@misc{WernerMuenzbergHassetal.2016,
  author    = {Werner, Peter and M{\"u}nzberg, Marvin and Hass, Roland and Reich, Oliver},
  title     = {Process analytical approaches for the coil-to-globule transition of poly(N-isopropylacrylamide) in a concentrated aqueous suspension},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {944},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-43116},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-431162},
  pages     = {807 -- 819},
  year      = {2016},
  abstract  = {The coil-to-globule transition of poly(N-isopropylacrylamide) (PNIPAM) microgel particles suspended in water has been investigated in situ as a function of heating and cooling rate with four optical process analytical technologies (PAT), sensitive to structural changes of the polymer. Photon Density Wave (PDW) spectroscopy, Focused Beam Reflectance Measurements (FBRM), turbidity measurements, and Particle Vision Microscope (PVM) measurements are found to be powerful tools for the monitoring of the temperature-dependent transition of such thermo-responsive polymers. These in-line technologies allow for monitoring of either the reduced scattering coefficient and the absorption coefficient, the chord length distribution, the reflected intensities, or the relative backscatter index via in-process imaging, respectively. Varying heating and cooling rates result in rate-dependent lower critical solution temperatures (LCST), with different impact of cooling and heating. Particularly, the data obtained by PDW spectroscopy can be used to estimate the thermodynamic transition temperature of PNIPAM for infinitesimal heating or cooling rates. In addition, an inverse hysteresis and a reversible building of micrometer-sized agglomerates are observed for the PNIPAM transition process.},
  language  = {en}
}
@article{SchlappaBrenkerBresseletal.2021,
  author    = {Schlappa, Stephanie and Brenker, Lee Josephine and Bressel, Lena and Hass, Roland and M{\"u}nzberg, Marvin},
  title     = {Process characterization of polyvinyl acetate emulsions applying inline photon density wave spectroscopy at high solid contents},
  series = {Polymers / Molecular Diversity Preservation International},
  volume    = {13},
  journal   = {Polymers / Molecular Diversity Preservation International},
  number    = {4},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2073-4360},
  doi       = {10.3390/polym13040669},
  pages     = {15},
  year      = {2021},
  abstract  = {The high solids semicontinuous emulsion polymerization of polyvinyl acetate using poly (vinyl alcohol-co-vinyl acetate) as protective colloid is investigated by optical spectroscopy. The suitability of Photon Density Wave (PDW) spectroscopy as inline Process Analytical Technology (PAT) for emulsion polymerization processes at high solid contents (>40\% (w/w)) is studied and evaluated. Inline data on absorption and scattering in the dispersion is obtained in real-time. The radical polymerization of vinyl acetate to polyvinyl acetate using ascorbic acid and sodium persulfate as redox initiator system and poly (vinyl alcohol-co-vinyl acetate) as protective colloid is investigated. Starved-feed radical emulsion polymerization yielded particle sizes in the nanometer size regime. PDW spectroscopy is used to monitor the progress of polymerization by studying the absorption and scattering properties during the synthesis of dispersions with increasing monomer amount and correspondingly decreasing feed rate of protective colloid. Results are compared to particle sizes determined with offline dynamic light scattering (DLS) and static light scattering (SLS) during the synthesis.},
  language  = {en}
}
@article{SandmannMuenzbergBresseletal.2022,
  author    = {Sandmann, Michael and M{\"u}nzberg, Marvin and Bressel, Lena and Reich, Oliver and Hass, Roland},
  title     = {Inline monitoring of high cell density cultivation of Scenedesmus rubescens in a mesh ultra-thin layer photobioreactor by photon density wave spectroscopy},
  series = {BMC Research Notes / Biomed Central},
  volume    = {15},
  journal   = {BMC Research Notes / Biomed Central},
  number    = {1},
  publisher = {Biomed Central (London)},
  address   = {London},
  issn      = {1756-0500},
  doi       = {10.1186/s13104-022-05943-2},
  pages     = {7},
  year      = {2022},
  abstract  = {Objective Due to multiple light scattering that occurs inside and between cells, quantitative optical spectroscopy in turbid biological suspensions is still a major challenge. This includes also optical inline determination of biomass in bioprocessing. Photon Density Wave (PDW) spectroscopy, a technique based on multiple light scattering, enables the independent and absolute determination of optical key parameters of concentrated cell suspensions, which allow to determine biomass during cultivation. Results A unique reactor type, called "mesh ultra-thin layer photobioreactor" was used to create a highly concentrated algal suspension. PDW spectroscopy measurements were carried out continuously in the reactor without any need of sampling or sample preparation, over 3 weeks, and with 10-min time resolution. Conventional dry matter content and coulter counter measurements have been employed as established offline reference analysis. The PBR allowed peak cell dry weight (CDW) of 33.4 g L-1. It is shown that the reduced scattering coefficient determined by PDW spectroscopy is strongly correlated with the biomass concentration in suspension and is thus suitable for process understanding. The reactor in combination with the fiber-optical measurement approach will lead to a better process management.},
