Applied Dielectric Spectroscopy of Polymeric Composites

Bánhegyi, György; Hedvig, P.; Petrovìć, Zoran S.; Karasz, Frank E.

doi:10.1080/03602559108020136

Cited by 19 publications

(13 citation statements)

References 81 publications

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“…The methods include dielectric spectroscopy, thermally stimulated currents, infrared spectroscopy, space charge measurement, and so on 7, 10–12. Dielectric spectroscopy, which is sensitive to a variety of relaxations, is a powerful experimental method for studying the dynamic behavior of polymer composites 13. Indeed, the spectra of nanocomposites have been studied by many researchers.…”

Section: Introductionmentioning

confidence: 99%

Sarcopenic obesity is more closely associated with knee osteoarthritis than is nonsarcopenic obesity: A cross‐sectional study

Lee

Kim

2012

Arthritis & Rheumatism

153

129

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Objective. Sarcopenic obesity is a body composition category in which obesity is accompanied by low skeletal muscle mass, offsetting the increase in body weight caused by increased adipose tissue. The purpose of this study was to analyze the association between knee osteoarthritis (OA) and 4 different categories of body composition: normal, sarcopenic nonobesity, nonsarcopenic obesity, and sarcopenic obesity.Methods. This was a cross-sectional study using the data from 2,893 participants in the Fifth Korean National Health and Nutrition Examination Survey. Radiographic knee OA was defined as a Kellgren/ Lawrence grade of >2. Appendicular skeletal muscle mass (ASM) and whole-body fat mass were measured using dual x-ray absorptiometry. Sarcopenia was defined as a skeletal muscle mass index (ASM/body weight [%]) below -2SD of the value in sex-matched young reference groups. Nonsarcopenic obesity was defined as a body mass index (BMI) >27.5 kg/m 2 .Results. The prevalence of each body composition category was as follows: 83.5% normal, 4.3% sarcopenic nonobesity, 9.2% nonsarcopenic obesity, and 3.0% sarcopenic obesity. Compared with nonsarcopenic obesity participants, participants with sarcopenic obesity were significantly older, had lower ASM, higher whole-body fat mass, and higher waist circumference. Conclusion. Sarcopenic obesity was more closely associated with knee OA than was nonsarcopenic obesity, although both groups had equivalent body weight. This finding supports the importance of the systemic metabolic effect of obesity in knee OA.Osteoarthritis (OA) is the most common articular disorder in the elderly, with ϳ40% of those over the age of 65 years affected at the knee joint (1). Although the exact pathophysiology of OA is unclear, the association between OA and obesity is well known (2-4). The biomechanical effect of increased body weight is one explanation for this association, especially in weightbearing joints such as the knee (5).The association between OA and obesity may be explained by factors other than biomechanical stress. Obesity is associated with OA not only in the weightbearing joints, but also in the joints of the hand (6), where mechanical load or factors such as grip strength (7) are unlikely to play an important role. Adipose tissue is an endocrine organ that secretes various adipokines (8). Data obtained in vitro have suggested a role of adipokines, including leptin, adiponectin, resistin, and visfatin, in the pathophysiology of OA (9). Recently, leptin, acting synergistically with other inflammatory cytokines, was shown to have a catabolic effect on articular cartilage metabolism via the up-regulation of proteolytic enzymes (10). In addition, extreme obesity induced in leptin (receptor)-deficient mice did not cause knee OA in the absence of leptin signaling (11).

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Section: Introductionmentioning

confidence: 99%

Sarcopenic obesity is more closely associated with knee osteoarthritis than is nonsarcopenic obesity: A cross‐sectional study

Lee

Kim

2012

Arthritis & Rheumatism

153

129

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“…Thus, the inability to characterize conductivity effects arising purely from the MWS effect implies that the two phases are closely associated because of strong interphase interactions. Bánhegyi et al65 reported an immiscible blend of 5% polyurethane in polypropylene and determined that mechanical interlocking occurred between phases; interfacial polarization in this heterogeneous system was undetectable. The MWS effect is often, but not always, observed in immiscible blends because its manifestation is dependent on both the material and morphology 50.…”

Section: Resultsmentioning

confidence: 99%

“…A detailed discussion of MWS behavior and equations used to model this interfacial polarization in blends with various morphologies and properties is given in van Beek 66. Theoretical and experimental discussions on the dielectric spectroscopy of heterogeneous composites are presented by Bánhegyi et al65…”

