Apparatus and method for detecting the saturated vapor pressure of aerosol single droplets

Abstract

The application relates to a device and a method for detecting saturated vapor pressure of aerosol single droplets, and belongs to the technical field of saturated vapor pressure detection. The device solves the problem of large detection result error of the existing aerosol single droplet saturated vapor pressure measuring device and method. The single droplet optical tweezers suspension device of the device comprises a sample cell, the sample cell comprises a concentric outer ring wall and an inner ring wall, the outer ring wall is connected with one side of the inner ring wall, a single droplet inlet penetrating the outer ring wall and the inner ring wall is arranged at the connecting position; a plurality of gas inlets and gas outlets penetrating the ring wall and being spaced apart are arranged on the outer ring wall and the inner ring wall, the gas inlets and the gas outlets on the outer ring wall are staggered with the gas inlets and the gas outlets on the inner ring wall; the diameter of the gas inlets and the diameter of the gas outlets are both smaller than the diameter of the single droplet inlet. The device can reduce the error caused by the wall effect on the saturated vapor pressure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of saturated vapor pressure detection, and particularly to a device and method for detecting saturated vapor pressure of aerosol single droplets. BACKGROUND

[0002] The accurate measurement of saturated vapor pressure parameters is important for understanding PM 2.5 An important physicochemical parameter of the driving force for the formation of secondary organic aerosols in the process of explosive growth. By observing the changes of single droplets in a specific atmosphere in real time and in situ, the changes of particle size and composition are solved, thereby solving the problem of high-quality data measurement of key physical and chemical parameters in the gas-particle distribution process of volatile substances. It is of great significance to develop a single droplet saturated vapor pressure measurement device for volatile substances to reveal the key driving force for the formation of secondary organic aerosols in atmospheric fine particulate matter pollution.

[0003] The existing aerosol single droplet saturated vapor pressure measurement device and method have large errors in the detection results. SUMMARY

[0004] In view of the above analysis, the embodiments of the present application aim to provide a device and method for detecting saturated vapor pressure of aerosol single droplets to solve the problem of large errors in the detection results of the existing aerosol single droplet saturated vapor pressure measurement device and method.

[0005] In one aspect, the present application provides a device for detecting saturated vapor pressure of aerosol single droplets, which comprises a single droplet optical tweezers suspension device, a gas atmosphere control system, a microdroplet pumping system, a light beam coupling system, a signal detection system and a microdroplet detection device.

[0006] The gas atmosphere control system is in communication with the microdroplet pumping system, the microdroplet pumping system is in communication with the single droplet optical tweezers suspension device, and the light beam coupling system is in communication with the single droplet optical tweezers suspension device, the signal detection system and the microdroplet detection device, respectively.

[0007] The single droplet optical tweezers suspension device comprises a sample cell, the sample cell comprises a concentric outer ring wall and an inner ring wall, one side of the outer ring wall and the inner ring wall is connected, and a single droplet inlet penetrating the outer ring wall and the inner ring wall is arranged at the connection; the outer ring wall and the inner ring wall are both provided with a plurality of gas inlets and gas outlets penetrating the ring wall and arranged at intervals, and the gas inlets and gas outlets on the outer ring wall are staggered with the gas inlets and gas outlets on the inner ring wall.

[0008] The diameter of the gas inlet and the diameter of the gas outlet are both smaller than the diameter of the single droplet inlet.

[0009] Preferably, the diameter of the single droplet inlet is 3-4 times the diameter of the gas inlet, and the diameter of the single droplet inlet is 2-2.5 times the diameter of the gas outlet.

[0010] Preferably, the bottom of the sample cell is provided with a quartz glass sheet, and the quartz glass sheet is provided with a layer of anionic surfactant.

[0011] Preferably, the microdroplet pumping system comprises, in sequence, an aerosol generator, a stop valve, and a droplet beam device, and the droplet beam device is in communication with the sample cell.

[0012] Preferably, the droplet beam device comprises a plurality of pipes of different inner diameters connected in sequence, and the inner diameters of the plurality of pipes gradually decrease along the direction of aerosol flow.

[0013] Preferably, the inside of the pipe is provided with a plurality of diaphragms of different inner diameters, and the inner diameters of the plurality of diaphragms gradually decrease along the direction of aerosol flow.

[0014] Preferably, the gas atmosphere control system comprises an ambient gas control device and a reaction gas control device, the ambient gas control device is in communication with the pipe between the stop valve and the droplet beam device, and the reaction gas control device is in communication with the pipe between the droplet beam device and the sample cell.

[0015] In another aspect, the present application also provides a method for detecting the saturated vapor pressure of aerosol single droplets, which uses the above-mentioned device, and the method comprises:

[0016] The microdroplet pumping system pumps the aerosol into the sample cell of the single droplet optical tweezer suspension device in the form of single droplets;

[0017] The laser emitted by the light beam coupling system serves as a reaction light beam, and a single droplet is captured and suspended in the sample cell by the optical tweezer technology;

[0018] The required gas is introduced into the sample cell by the gas atmosphere control system;

[0019] The scattered light signal of the single droplet is input into the signal detection system and the microdroplet detection device, respectively, the change in the radius value of the single droplet before and after the reaction is analyzed according to the light signal data, and then the saturated vapor pressure is calculated.

[0020] Preferably, the droplets are arranged into a string by the droplet beam device of the microdroplet pumping system, forming an aerosol droplet beam, so that the aerosol droplets enter the sample cell one by one in the form of single dispersed single string droplets.

[0021] Preferably, the method further comprises: after suspending the single droplet by the optical tweezer technology, lowering the humidity in the sample cell to below the weathering point humidity of the volatile chemical component in the droplet by introducing dry gas and / or wet gas into the sample cell through the gas atmosphere control system, weathering and crystallizing the droplet on the inner wall of the sample cell, and then increasing the humidity in the sample cell to the required humidity for the reaction.

