CN110006875B

CN110006875B - Method for measuring melting point of biphenyl crystal by using Raman spectrum

Info

Publication number: CN110006875B
Application number: CN201910371123.9A
Authority: CN
Inventors: 梅红樱; 姚汝贤; 陈富军; 郑新艳; 姚海子; 胡坡
Original assignee: Huanghuai University
Current assignee: Huanghuai University
Priority date: 2019-05-06
Filing date: 2019-05-06
Publication date: 2021-06-01
Anticipated expiration: 2039-05-06
Also published as: CN110006875A

Abstract

The invention discloses a method for determining the melting point of biphenyl crystals by using Raman spectroscopy. The Raman spectroscopy technology is used to measure the intermolecular and intramolecular vibration modes of biphenyl crystals at high temperature. When the biphenyl material changes from a crystalline state to a liquid state , the intermolecular vibrational modes will all disappear, and only a very broad peak can be seen; while the frequency, linewidth and intensity of the intramolecular vibrational modes all appear to jump to a certain extent. Using this phenomenon, the melting point of biphenyl crystals can be easily and quickly determined. The method is convenient and quick, has no damage or contact to the sample, and the sample does not need to be in contact with air, and can be applied to various Raman measurement systems and most organic materials.

Description

Method for measuring melting point of biphenyl crystal by using Raman spectrum

Technical Field

The invention relates to the technical field of spectrum application, in particular to a method for measuring a melting point of a biphenyl crystal by using Raman spectrum.

Background

The biphenyl material has inflammability and higher volatility, belongs to low-toxicity class and has irritation to people. Its steam can stimulate eyes, nose and trachea, cause inappetence, vomiting and the like, has certain toxicity to nervous system, digestive system and kidney, and the characteristics limit the determination of its melting point to a certain extent. The conventional methods for measuring the melting point of biphenyl materials at present include capillary tube measurement, microscope hotplate measurement, automatic melting point measurement, and the like. Biphenyl samples, however, have low toxicity, pungent odor, and are volatile in air, which all affect the melting point determination of the samples and may be detrimental to the physical health of the operator.

Disclosure of Invention

The invention provides a method for rapidly and conveniently detecting the melting point of a biphenyl crystal by using a Raman spectrum measurement technology by using the characteristics of the biphenyl material before and after the melting point.

In order to solve the technical problems, the invention adopts the following technical scheme:

a method for measuring the melting point of a biphenyl crystal by using Raman spectroscopy is designed, and comprises the following steps:

(1) packaging a biphenyl crystal sample to be detected in a transparent container, and keeping the container in a vacuum or inert gas atmosphere;

(2) assembling the container to a heating device, heating and stabilizing the sample at different temperatures to measure raman spectra;

(3) exciting a biphenyl crystal sample by using laser at different temperatures, and measuring a Raman scattering spectrum of the biphenyl crystal sample;

(4) and observing the intermolecular vibration mode of the biphenyl crystal under low wave number, and if the intermolecular vibration mode disappears suddenly at a certain temperature, determining the temperature as the melting point temperature of the biphenyl crystal sample.

Preferably, the transparent container is a quartz glass tube; heating device includes warm table, nickel chromium heater strip, temperature sensor and temperature controller, the carbon glue is fixed on the warm table for the quartz glass pipe, temperature sensor's bottom is also fixed on the warm table and is located near quartz glass pipe with the carbon glue. Wherein, heat through temperature controller control heater strip, the setting of nickel chromium heater strip is in the warm table, realizes the heating to the sample, obtains sample container's temperature through temperature sensor to feed back to the temperature controller, and then realize heating temperature's accurate control.

Preferably, the temperature sensor is a diode temperature sensor; the model of the temperature controller is Lakeshore335, and the temperature control precision is 0.1K.

Preferably, the heating temperature in the step (2) is stabilized between 300K and 360K at intervals of 5K.

