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SUMMARY:Hygroscopicity and Phase Transition of Several Kinds of Aerosols -
  Dr Hai-Jie Tong (University of Cambridge)
DTSTART:20130211T141500Z
DTEND:20130211T153000Z
UID:TALK41909@talks.cam.ac.uk
CONTACT:Dr Amanda Maycock
DESCRIPTION:Aerosols are small droplets or particles that suspended in the
  air. They have diverse sizes\, phases and components\, influencing the cl
 imate and people’s health through different processes. Two important pro
 perties of aerosols that correlate with these influences are hygroscopicit
 y and phase transition.\n \nThe amount ratio of water vapour in the air at
  a specific temperature to the maximum value of that could hold at that te
 mperature is defined as relative humidity (RH)\, and is normally given as 
 a percentage value. \n\nDuring a RH increasing (humidifying) process\, li
 quid aerosols absorb water and grow. Some solid particles transform into l
 iquid droplet upper special RH (deliquescence point).   \n\nDuring a RH de
 creasing (drying) process\, aerosol droplets lose water and shrink. Most i
 norganic aerosols transform into crystals at some special RH (efflorescenc
 e point). However\, some inorganic and many low evaporating organic aeroso
 ls will lose water at a really low speed and finally transform into amorph
 ous\, gel\, glassy or semi solid particles with high viscosity. \n\nSome l
 ab work through Fourier transform infrared spectroscopy (FTIR)\, Confocal 
 Raman\, Optical Tweezers and High Speed Camera will be shown at this semin
 ar.\n\nThe efflorescence and deliquescence process of some sulphate and ni
 trate aerosols are detected through attenuated total reflectance (ATR) FTI
 R methods. 5 µm diameter aerosols are dispensed and deposited on ATR subs
 trate\, which is surrounded by a RH controlled small chamber. Room tempera
 ture efflorescence and deliquescence can be observed at 4 cm-1 resolution.
  The observation of sulphate and nitrates and their mixed components aeros
 ols will be displayed.\n\nConfocal Raman is used to detect the hygroscopic
 ity and phase transition of 1-100 µm single aerosols deposited on substra
 tes (quarts or PTFE). A spectrum resolution of 1 cm-1 and spatial resoluti
 on of 1 µm can be obtained. \n\nAerosol Optical Tweezers (AOT) is used to
  levitate single 1~15 µm diameter particle by 532 nm laser through gradie
 nt scattering force. Water absorption and desorption process and some phas
 e transition processes can be observed by changing the RH surrounds the ae
 rosols. Cavity enhanced Raman and whispering gallery mode (WGMs) will be u
 sed to characterize the size of the droplets at a spatial resolution of na
 nometres. The morphology of the droplets or particles can be observed by C
 CD cameras at the same time. Glassy sucrose aerosol and evaporation of org
 anic acid droplets will be talked about. \n\nHigh speed camera combined wi
 th microscope system is used to observe the efflorescence and deliquescenc
 e processes of single substrate deposited sea water droplets and some inor
 ganic droplets at microsecond time resolution and several micrometer spati
 al resolution. \n\nBy using the FTIR-ATR\, Confocal Raman\, Optical Tweeze
 rs and High Speed Camera strategies\, the hygroscopicity and phase transit
 ion of several kinds of aerosols with size from several microns to hundred
 s microns are observed. Some interested phenomenon and corresponding param
 eters will be talked about.
LOCATION:Unilever Lecture Theatre\, Department of Chemistry
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