[0022] Compared with the prior art, the present application can achieve at least one of the following beneficial effects:

[0023] 1. The sample cell of the present application comprises an outer ring wall and an inner ring wall, a single droplet inlet is arranged at the connection between the outer ring wall and the inner ring wall, and a plurality of gas inlets and gas outlets are arranged on the outer ring wall and the inner ring wall and spaced apart through the ring wall, the gas inlets and gas outlets on the outer ring wall are staggered with the gas inlets and gas outlets on the inner ring wall, which can make the gas enter and exit the sample cell uniformly and ensure the stability of the gas pressure in the sample cell, thereby stably suspending the single droplet by the optical tweezer; in addition, the uniform entry and exit of the gas into and out of the sample cell can avoid local overpressure or underpressure and reduce the uneven distribution of the droplets when entering the sample cell due to uneven gas pressure, effectively solving the problem that uneven gas pressure may cause the droplets to deposit on the wall; moreover, the stable gas pressure in the sample cell helps to maintain the suspended state of the single droplet, reduces the contact between the droplet and the wall caused by gas pressure fluctuations, and thereby reduces the error influence of the wall effect on the saturated vapor pressure.

[0024] The diameter of the gas inlet and the diameter of the gas outlet are both smaller than the diameter of the single droplet inlet, and when the single droplet is pumped into the sample cell from the single droplet inlet, the turbulent flow effect of the aerosol droplet in the sample cell can be generated and enhanced, the turbulent flow can enhance the mixing and movement of the droplet in the sample cell, and reduce the probability and possibility of the droplet depositing on the inner wall; the swirling gas flow does not simply go from the inlet to the outlet, but tends to approach the center of the sample cell (i.e. the focus center of the laser) by virtue of the turbulent flow effect, and at the same time, the swirling effect can also increase the probability of the gas flow outside the focus center returning to the focus point, thereby increasing the capture efficiency and reducing the probability of the aerosol droplet depositing on the inner wall of the sample cell, and reducing the error influence of the wall effect on the saturated vapor pressure.

[0025] 2. The sample cell of the present application is provided with a quartz glass sheet coated with an anionic surfactant at the bottom, the anionic surfactant reduces the surface tension of the spheroidal droplet, at the same time, the droplet at the bottom of the sample cell is no longer deposited in the form of a spheroid, but directly spreads on the bottom of the sample cell, avoiding the saturated vapor pressure error caused by the curved surface pressure of the droplet containing volatile chemical components at the bottom of the sample cell.

[0026] 3、The present application sets up a droplet beam device in the microdroplet pumping system, when the aerosol droplets pass through the droplet beam device, the droplet beam device changes the droplets from the aggregated state to the single dispersed single string droplets which enter the sample cell one by one.

[0027] 4、The present application sets up a stop valve between the aerosol generator and the droplet beam device, when the droplets enter the droplet beam device, the stop valve can be closed, the ambient background gas is introduced into the droplet beam device, the droplets in the droplet beam device are diluted, and the droplet beam device further changes the droplets from the aggregated state to the single dispersed single string droplets which enter the sample cell one by one.

[0028] 5、In the method of the present application, after the single droplet is suspended by the optical tweezer technology, the dry gas and / or wet gas is introduced into the sample cell through the gas atmosphere control system, the humidity in the sample cell is reduced to below the weathering point humidity of the chemical components in the droplet, the droplets on the inner wall of the sample cell are weathered and crystallized, and then the humidity in the sample cell is increased to the required humidity for reaction. In the process of weathering and crystallization, the volatile components in the droplets deposited on the wall have been volatilized, when the environmental humidity increases to the reaction humidity, the crystal on the wall adsorbs the water molecules in the environment to form a solid-liquid mixture, the liquid phase in the solid-liquid mixture is only the adsorbed water molecules, and the volatile organic components in the aerosol droplets are no longer present, and the volatile components in the single droplet suspended by the optical tweezer remain unchanged in the process, so that the influence of the volatile components in the droplets deposited on the wall on the saturated vapor pressure of the single droplet suspended by the optical tweezer is effectively avoided.

[0029] In the present application, the above-mentioned technical solutions can be combined with each other to realize more preferred combination schemes. Other features and advantages of the present application will be described in the subsequent description, and some advantages will become apparent from the description, or will be understood by implementing the present application. The purposes and other advantages of the present application can be realized and obtained from the contents specifically pointed out in the description and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0030] The accompanying drawings are included to provide a further understanding of the application, and are incorporated in and constitute a part of this specification, illustrate embodiments of the application, and together with the description serve to explain the principles of the application. In the drawings:

[0031] Figure 1 The device for detecting the saturated vapor pressure of aerosol single droplet of the present application;

[0032] Figure 2 The schematic diagram of the sample cell structure of the present application;

[0033] Figure 3 The structure discrete diagram of the droplet beam device of the present application (the diaphragm and the gasket are separately shown outside);

[0034] Figure 4A sectional view of the droplet beam flow device of the present application;

[0035] Figure 5 A schematic diagram of the monodisperse principle of the droplet beam flow device of the present application;

[0036] Figure 6 A topography of a suspended single droplet of Example 2 in a microscopic imaging camera;

[0037] Figure 7 A spontaneous / stimulated Raman spectrum of a suspended single droplet of Example 2.

