"How does the light interact with polymer crystals?"
Here, I was trying to understand the nature of how amorphous polymer chains transform into certain lamellar arrangements below melting point, and thus various optical morphology, particularly ring-banded morphology. The polymer selected for this study is poly(nonamethylene terephthalate) (PNT), one of aromatic polyesters, provided that dual types of banded spherulites can be formed at certain temperature region, so called Type-1 (single-band) and Type-2 (double-bands). I tried to correlate the lamellar arrangements in top surface and in cross-section of cryo-fractured PNT sample by scanning electron microscopy (SEM). In addition, polarized optical microscopy (POM) was employed to in situ follow the formation of banded spherulites. In terms of my SEM and POM results including previous AFM findings, I constructed three-dimensional (3D) models for Type-1 and Type-2 banded spherulites. These models are very much different from the commonly proposed continuous twisting theory. Details can refer to my publication.
C.-H. Tu, et al. Science Advances (2023).
C.-H. Tu, et al. Crystals (2021)
C.-H. Tu, et al. Crys.Eng.Comm. (2020)
C.-H. Tu, et al. RSC Adv. (2017)
Coexistence of dual banded spherulites
(PNT isothermal crystallized at T=85oC)
Scanning Electron Microscopy
Lamellar growth mechanism of Type-1 banded spherulite
Given enough time semicrystalline polymer crystals can enter into nanopores at temp below melting point!
SEM and AFM together revealed the morphology of PEO crystals inside AAO 400nm pores. (Figure 2 in the paper)
Selected as Front Cover in Science Advances journal!
"Can we decipher the fluctuation of polymer chains in nonequilibrium conditions and in finite spaces?"
Polymer per se is composed of abundant chain-like structures like the Italian food "Spaghetti". Understanding how these crowded polymer chains move is a nontrivial task. Motivated by the interesting nature of polymer chains, I followed my passion in polymers and continued my research in polymer chain dynamics at Max Planck Institute for Polymer Research in Germany. The research herein was more challenging provided that I was trying to understand how polymer chains move in small pores (rather than bulk material) with finite space close to the size of polymer chains. The motivation for such investigation relies on its strong implications to several applications including separation of proteins with relevance in cell biology and the development of inkjet printing for commercial xerography. To that end, I develop an nanofluidic approach based on dielectric spectroscopy, so called in situ nanodielectric spectroscopy (nDS), enabling the direct investigation of polymer segmental and chain dynamics (for the first time by dielectric type-A polymer as cis-1.4-polyisoprene) during flow inside the nanopores. Several interesting and fundamentally important findings can refer to my publication.
C.-H. Tu, et al. Macromolecules (2022)
C.-H. Tu, et al. Macromolecules (2021)
C.-H. Tu, et al. Physical Review Letters (2020)
C.-H. Tu, et al. Macromolecules (2019)
Book Chapter (Invited)
C.-H. Tu, et al. ACS Symposium Series (2021)
Dielectric spectroscopy measures the fluctuation of molecule dipoles under the oscillating electric field. Given that polymers have dipoles on polymer segments/chains, we can use DS to study relaxational dynamics of polymers.
During my PhD research I successfully established a nanofluidic approach enabling in situ determination of polymer dynamics and viscosity during imbibition within nanopores, so called in situ nanodielectric spectroscopy. (Tu et al. Macromolecules 2019 and followed by my other papers)
Direct experimental evidence of increasing adsorption of polymer chains during imbibition was provided using in situ nanodielectric spectroscopy on cis-1,4-polyisoprene! (Tu et al. PRL 2020)
"It is, now more than ever, to think about how to save our planet by recycling plastics as a polymer scientist."
Recently, I am highly concerned with a fact that our planet is indeed suffering from the pollution of artificial plastics, even at this moment when you are looking at this page. These waste are commonly made of (highly stable) polymers like polyolefin, which is initially designed for the long-term usage, now becoming a detrimental issue for recycling provided that high temperature process as pyrolysis or strong mechanical force are usually required to break it apart. Moreover, traditional physical recycling methods sabotage the physical stability of newly-made polymers. Therefore, there is a growing trend to design a chemical approach to recycle wasted polymer and followed by dehydrogenation and functionalization to fabricate a new polymer with higher economic value, i.e., polymer upcycling (PolyUp).
As a polymer scientist, I realize that I have responsibility to join the efforts for PolyUp with my knowledge in polymers gained from my previous research experience. Therefore, I am currently performing my PolyUp research in Prof. Karen Winey group in Department of Materials Science and Engineering at University of Pennsylvania (UPenn) collaborating with polymer chemists at Penn and UMass to explore the most efficient recycling approach and save our planet! Any interested people can refer to the report issued by Department of Energy (USA) in 2019 (click the book cover in the right) and the official website of Karen Winey group (click the pink button below). Keep in mind: Sustainable economy is the future of our Earth!