**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 (Tc). **Figure 4B** shows the 1 H NMR spectrum of MBBA in the liquid crystalline state at 35°C, which is 5.5°C below the phase transition temperature (Tc = 40.5°C). A broad 1 H NMR spectrum with a 20 kHz linewidth was obtained for the liquid crystalline sample due to residual 1 H-1 H dipolar couplings. MBBA molecules tend to align along the magnetic field in the liquid crystalline phase; therefore, residual 1 H-1 H dipolar 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 highresolution 1 H NMR spectrum of MBBA in the isotropic phase that was obtained at 45°C, in which the narrow proton signals are well resolved, which enabled the assignment of the signals to their respective protons in the molecules [33].

The MBBA temperature was significantly increased by 5.0°C steps from 20.0°C below Tc to 40.5°C. As shown in **Figure 4D**, broad 1 H NMR signals of the liquid 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 and isotropic phases coexist near the phase transition temperature [33].

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

*Microwave Heating - Electromagnetic Fields Causing Thermal and Non-Thermal Effects*

The Δδ values for individual protons of ethanol and hexane changed linearly to the higher field in the range from 0 to 60°C as shown in **Figure 2a** and **b**. Δδ for the OH proton changed 0.9 ppm during the temperature increase from 0 to 60°C, while those for CH2 and CH3 changed 0.1 ppm during the temperature increase from 0 to 60°C. Thus, the CSC-temperature under microwave irradiation was accurately determined using these relations for individual protons of a sample solution.

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

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

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

*A(a). CSC-temperatures as a function of microwave irradiation time. CSC-temperatures were determined* 

*(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 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* 

*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.*

H NMR spectrum of ethanol measured at 55°C (black)

*H NMR spectrum for ethanol regulated at 55°C* 

*H NMR spectra of hexane regulated at 25°C (black) and that under CW* 

*H NMR spectra of ethanol-hexane (1:1, v/v) mixed* 

**5. CSC-temperature of ethanol-hexane mixed solution**

**mixed solution**

by 15°C under microwave irradiation for 10 min.

*using the slopes obtained for the individual protons. A(b). 1*

*as a function of microwave irradiation time. C(b). 1*

*microwave irradiation time. B(b). 1*

**Figure 3A(b)** shows the 1

**174**

**Figure 3.**

**Figure 4.**

*A. Molecular structure of MBBA. B. 1 H NMR spectrum of MBBA in the liquid crystalline phase at 35°C. C. 1 H NMR spectrum of MBBA in the isotropic phase at 45°C, together with signal assignments for the individual protons. D. Series of 1 H NMR spectra of MBBA during the thermal heating processes. E. Series of 1 H NMR spectra during the microwave heating processes [33].*

signals among the liquid crystalline phase signals (**Figure 4E**) even at a temperature lower than Tc. The temperature of the liquid crystalline phase was estimated to be 35°C from the assessment of the NMR linewidths with respect to the temperature. Such signals would not typically be expected until the temperature of the sample is close to its isotropic phase transition temperature of 40.5°C. This result indicates that microwave irradiation generated localized heating in the sample to form a small region of the higher temperature isotropic phase.

The temperature of the sample was successfully determined using *in situ* microwave irradiation NMR because the temperature of the MBBA liquid crystal was estimated with the NMR signal linewidth. It is noted that microwave irradiation generated a small fraction of the isotropic phase in the bulk liquid crystal at 35°C, even though this is 5.5°C lower than Tc (40.5°C). This result suggests nonequilibrium localized heating within the liquid crystalline sample [24].
