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Romberg SK, Roberts P, Snyder CR, Kotula AP. Evaluating models that predict epoxy conversion using rheological properties. ACS APPLIED POLYMER MATERIALS 2024; 6:10.1021/acsapm.4c00607. [PMID: 38867885 PMCID: PMC11167731 DOI: 10.1021/acsapm.4c00607] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2024]
Abstract
Simultaneous rheology and conversion measurements of neat and composite epoxy resins reveal that conventional models neither accurately nor fully describe the relationship between rheology and conversion. We find that models predicting thermoset conversion based on mixing rules of rheological properties are quantitatively inaccurate and do not account for chemical gelation. Models based on percolation theory and the divergence of the viscosity at the gel point are more accurate but only valid before the gel point. Here, we propose the use of the generalized effective medium (GEM) model, which incorporates the divergence of rheological properties on both sides of the critical gel point. We show that the GEM model works well for both neat resins and filled systems, and the resulting parameters estimate the gel point and scaling behavior on either side of the sol-gel transition.
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Affiliation(s)
- Stian K. Romberg
- Materials Science and Engineering Division, National Institute of Standards and Technology Gaithersburg, MD 20899, United States of America
| | - Paul Roberts
- Materials Science and Engineering Division, National Institute of Standards and Technology Gaithersburg, MD 20899, United States of America
| | - Chad R. Snyder
- Materials Science and Engineering Division, National Institute of Standards and Technology Gaithersburg, MD 20899, United States of America
| | - Anthony P. Kotula
- Materials Science and Engineering Division, National Institute of Standards and Technology Gaithersburg, MD 20899, United States of America
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Yamamoto T, Nagae Y, Wakabayashi T, Kamiyama T, Suzuki H. Calorimetry of phase transitions in liquid crystal 8CB under shear flow. SOFT MATTER 2023; 19:1492-1498. [PMID: 36734340 DOI: 10.1039/d2sm01652d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
A differential scanning calorimeter equipped with a shearing system (shear rate of < 400 s-1) was developed to elucidate the thermodynamic properties of liquid crystalline phase transitions under shear flow. An analytical method was proposed to accurately estimate the heat flow caused by shear friction to evaluate the transition entropies. The phase transitions of 4'-n-octyl-4-cyano-biphenyl (8CB) under shear flow were investigated using the developed calorimeter. Although several shear-induced transitions for 8CB have been reported in the past using viscosity and small-angle X-ray scattering (SAXS) measurements, only the nematic-isotropic (N-I) and smectic-A-nematic (SA-N) transitions were detected as heat flow peaks. The N-I transition temperature was almost independent of the shear rate. The SA-N transition temperature was also independent of the shear rate, but the transition peak was broadened by applying shear flow. For both transitions, the transition entropies were independent of the shear rate. These results suggest that the thermodynamic properties were not considerably changed by shearing because the molecular alignments in the domains were not substantially changed, whereas shearing changed the LC domain directions, which can be detected by viscosity and SAXS measurements.
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Affiliation(s)
- Taro Yamamoto
- Department of Chemistry, Kindai University, Higashiosaka, Osaka, 577-8502, Japan.
| | - Yuki Nagae
- Department of Chemistry, Kindai University, Higashiosaka, Osaka, 577-8502, Japan.
| | - Tomonari Wakabayashi
- Department of Chemistry, Kindai University, Higashiosaka, Osaka, 577-8502, Japan.
| | - Tadashi Kamiyama
- Department of Chemistry, Kindai University, Higashiosaka, Osaka, 577-8502, Japan.
| | - Hal Suzuki
- Department of Chemistry, Kindai University, Higashiosaka, Osaka, 577-8502, Japan.
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Kotula AP, Migler KB. Percolation Implications in the Rheology of Polymer Crystallization. POLYMER CRYSTALLIZATION 2021; 4:10.1002/pcr2.10162. [PMID: 34124594 PMCID: PMC8193685 DOI: 10.1002/pcr2.10162] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2020] [Accepted: 10/14/2020] [Indexed: 11/06/2022]
Abstract
The rheology of polymer crystallization is an old problem that often defies explanation due to the complex interrelationships between crystallization and flow properties. Although separate measurements of rheology and crystallinity can give some information on their relationship, it is only through simultaneous measurements that ideas on the rheology of polymer crystallization can be tested and developed. This Perspective details recent experimental developments in simultaneous crystallinity and rheology measurements as well as continuum modeling efforts for the case of quiescent and isothermal crystallization. Experimental results reveal that the rheology is dominated initially by growth of individual spherulites that evolve into spherulitic superstructures that eventually span the measurement geometry. A generalized effective medium model based on this concept of percolation can explain both the growth of the viscoelastic modulus during crystallization and the changes in the relaxation spectrum of the crystallizing polymer, including a critical gel response at percolation. The success of the combined measurement techniques and percolation concepts motivate research to extend the semicrystalline polymer materials space where these methods are applied as well as further develop novel techniques to gain additional insight into the evolution of structure and relaxation dynamics during crystallization.
