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Polymerization and copolymerization reaction observed in optically levitated aerosol particles
~ Pergamon
J.
""0"" s«, Copyright Vol. 27, Suppl. I. pp. 1996 1996ElsevierScience Ltd ~
PH: 80021-8502(96)00353-9
S~I-S~2.
Printed in Grell Bnla.n. All nghU reserved 0021-8502/96 SIS.oo + 0.00
POLYMERIZATION AND COPOLYMERIZATION REACTION OBSERVED IN OPTICALLY LEVITATED AEROSOL PARTICLES
J. MUSICK, J. POPP, M. TRUNK, and W. KIEFER Institut fiir Physikalische Chemie, Universitat Wiirzburg, Marcusstr. 9-11, D-97070 Wiirzburg, Germany
KEYWORDS Morphology dependent resonances; optical levitation; microdroplets; inelastic light scattering; polymerization reaction Investigations of polymerization reactions are useful for several applications. In particular the polymerization of microparticles consisting of synthetic materials are of great interest in material sciences and electrical industries. The linking of many monomer units into larger polymer molecules is often accomplished by radical chain reactions. In this context we present measurements of polymerization and copolymerization reactions of styrene and unsaturated-polyester-resin (UP-resin) in single isolated microdroplets. The technique of optical levitation utilizes optical forces generated by a focused laser beam to spatially stabilize single microparticles. The laser beam can simultaneously be used to trap a single particle and to excite the light scattering. In our experiment the chemical composition of the microdroplet is investigated by Raman spectroscopy (inelastically scattered light). The combination of these techniques have frequently been applied to analyse aerosols non instructively. Polymerization is the formation of chains and copolymerization is the 3-dimensional linking up of these polymer chains. The polymerization and copolymerization processes can be monitored with the Raman spectra by observing changes in signals originating from educt and product. In panel A of Fig.I, a Raman spectrum in the region between 1500 and 1850 em"? is shown. In panel B of Fig.l Raman spectra as a function of time are shown as a contour plot. The polymerization is characterized by the fast decrease of the doublebonding vibration of styrene at 1628 cm"". The copolymerization is determined through the decrease of the C=C doublebonding of UP-resin at 1655 cm"". At 1596 em-I the phenyl-vibration of styrene and at 1725 em"! the C=O-stretching vibration of UP-resin are observed. The polymerization and copolymerization is characterized by morphology-dependent-resonances (MDR) , which are superimposed on the Raman spectra. These MDRs correspond to eigenfrequencies of the spherical microparticle and depend on the Miesize parameter xre,,(m) (x m = 21ra/ ~), which is a function of the radius and the relative refractive index m (m = min"ide/moubide). Therefore changes in the particle size, shape and refractive index during the reaction can be detected as spectral shifts of the MDRs. In the contour plot the course of the reaction is visible. The arrows mark the MDRs. SS61
S562
Abstracts of the 1996 European Aerosol Conference
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Fig.I. A: Raman spectrum with typical signals of a single levitated styrene/UPresin microparticle. B: Arrows mark the morphology-dependentresonances (MDR) in the Raman spectra of styrene/UP-resin microdroplet as revealed by a contour plot.
ACKNOWLEDGEMENTS Financial support from the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie is highly acknowledged.
REFERENCES A. Ashkin, (1970) Acceleration and trapping of particles by radiation pressure, Phys. Rev. Lett., 24 156-159. K. Schaschek, J. Popp, W. Kiefer, (1993) Observation of morphology-dependent input and output resonances in time-dependent Raman spectra of optically levitated microdroplets, J. Raman. Speetrosc., 24 69-75. H.J. Bowley, I.S. Biggin, and D.L. Gerrard, (1985) In situ Raman studies of homopolymerization and copolymerization reactions, Time-resolved vibrational spectroscopy, Springer NY, p. 194-195. J. Musick, J. Popp, M. Trunk, and W. Kiefer, to be published. W. Kiefer, (1988) Micro-Raman spectroscopy of particles in the micro-size range: a short review, Croat. Chim. Aeta,.61 473-486.