Preferably, the device for measuring the raman scattering spectrum of the biphenyl crystal sample in the step (3) comprises a laser, a plane mirror, a low-wave-number notch filter, an objective lens, a grating, a charge-coupled device, an imaging system, a semi-reflecting and semi-transmitting film and a PC terminal.

Laser emitted by the laser is reflected to a low-wave-number notch filter by a plane mirror, high-purity light reflected by the low-wave-number notch filter is focused on a biphenyl crystal sample through a 20-time objective lens and reacts with the sample to generate Raman scattering light, a scattering light original path returns to pass through the low-wave-number notch filter and then reaches a grating, light dispersed by the grating is incident into a charge coupling element, and the charge coupling element transmits a received signal to a PC (personal computer) end for processing and recording; a semi-reflecting and semi-transmitting film is arranged between the low wave number notch filter and the objective lens, one part of Raman scattering light penetrates through the semi-reflecting and semi-transmitting film to the low wave number notch filter and the grating, the other part of Raman scattering light is reflected to an imaging system by the semi-reflecting and semi-transmitting film, and the imaging system transmits received signals to a PC (personal computer) end for processing and recording.

Wherein the low wave number notch filter (BNF) is a reflector Bragg grating recorded in photosensitive silicate glass body, and the reflection bandwidth of BNF is as narrow as 5cm^-1But not other wavelengths, the overall transmission is almost 95%; the grating is used for separating the reflected scattered light with different wavelengths on space and entering the charge coupled device for collection; a charge-coupled device (CCD) is a silicon wafer for detecting light, and the change of a semiconductor potential well is generated and controlled by clock pulse voltage to realize a solid-state electronic device for storing and transmitting charge information.

Preferably, the laser is a titanium sapphire doped laser, the wavelength is 488nm, but not limited to 488nm, and the laser with different wavelengths can be selected according to the sample; the reflector is a silver-plated reflector; the low wave number notch filter is a volume Bragg grating low wave number notch filter; the specification of the grating is 1200 g/mm; the imaging system is a thorlabs imaging camera; the semi-reflecting and semi-transmitting film reflects 45% of incident light and transmits 55%; the device for measuring the Raman scattering spectrum of the biphenyl crystal sample can measure the lowest wave number of 5cm^-1The raman spectrum of (a).

Preferably, the step (3) adopts 488nm laser to measure the Raman spectra of the biphenyl crystals at different temperatures; step (a)4) The low wave number in the range of 5 to 200cm^-1。

Preferably, if the apparatus for measuring the Raman scattering spectrum of the biphenyl crystal sample in the step (3) is a commercially available Raman apparatus incapable of taking low wavenumber peaks, the Raman spectrum of the measurement sample is first excited by laser, and the Raman spectrum of the biphenyl crystal sample is measured at 1280 cm^-1And 1600cm^-1Two peaks nearby and fitting the peaks by using a Lorentzian function; observing the fitting results, if the frequency, line width and intensity of these peaks jump around a certain temperature, the temperature is the melting point temperature.

Preferably, the inert gas atmosphere in the container in the step (1) is argon, and the oxygen content and the moisture content are both less than 0.1 ppm.

The invention has the beneficial effects that:

1. the biphenyl molecule is formed by connecting two benzene rings at para positions through a carbon-carbon single bond, and the special structure can cause two opposite acting forces of repulsive force between hydrogen atoms and attractive force between pi electrons in the biphenyl crystal. In the crystalline state, these two forces reach a stable equilibrium. When the biphenyl crystal reaches a melting point or above, the internal periodic lattice structure disappears, which results in the disappearance of the low-wavenumber lattice vibration peaks in the raman spectrum. In addition, when the lattice structure disappears, the intermolecular force is weakened at the same time, which breaks the balance between the intramolecular and intermolecular forces, changes the property of the intramolecular vibration mode, and reflects the change of the frequency, line width and intensity of the high-wave-number intramolecular vibration mode on the Raman spectrum. As the biphenyl molecules are very sensitive to structural change and the Raman signal of the biphenyl crystal is very strong, the melting point of the biphenyl crystal is conveniently and accurately determined by using a Raman spectrum testing technology.

