Device and method for detecting saturated vapor pressure of aerosol single droplet

Abstract

The invention relates to a device and method for detecting the saturated vapor pressure of an aerosol single droplet, belongs to the technical field of saturated vapor pressure detection, and solves the problem that the error of the detection result of the existing device and method for measuring the saturated vapor pressure of the aerosol single droplet is large. A single-droplet optical tweezer suspension device of the device comprises a sample cell, the sample cell comprises an outer ring wall and an inner ring wall which are concentric, one side of the outer ring wall is connected with one side of the inner ring wall, and a single-droplet inlet penetrating through the outer ring wall and the inner ring wall is formed in the joint; the outer ring wall and the inner ring wall are each provided with a plurality of gas inlets and gas outlets which penetrate through the ring walls and are arranged at intervals, and the gas inlets and the gas outlets in the outer ring wall and the gas inlets and the gas outlets in the inner ring wall are arranged in a staggered mode. The diameter of the gas inlet and the diameter of the gas outlet are both smaller than the diameter of the single liquid drop inlet. The device can reduce the error caused by the wall effect on the saturated vapor pressure.

Description

Technical Field

[0001] The invention relates to the technical field of saturated vapor pressure detection, and in particular to a device and method for detecting the saturated vapor pressure of a single droplet of an aerosol. Background Art

[0002] Accurate measurement of saturated vapor pressure parameters is essential for understanding PM 2.5 An important physical and chemical parameter of the driving force of secondary organic aerosol generation during explosive growth. By real-time and in-situ observation of the changes in particle size and composition of a single droplet in a specific atmosphere, the problem of high-quality data measurement of key physical and chemical parameters in the gas-particle distribution process of volatile substances can be solved. In order to reveal the key driving force of secondary organic aerosol generation and growth in atmospheric fine particulate pollution, it is of great significance to develop a single droplet saturated vapor pressure measurement device for volatile substances.

[0003] The detection results of the existing aerosol single droplet saturated vapor pressure measurement devices and methods have large errors. Summary of the invention

[0004] In view of the above analysis, the embodiments of the present invention aim to provide a device and method for detecting the saturated vapor pressure of a single aerosol droplet, so as to solve the problem of large error in the detection results of the existing device and method for measuring the saturated vapor pressure of a single aerosol droplet.

[0005] On the one hand, the present invention provides a device for detecting the saturated vapor pressure of a single droplet of aerosol, the device comprising a single droplet optical tweezers suspension device, a gas atmosphere control system, a droplet pumping system, a beam coupling system, a signal detection system and a droplet detection device;

[0006] Wherein, the gas atmosphere control system is connected to the droplet pumping system, the droplet pumping system is connected to the single droplet optical tweezers suspension device, and the beam coupling system is respectively connected to the single droplet optical nickel suspension device, the signal detection system and the droplet detection device;

[0007] The single droplet optical tweezers suspension device comprises a sample pool, which comprises a concentric outer ring wall and an inner ring wall, wherein the outer ring wall is connected to one side of the inner ring wall, 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 walls and arranged at intervals, and the gas inlet and gas outlet on the outer ring wall are staggered with the gas inlet and gas outlet 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, a quartz glass sheet is disposed at the bottom of the sample cell, and an anionic surfactant layer is disposed on the quartz glass sheet.

[0011] Preferably, the droplet pumping system comprises an aerosol generator, a stop valve and a droplet beam device which are connected in sequence, and the droplet beam device is connected to the sample pool.

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

[0013] Preferably, a plurality of apertures with different inner diameters are arranged inside the pipeline, and the inner diameters of the plurality of apertures gradually decrease along the aerosol flow direction.

[0014] Preferably, the gas atmosphere control system includes an environmental gas control device and a reaction gas control device, the environmental gas control device is connected to the pipeline between the stop valve and the droplet beam device, and the reaction gas control device is connected to the pipeline between the droplet beam device and the sample pool.

[0015] On the other hand, the present invention also provides a method for detecting the saturated vapor pressure of a single droplet of an aerosol, using the above-mentioned device, the method comprising:

[0016] The droplet pumping system pumps the aerosol into the sample pool of the single droplet optical tweezers suspension device in the form of a single droplet;

[0017] The laser emitted by the beam coupling system is used as a reaction beam to capture a single droplet in the sample cell and suspend it using the optical tweezers technique;

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

[0019] The scattered light signal of a single droplet is input into the signal detection system and the droplet 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.

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

[0021] Preferably, the method further comprises: after suspending a single droplet by optical tweezers technology, introducing dry gas and / or wet gas into the sample pool by means of a gas atmosphere control system, reducing the humidity in the sample pool to below the weathering point humidity of the volatile chemical components in the droplet, causing the droplets on the inner wall of the sample pool to weather and crystallize, and then raising the humidity in the sample pool to the humidity required for the reaction.

