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Full-Text Articles in Engineering
Double Twist In Helical Polymer "Soft" Crystals, Christopher Y. Li, Stephen Z. D. Cheng, Jason J. Ge, Feng Bai, John Z. Zhang, Ian K. Mann, Frank W. Harris, Lang-Chy Chien, Donghang Yan, Tianbai He, Bernard Lotz
Double Twist In Helical Polymer "Soft" Crystals, Christopher Y. Li, Stephen Z. D. Cheng, Jason J. Ge, Feng Bai, John Z. Zhang, Ian K. Mann, Frank W. Harris, Lang-Chy Chien, Donghang Yan, Tianbai He, Bernard Lotz
College of Polymer Science and Polymer Engineering
In natural and synthetic materials having non-racemic chiral centers, chirality and structural ordering each play a distinct role in the formation of ordered states. Configurational chirality can be extended to morphological chirality when the phase, structures possess low liquid crystalline order. In the crystalline states the crystallization process suppresses the chiral helical morphology due to strong ordering interactions, In this Letter, we report the first observation of helical single lamellar crystals of synthetic non-racemic chiral polymers. Experimental evidence shows that the molecular chains twist along both the long and short axes of the helical lamellar crystals, which is the first …
Helical Single-Lamellar Crystals Thermotropically Formed In A Synthetic Nonracemic Chiral Main-Chain Polyester, Christopher Y. Li, Donghang Yan, Stephen Z. D. Cheng, Feng Bai, Jason J. Ge, Bret H. Calhoun, Tianbai He, Liang-Chy Chien, Frank W. Harris, Bernard Lotz
Helical Single-Lamellar Crystals Thermotropically Formed In A Synthetic Nonracemic Chiral Main-Chain Polyester, Christopher Y. Li, Donghang Yan, Stephen Z. D. Cheng, Feng Bai, Jason J. Ge, Bret H. Calhoun, Tianbai He, Liang-Chy Chien, Frank W. Harris, Bernard Lotz
College of Polymer Science and Polymer Engineering
Phase structures and transformation mechanisms of nonracemic chiral biological and synthetic polymers are fundamentally important topics in understanding their macroscopic responses in different environments. It has been known for many years that helical structures and morphologies can exist in low-ordered chiral liquid crystalline (LC) phases. However, when the chiral liquid crystals form highly ordered smectic liquid crystal phases, the helical morphology is suppressed due to the crystallization process. A double-twisted morphology has been observed in many liquid crystalline biopolymers such as dinoflaggellate chromosomes (in Prorocentrum micans) in an in vivo arrangement. Helical crystals grown from solution have been reported in …
Phase Structures And Morphologies Determined By Competitions Among Self-Organization, Crystallization, And Vitrification In A Disordered Poly(Ethylene Oxide)-B-Polystyrene Diblock Copolymer, Lei Zhu, Yan Chen, Anqui-Q. Zhang, Bret. H. Calhoun, Moonseok Chun, Stephen Z. D. Cheng, Benjamin S. Hsiao, Fengji Yeh, Takeji Hashimoto
Phase Structures And Morphologies Determined By Competitions Among Self-Organization, Crystallization, And Vitrification In A Disordered Poly(Ethylene Oxide)-B-Polystyrene Diblock Copolymer, Lei Zhu, Yan Chen, Anqui-Q. Zhang, Bret. H. Calhoun, Moonseok Chun, Stephen Z. D. Cheng, Benjamin S. Hsiao, Fengji Yeh, Takeji Hashimoto
College of Polymer Science and Polymer Engineering
A poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymer having a number-average molecular weight ((M) over bar(n)) of 11000 g/mol in the PEO blocks and an (M) over bar(n) of 5200 g/mol in the PS blocks has been synthesized (with a volume fraction of the PEO blocks of 0.66 in the molten state). Differential scanning calorimetry results show that this copolymer possesses a single endotherm, which is attributed to the melting of the PEG-block crystals. Based on real-time resolved synchrotron small-angle x-ray scattering (SAXS) observations, the diblock copolymer is in a disordered state above the glass transition temperature of the PS-rich phase (T-g(PS)) …
Rhythmic Growth Of Target And Spiral Spherulites Of Crystalline Polymer Blends, Thein Kyu, Hw Chiu, Aj Guenthner, Y Okabe, H Saito, T Inoue
Rhythmic Growth Of Target And Spiral Spherulites Of Crystalline Polymer Blends, Thein Kyu, Hw Chiu, Aj Guenthner, Y Okabe, H Saito, T Inoue
College of Polymer Science and Polymer Engineering
Numerical calculations reveal that the target and spiral growth patterns in spherulites can be generated from the time-dependent Ginzburg-Landau equations (model C) by coupling a conserved compositional order parameter and a nonconserved crystal ordering parameter. Of particular interest is that the periodic concentric rings (target) or the spirals at the spherulitic core remain stationary in both the crystal (orientational) ordering field and the concentration field. Another intriguing observation is that the growth of target and spiral spherulites occurs in a stepwise fashion in synchronism with the rhythmic energy dissipation during crystallization.