2. The invention utilizes Raman scattering technology to measure the melting point of the sample, the sample is packaged in the quartz glass tube to isolate air, the volatilization of the biphenyl sample in the air and the generation of low-toxicity and pungent odor can be avoided, and the safety of the measurement work can be ensured.

3. Since most organic materials have characteristics similar to those of biphenyl materials, such as derivatives of biphenyl, poly-p-phenylene oligomers, bipyridine and derivatives thereof, before and after the melting point, and the melting points of these similar materials can be measured by using the method, the present invention can be applied to the melting point measurement of most organic materials having the same properties.

4. The method can also be applied to some extreme environments such as high temperature, high pressure, strong field and the like, and in some extreme environment measurement such as measuring physicochemical properties of a sample under high pressure by using a diamond anvil cell device, searching for new substances under high pressure and the like, the method can also be used for determining the melting point of the corresponding material sample.

Drawings

FIG. 1 shows the vibration range (a) of 488nm laser excited biphenyl crystal at low wavenumber lattice and 1280 cm^-1Vicinity (b) and 1600cm^-1Raman spectrum of the vicinity (c).

FIG. 2 shows 1280 cm fitting of Lorentzian function^-1Frequency and line width of peak, 1600cm^-1The frequency of the two nearby peaks changes along with the temperature, the dotted line represents the melting point temperature, and the shaded part is the error.

Detailed Description

The following examples are given to illustrate specific embodiments of the present invention, but are not intended to limit the scope of the present invention in any way. The apparatus elements referred to in the following examples are, unless otherwise specified, conventional apparatus elements; the industrial raw materials are all conventional industrial raw materials which are sold on the market, if not specifically mentioned.

Example 1: a method for measuring the melting point of biphenyl crystals by using Raman spectroscopy comprises the following steps:

(1) a biphenyl crystal sample to be detected is packaged in a quartz glass tube with the diameter of 2 mm in a glove box, the atmosphere in the quartz glass tube is argon, and the oxygen content and the moisture content in the quartz glass tube are both less than 0.1 ppm.

(2) Assembling the container to a heating device, heating and stabilizing the sample at different temperatures to measure raman spectra; the heating temperature is stabilized between 300K and 360K at intervals of 5K.

Heating device includes warm table, nickel-chromium heater strip, temperature sensor and temperature controller, and quartz glass pipe and temperature sensor adopt the carbon to glue the bonding to fix on the warm table, and temperature sensor adopts the carbon to glue the bonding to fix on the warm table and be located near quartz glass pipe to reduce temperature error. The temperature is controlled by controlling the input current of the nickel-chromium heating wire through the temperature controller, so that the temperature is stabilized between 300K and 360K at an interval of 5K. The temperature sensor is a diode temperature sensor; the model of the temperature controller is Lakeshore335, and the temperature control precision is 0.1K.

(3) Exciting a biphenyl crystal sample by using laser at different temperatures, and measuring a Raman scattering spectrum of the biphenyl crystal sample; because the biphenyl crystal has good Raman spectrum intensity and spectrum resolution under 488nm laser irradiation, 488nm laser is adopted to measure the Raman spectrum of the biphenyl crystal under different temperatures in the embodiment.

The device for measuring the Raman scattering spectrum of the biphenyl crystal sample comprises a laser, a plane mirror, a low-wave-number notch filter, an objective lens, a grating, a charge coupling element, an imaging system, a semi-reflective and semi-transparent film and a PC (personal computer) end; laser emitted by a laser is reflected to a low-wave-number notch filter by a plane mirror, high-purity light reflected by the low-wave-number notch filter is focused on a biphenyl crystal sample through a 20-time objective lens and reacts with the sample to generate Raman scattering light, a scattering light original path returns to pass through the low-wave-number notch filter and then reaches a grating, light dispersed by the grating is incident into a charge coupling element, and the charge coupling element transmits a received signal to a PC (personal computer) end for processing and recording; a semi-reflecting and semi-transmitting film is arranged between the low wave number notch filter and the objective lens, one part of Raman scattering light penetrates through the semi-reflecting and semi-transmitting film to the low wave number notch filter and the grating, the other part of Raman scattering light is reflected to an imaging system by the semi-reflecting and semi-transmitting film, and the imaging system transmits received signals to a PC (personal computer) end for processing and recording.