  language  = {en}
}
@article{GutschmannSimoesSchieweetal.2022,
  author    = {Gutschmann, Bj{\"o}rn and Sim{\~o}es, Matilde Maldonado and Schiewe, Thomas and Schr{\"o}ter, Edith S. and M{\"u}nzberg, Marvin and Neubauer, Peter and Bockisch, Anika and Riedel, Sebastian Lothar Stefan},
  title     = {Continuous feeding strategy for polyhydroxyalkanoate production from solid waste animal fat at laboratory- and pilot-scale},
  series = {Microbial biotechnology / Society for Applied Microbiology},
  journal   = {Microbial biotechnology / Society for Applied Microbiology},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {1751-7915},
  doi       = {10.1111/1751-7915.14104},
  pages     = {12},
  year      = {2022},
  abstract  = {Bioconversion of waste animal fat (WAF) to polyhydroxyalkanoates (PHAs) is an approach to lower the production costs of these plastic alternatives. However, the solid nature of WAF requires a tailor-made process development. In this study, a double-jacket feeding system was built to thermally liquefy the WAF to employ a continuous feeding strategy. During laboratory-scale cultivations with Ralstonia eutropha Re2058/pCB113, 70\% more PHA (45 g(PHA) L-1) and a 75\% higher space-time yield (0.63 g(PHA) L-1 h(-1)) were achieved compared to previously reported fermentations with solid WAF. During the development process, growth and PHA formation were monitored in real-time by in-line photon density wave spectroscopy. The process robustness was further evaluated during scale-down fermentations employing an oscillating aeration, which did not alter the PHA yield although cells encountered periods of oxygen limitation. Flow cytometry with propidium iodide staining showed that more than two-thirds of the cells were viable at the end of the cultivation and viability was even little higher in the scale-down cultivations. Application of this feeding system at 150-L pilot-scale cultivation yielded in 31.5 g(PHA) L-1, which is a promising result for the further scale-up to industrial scale.},
  language  = {en}
}
@misc{MuenzbergHassKhanhetal.2016,
  author    = {M{\"u}nzberg, Marvin and Hass, Roland and Khanh, Ninh Dinh Duc and Reich, Oliver},
  title     = {Limitations of turbidity process probes and formazine as their calibration standard},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe},
  number    = {831},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-42826},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-428263},
  pages     = {12},
  year      = {2016},
  abstract  = {Turbidity measurements are frequently implemented for the monitoring of heterogeneous chemical, physical, or biotechnological processes. However, for quantitative measurements, turbidity probes need calibration, as is requested and regulated by the ISO 7027:1999. Accordingly, a formazine suspension has to be produced. Despite this regulatory demand, no scientific publication on the stability and reproducibility of this polymerization process is available. In addition, no characterization of the optical properties of this calibration material with other optical methods had been achieved so far. Thus, in this contribution, process conditions such as temperature and concentration have been systematically investigated by turbidity probe measurements and Photon Density Wave (PDW) spectroscopy, revealing an influence on the temporal formazine formation onset. In contrast, different reaction temperatures do not lead to different scattering properties for the final formazine suspensions, but give an access to the activation energy for this condensation reaction. Based on PDW spectroscopy data, the synthesis of formazine is reproducible. However, very strong influences of the ambient conditions on the measurements of the turbidity probe have been observed, limiting its applicability. The restrictions of the turbidity probe with respect to scatterer concentration are examined on the basis of formazine and polystyrene suspensions. Compared to PDW spectroscopy data, signal saturation is observed at already low reduced scattering coefficients.},
  language  = {en}
}
@phdthesis{Muenzberg2018,
  author    = {M{\"u}nzberg, Marvin},
  title     = {Inline-Untersuchung der Tr{\"u}bung und Partikelgr{\"o}ße von hochkonzentrierten Dispersionen mit Lichtstreutechniken},
  school      = {Universit{\"a}t Potsdam},
  pages     = {85},
  year      = {2018},
  language  = {de}
}
@article{HassMuenzbergBresseletal.2013,
  author    = {Hass, Roland and M{\"u}nzberg, Marvin and Bressel, Lena and Reich, Oliver},
  title     = {Industrial applications of photon density wave spectroscopy for in-line particle sizing [Invited]},
  series = {Applied optics},
  volume    = {52},
  journal   = {Applied optics},
  number    = {7},
  publisher = {Optical Society of America},
  address   = {Washington},
  issn      = {1559-128X},
  doi       = {10.1364/AO.52.001423},
  pages     = {1423 -- 1431},
  year      = {2013},
