**6. Microwave heating process of ethanol, hexane, and ethanol-hexane mixed solution**

The microwave heating processes of ethanol were measured by plotting the CSC-temperature increase as a function of the microwave irradiation time, as shown in **Figure 3A(a)**. The temperature was initially set at 0°C, and the samples were continuously irradiated with 135 W (output power of microwave generator) microwave, during which NMR spectra were acquired every 30 s. The CSCtemperature of the CH2 and CH3 protons of ethanol increased from 0 to 30°C within 1 min and gradually increased to 58°C under microwave irradiation for 10 min. In contrast, the CSC-temperature of the OH protons increased from 0 to 35°C within 1 min and only slightly increased to 43°C for 10 min. The CSC-temperature of the OH protons deviated to a lower temperature than those of the CH2 and CH3 protons by 15°C under microwave irradiation for 10 min.

**Figure 3A(b)** shows the 1 H NMR spectrum of ethanol measured at 55°C (black) and that measured under microwave irradiation (135 W) for 10 min (orange) where the temperature was set at 0°C using the temperature controller of the NMR

#### **Figure 3.**

*A(a). CSC-temperatures as a function of microwave irradiation time. CSC-temperatures were determined using the slopes obtained for the individual protons. A(b). <sup>1</sup> H NMR spectrum for ethanol regulated at 55°C (black) and that under CW microwave irradiation for 10 min while controlling the instrument temperature setting at 0°C (orange). B(a). CSC-temperatures of CH2 and CH3 protons of hexane as a function of microwave irradiation time. B(b). 1 H NMR spectra of hexane regulated at 25°C (black) and that under CW microwave irradiation with the same condition as A(b) (orange). C(a). CSC-temperatures of CH2, CH3, and OH protons of ethanol and the CH2 and CH3 protons of hexane in ethanol-hexane (1:1, v/v) mixed solution as a function of microwave irradiation time. C(b). 1 H NMR spectra of ethanol-hexane (1:1, v/v) mixed solution regulated at 55°C (black) and that under CW microwave irradiation with the same condition as A(b) (orange). Adapted with permission from [34]. Copyright (2020) American Chemical Society.*

**175**

1

*Microwave Heating of Liquid Crystals and Ethanol-Hexane Mixed Solution and Its Features…*

spectrometer. The signal for OH protons under microwave irradiation for 10 min appeared 0.2 ppm lower field (orange). It is noted that the chemical shifts of the CH2 and CH3 protons completely overlapped with those measured at 55°C. Therefore,

the solution because CH2 and CH3 are non-polar groups. The lower field 1

10 min microwave heating (orange), where the black and orange peaks were

of the OH proton was 15°C lower than those of the CH2 and CH3 protons.

indicates a 15°C lower temperature, as in the case of ethanol.

H-1

below Tc to 40.5°C. As shown in **Figure 4D**, broad 1

55°C (black) and those after microwave heating for 10 min (orange), where the black and orange peaks were almost overlapped. On the other hand, the NMR peak of the OH proton under microwave irradiation appeared 0.2 ppm lower field, which

**7. Microwave heating process of MBBA in the liquid crystalline state**

**Figure 4A** shows the molecular structure of MBBA, which is known to form a liquid crystal phase below the liquid crystalline to isotropic phase transition temperature

at 35°C, which is 5.5°C below the phase transition temperature (Tc = 40.5°C). A broad

H NMR spectrum with a 20 kHz linewidth was obtained for the liquid crystalline

interactions induce a number of transitions with various degrees of dipolar interactions and this generates a significant line broadening. These dipolar interactions can provide insight into the order parameter of liquid crystals. **Figure 4C** shows a high-

45°C, in which the narrow proton signals are well resolved, which enabled the assign-

crystalline phase appeared alone at 35°C. At 40°C, the liquid crystalline phase had partly transitioned to the isotropic phase (**Figure 4D**). It was also evident that the liquid signals obtained at this temperature were broader than those of the fully isotropic phase, which may be attributed to the interaction of the isotropic and liquid crystalline phases, which induces a temperature distribution. This phase transition was completed at 40.5°C (**Figure 4D**), which indicates that the liquid crystalline

The temperature was then set at 20°C (20.5°C blow the Tc), followed by CW microwave irradiation at 130 W for 90 s, which generated weak isotropic phase

The MBBA temperature was significantly increased by 5.0°C steps from 20.0°C

H NMR spectrum of MBBA in the isotropic phase that was obtained at

the magnetic field in the liquid crystalline phase; therefore, residual 1

ment of the signals to their respective protons in the molecules [33].

and isotropic phases coexist near the phase transition temperature [33].