The laser is a titanium-doped sapphire laser with the wavelength of 488 nm; the reflector is a silver-plated reflector; the low wave number notch filter is a volume Bragg grating low wave number notch filter; gratingThe specification of (2) is 1200 g/mm; the imaging system is a thorlabs imaging camera; the semi-reflecting and semi-transmitting film reflects 45% of incident light and transmits 55%; the device for measuring the Raman scattering spectrum of the biphenyl crystal sample can measure the lowest wave number of 5cm^-1The raman spectrum of (a).

(4) And observing the intermolecular vibration mode of the biphenyl crystal sample under the condition of low wave number, and if the intermolecular vibration mode disappears suddenly at a certain temperature, determining the temperature as the melting point temperature of the biphenyl crystal sample. FIG. 1 (a) is a diagram showing the low wave number of lattice vibration peaks of a biphenyl crystal, the low wave number ranging from 5 to 200cm^-1When this region was observed, the spectrum at 350K was greatly changed from that at 345K, and all the oscillation peaks disappeared and only one broad peak appeared. This indicates that the structure of the biphenyl crystals is lost, the crystals are melted, and the melting point is between 345 and 350K.

Example 2: a method for measuring the melting point of a biphenyl crystal by Raman spectroscopy, which is different from example 1 in that the device for measuring the Raman scattering spectrum of a biphenyl crystal sample in step (3) is a commercially available Raman device incapable of taking a low-wavenumber peak, and the Raman spectrum of the measurement sample is first excited by laser to measure the melting point of the biphenyl crystal sample at 1280 cm^-1And 1600cm^-1Two peaks nearby and fitting the peaks by using a Lorentzian function; observing the fitting results, if the frequency, line width and intensity of these peaks jump around a certain temperature, the temperature is the melting point temperature.

For a raman device in which the low wavenumber region is difficult to observe, the melting point can be determined by observing the high wavenumber intramolecular vibration region. FIGS. 1 (b) and (c) are samples of biphenyl crystals at 1280 cm^-1Peak sum 1600cm^-1Raman spectrum around the peak. In this example we fit these several peaks by a lorentzian function, the fitting result being in fig. 2. It can be seen that the lower temperature region of the peaks at 350K shows a large abnormality in frequency, line width and intensity. This indicates that intermolecular interactions within the crystal are greatly reduced and the crystal melts.

In example 1 and example 2, by observing the low wave number Raman vibration peak of biphenyl crystal, 1280 cm^-1Peak sum 1600cm^-1The melting point of the biphenyl crystal is determined by the variation trend of the two peaks at different temperatures, the determination method is simple and easy to operate, no damage and no contact are caused to a sample, the sample does not need to contact air, the operation process is high in safety, the detection result is rapid and accurate, and the method can be suitable for various Raman measurement systems and most organic materials.

While the present invention has been described in detail with reference to the embodiments, those skilled in the art will appreciate that various changes can be made in the specific parameters of the embodiments without departing from the spirit of the present invention, and that various specific embodiments can be made, which are common variations of the present invention and will not be described in detail herein.