[0038] Reference signs:

[0039] 1 - single droplet optical tweezers suspension device; 101 - microscopic objective; 102 - sample cell; 1021 - outer ring wall; 1022 - inner ring wall; 1023 - single droplet inlet; 1024 - gas inlet; 1025 - gas outlet; 103 - illumination light source; 2 - gas atmosphere control system; 201 - gas generating device; 202 - flow meter; 3 - microdroplet pumping system; 301 - aerosol generator; 302 - stop valve; 303 - droplet beam flow device; 3031 - pipeline; 3032 - diaphragm; 3033 - gasket; 3034 - clamp; 3035 - threaded cap; 4 - light beam coupling system; 401 - laser; 402 - focusing lens; 403 - half-transmission half-reflection mirror; 404 - full reflection mirror; 5 - signal detection system; 501 - optical imaging camera; 502 - Raman spectrometer; 503 - data processing unit; 6 - microdroplet detection device. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present application will be described in detail below with reference to the drawings, which form a part of this application, and together with the embodiments of the present application serve to explain the principles of the present application, but are not intended to limit the scope of the present application.

[0041] The inventor found in the research that the error of the detection result of the existing aerosol single droplet saturated vapor pressure measuring device and method is caused by the wall effect of the droplet in the sample cell, specifically as follows: after the aerosol droplets are pumped into the sample cell, due to the sedimentation effect and the wall effect caused by the gravity and the pumping force of the droplets, the droplets will be deposited on the inner wall and the bottom of the sample cell, and when the aerosol droplets are deposited, the shape of the droplets deposited on the inner wall and the bottom and the droplets captured by the laser are basically spherical, and the curved surface of the spherical droplets can enhance the volatile pressure of the droplets containing volatile chemical components, so that the measured saturated vapor pressure rate first reaches the threshold value, thereby the measured value of the saturated vapor pressure is much higher than the actual saturated vapor pressure value, that is, the error of the detection result of the saturated vapor pressure is large.

[0042] Based on this, the present application provides a device for detecting the saturated vapor pressure of aerosol single droplets, as shown inFigure 1 As shown in the figure, the device comprises a single droplet optical tweezers suspension device 1, a gas atmosphere control system 2, a microdroplet pumping system 3, a light beam coupling system 4, a signal detection system 5 and a microdroplet detection device 6.

[0043] The gas atmosphere control system 2 is in communication with the microdroplet pumping system 3, the microdroplet pumping system 3 is in communication with the single droplet optical tweezers suspension device 1, and the light beam coupling system 4 is in communication with the single droplet optical tweezers suspension device 1, the signal detection system 5 and the microdroplet detection device 6 respectively.

[0044] The single droplet optical tweezers suspension device 1 comprises a sample cell 102, as shown in the figure. Figure 2 As shown in the figure, the sample cell 102 comprises a concentric outer ring wall 1021 and an inner ring wall 1022, the outer ring wall 1021 is connected to one side of the inner ring wall 1022, and a single droplet inlet 1023 penetrating the outer ring wall 1021 and the inner ring wall 1022 is arranged at the connection; the outer ring wall 1021 and the inner ring wall 1022 are both provided with a plurality of gas inlets 1024 and gas outlets 1025 penetrating the ring wall and arranged at intervals, and the gas inlets 1024 and the gas outlets 1025 on the outer ring wall 1021 are staggered with the gas inlets 1024 and the gas outlets 1025 on the inner ring wall 1022.

[0045] The diameter of the gas inlet 1024 and the diameter of the gas outlet 1025 are both smaller than the diameter of the single droplet inlet 1023.

[0046] In implementation, the microdroplet pumping system 3 pumps aerosol in the form of single droplets into the sample cell 102 of the single droplet optical tweezers suspension device 1; the laser emitted by the light beam coupling system 4 serves as a reaction light beam, which captures a single droplet in the sample cell 102 and suspends it by optical tweezers technology; the gas atmosphere control system 2 introduces the required gas into the sample cell 102; the scattered light signal of the single droplet is input to the signal detection system 5 and the microdroplet detection device 6 respectively, and the change in the radius value of the single droplet before and after the reaction is analyzed according to the light signal data, and then the saturated vapor pressure is calculated.

[0047] Compared with the prior art, the sample cell structure of the present application can make the gas uniformly enter and uniformly discharge the sample cell, and ensure the gas pressure in the sample cell to be stable, thereby making the stable optical tweezers suspend the single liquid droplet, reducing the contact of the liquid droplet with the wall, and further reducing the wall effect; and the diameter of the gas inlet and the diameter of the gas outlet are both smaller than the diameter of the single liquid droplet inlet, when the single liquid droplet is pumped into the sample cell from the single liquid droplet inlet, the turbulent flow effect of the aerosol liquid droplet in the sample cell can be generated and enhanced, the swirling gas flow is not simply from the inlet to the outlet, but approaches the center of the sample cell (i.e. the focusing center of the laser) by virtue of the turbulent flow effect, at the same time, the swirling effect can also increase the probability of the gas flow outside the focusing center to return to the focus point, thereby increasing the capture efficiency and reducing the probability of the aerosol liquid droplet to deposit on the inner wall of the sample cell, and reducing the error influence of the wall effect on the saturated vapor pressure.

[0048] It should be noted that the outer ring wall 1021 and the inner ring wall 1022 are coaxially arranged and share a bottom surface.

[0049] Exemplarily, the spacing between the outer ring wall 1021 and the inner ring wall 1022 is 2-3 mm.

[0050] Exemplarily, the diameter of the single liquid droplet inlet 1023 is 3-4 times the diameter of the gas inlet 1024, and the diameter of the single liquid droplet inlet 1023 is 2-2.5 times the diameter of the gas outlet 1025.

[0051] Exemplarily, the diameter of the gas inlet 1024 is smaller than the diameter of the gas outlet 1025.

[0052] Exemplarily, the diameter of the single liquid droplet inlet 1023 is 3 mm, the diameter of the gas inlet 1024 is 1.0 mm, and the diameter of the gas outlet 1025 is 1.5 mm.