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

[0023] 1. The sample pool of the present invention comprises an outer ring wall and an inner ring wall, a single droplet inlet penetrating the outer ring wall and the inner ring wall is arranged at the connection of the outer ring wall and the inner ring wall, 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, the gas inlet and gas outlet on the outer ring wall are staggered with the gas inlet and gas outlet on the inner ring wall, this structure can make the gas enter and discharge the sample pool uniformly, and ensure the stability of the air pressure in the sample pool, so as to make the optical tweezers stably suspend the single droplet; in addition, the uniform entry and discharge of the gas into the sample pool can avoid excessively high or low local air pressure, reduce the uneven distribution of droplets when entering the sample pool due to uneven air pressure, and effectively solve the problem that uneven air pressure may cause droplets to deposit on the wall; moreover, the stable air pressure in the sample pool helps to maintain the suspension state of the single droplet, reduce the contact between the droplet and the wall caused by air pressure fluctuation, and thus reduce 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. When a single droplet is pumped into the sample pool from the single droplet inlet, the turbulence effect of the aerosol droplets in the sample pool can be generated and enhanced. The turbulence can enhance the mixing and movement of the droplets in the sample pool, and reduce the probability and possibility of the droplets depositing on the inner wall. The rapid and swirling airflow does not simply go from the inlet to the outlet, but approaches the center of the sample pool (i.e., the laser focusing center) by virtue of the turbulent effect. At the same time, the swirling effect can also increase the probability of the airflow outside the focusing center returning to the focus, thereby increasing its capture efficiency, reducing the probability of aerosol droplets depositing on the inner wall of the sample pool, and reducing the error influence of the wall effect on the saturated vapor pressure.

[0025] 2. A quartz glass sheet coated with an anionic surfactant is disposed at the bottom of the sample pool of the present invention. The anionic surfactant reduces the surface tension of the spherical droplets and causes the droplets at the bottom of the sample pool to no longer be deposited in a spherical form, but to spread directly on the bottom of the sample pool, thereby avoiding the saturated vapor pressure error caused by the curved surface pressure brought about by the curved surface structure of the droplets containing volatile chemical components at the bottom of the sample pool.

[0026] 3. The present invention provides a droplet beam device in the droplet pumping system. When the aerosol droplets pass through the droplet beam device, the droplet beam device changes the droplets from an aggregated state into a monodisperse single string of droplets that enter the sample pool one by one.

[0027] 4. A stop valve is arranged between the aerosol generator and the droplet beam device of the present invention. When the droplets enter the droplet beam device, the stop valve can be closed and the environmental background gas can be introduced into the droplet beam device to dilute the droplets in the droplet beam device, thereby further promoting the droplet beam device to change the droplets from an aggregated state into a monodisperse single string of droplets that enter the sample pool one by one.

[0028] 5. In the method of the present invention, after the single droplet is suspended by the optical tweezers technique, dry gas and / or wet gas is introduced into the sample pool through the gas atmosphere control system to reduce the humidity in the sample pool to below the weathering point humidity of the chemical components in the droplet, so that the droplets on the inner wall of the sample pool are weathered and crystallized, and then the humidity in the sample pool is adjusted to the humidity required for the reaction. During the weathering and crystallization process, the volatile components in the droplets deposited on the wall have volatilized. When the ambient humidity rises to the reaction humidity, the crystals on the wall adsorb 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 no longer has the volatile organic components in the aerosol droplets. In this process, the volatile components in the single droplet suspended by the optical tweezers remain unchanged, thereby effectively avoiding 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 tweezers.

[0029] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings are only for the purpose of illustrating specific embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0031] Figure 1 The device for detecting the saturated vapor pressure of a single droplet of aerosol according to the present invention;

[0032] Figure 2 It is a schematic diagram of the sample pool structure of the present invention;

[0033] Figure 3 A structural discrete diagram of the droplet beam device of the present invention (the aperture and the gasket are separately shown outside);

[0034] Figure 4is a cross-sectional view of the droplet beam device of the present invention;

[0035] Figure 5 It is a schematic diagram of the monodisperse action principle of the droplet beam device of the present invention;

[0036] Figure 6 This is a morphology image of a suspended single droplet in Example 2 in a microscopic imaging camera;

[0037] Figure 7 This is the spontaneous / stimulated Raman spectrum of the suspended single droplet of Example 2.

