1. Introduction

2. Materials and Methods

2.1. Experimental materials and equipment

Table 1. The main experimental material.

Table 1. The main experimental material.

No.	Name	Purity	Producer
1	n-Nonadecane	99%	Sigma-Aldrich
2	1-Octadecanol	99%	Sigma-Aldrich

Table 2. The main experimental equipment.

Table 2. The main experimental equipment.

No.	Name	Model	Producer
1	Differential Scanning Calorimetry	DSC 1	METTLER TOLEDO
2	Fourier-Transform Infrared Reflection	NICOLET iS10	Thermo Scientific
3	Aluminium-Crucibles	1/3 ME-51119870	METTLER TOLEDO
4	Aluminium-Piercing lids	1/5 ME-51119873	METTLER TOLEDO

2.2. Mass calculation

Twenty-one samples were made at the beginning of the experiment. The samples were differenced by 5% each. All the samples were thoroughly mixed to confirm they were in equilibrium. Then crush the sample into powder since all the analysis methods are using fine powder for the analysis.

The desired batch size of each glass is around 30-40 milligrams.

The total molar weight is:

$$M_{total}=\sum mole\%\times M(3.1)$$

The weight percentage of each chemical is:

$$Wt\%=\frac{mole\%\times M}{M_{total}}(3.2)$$

The mass of each chemical for making the samples is:

$$Mass(g)=Wt\%\times 20(3.3)$$

The compositions of samples(mol%) we prepared are listed below:

Table 3. The Chemicals information of each sample.

Table 3. The Chemicals information of each sample.

Sample No.	Molar fraction (C18OH/C19)	n-Nonadecane mass (g)	1-Octadecanol mass (g)	Total mass (g)
1	0	0	0.03	0.03
2	5	0.001923	0.037107	0.03903
3	10	0.003846	0.035154	0.039
4	15	0.005769	0.033201	0.03897
5	20	0.007692	0.031248	0.03894
6	25	0.009615	0.029295	0.03891
7	30	0.011538	0.027342	0.03888
8	35	0.013461	0.025389	0.03885
9	40	0.015384	0.023436	0.03882
10	45	0.017307	0.021483	0.03879
11	50	0.01923	0.01953	0.03876
12	55	0.021153	0.017577	0.03873
13	60	0.023076	0.015624	0.0387
14	65	0.024999	0.013571	0.03857
15	70	0.026922	0.011718	0.03864
16	75	0.028845	0.009765	0.03861
17	80	0.030768	0.007812	0.03858
18	85	0.032691	0.005859	0.03855
19	90	0.034614	0.003906	0.03852
20	95	0.036537	0.001953	0.03849
21	100	0.03	0	0.03

Table 4. The crucible weight and sample weight for Reproducibility (in crucible).

Table 4. The crucible weight and sample weight for Reproducibility (in crucible).

Sample No.	Molar fraction (C18OH/C19)	Crucible weight (empty)/mg	Crucible weight (full)/mg	Sample weight (mg)
Re-1 (1)	0	48.38	58.07	9.69
Re-1 (11)	50	48.63	58.54	9.91
Re-1 (21)	100	48.43	56.57	8.14
Re-2 (1)	0	48.26	56.19	7.93
Re-2 (11)	50	48.59	55.06	6.47
Re-2 (21)	100	49.19	59.61	7.93

3. Results

3.1. DSC diagrams

3.1.1. Cooling rate at 1℃/min

This is the cooling DSC diagram of heating and cooling cycle 1 at a rate of 1℃/min. As we can see, there are four peaks at most and two peaks at least. The peaks were moving when the composition was changing. The rightmost peak is 1-Octadecanol crystallizing from the liquid phase into a rotator phase. The next peak is the 1-Octadecanol transitioned into an ordered phase from the rotator phase. The two peaks on the left are about n-Nonadecane. The peak on the right is n-Nonadecane, crystallizing from the liquid phase into a rotator phase. The peak on the left is rotator-phase-n-Nonadecane transitioned into an ordered phase from the rotator phase.^[5]

Figure 1. Cooling Phase diagram at 1℃/min (Cycle 1).

Figure 1. Cooling Phase diagram at 1℃/min (Cycle 1).

Here are the overall DSC diagrams at the rate of 1dCpm. The upper three are the cooling diagrams, and the rest are the heating diagrams.

Figure 2. Cooling(a) and Heating(b) Phase diagram at 1℃/min (Cycle 1).

Figure 2. Cooling(a) and Heating(b) Phase diagram at 1℃/min (Cycle 1).

Figure 3. Cooling(a) and Heating(b) Phase diagram at 1℃/min (Cycle 2).

Figure 3. Cooling(a) and Heating(b) Phase diagram at 1℃/min (Cycle 2).

Figure 4. Cooling(a) and Heating(b) Phase diagram at 1℃/min (Cycle 3).