[0053] Exemplarily, the bottom of the sample cell 102 is provided with a quartz glass sheet (not shown in the figure), and the quartz glass sheet is provided with an anionic surfactant layer. The anionic surfactant reduces the surface tension of the spheroidal liquid droplet, and at the same time, makes the liquid droplet at the bottom of the sample cell no longer deposit in the form of spheroid, but spread directly on the bottom of the sample cell, avoiding the saturated vapor pressure error caused by the curved surface pressure of the liquid droplet containing volatile chemical components at the bottom of the sample cell.

[0054] Exemplarily, the thickness of the anionic surfactant layer is 0.1-0.2 mm.

[0055] Exemplarily, the anionic surfactant is sodium fatty alcohol ether sulfate and / or sodium dodecyl sulfonate.

[0056] Exemplarily, the single-droplet optical tweezers suspension device 1 further comprises a microscope objective 101 arranged between the sample cell 102 and the light beam coupling system, and an illumination light source 103 arranged above the sample cell 102. After the light beam from the light beam coupling system reaches the microscope objective 101, the microscope objective 101 introduces the light beam into the sample cell 102 for optical tweezers. The illumination light source 103 is used to image the light signal of the single droplet in the microdroplet detection device 6 and the signal detection system 5.

[0057] It should be noted that the droplets deposited on the inner wall of the sample cell cannot be directly solved by smearing anionic surfactant, because in the structure of the sample cell 102 of the present application, in addition to the single-droplet inlet 1023, there are also gas inlets 1024 and gas outlets 1025. If the anionic surfactant is coated on the inner wall surface, when the humidity in the sample cell 102 increases, water molecules and the anionic surfactant will emulsify on the inner wall of the sample cell 102 to generate foam, which may cause hole blockage. When the foam collides and accumulates to a certain weight, it cannot be hung on the wall and will slide to the bottom of the quartz glass sheet in the sample cell. If it slides to the vicinity of the focusing position, it will affect the macroscopic morphology effect of the suspended droplet imaging. If it slides to the focusing center position of the microscope objective 101, it will affect the refraction effect and cause the suspended droplet to fall off.

[0058] Exemplarily, the microdroplet pumping system 3 comprises an aerosol generator 301, a stop valve 302 and a droplet beam device 303 connected in sequence, and the droplet beam device 303 is in communication with the sample cell 102.

[0059] Exemplarily, as shown in Figure 3 The droplet beam device 303 comprises a plurality of pipes with different inner diameters connected in sequence, and the inner diameters of the plurality of pipes 3031 gradually decrease along the aerosol flow direction.

[0060] Further, a plurality of light diaphragms 3032 with different inner diameters are arranged inside the pipe 3031, and the inner diameters of the plurality of light diaphragms 3032 gradually decrease along the aerosol flow direction.

[0061] Exemplarily, Figure 4 As shown in the figure, along the aerosol droplet flow direction, three light diaphragms with gradually decreasing inner diameters are arranged in the first pipe in sequence, a light diaphragm with a smaller inner diameter than the second pipe is arranged at the outlet of the second pipe, and a light diaphragm with a smaller inner diameter than the third pipe is arranged at the outlet of the third pipe. This embodiment can gradually arrange the gathered droplets into a string and discharge them from the outlet. As shown in Figure 5

[0062] ​Exemplarily, the inner diameter of the diaphragm of the third tube outlet is greater than or equal to the diameter of the single droplet and less than the diameter of the single droplet x 2. That is, the diaphragm of the third tube outlet can only pass a single droplet at a time. As shown in Figure 5

[0063] Exemplarily, a gasket 3033 is arranged between the diaphragm and the inner wall of the tube.

[0064] Exemplarily, a clamp 3034 is arranged at the inlet end of the first tube, which is used to fix the tube and adjust the tube to align with the light capture point in the sample cell 102.

[0065] Exemplarily, a threaded cap 3035 with a central hole is arranged at the third tube outlet. The threaded cap 3035 is used to protect the outlet of the third tube.

[0066] Exemplarily, the gas atmosphere control system 2 includes an ambient gas control device and a reaction gas control device, the ambient gas control device is in communication with the tube between the stop valve 302 and the droplet beam device 303, and the reaction gas control device is in communication with the tube between the droplet beam device 303 and the sample cell 102.

[0067] Specifically, the ambient gas control device and the reaction gas control device each include a gas generating device 201 and a flow meter 202.

[0068] The functions of the ambient gas control device include: first, for introducing ambient gas, such as nitrogen, into the sample cell 102 through the droplet beam device 303; second, for diluting the aerosol droplets in the droplet beam device; third, for introducing dry gas and / or humid gas to adjust the ambient humidity in the sample cell. Details are described below in the method.

[0069] The function of the reaction gas control device is to introduce reaction gas into the sample cell 102 after suspending the single droplet. The reason why the reaction gas control device is connected to the tube between the droplet beam device 303 and the sample cell 102 is to avoid the contamination of the droplet beam device by the reaction gas.

[0070] ​Exemplarily, the light coupling system 4 comprises a laser 401, a focusing lens 402, a semi-transparent half mirror 403 and a full reflection mirror 404. The light beam emitted by the laser 401 is expanded by the focusing lens 402, and then split by the semi-transparent half mirror 403 into single-droplet light tweezers suspension device 1, light coupling system 4 and signal detection system 5. The light beam to the single-droplet light tweezers suspension device 1 is focused to the focal plane above the microscopic objective 101, and a single droplet in the sample cell 102 is captured and suspended. The scattering light signal of the single droplet is input to the signal detection system 5 and the microdroplet detection device 6, and the light signal can be processed by the filter before entering the signal detection system 5.

