLCS, the nematic range can be seen higher in heating and cooling both. This can be a future direction of study to use higher ratios of 5CB, 6CB, and 7CB but a lower ratio of 4CB in QLCS. Since all four LCs have different sizes of tails, they tangled with each other after they are cooled from their fully heated state of Isotropic state. When they are cooled, they go to a different state after crossing the Nematic state and that is not a crystalline state but a Frozen Nematic state (FN). This is the reason why QLCS does not show a crystalline state when it is cooled in DSC.

Table 4: Data details of the Gaussian Analysis of Figure 24.

Heating

 

M

N

Value

Uncertainty

Value

Uncertainty

H (W/g) = a

5.855

1.084

0.202

0.008807

C (?) = b

9.247

0.05812

38.09

0.07958

W (?) = c

39.9

4.275

-2.425

0.1333

A (W?/g) = d

-1.727

1.089

2.425

0.00441

Table 5: Data details of the Gaussian Analysis of Figure 25.

Heating

 

M1

M2

N1

N2

 

Value

Uncertainty

Value

Uncertainty

Value

Uncertainty

Value

Uncertainty

H (W/g) = a

1.362

0.06355

2.839

0.1884

0.1688

0.001844

0.6354

0.02989

W (?) = b

4.381

0.04067

11.96

0.01781

38.13

0.0134

45.61

0.02758

Tp (?) = c

14.39

0.456

-21.19

0.802

-1.86

0.02738

-5.015

0.1967

A (W?/g) = d

2.658

0.06359

1.27

0.1889

2.787

0.001403

2.174

0.03079

Table 6: Data details of the Gaussian Analysis of Figure 26.

Cooling - N

 

Value

Uncertainty

H (W/g) = a

-0.1788

0.1818

W (?) = b

29.53

0.03049

Tp (?) = c

3.094

1.845

A (W?/g) = d

-2.162

0.1828

Table 7: Data details of the Gaussian Analysis of Figure 27.

Cooling

 

N1

N2

 

Value

Uncertainty

Value

Uncertainty

H (W/g) = a

-7057

1456

-0.1582

0.0025

W (?) = b

29.640

0.024

22.73

0.03

Tp (?) = c

-490.7

51.53

4.05

0.08

A (W?/g) = d

7054

1456

-2.048

0.003

Table 8: Melting and nematic transition for endothermic and exothermic phase transitions.

nLC

T_M (?)

Heat T_N (?)

Cool T_N (?)

4CB [23]

50.11

-

14.33

5CB[14]

22

35.75

33.56

6CB [14]

14

29.82

26.92

7CB [14]

30

42.45

40.37

BLCS [19]

-0.79

45.15

45.15

TLCS [22]

6.32

42.23

35.4

QLCS

3.91

12.03

38.29

45.86

29.91

22.29

Table 9: Comparison of WJ, Cpp, and ΔCp for the nLC samples in the endothermic nematic state.

nLC

WJ (J/g?)

Cpp (J/g?)

ΔCp (J/g?)

4CB [23]

0.2

-

32.44

5CB[14]

0.24

-2.12

1.1

6CB [14]

0.09

-0.53

1.08

7CB [14]

0.2

-3.28

2

BLCS [19]

-0.25

2.68

0.66

TLCS [21]

-0.31767

2.0309

0.4011

QLCS

-0.02868

-0.40311

2.96268

2.79888

0.17913

0.04434

Table 10: Comparison of WJ, Cpp, and ΔCp for the nLC samples in the exothermic nematic state.

nLC

WJ (J/g?)

Cpp (J/g?)

ΔCp (J/g?)

4CB [23]

0.06

1.26

0.86

5CB [14]

0.03

-1.96

1

6CB [14]

0.3

-0.576

0.859

7CB [14]

0.08

-2.64

1.84

BLCS [19]

-0.07

-2.46

0.56

TLCS [22]

-0.0233

-1.6784

-0.5286

QLCS

-0.0749

-2.3416

-0.4192

Table 11: Comparison of the nematic range for heating and cooling of the samples (nLC).

nLC

RN (heat)

RN (cool)

BLCS [19]

45.94

55.12

TLCS [22]

35.91

55.4

QLCS (1, 2,*)

34.38

33.83

41.95

51.91

44.29

51.91

Table 12: Identity of the symbols.

Ts

Starting temperature

Te

Ending temperature

ΔT

Change in temperature

Cps

Starting specific heat capacity

Cpe

Ending specific heat capacity

Cpp

specific heat capacity peak value

ΔCp

Change in specific heat capacity

ΔH

Change in enthalpy

WJ

Wing Jump

M

Melting

N

Nematic

T_M

Temperature of melting phase transition

T_N

Temperature of nematic phase transition

RN

Range of nematic phase

Conclusion

This paper reports the detailed analysis of a combination of four different liquid crystals from the same family of nCB using the DSC techniques. In order to achieve a Quaternary Liquid Crystal System, four different LCs were mixed in a ratio of 3:2:1:3. The QLCS was heated and cooled in the range of -40? to 80? in DSC. The DSC results are analyzed further again using thermodynamics and Gaussian Analysis using Logger Pro. The DSC study revealed that the QLCS exhibits two melting and two Nematic phase transitions in heating not one as normal LC. The QLCS also shows two Nematic transitions in cooling that are not observed by any single LCs or double or triple LCs in the liquid crystal system. The QLCS never goes back to Crystallization in cooling when they are cooled to -40? using DSC technique. Since crystallization is not observed in cooling, it can be said that QLCS stays in Nematic state while it is cooled from its Isotropic state and freezes in its Nematic state that we call as Frozen Nematic state. It increases its Nematic Range in cooling compared to its single components of LCs and makes it a possible liquid crystal system for LCD or smart device world!

Acknowledgement

We would like to thank Professor J. C. MacDonald from the Department of Chemistry and Biochemistry, WPI, Worcester, MA, USA for DSC help and would like to acknowledge NETZSCH the DSC Company for their DSC 214 instruments and pans and lids. I as a student would like to thank Dr. Sharma for her guidance in this research work that is done as a senior research intern at Emmanuel College, Boston, MA, USA.

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