Figure 4. Cooling(a) and Heating(b) Phase diagram at 1℃/min (Cycle 3).

As we can see, there are no distinct difference among these three cycles in cooling and heating rate at 1℃ per minute. So, the samples are extraordinarily stable during the three cycles at the same cooling and heating rate.

A Specific DSC diagram was shown below. These are the two parts for a whole DSC scanning. Blue part means the Cooling procedure of the sample, red part means the Heating part. Integral the peaks then we can get the area of each peak and that is the Enthalpy of each phase transition.

Figure 5. An example of DSC diagram in STAR^e.

Figure 5. An example of DSC diagram in STAR^e.

Two tables of Phase transition temperature and enthalpy value of each peak was obtained by concluding all DSC diagram.

Table 5. Comparison of Transition Enthalpy between the Experimental Results and the Mean Values of the Literature.

Table 5. Comparison of Transition Enthalpy between the Experimental Results and the Mean Values of the Literature.

Cn	Molar Mass (g/mol)	Tm (K)	ΔHm (kJ/mol)	TR-C (K)	ΔHR-C (kJ/mol)	ΔHtotal (kJ/mol)	Reference
18	270.49	330.3	-	328.00	-	-	Miquel Àngel, 2021 [6]
		328.2	44.742	321.78	15.756	60.498	This study
19	268.52	304.9	45.580	295.5	13.750	59.330	Dirand et al., 2002 [5]
		305.1	46.047	294.5	13.801	59.848	Cholakova et al., 2019 [7]
		303.6	31.417	294.2	9.134	40.551	This study

Table 6. Comparison of Different Compositions between 1-Octadecanol and n-Nonadecane.

Table 6. Comparison of Different Compositions between 1-Octadecanol and n-Nonadecane.

Composition (C18OH %)	Mw (g/mol)	Tm (K)	ΔHm (kJ/mol)	TR-γ (K)	ΔHR-γ (kJ/mol)	TL-RI (K)	ΔHL-RI (kJ/mol)	TR-Oi (K)	ΔHR-Oi (kJ/mol)	ΔHtotal (kJ/mol)
0	268.5200	303.60	9.134	-	-	301.79	31.417	-	-	40.551
5	268.6185	305.02	7.211	-	-	301.89	31.093	-	-	38.304
10	268.7170	308.33	3.727	-	-	302.03	28.532	290.27	6.909	39.168
15	268.8155	316.75	4.449	-	-	301.71	27.107	290.18	6.804	38.36
20	268.9140	318.38	6.868	-	-	301.81	26.061	290.30	6.4619	39.391
25	269.0125	319.15	8.248	-	-	301.97	24.074	290.21	5.617	37.939
30	269.1110	319.62	9.368	-	-	301.86	22.662	290.11	5.253	37.283
35	269.2095	321.05	11.853	-	-	301.91	21.542	289.87	4.937	38.332
40	269.3080	321.55	13.024	-	-	301.84	21.203	289.69	4.551	38.778
45	269.4065	322.61	13.899	-	-	301.80	18.306	1289.83	3.483	35.688
50	269.5050	323.3	15.669	305.48	2.647	301.87	15.402	289.98	3.339	37.057
55	269.6035	324.42	17.565	307.68	4.341	302.02	13.270	290.07	2.879	38.055
60	269.7020	325.25	18.127	309.11	5.453	302.09	11.373	289.97	2.368	37.321
65	269.8005	325.62	19.431	310.47	6.904	302.07	10.279	289.78	1.983	38.597
70	269.8990	326.41	20.569	312.95	9.471	302.15	8.461	289.16	1.636	40.137
75	269.9975	326.55	19.872	313.68	9.080	302.14	5.989	289.91	1.237	36.178
80	270.0960	327.27	21.454	315.56	11.590	302.11	4.303	-	-	37.347
85	270.1945	328.26	21.983	317.07	13.839	302.04	3.132	-	-	38.954
90	270.2930	328.42	22.891	318.07	13.836	-	-	-	-	36.727
95	270.3915	329.6	26.114	320.77	15.407	-	-	-	-	41.521
100	270.4900	329.86	44.742	321.85	15.756	-	-	-	-	60.498

3.1.2. Cooling rate at 0.75℃/min and 0.5℃/min

The DSC diagrams at different cooling or heating rates for the same sample are shown below. The sample was No.11, and the composition was 50% n-Nonadecane and 50% 1-Octadecanol. The altitude of the peaks was getting lower when the rate went down. It is because the rate of temperature rise during sample testing has a significant impact on resolution and sensitivity. In general, the faster the rate of warming, the lower the resolution and the higher the sensitivity. Conversely, the higher the resolution, the lower the sensitivity. As the ramp rate increases, the melt peak onset temperature does not change much, while the peak top and end temperatures increase, and the peak shape becomes wider. During the ramp-up process, fast ramp-ups lead to superimposed thermal effects, and individual peaks or melts of different phases are not well separated. During the cooling down process, the cooling rate affects the crystallization behavior, and a fast-cooling rate leads to a delay in crystallization, but this method can be used to optimize the processing of the product.