  abstract  = {Optical spectroscopy in highly turbid liquid material is often restricted by simultaneous occurrence of absorption and scattering of light. Photon Density Wave (PDW) spectroscopy is one of the very few, yet widely unknown, technologies for the independent quantification of these two optical processes. Here, a concise overview about modern PDW spectroscopy is given, including all necessary equations concerning the optical description of the investigated material, dependent light scattering, particle sizing, and PDW spectroscopy itself. Additionally, it is shown how the ambiguity in particle sizing, arising from Mie theory, can be correctly solved. Due to its high temporal resolution, its applicability to highest particle concentrations, and its purely fiber-optical probe, PDW spectroscopy possesses all fundamental characteristics for optical in-line process analysis. Several application examples from the chemical industry are presented. (C) 2013 Optical Society of America},
  language  = {en}
}
@article{SchlappaBresselReichetal.2023,
  author    = {Schlappa, Stephanie and Bressel, Lena and Reich, Oliver and M{\"u}nzberg, Marvin},
  title     = {Advanced particle size analysis in high-solid-content polymer dispersions using photon density wave spectroscopy},
  series = {Polymers},
  volume    = {15},
  journal   = {Polymers},
  number    = {15},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2073-4360},
  doi       = {10.3390/polym15153181},
  pages     = {17},
  year      = {2023},
  abstract  = {High-solid-content polystyrene and polyvinyl acetate dispersions of polymer particles with a 50 nm to 500 nm mean particle diameter and 12-55\% (w/w) solid content have been produced via emulsion polymerization and characterized regarding their optical and physical properties. Both systems have been analyzed with common particle-size-measuring techniques like dynamic light scattering (DLS) and static light scattering (SLS) and compared to inline particle size distribution (PSD) measurements via photon density wave (PDW) spectroscopy in undiluted samples. It is shown that particle size measurements of undiluted polystyrene dispersions are in good agreement between analysis methods. However, for polyvinyl acetate particles, size determination is challenging due to bound water in the produced polymer. For the first time, water-swelling factors were determined via an iterative approach of PDW spectroscopy error (X-2) minimization. It is shown that water-swollen particles can be analyzed in high-solid-content solutions and their physical properties can be assumed to determine the refractive index, density, and volume fraction in dispersion. It was found that assumed water swelling improved the reduced scattering coefficient fit by PDW spectroscopy by up to ten times and particle size determination was refined and enabled. Particle size analysis of the water-swollen particles agreed well with offline-based state-of-the-art techniques.},
  language  = {en}
}
@article{AdebayoHashimHassetal.2017,
  author    = {Adebayo, Segun Emmanuel and Hashim, Norhashila and Hass, Roland and Reich, Oliver and Regen, Christian and M{\"u}nzberg, Marvin and Abdan, Khalina and Hanafi, Marsyita and Zude, Manuela},
  title     = {Using absorption and reduced scattering coefficients for non-destructive analyses of fruit flesh firmness and soluble solids content in pear},
  series = {Postharvest Biology and Technology},
  volume    = {130},
  journal   = {Postharvest Biology and Technology},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0925-5214},
  doi       = {10.1016/j.postharvbio.2017.04.004},
  pages     = {56 -- 63},
  year      = {2017},
  abstract  = {Quality attributes of fruit determine its acceptability by the retailer and consumer. The objective of this work was to investigate the potential of absorption (μa) and reduced scattering (μs') coefficients of European pear to analyze its fruit flesh firmness and soluble solids content (SSC). The absolute reference values, μa* (cm-1) and μs'* (cm-1), of pear were invasively measured, employing multi-spectral photon density wave (PDW) spectroscopy at preselected wavelengths of 515, 690, and 940 nm considering two batches of unripe and overripe fruit. On eight measuring dates during fruit development, μa and μs' were analyzed non-destructively by means of laser light backscattering imaging (LLBI) at similar wavelengths of 532, 660, and 830 nm by means of fitting according to Farrell's diffusion theory, using fix reference values of either μa* or μs'*. Both, the μa* and the μa as well as μs'* and μs' showed similar trends. Considering the non-destructively measured data during fruit development, μa at 660 nm decreased 91 till 141 days after full bloom (dafb) from 1.49 cm-1 to 0.74 cm-1 due to chlorophyll degradation. At 830 nm, μa only slightly decreased from 0.41 cm-1 to 0.35 cm-1. The μs' at all wavelengths revealed a decreasing trend as the fruit developed. The difference measured at 532 nm was most pronounced decreasing from 24 cm-1 to 10 cm-1, while at 660 nm and 830 nm values decreased from 15 cm-1 to 13 cm-1 and from 10 cm-1 to 8 cm-1, respectively. When building calibration models with partial least-squares regression analysis on the optical properties for non-destructive analysis of the fruit SSC, μa at 532 nm and 830 nm resulted in a correlation coefficient of R = 0.66, however, showing high measuring uncertainty. The combination of all three wavelengths gave an enhanced, encouraging R = 0.89 for firmness analysis using μs' in the freshly picked fruit.},
  language  = {en}
}