Dynamics Study On Debye Relaxation Of Pure And Binary Monoalcohols Glass-forming Systems

Water,protein and nucleic acid are important to constitute biological organisms,and achieving their functions requires the participation of hydrogen-bonded structures.However,the complete understanding of hydrogen bonding is still limited due to its complexity.In general,the dielectric relaxation spectra of monoalcohols liquids shows an"extra"Debye relaxation which is slower than that of structural relaxation and might be closely related to the hydrogen-bonded structure.Therefore,simple hydrogen-bonded liquids such as monoalcohols is a model system to study Debye relaxation.The study will not only help understand its physical origin and the organization of hydrogen-bonded clusters in Debye liquids,but also benefit in further explaining the structure and complex dynamic behavior of water,as well as deeply understanding the structure and function of biological macromolecules.In order to clarify the mechanism of the intermolecular association and the corresponding relaxation properties of monoalcohols,various experimental techniques including Broadband Dielectric Spectroscopy,Differential Calorimetry Scanner,and near infrared absorption was used in this dissertation to provide deep insights.Firstly,the dielectric technology in a wide range of temperature and frequency is used to study the primary monoalcohol（2-ethyl-1-hexanol）and the secondary monoalcohol（4-methyl-3-heptanol）in Debye relaxation with a small amount of carbon dots.It is found that the carbon dots significantly increases the relaxation strength and time of Debye relaxation in 4-methyl-3-heptanol,while the influence on 2-ethyl-1-hexanol is very small,which makes the the relaxation strength slightly reduced.Debye relaxation is closely correlated with the hydrogen bond structure,this difference can be explained by the change of the latter.That is,in 4-methyl-3-heptanol,the amount of chain structures increases while that of ring structures is reduced,resulting in more molecular to form chain-like structure.A comparison of these two alcohol demonstrates that the involvement of carbon dots have little influence on the chain structure yet the ring structure will change significantly,leading to the ring structure-to-chain structure for the hydrogen bond structure.Secondly,the pure monohydric alcohol 4-methyl-2-pentanol was studied using high-voltage dielectric technology,whereby the Debye relaxation changing with temperature and the relationship between Debye relaxation and structural relaxation were systematically analyzed.The calculated Kirkwood factor indicates that the configuration of hydrogen-bonded molecular clusters in 4-methyl-2-pentanol supercooled liquid is chain-like.Comparing the high pressure experimental results of 4-methyl-2-pentanol,2-ethyl-1-hexanol and 4-methyl-3-heptanol,it is found that the 4-methyl-2-pentanol and2-ethyl-1-hexanol have strong Debye relaxation,while that of 4-methyl-3-heptanol is weak.The evolution law of the relaxation intensity ratio and time ratio of Debye relaxation to structure relaxation in the dielectric spectrum with pressure indicates that with the increasing of pressure,both theΔε_D/Δε_αandτ_D/τ_αof 4-methyl-2-pentanol decrease,which is in contrast to those of 2-ethyl-1-hexanol and 4-methyl-3-heptanol.This may be attributed to the relative positions of the hydroxyl and methyl groups in the molecular structure of 4-methyl-2-pentanol wherein the steric hindrance results in a shorter supramolecular structure of internal chain hydrogen bonds.The experimental results provide a schematic diagram of the structural changes of hydrogen-bonded clusters in 4-methyl-2-pentanol under the influence of pressure,which offers new viewpoint on the origin of the Debye process from molecular standpoint.Finally,seven groups of binary mixed monoalcohol alcohol solutions are selected to study the glass formation dynamic.The mixing heatΔH_mixof the binary mixture is measured by the C80 calorimeter.According to the different value ofΔH_mix（either positive or negative）,the glass transition temperature（T_g）,composition dependence of T_g（T_g-x）,the relationship ofΔH_mixand T_g-x,as well as the deviation from the ideal mixing rule are all established.