[0071] Exemplarily, the signal detection system 5 comprises an optical imaging camera 501, a Raman spectrometer 502 and a data processing unit 503. The spectral information and Raman spectrum of different pixel elements are obtained by imaging the spectrum of the droplet on the optical imaging camera EMCCD 501 through the grating in the Raman spectrometer 502; the droplet radius is inversely calculated based on the whispering gallery mode of the spherical droplet and the Mie scattering theory; the spontaneous and stimulated Raman spectrum and resonance signal information of the suspended single droplet are obtained by the optical imaging camera 501 and the Raman spectrometer 502; and the spectrum information is converted into radius, refractive index and peak position information by the data processing unit 503. According to the red shift of the measured stimulated Raman peak of the droplet, the droplet radius change rate dr / dt can be obtained, and the chemical composition and component change of the droplet can be analyzed, and the saturated vapor pressure can be calculated.

[0072] Exemplarily, the microdroplet detection device 6 is a microscopic imaging camera. The microscopic imaging camera 6 is used to monitor the lateral macroscopic morphology of the droplet when it is suspended.

[0073] In another aspect, the present application also provides a method for detecting the saturated vapor pressure of aerosol single droplets, which uses the above device, and the method comprises:

[0074] The microdroplet pumping system pumps the aerosol into the sample cell of the single-droplet light tweezers suspension device in the form of single droplets;

[0075] The laser emitted by the light coupling system acts as a reaction light beam, and a single droplet is captured and suspended in the sample cell by the light tweezers technology;

[0076] The gaseous atmosphere control system introduces environmental gas and reaction gas into the sample cell;

[0077] The scattering light signal of the single droplet is input to the signal detection system and the microdroplet detection device, and the numerical change of the single droplet radius before and after the single droplet reaction is analyzed according to the light signal data, and then the saturated vapor pressure is calculated.

[0078] Further, the droplet beam device 303 of the microdroplet pumping system 3 arranges the droplets into a train, forming an aerosol droplet beam, so that the aerosol droplets enter the sample cell 102 one by one as monodisperse single-droplet trains. This effectively avoids the problem of aggregated aerosol droplets entering the sample cell and then easily depositing on the walls, causing a wall effect.

[0079] Further, the method further comprises: after suspending the single droplet by the optical tweezer technique, introducing dry gas and / or humid gas into the sample cell 102 through the environmental gas control device in the gas atmosphere control system 2, reducing the humidity in the sample cell 102 to below the weathering point humidity of the volatile chemical components in the droplet, allowing the droplets on the inner wall of the sample cell 102 to weather and crystallize, and then increasing the humidity in the sample cell 102 to the required humidity for the reaction.

[0080] The present application reduces the humidity to below the weathering point humidity, so that the droplets attached to the walls weather and crystallize first compared to the droplets trapped by the optical tweezer. The solid after weathering and crystallization no longer has the curvature radius of the liquid phase, and the curvature radius of the droplet determines the surface pressure, which is a key value dependent on the saturated vapor pressure of the droplet. Therefore, by reducing the humidity to make the wall droplets weather and crystallize first, the influence of the surface pressure and the saturated vapor pressure is eliminated, and then the humidity is increased to the required humidity condition for the reaction, so that the saturated vapor pressure value of the single droplet trapped by the optical tweezer is accurately obtained.

[0081] It should be noted that the reason why the droplets attached to the walls weather and crystallize first compared to the droplets trapped by the optical tweezer is: (1) The temperature of the walls is usually lower than that of the center of the sample cell, because the heat exchange between the walls and the surrounding environment is more direct, and this temperature difference causes the droplets on the walls to more easily reach the weathering and crystallization conditions; (2) The optical tweezer technique can accurately control the position of the single droplet, keeping it in the center of the sample cell away from the walls, which reduces the opportunity for the central droplet to contact the walls, while the droplets on the walls are more easily affected by the environmental conditions.

[0082] The principle of reducing the influence of the wall effect on the saturated vapor pressure of a single droplet by reducing the humidity below the weathering point so that the droplets attached to the walls crystallize first is as follows: (1) When the humidity is reduced below the weathering point, the droplets on the inner wall of the sample cell will begin to weather due to the decrease in ambient humidity, i.e., the water in the droplets gradually evaporates, resulting in an increase in the concentration of solutes in the droplets, eventually reaching a saturated state and beginning to crystallize, which reduces the content of volatile organic components in the droplets; (2) Because volatile organic components evaporate more easily in a low-humidity environment, these components are removed during the weathering and crystallization process, thereby reducing their potential impact on subsequent experiments. At this time, the saturated vapor pressure of the solid-liquid mixture is determined by the adsorbed water molecules, rather than the original volatile organic components; (3) When the humidity in the sample cell is adjusted to the required humidity for the reaction, the crystallization on the wall will adsorb water molecules from the environment, forming a solid-liquid mixture. At this time, the liquid phase in the solid-liquid mixture is composed only of adsorbed water molecules and no longer contains the original volatile organic components; (4) Kelvin effect shows that the smaller the radius of curvature, the greater the saturated vapor pressure.

[0083] In summary, the droplets attached to the bottom of the sample cell all reduce their curvature radius, thereby avoiding the saturated vapor pressure error of their inherent volatile components. The droplets on the inner wall are first reduced in humidity to below the weathering point of the volatile component droplets, causing the water molecules in the droplets to evaporate and the droplets to become smaller, increasing the curvature radius, resulting in the wall droplets weathering and crystallizing before the optical tweezer droplets. When the humidity rises, the saturated vapor pressure of the solid-liquid mixture is determined by the adsorbed water molecules, rather than the original volatile organic components.