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Affiliation(s)
- Anthony P. Kotula
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD 20899
| | - Kalman B. Migler
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD 20899
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Pasquino R, Auriemma F, Rosa CD, Grizzuti N. A Rheological Investigation of the Crystallization Kinetics of Syndiotactic Polypropylene of Varying Degree of Tacticity. INT POLYM PROC 2018. [DOI: 10.3139/217.3569] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Abstract
The crystallization behavior of five Syndiotactic Polypropylene (sPP) samples of varying degree of tacticity has been studied by means of rheological techniques and compared to the results of more standard DSC measurements. Small Amplitude Oscillatory Shear (SAOS) measurements have been performed on a controlled stress rotational rheometer equipped with a nitrogen-fed, forced convection oven, which allows for good temperature stability and relatively high heating/cooling rates. Both non-isothermal and isothermal crystallization tests have been carried out. The former proved useful to determine the melting and crystallization temperature of the polymers. The latter were exploited to determine the temperature dependence of the polymer crystallization rate. The results showed the strong influence of the degree of tacticity on the crystallization behaviour of sPP. In particular, it was confirmed that a decrease in the stereo-regularity of the polymer chain considerably shifts the crystallization process to lower temperatures. For the case of the lowest tacticity sample, rheology was crucial in determining the temperature where the maximum (but very small) crystallization rate is attained, a result that could not be achieved by standard calorimetry measurements.
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Affiliation(s)
- R. Pasquino
- Dipartimento di Ingegneria Chimica , dei Materiali e della Produzione Industriale, Università di Napoli “Federico II”, Napoli , Italy
| | - F. Auriemma
- Dipartimento di Scienze Chimiche , Università di Napoli “Federico II, Napoli , Italy
| | - C. De Rosa
- Dipartimento di Scienze Chimiche , Università di Napoli “Federico II, Napoli , Italy
| | - N. Grizzuti
- Dipartimento di Ingegneria Chimica , dei Materiali e della Produzione Industriale, Università di Napoli “Federico II”, Napoli , Italy
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Janssens V, Block C, Van Assche G, Van Mele B, Van Puyvelde P. RheoDSC Analysis of Hardening of Semi-Crystalline Polymers during Quiescent Isothermal Crystallization. INT POLYM PROC 2013. [DOI: 10.3139/217.2374] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Abstract
The crystallization of semi-crystalline polymers is often analyzed by rheometry and calorimetry. By rheometry the viscosity evolution during crystallization can be followed, whereas from a calorimetric measurement, the evolution of the degree of crystallinity can be calculated. The time evolution of these material properties is valuable input for polymer processing simulation software and in order to combine the data in a reliable manner, hardening curves are used as a characterization tool. Such a hardening curve correlates the relative increase of the viscosity resulting from crystallization, to the advancing degree of crystallinity. In this study, these are extracted from simultaneous measurements on one sample using a RheoDSC device. The RheoDSC technique allows for the direct combination of the rheological and calorimetric signal without the need of combining separate stand-alone measurement results. In this study, isothermal crystallization experiments are used to discuss the benefits of this approach. This will lead to the recommendation that measuring the hardening effect in steady shear measurements at very low shear rates in a direct combined RheoDSC setup is the most reliable method to compile unambiguously a material specific hardening curve for semi-crystalline polymers.
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Affiliation(s)
- V. Janssens
- Department of Chemical Engineering, Applied Rheology and Polymer Processing, Leuven Material Research Centre, Katholieke Universiteit Leuven, Leuven, Belgium
| | - C. Block
- Department of Materials and Chemistry, Physical Chemistry and Polymer Science, Vrije Universiteit Brussel, Brussels, Belgium
| | - G. Van Assche
- Department of Materials and Chemistry, Physical Chemistry and Polymer Science, Vrije Universiteit Brussel, Brussels, Belgium
| | - B. Van Mele
- Department of Materials and Chemistry, Physical Chemistry and Polymer Science, Vrije Universiteit Brussel, Brussels, Belgium
| | - P. Van Puyvelde
- Department of Chemical Engineering, Applied Rheology and Polymer Processing, Leuven Material Research Centre, Katholieke Universiteit Leuven, Leuven, Belgium
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Block C, Van Mele B, Van Puyvelde P, Van Assche G. Time–temperature-transformation (TTT) and temperature–conversion-transformation (TxT) cure diagrams by RheoDSC: Combined rheometry and calorimetry on an epoxy-amine thermoset. REACT FUNCT POLYM 2013. [DOI: 10.1016/j.reactfunctpolym.2012.05.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Affiliation(s)
- Sergey Vyazovkin
- Department of Chemistry, University of Alabama at Birmingham, 901S 14th Street, Birmingham, Alabama 35294
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