@misc{StoychevaGoeringKnoll2013, author = {Stoycheva, Vesela and Goering, Harald and Knoll, Uta}, title = {Molekulares Design f{\"u}r innovative PU-Systeme}, series = {Wissenschaftliche Beitr{\"a}ge 2013}, volume = {17}, journal = {Wissenschaftliche Beitr{\"a}ge 2013}, issn = {0949-8214}, doi = {10.15771/0949-8214_2013_1_14}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-3195}, pages = {77 -- 83}, year = {2013}, abstract = {Da Polyurethane (PU) mithilfe einer Polyadditionsreaktion gebildet werden, ist diese Stoffklasse besonders geeignet, durch den Einsatz neuartiger Komponenten, Materialien mit innovativen Eigenschaftsspektren zu synthetisieren. So wird es m{\"o}glich, f{\"u}r elektrische und elektronische Module, Verguss- und Einbettmassen mit den erforderlichen mechanischen Eigenschaften bei guter Verarbeitbarkeit herzustellen. Durch neuartige Synthesewege werden hierzu besonders hydrophobe Polyole auf Basis von 2-Ethylhexan-1,3-diol und Terephthals{\"a}ure entwickelt, die einen großen Anteil an nachwachsenden Rohstoffen in Form von nativem {\"O}l enthalten. F{\"u}r den praktischen Einsatz als 2-Komponenten-Vergussmasse muss jedoch aus verarbeitungstechnischen Gr{\"u}nden die Viskosit{\"a}t des entwickelten oligomeren Diols deutlich erniedrigt werden. Dazu dienen die eingesetzten pflanzlichen {\"O}le wie Raps- oder Soja{\"o}l. Da f{\"u}r die Eigenschaften nicht nur der chemische Aufbau der Molek{\"u}lketten, sondern auch die Morphologie des PU Systems entscheidend sind, wird mithilfe thermoanalytischer Messmethoden und abbildender Verfahren die bei dem neuartigen Syntheseweg ausgebildete Phasenstruktur charakterisiert.}, language = {de} } @misc{StoychevaGoeringWolffetal.2014, author = {Stoycheva, Vesela and Goering, Harald and Wolff, Dietmar and Herzog, Michael}, title = {Bestimmung der Koh{\"a}sionsenergie- und Vernetzungsdichte von Polymeren mit Hilfe von Quellungsmessungen}, series = {Wissenschaftliche Beitr{\"a}ge 2014}, volume = {18}, journal = {Wissenschaftliche Beitr{\"a}ge 2014}, issn = {0949-8214}, doi = {10.15771/0949-8214_2014_1_10}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-3372}, pages = {77 -- 84}, year = {2014}, abstract = {Bei der Absch{\"a}tzung der Best{\"a}ndigkeit von Kunststoffen gegen{\"u}ber niedermolekularen Fl{\"u}ssigkeiten ist die Koh{\"a}sionsenergiedichte CED ein wichtiger Parameter auf molekularer Ebene. Die Vernetzungsdichte ν eines polymeren Festk{\"o}rpers bildet hierbei einen bedeutsamen Kennwert, der dar{\"u}ber hinaus neben der L{\"o}slichkeit wichtige Eigenschaften wie thermische Stabilit{\"a}t und Steifigkeit des Materials charakterisiert. F{\"u}r die experimentelle Bestimmung von CED und ν eignet sich die Untersuchung des Quellverhaltens in unterschiedlichen L{\"o}sungsmitteln. Es werden zwei Messmethoden miteinander verglichen und die Ergebnisse unter Ber{\"u}cksichtigung des molekularen Aufbaus von Proben aus Polyurethan (PU) und hochmolekularem - (HMWPE) und ultrahochmolekularem Polyethylen (UHMWPE) diskutiert. Zum Verst{\"a}ndnis des Quellverhaltens dieser Polymerproben in niedermolekularen L{\"o}sungsmitteln werden neben den Messergebnissen Literaturdaten zu Grunde gelegt.}, language = {de} } @article{BauerGutkeHeinrichetal.2020, author = {Bauer, Joachim and Gutke, Marko and Heinrich, Friedhelm and Edling, Matthias and Stoycheva, Vesela and Kaltenbach, Alexander and Burkhardt, Martin and Gruenefeld, Martin and Gamp, Matthias and Gerhard, Christoph and Steglich, Patrick and Steffen, Sebastian and Herzog, Michael and Dreyer, Christian and Schrader, Sigurd}, title = {Novel UV-transparent 2-component polyurethane resin for chip-on-board LED micro lenses}, series = {Optical Materials Express}, volume = {10}, journal = {Optical Materials Express}, number = {9}, issn = {2159-3930}, doi = {10.1364/OME.393844}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-13472}, pages = {2085 -- 2099}, year = {2020}, abstract = {In this work we present a novel optical polymer system based on polyurethane elastomer components, which combines excellent UV transparency with high thermal stability, good hardness, high surface tension and long pot life. The material looks very promising for encapsulation and microlensing applications for chip-on-board (CoB) light-emitting diodes (LED). The extinction coefficient k, refractive index n, and bandgap parameters were derived from transmission and reflection measurements in a wavelength range of 200-890 nm. Thermogravimetry and differential scanning calorimetry were used to provide glass transition and degradation temperatures. The surface tension was determined by means of contact angle measurements. As proof of concept, a commercial InGaN-CoB-LED is used to demonstrate the suitability of the new material for the production of microlenses.}, language = {en} } @article{SchlegelEngelsStoychevaetal.2021, author = {Schlegel, Volker and Engels, Andreas and Stoycheva, Vesela and Bifaretti, Stefano and Foitzik, Andreas}, title = {From Biomaterial to Organoid - Bioprinting for Practice}, series = {Materials Science Forum}, volume = {1016}, journal = {Materials Science Forum}, publisher = {Trans Tech Publications}, issn = {0255-5476}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-18802}, pages = {1285 -- 1290}, year = {2021}, abstract = {The current state of technology for 3D printing with biomaterials is based on the extrusion of viscous materials. Mostly, extrusion heads utilize pneumatic pressure systems or stepper motors to force the substrate onto a surface. These methods are well developed for high viscouse materials. However, processing low viscous liquids may cause leakages in the system. This could be solved by applying continuous extrusion. Additionally, in order to process gelable substrates, such as gelatine and agar, tempered print heads in combination with a multi stage tempering system are required to prevent the system from clogging. The ongoing work presented in this paper focuses on the development of an extrusion system, which should be able to process multiple viscosities of gelatine sequentially. In order to achieve this, several measurements to examine the properties, as well as the material parameters of different biomaterials are performed. In this process gel point, force resistance and elasticity are the factors of particularly interest. Due to their ability to gel and their availability, the most relevant biomaterials are gelatine and agar. Using this data, an extrusion system involving a peristaltic pump, a heated tube and a nozzle, has been developed. The next step envisaged is to calibrate the extruder based on the obtained data and finally to validate the printing process by printing simple geometric structures. Assuming that a positive evaluation is obtained, the printing system will be tested for printing first organic test structures from patient data using the examined biomaterials.}, language = {en} }