**13. Microwave effects on chemical reaction processes**

According to the MD simulations under microwave irradiation, the interactions between coherently ordered polar groups increased the number of hydrogen bonds in the ethanol-hexane mixed solution due to their coherent polarization (**Figures 7** and **8**). The formation of hydrogen bonds is due to the interaction between two OH groups, thus causing the energy of the work term to be supplied as a non-thermal microwave effect. This non-thermal microwave effect was experimentally verified by the observation of a lower field 1 H chemical shift of the OH protons in ethanol. This coherently ordered state of OH groups only appears under microwave irradiation and is different from the molecular order achieved by conventional thermal heating, even at the same bulk temperature of the system. In this microwaveinduced ordered state, polar molecules are coherently aligned along with the alternately oscillated electric field. These coherently ordered molecules enable interaction between polar groups. Furthermore, the coherently ordered low entropy state may accelerate the chemical reaction rate between molecules with polar groups, as in the formation of hydrogen bonding in ethanol.

Similar to under microwave irradiation, polarizable molecules, or those with a dipole moment, will also gradually align with the direction of an oriented external electric field (OEEF). A sufficiently strong OEEF can completely orient a molecule or a molecular complex in space through interacting with its dipole and polarizability, thereby removing, in principle, the difficulty in orienting the molecules and the OEEF. Therefore, it is possible to enhance or control the chemical reactivity in catalysis by a decrease in the activation energy of the reaction [61, 62].

**183**

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

In the case of microwave irradiation, the electric field is oscillating at a frequency of 2.45 GHz. As discussed in the MD simulation and thermodynamics consideration, a polar molecule is coherently ordered along with the oscillating electric field. Unlike in the case of an applied OEEF, the coherent ordered state under microwave irradiation alternates at a frequency of 2.45 GHz. Nevertheless, the lifetime of a coherently ordered state is sufficiently long to accelerate the chemi-

The CSC-temperatures of an ethanol-hexane mixed solution and MBBA in the isotropic state under microwave irradiation were accurately evaluated using the

(Δδ) of individual protons. A CSC-temperature increase was observed as a function of the microwave irradiation time for CH2 and CH3 non-polar protons. The CSCtemperature for non-polar protons reflects the bulk temperature of the solution. A

polar protons than that with CH2 and CH3 non-polar protons in ethanol, and higher CSC-temperature was observed for H-C=N (7′) and CH3-O (α') protons in MBBA. The lowered CSC-temperature of OH protons in ethanol under microwave irradiation which was lower than the bulk temperature is concluded to be the experimental evidence of a non-thermal microwave effect. In the microwave heating process, microwave energy is absorbed into the polar molecular system by the formation of an ordered state with lower entropy. Ordered dipolar molecules cannot completely follow the oscillating electric field; therefore, the ordered state becomes partly disordered, increasing the entropy. Microwave energy is simultaneously dissipated to the system as thermal and non-thermal microwave effects. These coherently ordered molecules interact strongly with each other to form hydrogen bonds between the OH groups of ethanol, and these interactions are considered to be due to a non-thermal microwave effect. MD simulation was carried out to confirm the

theoretical validity of the experimentally observed increased lower field <sup>1</sup>

cal shift, and the results were found to agree well. These non-thermal microwave effects play an important role in the intrinsic acceleration of chemical reaction rates between polar molecules under microwave irradiation. It is considered that the coherently ordered state reduces the activation energy for the reaction, which

This work was supported by KAKENHI Grant-in Aid (JP16H00756 to AN and JP20H05211 to IK) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan and by KAKENHI Grant-in-Aid (JP15K06963 to AN and JP18H02387 to IK) from the Japan Society for the Promotion of Science (JSPS). The calculations were performed using clusters or supercomputers at the Research Center for Computational Science, Okazaki, Japan. The authors thank Ms. N.

H chemical shift changes

H chemi-

H chemical shift was observed for OH

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

linear relationship of temperature with respect to the 1

lowered CSC-temperature with lower field <sup>1</sup>

increases the reaction rate as catalysis.

Yamaguchi for her financial support.

**Acknowledgements**

cal reaction rate.

**14. Conclusion**

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

In the case of microwave irradiation, the electric field is oscillating at a frequency of 2.45 GHz. As discussed in the MD simulation and thermodynamics consideration, a polar molecule is coherently ordered along with the oscillating electric field. Unlike in the case of an applied OEEF, the coherent ordered state under microwave irradiation alternates at a frequency of 2.45 GHz. Nevertheless, the lifetime of a coherently ordered state is sufficiently long to accelerate the chemical reaction rate.
