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The dynamic deformation response of select model poly(urethane urea) elastomers (PUU) at high strain rates is investigated via an all-optical laser-induced projectile impact test (LIPIT). LIPIT measurements allow the direct visualization of the impact of micro-projectiles (silica spheres) on substrates and in-situ characterization, including depth of penetration and the extent of rebound of the micro-projectiles...
Biological composites, like nacre and bone, have captured the interest of the scientific community for their outstanding ability to amalgamate a host of properties such as stiffness, strength, toughness, and impact resistance. Nacre, which is composed of 95 wt.% mineral content and 5 wt.% soft biopolymeric matrix, has a toughness orders of magnitude greater than its mineral phase while having to sacrifice...
The glass transition processes of the soft-segments (SS) in a series of poly(urethane urea) (PUU) elastomers were studied by solid-state NMR. Two SS fractions, rigid (SSr) and mobile (SSm), can be discerned by time-domain wideline separation, 13C1H dipolar dephasing, and frequency-switched Lee-Goldberg spin-locked T1ρ relaxation experiments. At increasing temperature, part of the SSr population turns...
The use of solid-state nuclear magnetic resonance (ssNMR) spectroscopy as a technique for probing and interpretation of the molecular dynamics in select ultrahigh molecular weight poly(ethylene) (UHMWPE) fibers based prepreg materials is investigated. In particular, ssNMR is used to differentiate the influence of molecular dynamics associated with matrix elastomers. Polyurethane and Kraton® based...
The molecular influence on glass transition temperature (Tg) of select model polyamides was investigated by atomistic modeling. These include nylon 6,6, nylon 6,12, a cycloaliphatic polyamide consisting of 4,4′-methylene-bis(cyclohexylamine) and dodecanedioic acid, as well as a corresponding aromatic counterpart consisting of 4,4′-methylenedianiline and dodecanedioic acid. For each model system, all-atom...
Segmental dynamics in a series of 4,4′-dicyclohexylmethane diisocyanate–diethyltoluenediamine–poly(tetramethylene oxide) based poly(urethane urea) (PUU) elastomers have been investigated through a multi-scale characterization approach. This includes broadband dielectric analysis, solid-state nuclear magnetic resonance (NMR), plate impact, and impulsive stimulated scattering. Dielectric relaxation...
The dynamical heterogeneity in a series of 4,4′-dicyclohexylmethane diisocyanate-diethyltoluenediamine-poly(tetramethylene oxide) based poly(urethane urea) (PUU) elastomers was studied by solid-state nuclear magnetic resonance (NMR) methods. Extensive phase mixing was evidenced by the 1 H wideline signal, which can be approximately fitted by a single exponential model. 13 C T 1...
Morphology of 4,4′-dicyclohexylmethane diisocyanate–poly(tetramethylene oxide) (PTMO)–diethyltoluenediamine based poly(urethane urea) (PUU) elastomers is investigated by atomic force microscopy (AFM) and compared with elastic modulus data measured from AFM-enabled indentation, dynamic nanoindentation (nanoDMA), and dynamic mechanical analysis (DMA). These measurements highlight the effect of altering...
Poly(urethane urea) elastomers are versatile and can be tailored to exhibit a broad range of mechanical response under high strain rate deformation. In this work, we utilize coarse-grained molecular dynamics simulations to elucidate the molecular mechanisms, particularly the effects of hard segment content, intermolecular interaction, and rigidity of the interface between the hard and soft segments...
Segmented poly(urethane urea) materials (PUUs) exhibit versatile mechanical properties and have drawn great interest due to their potential for protection against projectile impacts and blast loadings. To optimize the performance of PUUs for various high rate applications, specific features of their mechanical behavior have to be suitably tailored by altering the microstructure. Hence the micromechanisms...
Poly(2-hydroxyethyl methacrylate-silica) hybrid materials with significantly lower volume shrinkage were synthesized by using acid-catalyzed sol–gel reactions of tetraethyl orthosilicate and free radical polymerization of 2-hydroxyethyl methacrylate (HEMA). The mechanical, thermal, and optical properties and internal porosities of the poly(HEMA-silica) hybrids with different silica contents (e.g.,...
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