H chemical shifts of the CH2 and CH3 protons reflect the bulk temperature of

shifts of OH protons under microwave irradiation are thus evidence of being induced by a non-thermal microwave effect in addition to the thermal microwave effect.

**Figure 3B(a)** shows the CSC-temperatures as a function of the microwave irradiation time. CSC-temperatures of the CH2 and CH3 protons of hexane increased gradually to 30°C under microwave irradiation for 10 min. A small temperature increase is attributed to the much lower dielectric loss factor of hexane than that of ethanol.

**Figure 3C(a)** shows the CSC-temperature of the CH2, CH3, and OH protons of ethanol, and the CH2 and CH3 protons of hexane in ethanol-hexane (1:1, v/v) mixed solution. The CSC-temperature of the CH2 and CH3 protons increased to 40°C within 1 min and gradually increased to 55°C for 10 min. It is noted that all CH2 and CH3 protons increased in the same manner. On the other hand, the CSC-temperature

H NMR spectra of hexane at 30°C (black) and that after

H NMR spectra of the ethanol-hexane mixed solution at

H NMR spectrum of MBBA in the liquid crystalline state

H dipolar couplings. MBBA molecules tend to align along

H-1

H NMR signals of the liquid

H dipolar

H chemical

*DOI: http://dx.doi.org/10.5772/intechopen.97356*

**Figure 3B(b)** shows <sup>1</sup>

**Figure 3C(b)** shows 1

(Tc). **Figure 4B** shows the 1

sample due to residual 1

resolution 1

completely overlapped.

the 1

#### *Microwave Heating of Liquid Crystals and Ethanol-Hexane Mixed Solution and Its Features… DOI: http://dx.doi.org/10.5772/intechopen.97356*

spectrometer. The signal for OH protons under microwave irradiation for 10 min appeared 0.2 ppm lower field (orange). It is noted that the chemical shifts of the CH2 and CH3 protons completely overlapped with those measured at 55°C. Therefore, the 1 H chemical shifts of the CH2 and CH3 protons reflect the bulk temperature of the solution because CH2 and CH3 are non-polar groups. The lower field 1 H chemical shifts of OH protons under microwave irradiation are thus evidence of being induced by a non-thermal microwave effect in addition to the thermal microwave effect.

**Figure 3B(a)** shows the CSC-temperatures as a function of the microwave irradiation time. CSC-temperatures of the CH2 and CH3 protons of hexane increased gradually to 30°C under microwave irradiation for 10 min. A small temperature increase is attributed to the much lower dielectric loss factor of hexane than that of ethanol.

**Figure 3B(b)** shows <sup>1</sup> H NMR spectra of hexane at 30°C (black) and that after 10 min microwave heating (orange), where the black and orange peaks were completely overlapped.

**Figure 3C(a)** shows the CSC-temperature of the CH2, CH3, and OH protons of ethanol, and the CH2 and CH3 protons of hexane in ethanol-hexane (1:1, v/v) mixed solution. The CSC-temperature of the CH2 and CH3 protons increased to 40°C within 1 min and gradually increased to 55°C for 10 min. It is noted that all CH2 and CH3 protons increased in the same manner. On the other hand, the CSC-temperature of the OH proton was 15°C lower than those of the CH2 and CH3 protons.

**Figure 3C(b)** shows 1 H NMR spectra of the ethanol-hexane mixed solution at 55°C (black) and those after microwave heating for 10 min (orange), where the black and orange peaks were almost overlapped. On the other hand, the NMR peak of the OH proton under microwave irradiation appeared 0.2 ppm lower field, which indicates a 15°C lower temperature, as in the case of ethanol.
