Search NASA⌕ Search

Engineering topics

Park, Chi Hoon

Publications and source records attributed to Park, Chi Hoon.

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Biodegradation Studies of Polyhydroxybutyrate and Polyhydroxybutyrate- co -Polyhydroxyvalerate Films in Soil

Due to increased environmental pressures, significant research has focused on finding suitable biodegradable plastics to replace ubiquitous petrochemical-derived polymers. Polyhydroxyalkanoates (PHAs) are a class of polymers that can be synthesized by microorganisms and are biodegradable, making them suitable candidates. The present study looks at the degradation properties of two PHA polymers: polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-polyhydroxyvalerate (PHBV; 8 wt.% valerate), in two different soil conditions: soil fully saturated with water (100% relative humidity, RH) and soil with 40% RH. The degradation was evaluated by observing the changes in appearance, chemical signatures, mechanical properties, and molecular weight of samples. Both PHB and PHBV were degraded completely after two weeks in 100% RH soil conditions and showed significant reductions in mechanical properties after just three days. The samples in 40% RH soil, however, showed minimal changes in mechanical properties, melting temperatures/crystallinity, and molecular weight over six weeks. By observing the degradation behavior for different soil conditions, these results can pave the way for identifying situations where the current use of plastics can be replaced with biodegradable alternatives.

36 MATERIALS SCIENCE↗
DOE OSTI2021

High-performance multiblock PEMs containing a highly acidic fluorinated-hydrophilic domain for water electrolysis

The present paper describes the design and evaluation of novel hydrophilic–hydrophobic poly(arylene ether sulfone) (PAES) multiblock copolymers for their synergistic effects upon transport properties and their potential use in proton exchange membrane water electrolysis. The multiblock copolymers are prepared via a coupling reaction between (i) a hydrophilic segment consisting of a disulfonated quinone fluorinated biphenyl group that contains fluorine moieties next to the sulfonated groups to increase the acidity, and (ii) hydrophobic segments composed of non-sulfonated biphenyl sulfone to provide dimensional stability. Two different lengths (molecular weights; 5k and 10k, where k represents 10 3 g mol -1 ) of hydrophobic segments are used to investigate the effects of the membrane properties compared with those of Nafion® and PAES random copolymer (i.e., BPSH40). Atomic force microscopy images of the BPSH40 and multiblock membranes are shown to agree closely with a mesoscale simulation, thus confirming the importance of the morphological effect upon the transport properties. Furthermore, the multiblock copolymer with a higher proportion of hydrophilic segments (10 k–5k) was shown to provide enhanced performance (3.41 A cm -2 at 1.9 V) compared to the multiblock copolymer with equal proportions of hydrophilic and hydrophobic segments (10 k–10 k) due to the greater continuity of nano-sized ionic channels.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Rapid custom prototyping of soft poroelastic biosensor for simultaneous epicardial recording and imaging

Abstract The growing need for the implementation of stretchable biosensors in the body has driven rapid prototyping schemes through the direct ink writing of multidimensional functional architectures. Recent approaches employ biocompatible inks that are dispensable through an automated nozzle injection system. However, their application in medical practices remains challenged in reliable recording due to their viscoelastic nature that yields mechanical and electrical hysteresis under periodic large strains. Herein, we report sponge-like poroelastic silicone composites adaptable for high-precision direct writing of custom-designed stretchable biosensors, which are soft and insensitive to strains. Their unique structural properties yield a robust coupling to living tissues, enabling high-fidelity recording of spatiotemporal electrophysiological activity and real-time ultrasound imaging for visual feedback. In vivo evaluations of custom-fit biosensors in a murine acute myocardial infarction model demonstrate a potential clinical utility in the simultaneous intraoperative recording and imaging on the epicardium, which may guide definitive surgical treatments.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Tailoring properties and processing of Sylgard 184: Curing time, adhesion, and water affinity

The curing time, surface adhesion, and water absorption characteristics of Sylgard 184 were modified through the addition of catalysts and fillers. Incorporation of small amounts of a platinum-based Karstedt catalyst greatly decreased curing time at room temperature, whereas the addition of talcum powder (talc), polytetrafluoroethylene (PTFE), and NaY zeolite fillers changed surface adhesion and functionality of Sylgard 184. Fourier-transform infrared spectroscopy (FT-IR), rheological and mechanical tests (tensile strength and hardness) were used to quantify the acceleration in the curing time. The surface adhesion was evaluated for aluminum and glass-like substrates using a 90° peel-off test. The interaction between fillers and Sylgard was studied by molecular dynamics simulations, which showed the interaction between NaY and Sylgard is greater than that for PTFE. Finally, water absorption studies indicated that 10 wt% NaY added to Sylgard 184 helped to improve water absorption, whereas incorporation of talc had the opposite effect.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Extending the working life of toluene diisocyanate-based polyurethanes

This work demonstrates that the addition of tridecanoic acid to a toluene diisocyante (TDI)–based polyurethane considerable increases its working life. Formulations with the additive exhibited little changes in chemistry, glass–transition temperatures, and thermal stability as determined by Fourier transform infrared spectroscopy, rheology studies, nuclear magnetic resonance, solvent swelling tests, and thermal analyses. There was a slight increase in toughness of the additive formulation associated with an increase in engineering strain and a decrease in peak engineering stress. Molecular dynamics simulations indicated that the acid forms hydrogen bonding with the OH groups from the diols, slowing down the polymerization. Lastly, these studies demonstrate that tridecanoic acid can be used to extend working time of a TDI–based polyurethane with minimal changes to physical and chemical properties when compared to the pristine polyurethane.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