[0038] Reference numerals:

[0039] 1-single droplet optical tweezers suspension device; 101-microscope objective lens; 102-sample pool; 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; 3 03-droplet beam device; 3031-pipeline; 3032-aperture; 3033-gasket; 3034-clamp; 3035-threaded cover; 4-beam coupling system; 401-laser; 402-focusing lens; 403-semi-transparent and semi-reflective mirror; 404-total reflection mirror; 5-signal detection system; 501-optical imaging camera; 502-Raman spectrometer; 503-data processing unit; 6-droplet detection device. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0041] The inventors discovered in their research that the large error in the detection results of the existing aerosol single droplet saturated vapor pressure measurement device and method is caused by the wall effect of the droplets in the sample pool, which is specifically as follows: after the aerosol droplets are pumped into the sample pool, the droplets will be deposited on the inner wall and bottom of the sample pool due to the sedimentation effect and wall impact effect caused by the droplet gravity and the pumping impulse. After the aerosol droplets are deposited, the droplets deposited on the inner wall and bottom and the droplets captured by the laser are basically spherical in shape, and the curved surface of the spherical droplets can enhance the volatility pressure of the droplets containing volatile chemical components, causing the measured saturated vapor pressure of the droplets to reach the threshold first, thereby making the measured value of the saturated vapor pressure much higher than the actual saturated vapor pressure value, that is, the error in the detection result of the saturated vapor pressure is large.

[0042] Based on this, the present invention provides a device for detecting the saturated vapor pressure of a single droplet of aerosol, such as Figure 1 As shown, the device includes a single droplet optical tweezers suspension device 1, a gas atmosphere control system 2, a droplet pumping system 3, a beam coupling system 4, a signal detection system 5 and a droplet detection device 6;

[0043] The gas atmosphere control system 2 is connected to the droplet pumping system 3, the droplet pumping system 3 is connected to the single droplet optical tweezers suspension device 1, and the beam coupling system 4 is connected to the single droplet optical tweezers suspension device 1, the signal detection system 5 and the droplet detection device 6 respectively;

[0044] The single droplet optical tweezers suspension device 1 includes a sample pool 102, such as Figure 2 As shown, the sample pool 102 includes a concentric outer annular wall 1021 and an inner annular wall 1022, the outer annular wall 1021 is connected to one side of the inner annular wall 1022, and a single droplet inlet 1023 penetrating the outer annular wall 1021 and the inner annular wall 1022 is provided at the connection; the outer annular wall 1021 and the inner annular wall 1022 are provided with a plurality of gas inlets 1024 and gas outlets 1025 penetrating the annular walls and arranged at intervals, and the gas inlet 1024 and gas outlet 1025 on the outer annular wall 1021 are staggered with the gas inlet 1024 and gas outlet 1025 on the inner annular 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] During implementation, the droplet pumping system 3 pumps the aerosol into the sample pool 102 of the single droplet optical tweezers suspension device 1 in the form of a single droplet; the laser emitted by the beam coupling system 4 is used as a reaction beam to capture a single droplet in the sample pool 102 and suspend it through the optical tweezers technology; the required gas is introduced into the sample pool 102 through the gas atmosphere control system 2; the scattered light signal of the single droplet is respectively input into the signal detection system 5 and the droplet detection device 6, and the numerical change of the single droplet radius before and after the single droplet reaction is analyzed according to the optical signal data, and then the saturated vapor pressure is calculated.

[0047] Compared with the prior art, the sample pool structure of the present invention can make the gas enter and discharge the sample pool evenly, and ensure the stability of the gas pressure in the sample pool, thereby stabilizing the optical tweezers to suspend a single droplet, and reducing the contact between the droplet and the wall, thereby 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 droplet inlet. When a single droplet is pumped into the sample pool from the single droplet inlet, the turbulent effect of the aerosol droplets in the sample pool can be generated and enhanced. The rapid and swirling airflow does not simply go from the inlet to the outlet, but approaches the center of the sample pool (i.e., the laser focusing center) by means of turbulent action. At the same time, the swirling effect can also increase the probability of the airflow outside the focusing center returning to the focus, thereby increasing its capture efficiency, and reducing the probability of aerosol droplets depositing on the inner wall of the sample pool, reducing the error influence of the wall effect on the saturated vapor pressure.

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

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

[0050] Exemplarily, the diameter of the single droplet inlet 1023 is 3-4 times the diameter of the gas inlet 1024 , and the diameter of the single 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 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, a quartz glass sheet (not shown) is disposed at the bottom of the sample pool 102, and an anionic surfactant layer is disposed on the quartz glass sheet. The anionic surfactant reduces the surface tension of the spherical droplets, and makes the droplets at the bottom of the sample pool no longer deposit in a spherical form, but directly spread on the bottom of the sample pool, thereby avoiding the saturated vapor pressure error caused by the curved surface pressure brought by the curved surface structure of the droplets containing volatile chemical components at the bottom of the sample pool.

