Study On The Effect Of Hydrogen Bonding On Molecular Structure And Macroscopic Properties Of Several Typical Organic Aqueous Solutions By Raman Spectroscopy

Water is a fascinating science topic,and many phenomena in nature must use this simple and peculiar substance.The structure of liquid water and aqueous solutions is one of the most basic and challenging scientific problems.Investigating the microstructure and properties of water systems from molecule level is essential for understanding fundamental problems in related fields.As the fundamental reason for the association of liquid water molecules,hydrogen bonding also directly affects the physicochemical properties of aqueous solutions.Hydrogen bond network is formed by the interaction between water molecules.Owing to the complex behaviors of hydrogen bond networks,the properties of aqueous systems are not only limited by those of individual water molecules.Studying the microstructure of liquid water and aqueous solutions and establishing the connection between the microstructure and the macroscopic properties are still the core issues of water science research.In this thesis,Raman spectroscopy is used as the main experimental method to study a series of aqueous systems with typical hydrogen bonds.The effect of hydrogen bond in aqueous solution system is revealed at the molecular level.At the same time,this thesis intends to carry out the relation between the microstructure and the macroscopic physical properties of the aqueous solution system,and establish a correlation model among hydrogen bonding interaction,microstructure and macroscopic properties of aqueous solution.The valuable experiments would be provided for enriching water science research.The organic compounds are selected,such as dimethyl sulfoxide(DMSO),tetrahydrofuran(THF),methanol,and polyvinyl alcohol(PVA).The experimental samples are prepared with pure water in different proportions.Using the Raman spectrometer and it’s analysis software,combined with the change rule of surface tension and viscosity with concentration,a series of studies on hydrogen bond structure and macroscopic physical properties have been carried out,and the research results were obtained:1.The Raman spectra of dimethyl sulfoxide aqueous solutions show that the Raman peak corresponding to S=O stretching vibration mode moves to higher wavenumber with the increase of dimethyl sulfoxide,and the Raman peak corresponding to OH stretching vibration mode moves to lower wavenumber with the increase of dimethyl sulfoxide.This proves that hydrogen bonds are formed between dimethyl sulfoxide molecules and water molecules.The experimental results show that dimethyl sulfoxide weakens the surface tension of water.As the concentration of dimethyl sulfoxide increases,the viscosity of the solutions shows a quadratic function trend.The maximum is reached when the mole fraction is 0.7.With the decrease of dimethyl sulfoxide,the hydrogen bond network structure changes from DMSO…H2O to a new one which a dimethyl sulfoxide molecule interacts with two water molecules.The change of hydrogen bond network structure in the solutions makes the viscosity change.2.Observed the extent of intermolecular association in the tetrahydrofuran-water mixtures of different molar ratios via Raman spectra.The spectra of the mixtures in the region of 800-1000 cm-1 are deconvoluted to three Raman peaks,corresponding to v(C-O)mode,v(C-C)mode,and the hydrogen bonding,respectively.As the concentration of tetrahydrofuran increases,the Raman peak corresponding to hydrogen bonding mode becomes stronger and shifts left.At high dilution,tetrahydrofuran molecules preferentially interact with water molecules,which come from the tetrahedral hydrogen bond structure in water.At this time,the double hydrogen bond structures formed between one tetrahydrofuran molecule and two surrounding water molecules.When the content of tetrahydrofuran increases,the double hydrogen bond structure is going to be converted into single hydrogen bond structure.The surface tension fluctuates only in a small range in the tetrahydrofuran-rich area.It shows that the double hydrogen bond structure and the single hydrogen bond structure have minor effect on the surface tension,but much on the viscosity.3.Use Raman spectra to analyze the hydrogen bond between methanol molecules and water molecules in methanol aqueous solutions with different concentrations.When the molar ratio(nCH3OH:nH2O)is lower than 1:3 and above 3:1,the v(C-O)mode of the characteristic peak hardly shifts.The v(C-H)mode of the characteristic peak shifts red.When the molar ratio is higher than 1:3,the v(C-O)mode of the characteristic peak shifts blue,and the v(C-H)mode of the characteristic peak still shifts red.The methanol weakens surface tension of water,due to the depletion of solutes on the interface.The content of methanol effects the hydrogen bond network structure of the solutions.It makes the viscosity of the mixed solutions change.4.Use Raman spectra to analyze the hydrogen bonding between polyvinyl alcohol molecules and water molecules in different concentrations.The wavenumber of the CH stretching vibration and OH stretching vibration modes in solutions with different molar ratios shifts different.As the concentration of polyvinyl alcohol increases,the width of Raman peak corresponding to the OH stretching vibration mode decreases and the wavenumber shifts red.The intensity of the Raman peak corresponding to the CH stretching vibration gradually increases and the wavenumber moves to higher wavenumber.The increase of polyvinyl alcohol induces a change of the microstructure in the solution.When the content of polyvinyl alcohol in the solution increases,the surface tension of the polyvinyl alcohol aqueous solution decreases and the viscosity increases.The molecular weight of polyvinyl alcohol also affects viscosity.