@article{KutlugHassRecketal.2018,
  author    = {Kutlug, Oezg{\"u}r and Hass, Roland and Reck, Stephan and Hartwig, Andreas},
  title     = {Inline characterization of dispersion formation of a solvent-borne acrylic copolymer by Photon Density Wave spectroscopy},
  series = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects},
  volume    = {556},
  journal   = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0927-7757},
  doi       = {10.1016/j.colsurfa.2018.08.011},
  pages     = {113 -- 119},
  year      = {2018},
  abstract  = {Most investigations on phase inversion (PI) of resins upon addition of water have been carried out by dynamic light scattering (DLS), torque, and viscosity measurements. The main problem, however, is analytic discontinuity due to sample removal and a changing matrix due to dilution during the preparation of the aqueous resin dispersions. This work presents Photon Density Wave (PDW) spectroscopy as a tool for the inline characterization of the acetone process for an acrylic copolymer with high acrylic acid (AA) content. PDW spectroscopy revealed different trends for optical properties compared to torque during water feed. Also the absence of PI due to dissolution of copolymer in the solvent/water mixture is observed by PDW spectroscopy. PI for the investigated copolymer did not occour during water feed but during removal of solvent. Different feeding rates of water gave similar trends while a change in temperature and degree of AA neutralization led to changes in optical properties and torque. Thermal processing showed that the optical properties of mixtures prior and after removal of solvent were completely different caused by changes of solubility.},
  language  = {en}
}
@article{HassMunzkeRuizetal.2015,
  author    = {Hass, Roland and Munzke, Dorit and Ruiz, Salome Vargas and Tippmann, Johannes and Reich, Oliver},
  title     = {Optical monitoring of chemical processes in turbid biogenic liquid dispersions by Photon Density Wave spectroscopy},
  series = {Analytical \& bioanalytical chemistry},
  volume    = {407},
  journal   = {Analytical \& bioanalytical chemistry},
  number    = {10},
  publisher = {Springer},
  address   = {Heidelberg},
  issn      = {1618-2642},
  doi       = {10.1007/s00216-015-8513-9},
  pages     = {2791 -- 2802},
  year      = {2015},
  abstract  = {In turbid biogenic liquid material, like blood or milk, quantitative optical analysis is often strongly hindered by multiple light scattering resulting from cells, particles, or droplets. Here, optical attenuation is caused by losses due to absorption as well as scattering of light. Fiber-based Photon Density Wave (PDW) spectroscopy is a very promising method for the precise measurement of the optical properties of such materials. They are expressed as absorption and reduced scattering coefficients (mu (a) and mu (s)', respectively) and are linked to the chemical composition and physical properties of the sample. As a process analytical technology, PDW spectroscopy can sense chemical and/or physical processes within such turbid biogenic liquids, providing new scientific insight and process understanding. Here, for the first time, several bioprocesses are analyzed by PDW spectroscopy and the resulting optical coefficients are discussed with respect to established mechanistic models of the chosen processes. As model systems, enzymatic casein coagulation in milk, temperature-induced starch hydrolysis in beer mash, and oxy- as well as deoxygenation of human donor blood were investigated by PDW spectroscopy. The findings indicate that also for very complex biomaterials (i.e., not well-defined model materials like monodisperse polymer dispersions), obtained optical coefficients allow for the assessment of a structure/process relationship and thus for a new analytical access to biogenic liquid material. This is of special relevance as PDW spectroscopy data are obtained without any dilution or calibration, as often found in conventional spectroscopic approaches.},
  language  = {en}
}
@article{BresselHassReich2013,
  author    = {Bressel, Lena and Hass, Roland and Reich, O.},
  title     = {Particle sizing in highly turbid dispersions by Photon Density Wave spectroscopy},
  series = {JOURNAL OF QUANTITATIVE SPECTROSCOPY \& RADIATIVE TRANSFER},
  volume    = {126},
  journal   = {JOURNAL OF QUANTITATIVE SPECTROSCOPY \& RADIATIVE TRANSFER},
  number    = {1},
  publisher = {PERGAMON-ELSEVIER SCIENCE LTD},
  address   = {OXFORD},
  issn      = {0022-4073},
  doi       = {10.1016/j.jqsrt.2012.11.031},
  pages     = {122 -- 129},
  year      = {2013},
  abstract  = {Photon Density Wave (PDW) spectroscopy is presented as a fascinating technology for the independent determination of scattering (mu(s)\’ and absorption (ita) properties of highly turbid liquid dispersions. The theory is reviewed introducing new expressions for the PDW coefficients k(I) and k(Phi). Furthermore, two models for dependent scattering, namely the hard sphere model in the Percus-Yevick Approximation (HSPYA) and the Yukawa model in the Mean Spherical Approximation (YMSA), are experimentally examined. On the basis of the HSPYA particle sizing is feasible in dispersions of high ionic strength. It is furthermore shown that in dialyzed dispersions or in technical copolymers with high particle charge only the YMSA allows for correct dilution-free particle sizing. (C) 2013 Elsevier Ltd. All rights reserved.},
  language  = {en}
}