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The crystallization pathway of long and flexible polymer chains is debatable because of the lack of an initial melt/glass structure. To identify the crystallization pathway, we focus on two binary blends of poly(lactic acid) racemates that form stereocomplex crystals (SCCs). NMR crystallography is used to identify the stereocomplex (SC) structure and SC fraction with or without long-range order. There are significant structural analogies between glass and crystals for both high-molecular-weight (M) and low-M racemates. The observed analogies and kinetics of crystallization indicate that polymer crystallization proceeds via chain segments moving the least possible distance (“freezing in” mechanism) and that topological constraints govern nucleation barriers. 

Semicrystalline polymers exhibit different re-organization behaviors during heating depending on crystal growth methods. Upon heating, solution-grown crystals (SGCs) undergo lamellar doubling while melt-grown crystals (MGCs) show a gradual increase in lamellar thickness. However, the molecular-level mechanisms driving these distinct reorganization processes remain unresolved. In this study, we investigate the morphological development, crystalline chain dynamics, chain packing, and chain-folding structures of poly (L-Lactic Acid) in both SGCs and MGCs upon heating by using solid-state NMR spectroscopy and in-situ Small Angle X-ray Scattering (SAXS). By comparing the hierarchical semicrystalline structures and crystalline chain dynamics in SGCs and MGCs, it is found that the chain-folding structure and the presence or absence of entanglements are key factors influencing the thermal stability and different reorganization mechanisms of mobile polymer crystals. 

In the earlier theoretical research, impact of entanglement on folding during crystallization was minimized. The combination of 13C isotope labeling and NMR spectroscopy allows us to quantitatively determine stem to stem distance as well as chain folding distance, hence, we are able to probe chain-level structure. Our recent work indicated that polymer chains are possible to fold prior to crystallization. In this poster, we would like to investigate the folding structure of a semi-crystalline polymer in melt-grown crystals (mgc) by using solid-state NMR spectroscopy and SAXS measurement. First, various 13C enriched poly(L-lactic acid) (PLLA) samples with different molecular weights (Mw = 2.5k – 300k g/mol) across critical entanglement length (Mc = 16k g/mol) were prepared in order to observe the molecular weight dependence of folding structure of PLLA. We revealed that entanglements influence the folding number during crystallization. Second, we attempt to observe the entanglement effect through diluting entanglement density, i.e., blending the PLLA above and below the Mc with different ratio and molecular weight. Based on the experimental results, we would like to highlight the impact of entanglements on folding of semicrystalline polymer in the melt-grown crystal. 

Bacterial biofilms are communities of bacteria that exist as aggregates that can adhere to surfaces or be free-standing. This complex, social mode of cellular organization is fundamental to the physiology of microbes and often exhibits surprising behaviour. Bacterial biofilms are more than the sum of their parts: Single cell behaviour has a complex relation to collective community behaviour, in a manner perhaps cognate to the complex relation between atomic physics and condensed matter physics. Biofilm microbiology is a relatively young field by biology standards, but it has already attracted intense attention from physicists. Sometimes, this attention takes the form of seeing biofilms as inspiration for new physics. In this roadmap, we highlight the work of those who have taken the opposite strategy: We highlight work of physicists and physical scientists who use physics to engage fundamental concepts in bacterial biofilm microbiology, including adhesion, sensing, motility, signalling, memory, energy flow, community formation and cooperativity. These contributions are juxtaposed with microbiologists who have made recent important discoveries on bacterial biofilms using state-of-the-art physical methods. The contributions to this roadmap exemplify how well physics and biology can be combined to achieve a new synthesis, rather than just a division of labour.