Structural Studies of Extension-Induced Mesophase Formation in Poly(diethylsiloxane) Elastomers:  In Situ Synchrotron WAXS and SAXS

Koerner, Hilmar; Luo, Yixia; Li, Xuefa; Cohen, Claude; Hedden, Ronald C.; Ober, Christopher K.

doi:10.1021/ma020856j

Cited by 34 publications

(27 citation statements)

References 19 publications

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“…However, cold drawing is rarely observed, if ever, in noncrystallizable elastomers above their respective glass transition temperatures. Previous reports of necking in elastomers have been limited to smectic polydomain MCLCE and mesomorphic poly(diethylsiloxane) (PDES) elastomers 30–35. Like semicrystalline polymers, smectic MCLCE are also thought to contain high concentrations of chain‐folded conformers (hairpins),5, 12 suggesting that the necking transition might involve loss of chain folding, a view supported by our recent X‐ray diffraction studies 12…”

Section: Introductionmentioning

confidence: 68%

Influence of strain rate and temperature on necking transition in a polydomain smectic main chain elastomer

Lentz

Chen

et al. 2011

J Polym Sci B Polym Phys

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Smectic main-chain liquid crystalline elastomers (MCLCE) with polydomain morphology are rare examples of elastomers that can form a neck and undergo cold drawing under tension. However, not all previous studies of the mechanical behavior of smectic MCLCE reported neck formation. The mechanical response of a polydomain smectic MCLCE has therefore been characterized by elongation at varying strain rates and temperatures to identify factors favoring mechanical instability. Yielding and neck formation are increasingly favored as the strain rate increases at constant temperature, or as the temperature decreases toward T g . As cold drawing pro-ceeds, significant creep occurs continuously within the neck, in contrast to the behavior of certain linear polymers that exhibit a ''natural'' draw ratio. Thermal imaging during elongation indicates that viscous heating is not a prerequisite for neck formation. Rather, inherent softening of the material during yielding due to morphological changes leads to an enhanced rate of deformation and contraction at the neck. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 591-598, 2011

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Section: Introductionmentioning

confidence: 68%

Influence of strain rate and temperature on necking transition in a polydomain smectic main chain elastomer

Lentz

Chen

et al. 2011

J Polym Sci B Polym Phys

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“…The correlation length of the low‐angle (high intensity) peak was calculated using the Scherrer equation46 ( $L^\prime = k\Lambda \Big/ \beta^{\prime} \cos {\Theta}_{\max}$ , where k is a material parameter, commonly ∼1 for polymers, Λ the wavelength of the X‐ray, β′ the full width at half‐maximum of the WAXS peak, and θ max is the scattering angle of the peak under investigation). Under the assumption of a perfect two‐phase system, the correlation length L ′ can be identified to the domain size.…”

Section: In Situ X‐ray Results: Saxs and Waxs Measurements Combinedmentioning

confidence: 99%

Impact of the diagnostic label of osteoarthritis on perceptions of disability and willingness to help a parent in African Americans and whites

Mingo¹,

McIlvane²,

Haley³

2006

Arthritis & Rheumatism

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Objective. Family members are central to arthritis care, but little is known about public perceptions of osteoarthritis (OA) and how cultural diversity affects these perceptions. We examined the effects of participant race and diagnostic label of OA on family members' perceptions and willingness to help a parent with OA. Methods. A total of 105 young adult African American and 308 young adult white participants were randomly assigned to read 1 of 2 vignettes (OA label versus no label) describing an older mother with marked pain and disability. Effects for race and diagnostic label were examined. Results. Participants who were told that the mother had OA were more likely to believe the mother's problems were due to illness, but were less likely to believe that better health care would improve her condition than participants not told a diagnosis. African Americans attributed less blame to the mother, showed less anger, more sympathy, and were more willing to help compared with whites. Conclusion. The finding that the OA label leads to pessimism concerning the benefits of health care for a parent suggests a need for public education on the effectiveness of arthritis care. Race differences in perceptions of the parent and willingness to provide care are consistent with previous literature on race and family caregiving, and indicate that cultural values regarding family caregiving may be important in arthritis care. Family members could serve as important allies for elderly individuals with OA, and public health efforts should not just target older adults but should also provide information on arthritis care for families.