[0084] The reasons why the optical tweezer suspended droplets do not weather and crystallize compared to the inner wall droplets are as follows: the optical tweezer suspended single droplet always maintains a spherical shape and always has a radius of curvature. From the perspective of avoiding the wall effect: (1) the optical tweezer technology can accurately control the position of the droplet, keeping it in the center area of the sample cell, which may be relatively more stable in terms of temperature and humidity conditions and less susceptible to changes in the external environment; (2) the optical tweezer manipulates the droplet through the radiation pressure generated by the focused laser beam, which can isolate the droplet from direct heat exchange with the wall to some extent, reducing the temperature drop and evaporation of the droplet surface caused by wall cooling; (3) the humidity in the wall area is first reduced, promoting the weathering and crystallization of the droplets on the wall, while the humidity change in the center area is slower than that on the wall, so the wall first appears weathering and crystallization phenomenon; (4) the aerosol droplet suspended by the optical tweezer is already in a supersaturated state, and the particle size is small, the surface characteristics are different from those of the droplets deposited on the wall, and the differences in the surface interfacial colloidal properties of the aerosol itself may also be the reason why the evaporation rate of the wall droplets is faster than that of the optical tweezer droplets.

[0085] Exemplarily, after a single droplet is suspended by the optical tweezer technology, dry gas and / or humid gas is introduced into the sample cell 102 by the gas atmosphere control system 2 to adjust the humidity in the sample cell 102 to 30%-40%, and then the humidity in the sample cell 102 is increased to 80% after the droplets on the inner wall of the sample cell 102 are weathered and crystallized.

[0086] The adjustment of the humidity can be controlled by the mass flow ratio of the dry gas and the humid gas, for example, the dry gas flow rate is 0.05-0.15 SLPM, and the humid gas flow rate is 0.15-0.05 SLPM. The humidity of the dry and humid gas is adjusted by adjusting the flow rate of the dry gas and the humid gas, that is, adjusting the ratio of the dry gas and the humid gas. The higher the dry gas / humid gas ratio, the lower the humidity; the lower the dry gas / humid gas ratio, the higher the humidity.

[0087] Exemplarily, the method further comprises: when the droplets enter the droplet beam current device 303, the stop valve 302 is closed, and the ambient background gas is introduced into the droplet beam current device 303 by the ambient gas control device of the gas atmosphere control system 2 to dilute the droplets in the droplet beam current device 303, and further promote the droplet beam current device 303 to change the droplets from the aggregated state to single dispersed single string droplets entering the sample cell one by one.

[0088] The device and method for detecting the saturated vapor pressure of aerosol single droplets of the present application will be further described below by specific embodiments

[0089] Embodiment 1

[0090] This embodiment provides a device for detecting the saturated vapor pressure of aerosol single droplets, which comprises a single droplet optical tweezer suspension device 1, a gas atmosphere control system 2, a microdroplet pumping system 3, a light beam coupling system 4, a signal detection system 5, and a microdroplet detection device 6. The gas atmosphere control system 2 is in communication with the microdroplet pumping system 3, the microdroplet pumping system 3 is in communication with the single droplet optical tweezer suspension device 1, and the light beam coupling system 4 is in communication with the single droplet optical tweezer suspension device 1, the signal detection system 5, and the microdroplet detection device 6, respectively. The single droplet optical tweezer suspension device 1 comprises a sample cell 102, such as Figure 2As shown, the sample cell 102 comprises a concentric outer ring wall 1021 and inner ring wall 1022, the outer ring wall 1021 is connected with one side of the inner ring wall 1022, and a single droplet inlet 1023 is arranged through the outer ring wall 1021 and the inner ring wall 1022 at the connection; the outer ring wall 1021 and the inner ring wall 1022 are both provided with a plurality of gas inlets 1024 and gas outlets 1025 arranged through the ring wall and spaced apart, the gas inlets 1024 and the gas outlets 1025 on the outer ring wall 1021 are staggered with the gas inlets 1024 and the gas outlets 1025 on the inner ring wall 1022; the diameter of the single droplet inlet 1023 is 3mm, the diameter of the gas inlet 1024 is 1.0mm, and the diameter of the gas outlet 1025 is 1.5mm. The spacing between the outer ring wall 1021 and the inner ring wall 1022 is 2mm.

[0091] The bottom of the sample cell 102 is provided with a quartz glass sheet, and the quartz glass sheet is provided with an anionic surfactant layer (sodium fatty alcohol ether sulfate) with a thickness of 0.2mm.

[0092] The single droplet optical tweezers suspension device 1 further comprises a microscope objective 101 and an illumination light source 103, the microscope objective 101 is arranged between the sample cell 102 and the light beam coupling system, and the illumination light source 103 is arranged above the sample cell 102.

[0093] The microdroplet pump-in system 3 comprises an aerosol generator 301, a stop valve 302 and a droplet beam flow device 303 which are sequentially communicated, and the droplet beam flow device 303 is communicated with the sample cell 102. The droplet beam flow device 303 comprises three pipes with different inner diameters which are sequentially connected, and the inner diameters of the three pipes 3031 gradually decrease along the aerosol flow direction. The inside of the pipe 3031 is provided with a plurality of light barriers 3032 with different inner diameters, and the inner diameters of the plurality of light barriers 3032 gradually decrease along the aerosol flow direction. Three light barriers with gradually decreasing inner diameters are sequentially arranged in the first pipe, a light barrier with a smaller inner diameter than the second pipe is arranged at the outlet of the second pipe, and a light barrier with a smaller inner diameter than the third pipe is arranged at the outlet of the third pipe. The inner diameters of the pipes and the light barriers are shown in the table as follows. Figure 4

[0094] The gas atmosphere control system 2 comprises an environmental gas control device and a reaction gas control device, the environmental gas control device is communicated with the pipe between the stop valve 302 and the droplet beam flow device 303, and the reaction gas control device is communicated with the pipe between the droplet beam flow device 303 and the sample cell 102. The environmental gas control device and the reaction gas control device both comprise a gas generating device 201 and a flow meter 202.