Spatio-Temporal Growth Of Nematic Domains In Liquid Crystal Polymer Mixtures, Hao-Wen Chiu, Thein Kyu
Spatio-Temporal Growth Of Nematic Domains In Liquid Crystal Polymer Mixtures, Hao-Wen Chiu, Thein Kyu
College of Polymer Science and Polymer Engineering
Dynamics of phase separation and morphology development in mixtures of a low molar mass liquid crystal (LC) and a polymer have been investigated theoretically in comparison with experimental results. In the theoretical model, the combined free-energy densities of Flory-Huggins theory for isotropic mixing and Maier-Saupe theory for nematic ordering have been incorporated into the time-dependent Ginzburg-Landau equation (type C). The temporal evolution of the structure factor and the emergence of phase-separated liquid crystal domains have been simulated on the basis of an explicit central difference method based on a square lattice (128 x 128) with a periodic boundary condition. Of …
The Integrated Systems Engineering Laboratory- An Innovative Approach To Vertical Integration Using Modern Instrumentation, Ajay Mahajan, Maurice Walworth, David Mcdonald, Kevin Scmaltz
The Integrated Systems Engineering Laboratory- An Innovative Approach To Vertical Integration Using Modern Instrumentation, Ajay Mahajan, Maurice Walworth, David Mcdonald, Kevin Scmaltz
Mechanical Engineering Faculty Research
The current paradigm in engineering course instruction builds on a lecture prerequisite structure but ignores the need for a laboratory prerequisite structure. Educational quality is therefore diminished as instructors optimize specific laboratories but fail to optimize the overall program laboratory experience. This paper presents a learning environment based on modern instrumentation that forces students to use not only concepts and skills acquired from the lecture, but also actual data and models acquired from lower division laboratories, in upper division laboratories. The vertical integration occurs because students must utilize their previous laboratory work as a reference and/or building blocks as they …
Analysis Of Ductile To Cleavage Transition In Part-Through Cracks Using The Cell Model Incorporating Statistics, Xiaosheng Gao, J. Faleskog, C. Fong Shih
Analysis Of Ductile To Cleavage Transition In Part-Through Cracks Using The Cell Model Incorporating Statistics, Xiaosheng Gao, J. Faleskog, C. Fong Shih
Mechanical Engineering Faculty Research
This paper describes an approach to study ductile/cleavage transition in ferritic steels using the methodology of a cell model for ductile tearing incorporating weakest link statistics. The model takes into account the constraint effects and puts no restriction on the extent of plastic deformation or amount of ductile tearing preceding cleavage failure. The parameters associated with the statistical model are calibrated using experimental cleavage fracture toughness data, and the effect of threshold stress on predicted cleavage fracture probability is investigated. The issue of two approaches to compute Weibull stress, the ‘history approach’ and the ‘current approach’, is also addressed. The …