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“…For a system with a relatively low viscosity (1 wt.-% I.30E in Epon 862, g 25C = 15 Poise) alignment at room temperature occurred in less than 5 s for 2 V lm ±1 , whereas randomization upon removal of the field required 30 s. For a system with higher viscosity (10 wt.-% layered silicate in Epon 862/Cure W mixture, g 25C = 100 Poise) alignment at room temperature required longer than 5 min, and corresponding randomization took more than 10 h. The threshold voltage for alignment was slightly less than 1 V lm ±1 with no dependence on the examined range of frequencies (0.1± 50 MHz). In general, the orientation parameter (Hermans orientation function, see Koerner et al [13] ) of the fully aligned systems was consistently between 0.6±0.7. These values are comparable to aligned nematic liquid crystals.…”

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confidence: 88%

Tuning Polymer Nanocomposite Morphology: AC Electric Field Manipulation of Epoxy–Montmorillonite (Clay) Suspensions

et al. 2004

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Over the last decade, the utility of inorganic nanoparticles as additives to enhance polymer performance has been established and now provides numerous commercial opportunities, ranging from advanced aerospace systems to commodity plastics.[1] Low-volume additions (1±5 wt.-%) of highly anisotropic nanoparticles, such as layered silicates or carbon nanotubes, provide property enhancements with respect to the neat polymer that are comparable to those achieved by conventional loadings (15±40 wt.-%) of traditional fillers. The lower loadings facilitate processing and reduce component weight. In addition, unique value-added properties not normally possible with traditional fillers are also observed, such as reduced permeability, tailored biodegradability, optical clarity, self-passivation, electrical conductivity, electrostatic discharge, remoteactuated shape recovery, and flammability, oxidation, and ablation resistance.[2] Many references to this technology utilize the moniker nanocomposites', which invokes parallels to traditional fiber-reinforced composite technology and the ability to spatially engineer, design, and tailor' materials performance for a given application. However, development of chemical and processing procedures to disrupt the low-dimensional crystallites (tactoids and ropes) and achieve uniform distribution of the nanoelement (layered silicate and single wall carbon nanotube, respectively) is system specific and, in general, inadequate. Even less developed are approaches to provide spatial and orientational control of the hierarchical morphology with precision comparable to that conventionally obtained through fiber plies and weaving. Herein, we demonstrate the utility of AC electric fields to direct the morphology of polymer±inorganic nanocomposites, specifically epoxylayered silicate systems, through dielectrophoretic effects. [3] This provides an unprecedented ability to tailor physical properties of bulk nanocomposites such as modulus, thermal expansivity, and optical clarity and to develop detailed structure±property relationships through tuning of the nanoscale orientational distribution of nanoelements. Previous morphology±processing studies of polymer± layered silicate nanocomposites have focused on the influence of shear and elongational forces on nanoelement orientation. For example, Krishnamoorti and co-workers have extensively examined and correlated the impact of layered silicate dispersion on melt rheometry and relaxation dynamics.[4] In parallel, recent studies have indicated that shear-induced orientation of these semi-rigid plates, even in simple shear flows, is highly complex, potentially exhibiting tumbling and kayaking behavior reminiscent of the behavior of complex fluids such as liquid crystals and block copolymers. [5] This complexity restricts the general utility of shear forces for precision morphology to uniaxial in-plane alignment, for applications such as ultra-high barrier films. Optimization for other potential applications, such as dielectric under-fills for electro...

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Structural Studies of Extension-Induced Mesophase Formation in Poly(diethylsiloxane) Elastomers: In Situ Synchrotron WAXS and SAXS

Cited by 34 publications

References 19 publications

Influence of strain rate and temperature on necking transition in a polydomain smectic main chain elastomer

Influence of strain rate and temperature on necking transition in a polydomain smectic main chain elastomer

Impact of the diagnostic label of osteoarthritis on perceptions of disability and willingness to help a parent in African Americans and whites

Tuning Polymer Nanocomposite Morphology: AC Electric Field Manipulation of Epoxy–Montmorillonite (Clay) Suspensions

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