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

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

[0056] Exemplarily, the single droplet optical tweezers suspension device 1 further includes a microscope objective 101 and an illumination light source 103, wherein the microscope objective 101 is disposed between the sample pool 102 and the beam coupling system, and the illumination light source 103 is disposed above the sample pool 102. After the light beam from the beam coupling system reaches the microscope objective 101, the microscope objective 101 introduces the light beam into the sample pool 102 for optical tweezers. The illumination light source 103 is used to image the optical signal of the single droplet in the droplet 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 pool cannot be solved directly by applying anionic surfactants. This is because, in addition to the single droplet inlet 1023, the structure of the sample pool 102 of the present invention also includes a gas inlet 1024 and a gas outlet 1025. If the anionic surfactant is applied to the inner wall surface, when the humidity in the sample pool 102 increases, water molecules and the anionic surfactant will be emulsified on the inner wall of the sample pool 102 to produce foam, which may cause pore blockage, and when the foam collides and accumulates to a certain weight, it cannot hang on the wall and will slide to the quartz glass sheet at the bottom of the sample pool. If it slides to the vicinity of the focusing position, it will cause a macroscopic morphological effect of suspended droplet imaging. If it slides to the focusing center of the microscope objective 101, it will affect the refraction effect and cause the suspended droplets to fall.

[0058] Exemplarily, the droplet pumping system 3 includes an aerosol generator 301 , a stop valve 302 , and a droplet beam device 303 which are connected in sequence, and the droplet beam device 303 is connected to the sample pool 102 .

[0059] For example, Figure 3 As shown, the droplet beam device 303 includes a plurality of pipelines with different inner diameters connected in sequence, and the inner diameters of the plurality of pipelines 3031 gradually decrease along the aerosol flow direction.

[0060] Furthermore, a plurality of apertures 3032 with different inner diameters are arranged inside the pipeline 3031, and the inner diameters of the plurality of apertures 3032 gradually decrease along the aerosol flow direction.

[0061] For example, Figure 4 As shown, along the flow direction of the aerosol droplets, three apertures with gradually decreasing inner diameters are sequentially arranged in the first pipeline, an aperture with a smaller inner diameter than the inner diameter of the second pipeline is arranged at the outlet of the second pipeline, and an aperture with a smaller inner diameter than the inner diameter of the third pipeline is arranged at the outlet of the third pipeline. This embodiment can gradually arrange the gathered droplets into a string and discharge them from the outlet. Figure 5 shown.

[0062] For example, the inner diameter of the aperture at the outlet of the third pipeline is greater than or equal to the diameter of a single droplet and less than the diameter of the single droplet × 2. In other words, the aperture at the outlet of the third pipeline can only pass a single droplet at a time. Figure 5 shown.

[0063] Exemplarily, a gasket 3033 is provided between the aperture and the inner wall of the pipe.

[0064] Exemplarily, a clamp 3034 is provided at the inlet end of the first tube for fixing the tube and adjusting the tube so that it is aligned with the light capture point in the sample pool 102 .

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

[0066] Exemplarily, the gas atmosphere control system 2 includes an environmental gas control device and a reaction gas control device, the environmental gas control device is connected to the pipeline between the stop valve 302 and the droplet beam device 303, and the reaction gas control device is connected to the pipeline between the droplet beam device 303 and the sample pool 102.

[0067] Specifically, the environmental 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, to pass ambient gas, such as nitrogen, into the sample pool 102 through the droplet beam device 303; second, to dilute the aerosol droplets in the droplet beam device; third, to pass dry gas and / or wet gas to adjust the ambient humidity in the sample pool. See the description of the method below for details.

[0069] The function of the reaction gas control device is to pass the reaction gas into the sample pool 102 after suspending a single droplet. The reason why the reaction gas control device is connected to the pipeline between the droplet beam device 303 and the sample pool 102 is to prevent the reaction gas from contaminating the droplet beam device.

[0070] Exemplarily, the optical coupling system 4 includes a laser 401, a focusing lens 402, a semi-transparent and semi-reflective mirror 403, and a total reflection mirror 404. The light beam emitted by the laser 401 is expanded by a group of focusing lenses 402, and then the single-beam optical tweezers split the light beam through the semi-transparent and semi-reflective mirror 403, and the light beam is respectively divided into the single-droplet optical tweezers suspension device 1, the light beam coupling system 4, and the signal detection system 5. The light beam divided into the single-droplet optical tweezers suspension device 1 is sent to the microscope objective 101, and the laser is focused above the focal plane to capture the single droplet in the sample pool 102 and suspend it. The scattered light signal of the single droplet is respectively input into the signal detection system 5 and the droplet 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 includes an optical imaging camera 501, a Raman spectrometer 502, and a data processing unit 503. The spectral imaging of the droplet is performed on the optical imaging camera EMCCD 501 through the grating in the Raman spectrometer 502, and the spectral information and Raman spectrum of different pixel elements are obtained; based on the whispering gallery mode of the spherical droplet, the droplet radius is inverted according to the Mie scattering theory; the spontaneous and stimulated Raman spectra and resonance signals of the suspended single droplet are obtained through the optical imaging camera 501 and the Raman spectrometer 502; and the spectrum information is converted into radius, refractive index, and peak position information through the data processing unit 503. According to the measured red shift of the stimulated Raman peak of the droplet, the droplet radius change rate dr / dt can be obtained, and then the chemical composition and component changes of the droplet are analyzed, and the saturated vapor pressure is calculated.