Section: Resultsmentioning

confidence: 99%

A Novel Genetic Selection System for Improved Enantioselectivity of Bacillus subtilis Lipase A

Boersma

Dröge²,

Sloot

et al. 2008

ChemBioChem

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In directed evolution experiments, success often depends on the efficacy of screening or selection methods. Genetic selections have proven to be extremely valuable for evolving enzymes with improved catalytic activity, improved stability, or with altered substrate specificity. In contrast, enantioselectivity is a difficult parameter to select for. In this study, we present a successful strategy that not only selects for catalytic activity, but for the first time also for enantioselectivity, as demonstrated by the selection of Bacillus subtilis lipase A variants with inverted and improved enantioselectivity. A lipase mutant library in an aspartate auxotroph Escherichia coli was plated on minimal medium that was supplemented with the aspartate ester of the desired enantiomer (S)-(+)-1,2-O-isopropylidene-sn-glycerol. To inhibit growth of less enantioselective variants, a covalently binding phosphonate ester of the opposite (R)-(-)-1,2-O-isopropylidene-sn-glycerol enantiomer was added as well. After three selection rounds in which the selection pressure was increased by raising the phosphonate ester concentration, a mutant was selected with an improved enantioselectivity increased from an ee of -29.6 % (conversion 23.4 %) to an ee of +73.1 % (conversion 28.9 %) towards the (S)-(+)-enantiomer. Interestingly, its amino acid sequence showed that the acid of the catalytic triad had migrated to a position further along the loop that connects beta7 and alphaE; this shows that the position of the catalytic acid is not necessarily conserved in this lipase.

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“…Thus, the inability to characterize conductivity effects arising purely from the MWS effect implies that the two phases are closely associated because of strong interphase interactions. Bá nhegyi et al 65 reported an immiscible blend of 5% polyurethane in polypropylene and determined that mechanical interlocking occurred between phases; interfacial polarization in this heterogeneous system was undetectable. The MWS effect is often, but not always, observed in immiscible blends because its manifestation is dependent on both the material and morphology.…”

Section: Deamentioning

confidence: 99%

“…50 A detailed discussion of MWS behavior and equations used to model this interfacial polarization in blends with various morphologies and properties is given in van Beek. 66 Theoretical and experimental discussions on the dielectric spectroscopy of heterogeneous composites are presented by Bá nhegyi et al 65 …”

Section: Deamentioning

confidence: 99%

Viscoelastic properties and phase behavior of 12‐tert‐butyl ester dendrimer/poly(methyl methacrylate) blends

Emran

Liu

Newkome

et al. 2001

J Polym Sci B Polym Phys

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This study used refractometry, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, and dielectric analysis to assess the viscoelastic properties and phase behavior of blends containing 0 -20% (w/w) 12-tert-butyl ester dendrimer in poly(methyl methacrylate) (PMMA). Dendritic blends were miscible up through 12%, exhibiting an intermediate glasstransition temperature (T g ; ␣) between those of the two pure components. Interactions of PMMA CAO groups and dendrimer NOH groups contributed to miscibility. T g decreased with increasing dendrimer content before phase separation. The dendrimer exhibited phase separation at 15%, as revealed by Rayleigh scattering in ultravioletvisible spectra and the emergence of a second T g in dielectric studies. Before phase separation, clear, secondary ␤ relaxations for PMMA were observed at low frequencies via dielectric analysis. Apparent activation energies were obtained through Arrhenius characterization. A merged ␣␤ process for PMMA occurred at higher frequencies and temperatures in the blends. Dielectric data for the phase-separated dendrimer relaxation (␣ D ) in the 20% blend conformed to Williams-Landel-Ferry behavior, which allowed the calculation of the apparent activation energy. The ␣ D relaxation data, analyzed both before and after treatment with the electric modulus, compared well with neat dendrimer data, which confirmed that this relaxation was due to an isolated dendrimer phase.

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Applied Dielectric Spectroscopy of Polymeric Composites

Cited by 19 publications

References 81 publications

Sarcopenic obesity is more closely associated with knee osteoarthritis than is nonsarcopenic obesity: A cross‐sectional study

Sarcopenic obesity is more closely associated with knee osteoarthritis than is nonsarcopenic obesity: A cross‐sectional study

A Novel Genetic Selection System for Improved Enantioselectivity of Bacillus subtilis Lipase A

Viscoelastic properties and phase behavior of 12‐tert‐butyl ester dendrimer/poly(methyl methacrylate) blends

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