J.
""0"" s«, Copyright Vol. 27, Suppl. I. pp. 1996 1996ElsevierScience Ltd ~
PH: 80021-8502(96)00353-9
S~I-S~2.
Printed in Grell Bnla.n. All nghU reserved 0021-8502/96 SIS.oo + 0.00
POLYMERIZATION AND COPOLYMERIZATION REACTION OBSERVED IN OPTICALLY LEVITATED AEROSOL PARTICLES
J. MUSICK, J. POPP, M. TRUNK, and W. KIEFER Institut fiir Physikalische Chemie, Universitat Wiirzburg, Marcusstr. 9-11, D-97070 Wiirzburg, Germany
KEYWORDS Morphology dependent resonances; optical levitation; microdroplets; inelastic light scattering; polymerization reaction Investigations of polymerization reactions are useful for several applications. In particular the polymerization of microparticles consisting of synthetic materials are of great interest in material sciences and electrical industries. The linking of many monomer units into larger polymer molecules is often accomplished by radical chain reactions. In this context we present measurements of polymerization and copolymerization reactions of styrene and unsaturated-polyester-resin (UP-resin) in single isolated microdroplets. The technique of optical levitation utilizes optical forces generated by a focused laser beam to spatially stabilize single microparticles. The laser beam can simultaneously be used to trap a single particle and to excite the light scattering. In our experiment the chemical composition of the microdroplet is investigated by Raman spectroscopy (inelastically scattered light). The combination of these techniques have frequently been applied to analyse aerosols non instructively. Polymerization is the formation of chains and copolymerization is the 3-dimensional linking up of these polymer chains. The polymerization and copolymerization processes can be monitored with the Raman spectra by observing changes in signals originating from educt and product. In panel A of Fig.I, a Raman spectrum in the region between 1500 and 1850 em"? is shown. In panel B of Fig.l Raman spectra as a function of time are shown as a contour plot. The polymerization is characterized by the fast decrease of the doublebonding vibration of styrene at 1628 cm"". The copolymerization is determined through the decrease of the C=C doublebonding of UP-resin at 1655 cm"". At 1596 em-I the phenyl-vibration of styrene and at 1725 em"! the C=O-stretching vibration of UP-resin are observed. The polymerization and copolymerization is characterized by morphology-dependent-resonances (MDR) , which are superimposed on the Raman spectra. These MDRs correspond to eigenfrequencies of the spherical microparticle and depend on the Miesize parameter xre,,(m) (x m = 21ra/ ~), which is a function of the radius and the relative refractive index m (m = min"ide/moubide). Therefore changes in the particle size, shape and refractive index during the reaction can be detected as spectral shifts of the MDRs. In the contour plot the course of the reaction is visible. The arrows mark the MDRs. SS61
S562
Abstracts of the 1996 European Aerosol Conference
o
100
Fig.I. A: Raman spectrum with typical signals of a single levitated styrene/UPresin microparticle. B: Arrows mark the morphology-dependentresonances (MDR) in the Raman spectra of styrene/UP-resin microdroplet as revealed by a contour plot.
ACKNOWLEDGEMENTS Financial support from the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie is highly acknowledged.
REFERENCES A. Ashkin, (1970) Acceleration and trapping of particles by radiation pressure, Phys. Rev. Lett., 24 156-159. K. Schaschek, J. Popp, W. Kiefer, (1993) Observation of morphology-dependent input and output resonances in time-dependent Raman spectra of optically levitated microdroplets, J. Raman. Speetrosc., 24 69-75. H.J. Bowley, I.S. Biggin, and D.L. Gerrard, (1985) In situ Raman studies of homopolymerization and copolymerization reactions, Time-resolved vibrational spectroscopy, Springer NY, p. 194-195. J. Musick, J. Popp, M. Trunk, and W. Kiefer, to be published. W. Kiefer, (1988) Micro-Raman spectroscopy of particles in the micro-size range: a short review, Croat. Chim. Aeta,.61 473-486.