[0072] Exemplarily, the droplet 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] On the other hand, the present invention also provides a method for detecting the saturated vapor pressure of a single droplet of an aerosol, using the above-mentioned device, the method comprising:

[0074] The droplet pumping system pumps the aerosol into the sample pool of the single droplet optical tweezers suspension device in the form of a single droplet;

[0075] The laser emitted by the beam coupling system is used as a reaction beam to capture a single droplet in the sample cell and suspend it using the optical tweezers technique;

[0076] Ambient gas and reaction gas are introduced into the sample cell through a gas atmosphere control system;

[0077] The scattered light signal of a single droplet is input into the signal detection system and the droplet 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.

[0078] Furthermore, the droplets are arranged into a string by the droplet beam device 303 of the droplet pumping system 3 to form an aerosol droplet beam, so that the aerosol droplets enter the sample pool 102 one by one as a monodisperse single string of droplets. This can effectively prevent the aggregated aerosol droplets from easily depositing on the wall of the sample pool after entering the sample pool at the same time, thereby generating a wall effect.

[0079] Furthermore, the method also includes: after suspending a single droplet by optical tweezers technology, dry gas and / or wet gas is introduced into the sample pool 102 through the environmental gas control device in the gas atmosphere control system 2, so as to reduce the humidity in the sample pool 102 to below the weathering point humidity of the volatile chemical components in the droplet, so that the droplets on the inner wall of the sample pool 102 are weathered and crystallized, and then the humidity in the sample pool 102 is increased to the humidity required for the reaction.

[0080] The present invention reduces the humidity to below the weathering point humidity, so that the droplets attached to the vessel wall are weathered and crystallized first compared to the droplets being tweezed. 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 also the key value on which the saturated vapor pressure of the droplet depends. Therefore, by reducing the humidity to first weather and crystallize the droplets on the vessel wall, the influence of the surface pressure and saturated vapor pressure is eliminated, and then the humidity is raised to the humidity conditions required for the reaction, thereby accurately obtaining the saturated vapor pressure value of the single droplet of the optical tweezers.

[0081] It should be noted that the reasons why the droplets attached to the vessel wall weather and crystallize before the droplets tweezed by the optical tweezers are: (1) The temperature of the vessel wall is usually lower than that of the center of the sample pool because the heat exchange between the vessel wall and the surrounding environment is more direct. This temperature difference makes it easier for the droplets on the vessel wall to reach the conditions for weathering and crystallization; (2) The optical tweezers technique can precisely control the position of a single droplet, keeping it in the center of the sample pool and away from the vessel wall, which reduces the chance of the central droplet contacting the vessel wall, while the droplets on the vessel wall are more easily affected by environmental conditions.

[0082] By reducing the humidity to below the weathering point, the droplets attached to the vessel wall will weather and crystallize before the droplets being tweezed, thereby reducing the influence of the vessel wall effect on the saturated vapor pressure of a single droplet. The principle is as follows: (1) When the humidity is reduced to below the weathering point, the droplets on the inner wall of the sample pool will begin to weather due to the decrease in ambient humidity, that is, the water in the droplets will gradually evaporate, resulting in an increase in the solute concentration in the droplets, eventually reaching a saturated state and beginning to crystallize. This process reduces the content of volatile organic components in the droplets; (2) Since volatile organic components are more likely to evaporate in a low humidity environment, these components will be 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 pool is readjusted to the humidity required for the reaction, the crystals on the vessel wall will adsorb water molecules in the environment to form 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) The Kelvin effect shows that the smaller the radius of curvature, the greater its saturated vapor pressure.

[0083] In summary, the droplets attached to the bottom of the sample pool all reduce their radius of curvature to avoid the error of the saturated vapor pressure of the volatile components inside. The droplets on the inner wall are first dehumidified to below the weathering point of the volatile component droplets by first dehumidifying and then rehumidifying, so that the water molecules inside the droplets evaporate and the droplets become smaller and the radius of curvature increases, causing the droplets on the wall to weather and crystallize before the droplets on the optical tweezers; 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] Compared with the droplets on the inner wall, the droplets suspended by optical tweezers do not show weathering and crystallization for the following reasons: the single droplet suspended by optical tweezers always maintains a spherical shape and always has a radius of curvature. From the perspective of avoiding the vessel wall effect: (1) The optical tweezers technique can precisely control the position of the droplets, keeping them in the center of the sample pool. The temperature and humidity conditions in this area may be relatively stable and less susceptible to changes in the external environment. (2) The optical tweezers manipulate the droplets by focusing the radiation pressure generated by the laser beam. This manipulation method can isolate the direct heat exchange between the droplets and the vessel wall to a certain extent, reducing the drop in surface temperature and evaporation of the droplets caused by the cooling of the vessel wall. (3) The humidity in the vessel wall area decreases first, prompting the weathering and crystallization of the droplets on the vessel wall, while the humidity change in the central area is slower than that of the vessel wall, so the vessel wall first experiences weathering and crystallization. (4) The aerosol droplets suspended by the optical tweezers are already in a supersaturated state and have a small particle size. Their surface properties are different from those of the droplets deposited on the vessel wall. The differences in the surface and interface colloidal properties of the aerosol itself may also be the reason why the evaporation rate and weathering and crystallization of the vessel wall droplets take precedence over the optical tweezers droplets.