Besides, the overall peak shape was similar to the diagram at which the rate of 1℃/min. It means the sample we used for different-rate scanning was stable, so that can conclude the So it can be deduced that all samples are at the same stability.

Figure 6. Differential Scanning Calorimetry (DSC) diagram at cooling(a)/ heating(b) different rates (1,0.75,0.5℃/min, Cycle 1).

Figure 6. Differential Scanning Calorimetry (DSC) diagram at cooling(a)/ heating(b) different rates (1,0.75,0.5℃/min, Cycle 1).

Figure 7. Differential Scanning Calorimetry (DSC) diagram at cooling(a)/ heating(b) different rates (1,0.75,0.5℃/min, Cycle 2).

Figure 7. Differential Scanning Calorimetry (DSC) diagram at cooling(a)/ heating(b) different rates (1,0.75,0.5℃/min, Cycle 2).

Figure 8. Differential Scanning Calorimetry (DSC) diagram at cooling(a)/ heating(b) different rates (1, 0.75, 0.5℃/min, Cycle 3).

Figure 8. Differential Scanning Calorimetry (DSC) diagram at cooling(a)/ heating(b) different rates (1, 0.75, 0.5℃/min, Cycle 3).

3.1.3. Reproducibility

This part is the reproducibility of this experiment. Three samples were run at 1dCpm two more times and checked for the reproducibility of the whole experiment. As shown in Figure 9, the shape and height of peaks are very similar, almost identical. So, we can confirm the reproducibility of this experiment was acceptable.

Figure 9. Reproducibility Differential Scanning Calorimetry (DSC) diagram (1℃/min) with different compositions; (a)1-Octadecanol 0% / n-Nonadecane 100%; (b)1-Octadecanol 50% / n-Nonadecane 50%; (c)1-Octadecanol 100% / n-Nonadecane 0%.

Figure 9. Reproducibility Differential Scanning Calorimetry (DSC) diagram (1℃/min) with different compositions; (a)1-Octadecanol 0% / n-Nonadecane 100%; (b)1-Octadecanol 50% / n-Nonadecane 50%; (c)1-Octadecanol 100% / n-Nonadecane 0%.

3.2. Phase diagram

3.2.1. Cooling phase diagram

A binary system phase diagram was plotted by summarizing the peak temperatures in the DSC diagram. It shows the phase transitions of each partial material. We can confirm there’s no evidence of Eutectic/Peritectic reactions by reading the diagram.

From high temperature to low temperature, the phase transitions of 1-Octadecanol are Liquid → R’IV → Monoclinic (γ) (Cuevas-Diarte and Oonk, n.d.); on the other hand, the phase transitions of n-Nonadecane are Liquid → R’I → Orthorhombic (β). ^[5]

Figure 10. A binary system Phase Diagram of n-Nonadecane and 1-Octadecanol (Cooling) and Phases.

Figure 10. A binary system Phase Diagram of n-Nonadecane and 1-Octadecanol (Cooling) and Phases.

3.2.2. Heating phase diagram

Comparing the Cooling and Heating Phase diagram, we can see the phase transition of 1-Octadecanol, which went from a stable phase into a rotator phase disappeared. It means the disordered phase is not thermodynamically stable in during heating. However, there was a phase transition there, but it was too weak, not strong enough for DSC to recognize it.

Figure 11. A binary system Phase Diagram of n-Nonadecane and 1-Octadecanol (Heating).

Figure 11. A binary system Phase Diagram of n-Nonadecane and 1-Octadecanol (Heating).

3.3. FTIR spectra

Seven of the samples in Table 3.4 were utilized for the FTIR analysis. These seven samples’ composition are: 100%, 80%, 60%, 50%, 40%, 20%, 0% in percentage of 1-Octadecanol.

A FTIR spectra of these seven samples was shown below. A spectrum compared between transmittance and wavenumber (Figure 12) and other spectra which compared with absorbance and wavenumber (Figure 13, transformed from Figure 12 by OMNIC). The peak around wavenumber 750cm-1 was out-of-plane bending of O-H bond. The peak around 1000 was stretching vibration of C-O bond. The peak around 1500 was bending vibration of C-H bond. The double-peak around 3000 was Saturated C-H stretching vibration absorption peak. An inconspicuous wide peak around 3300 was the O-H stretching vibration of intermolecular hydrogen bond. ^[8]

Figure 12. FTIR spectra (Transmittance).

Figure 12. FTIR spectra (Transmittance).

Figure 13. FTIR spectra (Absorbance).

Figure 13. FTIR spectra (Absorbance).

4. Discussion

References

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