Claims

1. a method utilizing Raman spectroscopy to measure the fusing point of biphenyl crystal, is characterized in that, comprises the following steps:

(1) Encapsulate the biphenyl crystal sample to be detected in a transparent container, and keep the container in a vacuum or inert gas atmosphere;

(2) Assemble the container to the heating device, heat the sample and stabilize it at different temperatures to measure the Raman spectrum;

(3) Exciting the biphenyl crystal samples with laser light at different temperatures, and measuring the Raman scattering spectra of the biphenyl crystal samples;

(4) Observing the intermolecular vibration mode of biphenyl crystal at low wavenumber, if the vibration peak suddenly disappears at a certain temperature, then the temperature is the melting point temperature of the biphenyl crystal sample; the range of the low wave number is 5-200cm ^-1 .

2. The method for measuring the melting point of biphenyl crystals by Raman spectroscopy according to claim 1, wherein the transparent container is a quartz glass tube; the heating device comprises a heating table, a nickel-chromium heating wire, a temperature sensor and In the temperature controller, the quartz glass tube is fixed on the heating table with carbon glue, and the temperature sensor is also fixed on the heating table with carbon glue and is located near the quartz glass tube.

3. the method that utilizes Raman spectroscopy to measure biphenyl crystal melting point according to claim 2, is characterized in that, described temperature sensor is diode temperature sensor; The model of described temperature controller is Lakeshore335, and temperature control precision is 0.1K .

4 . The method for determining the melting point of biphenyl crystals by Raman spectroscopy according to claim 1 , wherein in the step (2), the heating temperature is stabilized between 300K and 360K at intervals of 5 K. 5 .

5 . The method for measuring the melting point of biphenyl crystals by using Raman spectroscopy according to claim 1 , wherein the device for measuring the Raman scattering spectrum of the biphenyl crystal samples in the step (3) comprises a laser, a plane mirror, a low temperature Wavenumber notch filter, objective lens, grating, charge-coupled element, imaging system, transflective film and PC terminal;

The laser light emitted by the laser is reflected by the plane mirror to the low wavenumber notch filter, and the high-purity light reflected by the low wavenumber notch filter is focused on the biphenyl crystal sample by a 20 times objective lens, and generated after interacting with the sample. Raman scattered light, the scattered light returns to the grating through the low wavenumber notch filter, the light scattered by the grating is incident on the charge-coupled element, and the charge-coupled element transmits the received signal to the PC for processing and recording; A transflective film is set between the low wavenumber notch filter and the objective lens, part of the Raman scattered light passes through the transflective film to the low wavenumber notch filter and grating, and the other part is reflected by the transflective film To the imaging system, the imaging system transmits the received signal to the PC for processing and recording.

6. The method for measuring the melting point of biphenyl crystals by Raman spectroscopy according to claim 5, wherein the laser is a titanium-doped sapphire laser; the reflector is a silver-coated reflector; the low wavenumber notch The filter is a volume Bragg grating low wavenumber notch filter; the specification of the grating is 1200 g/mm; the imaging system is a thorlabs imaging camera; the transflective film reflects 45% of incident light and transmits 55% %; the device for measuring the Raman scattering spectrum of biphenyl crystal samples can measure the Raman spectrum with the lowest wave number of 5 cm ^-1 .

7 . The method for determining the melting point of biphenyl crystals by Raman spectroscopy according to claim 1 , wherein the step (3) uses a 488 nm laser to measure the Raman spectra of biphenyl crystals at different temperatures. 8 .

8 . The method for measuring the melting point of biphenyl crystals by Raman spectroscopy according to claim 1 , wherein in the step (3), the device for measuring the Raman scattering spectrum of the biphenyl crystal samples cannot take low wavenumber peaks. 9 . For the commercially available Raman device, the Raman spectrum of the sample is first measured with laser excitation, two peaks near 1280 cm ^-1 and 1600 cm ^-1 of the biphenyl crystal sample are measured, and the Lorentzian function is used to fit these two peaks. If the frequency, line width and intensity of these peaks jump around a certain temperature, the temperature is the melting point temperature.

9 . The method for determining the melting point of biphenyl crystals by Raman spectroscopy according to claim 1 , wherein the inert gas atmosphere in the container in step (1) is argon, and the oxygen content and the moisture content in the container are both argon. 10 . less than 0.1 ppm.