[0085] Illustratively, after a single droplet is suspended by optical tweezers technology, dry gas and / or wet gas is introduced into the sample pool 102 through the gas atmosphere control system 2, and the humidity in the sample pool 102 is adjusted to 30%-40%. After the droplets on the inner wall of the sample pool 102 are weathered and crystallized, the humidity in the sample pool 102 is increased to 80%.

[0086] Humidity can be adjusted by the mass flow ratio of dry gas and wet gas. For example, the dry gas reading range is 0.05-0.15SLPM and the wet gas reading range is 0.15-0.05SLPM. The humidity of dry and wet gas can be adjusted by adjusting the readings of dry gas and wet gas, that is, adjusting the ratio of dry gas and wet gas. The larger the dry gas / wet gas ratio, the lower the humidity; the smaller the dry gas / wet gas ratio, the higher the humidity.

[0087] Exemplarily, the method also includes: after the droplets enter the droplet beam device 303, closing the stop valve 302, and introducing ambient background gas into the droplet beam device 303 through the ambient gas control device of the gas atmosphere control system 2, so as to dilute the droplets in the droplet beam device 303, and further promote the droplet beam device 303 to change the droplets from an aggregated state into a monodisperse single string of droplets that enter the sample pool one by one.

[0088] The following is a further explanation of the device and method for detecting the saturated vapor pressure of a single droplet of aerosol by means of specific embodiments.

[0089] Example 1

[0090] This embodiment provides a device for detecting the saturated vapor pressure of a single droplet of an aerosol, comprising a single droplet optical tweezers suspension device 1, a gas atmosphere control system 2, a droplet pumping system 3, a beam coupling system 4, a signal detection system 5 and a droplet detection device 6; wherein the gas atmosphere control system 2 is connected to the droplet pumping system 3, the droplet pumping system 3 is connected to the single droplet optical tweezers suspension device 1, the beam coupling system 4 is connected to the single droplet optical tweezers suspension device 1, the signal detection system 5 and the droplet detection device 6 respectively; the single droplet optical tweezers suspension device 1 comprises a sample pool 102, such as Figure 2As shown, the sample pool 102 includes 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 provided at the connection; the outer ring wall 1021 and the inner ring wall 1022 are provided with a plurality of gas inlets 1024 and gas outlets 1025 penetrating the ring wall and arranged at intervals, and the gas inlet 1024 and gas outlet 1025 on the outer ring wall 1021 are staggered with the gas inlet 1024 and gas outlet 1025 on the inner ring wall 1022; the diameter of the single 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. The spacing between the outer ring wall 1021 and the inner ring wall 1022 is 2 mm.

[0091] A quartz glass sheet is disposed at the bottom of the sample pool 102 , and an anionic surfactant layer (sodium fatty alcohol ether sulfate) with a thickness of 0.2 mm is disposed on the quartz glass sheet.

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

[0093] The droplet pumping system 3 includes an aerosol generator 301, a stop valve 302 and a droplet beam device 303 which are connected in sequence, and the droplet beam device 303 is connected to the sample pool 102. The droplet beam device 303 includes three pipelines with different inner diameters which are connected in sequence, and the inner diameters of the three pipelines 3031 gradually decrease along the aerosol flow direction. A plurality of diaphragms 3032 with different inner diameters are arranged inside the pipeline 3031, and the inner diameters of the plurality of diaphragms 3032 gradually decrease along the aerosol flow direction. Three diaphragms with gradually decreasing inner diameters are arranged in sequence in the first pipeline, an diaphragm with an inner diameter smaller than that of the second pipeline is arranged at the outlet of the second pipeline, and an diaphragm with an inner diameter smaller than that of the third pipeline is arranged at the outlet of the third pipeline. The inner diameters of each pipeline and diaphragm are as follows: Figure 4 shown.

[0094] The gas atmosphere control system 2 includes an environmental gas control device and a reaction gas control device, wherein the environmental gas control device is connected to the pipeline between the stop valve 302 and the droplet beam flow device 303, and the reaction gas control device is connected to the pipeline between the droplet beam flow device 303 and the sample pool 102. The environmental gas control device and the reaction gas control device each include a gas generating device 201 and a flow meter 202.

