Fred Brouwer学术报告--《化学选论》系列之二十二
报告题目：Fluorescence microspectroscopy in materials science
报告人：Fred Brouwer
单位：van ‘t Hoff Institute for Molecular Sciences, University of Amsterdam, Amsterdam, The Netherlands.
报告时间：2011、8、15（周一）上午9:30；地点：教八-218
Fluorescence micro(spectro)scopy is intensively used in biology and medical sciences, but is still less popular in materials science.[1] In this seminar I will present three applications in which molecular fluorescent probes provide local information via their various fluorescence properties such as intensity, excited state lifetime and spectrum. The first two topics are related to polymer dynamics, the third one to models of granular matter.
The first example demonstrates how single molecule spectroscopy can be used to map out the glass transition in polymer films, both spatially and temporally. Below Tg essentially all molecules are fluorescent. As the temperature is increased, more and more individual molecules appear to be switched off in wide field images. Confocal observation of molecules one-by-one, however, shows that even molecules that are mostly “off” at temperatures > Tg, occasionally are turned on again. The working principle of the method is based on excited state electron transfer. This type of process requires a thermodynamic driving force, but also enough free volume to occur on the short timescale of the excited state lifetime.[2] The free volume experienced by the individual probe molecules apparently fluctuates on a timescale of tens of seconds.
A second area of application is film formation of latex emulsions. In this case, labelling of individual latex particles allows the direct observation of the spreading of polymer particles across the interparticle boundaries in the last stage of film formation.[3] It is anticipated that this simple technique for the evaluation of the crucial step in film formation can become a standard method for the coatings industry.
The third example is related to the force networks that control the dynamics (flow/arrest, depending on the density) of granular matter. We use fluorescence microscopy to observe the contact points between different particles of micrometer to millimeter sizes. Our ultimate goal is to quantify the forces at the contact points.
References:
[1] H. Morawetz, Science 240, (1988) 172; P. Bosch et al., Chem. Eur. J. 11, (2005) 4314; T.
N. Raja, et al., Photochem. Photobiol. Sci. 9, (2010) 975; D. Wöll, et al., Chem. Soc. Rev. 38, (2009) 313.
[2] J. R. Siekierzycka, et al., J. Am. Chem. Soc. 132, (2010) 1240. [3] J.L. Keddie, Mat. Sci.