[0095] ​The light coupling system 4 includes a laser 401, a focusing lens 402, a semi-transparent half-mirror 403, and a full reflection mirror 404. The signal detection system 5 includes an optical imaging camera 501, a Raman spectrometer 502, and a data processing unit 503. The microdroplet detection device 6 is a microscopic imaging camera.

[0096] Embodiment 2

[0097] This embodiment provides a method for detecting the saturated vapor pressure of an aerosol single droplet, using the device of embodiment 1. It includes:

[0098] The aerosol generator 301 generates aerosol droplets, which enter the microdroplet beam current device 303. When the droplets enter the microdroplet beam current device 303, the stop valve 302 is closed, and the ambient gas control device of the gas atmosphere control system 2 is used to introduce ambient background gas into the microdroplet beam current device 303, dilute the droplets in the microdroplet beam current device 303, and promote the microdroplet beam current device 303 to arrange the droplets into a single string, forming an aerosol droplet beam current, so that the aerosol droplets enter the sample cell 102 of the single-droplet optical tweezers suspension device 1 one by one in the form of single-dispersed single-string droplets;

[0099] The laser 401 of the light coupling system 4 emits a light beam, which is expanded by a set of focusing lenses 402, and the single-beam light tweezers pass through the semi-transparent half-mirror 403 to split the beam, with a part of the beam being split to the microscopic objective lens 101 and the laser being focused above the focal plane to capture and suspend the single droplet in the sample cell 102;

[0100] The ambient gas control device in the gas atmosphere control system 2 is used to introduce ambient gas into the sample cell, and the proportion of dry gas and / or wet gas in the ambient gas is adjusted to adjust the humidity in the sample cell 102 to 30% (the organic component in the droplet is ammonium chloride, and the humidity at which the droplet is weathered is 40%), so that the droplets on the inner wall of the sample cell 102 weather and crystallize, and then the humidity in the sample cell 102 is increased to the reaction humidity (50%, 60%, 70%); the reaction gas control device in the gas atmosphere control system 2 is used to introduce reaction gas into the sample cell 102;

[0101] The returned single-droplet scattered light signal is input to the signal detection system 5 and the microdroplet detection device 6 through a focusing lens 402 and a full reflection mirror 404, respectively, and the change in the single-droplet radius value before and after the single-droplet reaction is analyzed according to the light signal data, and then the saturated vapor pressure is calculated.

[0102] Figure 6 This is a morphology diagram of the suspended single droplet in the microscopic imaging camera of embodiment 2, which shows that a single microdroplet is stably captured at the focal point of the light tweezers; Figure 7 This is a spontaneous / stimulated Raman spectrum of the suspended single droplet of embodiment 2.

[0103] Typical measurement precision of droplet radius under stable RH (relative humidity) conditions is ±0.57 nm (expressed as standard deviation of 30 s data acquisition) and ±0.00027 of refractive index. Therefore, when the environmental RH fluctuates significantly, the actual micro-environmental change around the droplet is much smaller than the noise effect of RH measurement. The local stability of the droplet in the optical tweezer is high and the local humidity field around the droplet is relatively constant, the droplet composition remains unchanged before the reaction, and the RH is fixed. As the reaction proceeds, the continuous decrease of the droplet radius will be entirely attributed to the volatilization of the components and water in the droplet.

[0104] Under the humidity conditions specified by the reaction conditions (70%, 60% and 50%), the control of humidity is relatively stable, and the radius of the ammonium chloride droplet gradually decreases, and the refractive index is continuously stable under the corresponding humidity. The whole test was measured for 137000 s (-38.06 h), with a fluctuation of about ±0.1% per 30 s, a fluctuation of about ±0.3% per 30 s of refractive index, and a fluctuation of about ±3 nm per 30 s of radius.

[0105] The saturated vapor pressure of the internal components of the single droplet is measured in real time, mainly based on the changes of the droplet radius and the droplet mass, and then the mass flux of the volatile components is obtained, so as to calculate the average saturated vapor pressure (for specific calculation method, see Phys. Chem. Chem. Phys., 2014, 16, 3162 DOI: 10.1039 / c3cp54948h; J. Phys. Chem. A 2015, 119, 704-718 DOI: 10.1021 / jp510525r).

[0106] It is calculated that the average saturated vapor pressures at the reaction humidities RH of 70%, 60% and 50% are 1.69×10 - 5 pa, 1.36×10 -5 paand 6.78×10 -6 pa, respectively.

[0107] Example 3

[0108] This example provides a method for detecting the saturated vapor pressure of an aerosol single droplet similar to Example 2, except that the quartz glass sheet at the bottom of the sample cell is not coated with an anionic surfactant layer.

[0109] In this example, the average saturated vapor pressures at the reaction humidities RH of 70%, 60% and 50% are 6.71×10 -5 pa, 5.65×10 -5 paand 2.01×10 -5 pa, respectively.

[0110] Example 4

[0111] This example provides a method for detecting the saturated vapor pressure of an aerosol single droplet similar to that of Example 2, except that the droplet beam device 303 is not provided in the microdroplet pumping system 3.

[0112] In this example, the average saturated vapor pressure at a reaction humidity RH of 70%, 60%, and 50% is 6.92 x 10 -5 pa, 5.35 x 10 -5 pa, and 4.05 x 10 -5 pa, respectively.

[0113] Example 5

[0114] This example provides a method for detecting the saturated vapor pressure of an aerosol single droplet similar to that of Example 2, except that the droplets in the droplet beam device 303 are not diluted by closing the stop valve 302.

[0115] In this example, the average saturated vapor pressure at a reaction humidity RH of 70%, 60%, and 50% is 8.69 x 10 -5 pa, 5.30 x 10 -5 pa, and 6.15 x 10 -6 pa, respectively.