[0095] The optical coupling system 4 includes a laser 401, a focusing lens 402, a semi-transparent mirror 403 and a total 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 droplet detection device 6 is a microscopic imaging camera.

[0096] Example 2

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

[0098] The aerosol generator 301 forms droplets from the aerosol, and the aerosol droplets enter the droplet beam device 303. After the droplets enter the droplet beam device 303, the stop valve 302 is closed, and the ambient background gas is introduced into the droplet beam device 303 through the ambient gas control device of the gas atmosphere control system 2 to dilute the droplets in the droplet beam device 303, so as to promote the droplet beam device 303 to arrange the droplets into a string to form an aerosol droplet beam, so that the aerosol droplets enter the sample pool 102 of the single droplet optical tweezers suspension device 1 one by one in the form of a monodispersed single string of droplets;

[0099] The light beam emitted by the laser 401 of the beam coupling system 4 is expanded by a group of focusing lenses 402, and then the single-beam optical tweezers split the beam through a semi-transparent and semi-reflective mirror 403, and a part of the light beam is split to the microscope objective 101, and the laser is focused above the focal plane to capture the single droplet in the sample pool 102 and suspend it;

[0100] Ambient gas is introduced into the sample pool through the ambient gas control device in the gas atmosphere control system 2, and the ratio of dry gas and / or wet gas in the ambient gas is adjusted to adjust the humidity in the sample pool 102 to 30% (the organic component in the droplets is ammonium chloride, and the humidity at the weathering point is 40%), so that the droplets on the inner wall of the sample pool 102 are weathered and crystallized, and then the humidity in the sample pool 102 is increased to the reaction humidity (50%, 60%, 70%); reaction gas is introduced into the sample pool 102 through the reaction gas control device in the gas atmosphere control system 2;

[0101] The returned single droplet scattered light signal is input into the signal detection system 5 and the droplet detection device 6 through a focusing lens 402 and a total reflection mirror 404 respectively. The change in the single droplet radius before and after the single droplet reaction is analyzed based on the light signal data, and the saturated vapor pressure is calculated.

[0102] Figure 6 This is a morphology image of a suspended single droplet in Example 2 in a microscopic imaging camera, which illustrates that a single microdroplet is stably captured at the focus of the optical tweezers; Figure 7 This is the spontaneous / stimulated Raman spectrum of the suspended single droplet of Example 2.

[0103] Under stable RH (relative humidity) conditions, the typical measurement accuracy of the droplet radius is ±0.57nm (expressed as the standard deviation of 30 seconds of data acquisition) and the refractive index is ±0.00027. Therefore, when the ambient RH fluctuates greatly, the actual change in the microenvironment around the droplet is much smaller than the noise effect of the RH measurement. The local stability of the droplet in the optical tweezers 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 reduction in 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 humidity control is relatively stable, the radius of the ammonium chloride droplet gradually decreases, and the refractive index remains stable at the corresponding humidity. The test was measured for 137,000 seconds (~38.06 hours), with fluctuations of about ±0.1% every 30 seconds, about ±0.3% every 30 seconds of refractive index, and about ±3nm every 30 seconds of radius.

[0105] The saturated vapor pressure of the components inside a single droplet is measured in real time. The mass flux of the volatile components is obtained based on the changes in the droplet radius and the droplet mass, and the average saturated vapor pressure is calculated (for specific calculation methods, 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] The average saturated vapor pressures when the reaction humidity RH is 70%, 60%, and 50% are calculated to be 1.69×10 - 5 pa, 1.36×10 -5 pa and 6.78×10 -6 pa.

[0107] Example 3

[0108] This embodiment provides a method for detecting the saturated vapor pressure of a single droplet of aerosol similar to that of Embodiment 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 embodiment, the average saturated vapor pressures when the reaction humidity RH is 70%, 60% and 50% are 6.71×10 -5 pa、5.65×10 -5 pa and 2.01×10 -5 pa.

[0110] Example 4

[0111] This embodiment provides a method for detecting the saturated vapor pressure of a single aerosol droplet similar to that of Embodiment 2, except that no droplet beam device 303 is provided in the droplet pumping system 3 .

[0112] In this embodiment, the average saturated vapor pressures when the reaction humidity RH is 70%, 60% and 50% are 6.92×10 -5 pa、5.35×10 -5 pa and 4.05×10 -5 pa.

[0113] Example 5

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

[0115] In this embodiment, the average saturated vapor pressures when the reaction humidity RH is 70%, 60% and 50% are 8.69×10 -5 pa, 5.30×10 -5 pa and 6.15×10 -6 pa.