[0116] Example 6

[0117] This example provides a method for detecting the saturated vapor pressure of an aerosol single droplet similar to that of Example 2, except that after the single droplet is suspended by the optical tweezer, the humidity is not reduced to 40%, but is directly adjusted to the reaction humidity value.

[0118] In this example, the average saturated vapor pressure at a reaction humidity RH of 70%, 60%, and 50% is 6.69 x 10 -5 pa, 6.30 x 10 -5 pa, and 4.02 x 10 -5 pa, respectively.

[0119] Comparative Example 1

[0120] A device for detecting the saturated vapor pressure of an aerosol single droplet is used, which is similar to that of Example 1, except that the sample cell is single-walled; the diameter of the single droplet inlet is equal to that of the gas outlet, and the bottom of the sample cell is not coated with an anionic surfactant; a stop valve and a droplet beam device are not provided in the microdroplet pumping system; and a method for detecting the saturated vapor pressure of an aerosol single droplet is used, which is similar to that of Example 2, except that after the single droplet is suspended by the optical tweezer, the humidity is directly adjusted to the reaction humidity value.

[0121] In the comparative example, the average saturated vapor pressure at 70%, 60% and 50% of the reaction humidity RH is 9.31 x 10 -5 pa, 9.12 x 10 -5 paand 6.13 x 10 -5 pa, respectively.

[0122] According to the average saturated vapor pressure detection data of Examples 1-6 and Comparative Example 1, it can be seen that the saturated vapor pressure data obtained by using the device and method of the present application is less than that of Comparative Example 1, because the present application reduces the error influence of the organic volatile components in the droplets deposited on the wall of the vessel and the bottom of the sample cell on the saturated vapor pressure, thus the saturated vapor pressure measured by the present application is closer to the true saturated vapor pressure value, i.e. the error of the saturated vapor pressure value measured by the present application is smaller.

[0123] The above description is merely preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions easily thought of by those skilled in the art within the technical scope disclosed by the present application should be encompassed within the protection scope of the present application.

Claims

1. An apparatus for detecting the saturated vapor pressure of an aerosol single droplet, comprising: The device comprises a single droplet optical tweezers suspension device, a gas atmosphere control system, a microdroplet pumping system, a light beam coupling system, a signal detection system and a microdroplet detection device. The gas atmosphere control system is in communication with the microdroplet pumping system, the microdroplet pumping system is in communication with the single droplet optical tweezers suspension device, and the light beam coupling system is in communication with the single droplet optical tweezers suspension device, the signal detection system and the microdroplet detection device respectively. The single droplet optical tweezers suspension device comprises a sample cell, the sample cell comprises a concentric outer ring wall and an inner ring wall, one side of the outer ring wall is connected with the inner ring wall, and a single droplet inlet penetrating the outer ring wall and the inner ring wall is arranged at the connection; a plurality of gas inlets and gas outlets penetrating the ring wall and arranged at intervals are arranged on the outer ring wall and the inner ring wall, and the gas inlets and gas outlets on the outer ring wall are staggered with the gas inlets and gas outlets on the inner ring wall. The diameter of the gas inlet and the diameter of the gas outlet are both smaller than the diameter of the single droplet inlet.

2. The apparatus of claim 1, wherein, The diameter of the single droplet inlet is 3-4 times the diameter of the gas inlet, and the diameter of the single droplet inlet is 2-2.5 times the diameter of the gas outlet.

3. The apparatus of claim 1, wherein, A quartz glass sheet is arranged at the bottom of the sample cell, and an anionic surfactant layer is arranged on the quartz glass sheet.

4. The apparatus of claim 1, wherein, The microdroplet pumping system comprises an aerosol generator, a stop valve and a droplet beam device which are sequentially connected in communication, and the droplet beam device is in communication with the sample cell.

5. The apparatus of claim 4, wherein, The droplet beam device comprises a plurality of pipes with different inner diameters connected in sequence, and the inner diameters of the plurality of pipes gradually decrease along the aerosol flow direction.

6. The apparatus of claim 5, wherein, The inside of the pipe is provided with a plurality of light barriers with different inner diameters, and the inner diameters of the plurality of light barriers gradually decrease along the aerosol flow direction.

7. The apparatus of claim 4, wherein, The gas atmosphere control system comprises an environmental gas control device and a reaction gas control device, the environmental gas control device is in communication with the pipe between the stop valve and the droplet beam device, and the reaction gas control device is in communication with the pipe between the droplet beam device and the sample cell.

8. A method of detecting the saturated vapor pressure of an aerosol single droplet, characterized by, The device of any one of claims 1-7 is used, and the method comprises: The microdroplet pumping system pumps the aerosol into the sample cell of the single droplet optical tweezers suspension device in the form of a single droplet; The laser emitted by the light beam coupling system serves as a reaction light beam, and a single droplet is captured and suspended in the sample cell by the optical tweezers technology; The required gas is introduced into the sample cell by the gas atmosphere control system; The scattering light signal of the single droplet is input into the signal detection system and the microdroplet detection device respectively, the numerical change of the single droplet radius before and after the single droplet reaction is analyzed according to the light signal data, and then the saturated vapor pressure is calculated.

9. The method of claim 8, wherein, The droplet beam device of the microdroplet pumping system arranges the droplets into a string to form an aerosol droplet beam, so that the aerosol droplets enter the sample cell one by one in the form of single dispersed single string droplets.

10. The method of claim 8, wherein, The method further comprises: after suspending the single droplet by the optical tweezers technology, dry gas and / or humid gas is introduced into the sample cell by the gas atmosphere control system, the humidity in the sample cell is reduced to below the weathering point humidity of the volatile chemical components in the droplet, the droplets on the inner wall of the sample cell are weathered and crystallized, and then the humidity in the sample cell is adjusted to the required humidity for the reaction.

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