[0116] Example 6

[0117] This embodiment provides a method for detecting the saturated vapor pressure of a single aerosol droplet similar to that of Embodiment 2, except that after the optical tweezers suspend the single droplet, the humidity is not reduced to 40%, but is directly adjusted to the reaction humidity value.

[0118] In this embodiment, the average saturated vapor pressures when the reaction humidity RH is 70%, 60% and 50% are 6.69×10 -5 pa、6.30×10 -5 pa and 4.02×10 -5 pa.

[0119] Comparative Example 1

[0120] An existing device and method for detecting the saturated vapor pressure of a single droplet of aerosol is used. The device is similar to the device of Example 1, except that the sample cell is single-walled; the diameters of the single droplet inlet and the gas outlet are equal, and the bottom of the sample cell is not coated with anionic surfactant; no stop valve and droplet beam device are set in the droplet pumping system; when the device is used to detect the saturated vapor pressure of a single droplet of aerosol, the method is similar to the method of Example 2, except that after the optical tweezers suspend the single droplet, the humidity is directly adjusted to the reaction humidity value.

[0121] In this comparative example, the average saturated vapor pressures when the reaction humidity RH is 70%, 60%, and 50% are 9.31×10 -5 pa、9.12×10 -5 pa and 6.13×10 -5 pa.

[0122] It can be seen from the average saturated vapor pressure detection data of Examples 1-6 and Comparative Example 1 that the saturated vapor pressure data obtained by using the device and method of the present invention are smaller than the data of Comparative Example 1. This is because the present invention reduces the error effect on the saturated vapor pressure caused by the organic volatile components in the droplets deposited on the wall and the bottom of the sample pool. Therefore, the saturated vapor pressure measured by the present invention is closer to the true saturated vapor pressure value, that is, the saturated vapor pressure value measured by the present invention has a smaller error.

[0123] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A device for detecting the saturated vapor pressure of a single droplet of an aerosol, characterized in that: The device comprises a single droplet optical tweezers suspension device, a gas atmosphere control system, a droplet pumping system, a beam coupling system, a signal detection system and a droplet detection device; Wherein, the gas atmosphere control system is connected to the droplet pumping system, the droplet pumping system is connected to the single droplet optical tweezers suspension device, and the beam coupling system is connected to the single droplet optical tweezers suspension device, the signal detection system and the droplet detection device respectively; The single droplet optical tweezers suspension device comprises a sample pool, which comprises a concentric outer ring wall and an inner ring wall, wherein the outer ring wall is connected to one side of the inner ring wall, 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 walls and arranged at intervals, and the gas inlet and gas outlet on the outer ring wall are staggered with the gas inlet and gas outlet 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 device according to claim 1, characterized in that 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 device according to claim 1, characterized in that A quartz glass sheet is arranged at the bottom of the sample pool, and an anionic surfactant layer is arranged on the quartz glass sheet.

4. The device according to claim 1, characterized in that The droplet pumping system comprises an aerosol generator, a stop valve and a droplet beam flow device which are connected in sequence, and the droplet beam flow device is connected to the sample pool.

5. The device according to claim 1, characterized in that The droplet beam device comprises a plurality of pipelines with different inner diameters connected in sequence, and the inner diameters of the plurality of pipelines gradually decrease along the aerosol flow direction.

6. The device according to claim 5, characterized in that A plurality of apertures with different inner diameters are arranged inside the pipeline, and the inner diameters of the plurality of apertures gradually decrease along the aerosol flow direction.

7. The device according to claim 4, characterized in that The gas atmosphere control system comprises an environmental gas control device and a reaction gas control device. The environmental gas control device is connected to the pipeline between the stop valve and the droplet beam device, and the reaction gas control device is connected to the pipeline between the droplet beam device and the sample pool.

8. A method for detecting the saturated vapor pressure of a single droplet of an aerosol, characterized in that: Using the device according to any one of claims 1 to 7, the method comprises: The droplet pumping system pumps the aerosol into the sample pool of the single droplet optical tweezers suspension device in the form of a single droplet; The laser emitted by the beam coupling system is used as a reaction beam to capture a single droplet in the sample cell and suspend it using the optical tweezers technique; The required gas is introduced into the sample cell through a gas atmosphere control system; The scattered light signal of a single droplet is input into the signal detection system and the droplet 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 according to claim 8, characterized in that The droplet beam device of the droplet pumping system arranges the droplets into a string to form an aerosol droplet beam, so that the aerosol droplets enter the sample pool one by one in the form of monodisperse single string droplets.

10. The method according to claim 8, characterized in that The method also includes: after suspending a single droplet by optical tweezers technology, introducing dry gas and / or wet gas into the sample pool through a gas atmosphere control system, reducing the humidity in the sample pool to below the weathering point humidity of the volatile chemical components in the droplet, allowing the droplets on the inner wall of the sample pool to weather and crystallize, and then increasing the humidity in the sample pool to the humidity required for the reaction.

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