Is the Reduction in Tracer Diffusivity under Nanoscopic Confinement Related to a Frustrated Segmental Mobility?

Limitations in fuel cell electrode performance have motivated the development of ion-conducting binders (ionomers) with high gas permeability. Such ionomers have been achieved by copolymerization of perfluorinated sulfonic acid (PFSA) monomers with bulky and asymmetric monomers, leading to a glassy ionomer matrix with chemical and mechanical properties that differ substantially from common PFSA ionomers (e.g., Nafion™). In this study, we use perfluorodioxolane-based ionomers to provide fundamental insights into the role of the matrix chemical structure on the dynamics of structural and transport processes in ion-conducting polymers. Through in-situ water uptake measurements, we demonstrate that ionomer water sorption kinetics depend strongly on the properties and mass fraction of the matrix. As the PFSA mass fraction was increased from 0.26 to 0.57, the Fickian swelling rate constant decreased from 0.8 s-1 to 0.2 s-1, while the relaxation rate constant increased from 3.1×10-3 s-1 to 4.0×10-3. The true swelling rate, in nm s-1, was determined by the chemical nature of the matrix; all dioxolane-containing materials exhibited swelling rates ~1.5 - 2 nm s-1 compared to ~3 nm s-1 for Nafion. Likewise, Nafion underwent relaxation at twice the rate of the fastest-relaxing dioxolane ionomer. Reduced swelling and relaxation kinetics are due to limited matrix segmental mobility of the dioxolane-containing ionomers. We demonstrate that changes in conductivity are strongly tied to the polymer relaxation, revealing the decoupled roles of initial swelling and relaxation on hydration, nanostructure, and ion transport in perfluorinated ionomers.

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Inter-examinerreliability study of physical examination procedures to assess the cervical spine

Chiropractic & Manual Therapies ◽

10.1186/s12998-021-00377-2 ◽

2021 ◽

Vol 29 (1) ◽

Author(s):

Karthik V. Hariharan ◽

Michael G. Timko ◽

Christopher G. Bise ◽

Meenakshi Sundaram ◽

Michael J. Schneider

Keyword(s):

Cervical Spine ◽

Physical Examination ◽

Facet Joint ◽

Physical Therapists ◽

Clinical Status ◽

Clinical Findings ◽

Qualitative Assessment ◽

Segmental Mobility ◽

Convenience Sample ◽

Pain Provocation

Abstract Objective The objective of this study was to establish the level of inter-examiner reliability for six common cervical manual and physical examination procedures used to assess the cervical spine. Materials: Reliability study that used a convenience sample of 51 patients between the ages of 16–70 years presenting with a chief complaint of neck pain. Two physical therapists independently performed the same series of cervical physical examination procedures on each of the participant. The clinicians were blinded to each other’s findings and the clinical status of the patient. Kappa coefficients (κ) were calculated for levels of agreement between the clinicians for each procedure. Results When assessing for asymmetrical motion, excellent levels of reliability (κ range: 0.88–0.96) were observed for the Bilateral Modified Lateral Shear (asymmetry criterion), Bilateral C2 Spinous Kick (asymmetry criterion) and Flexion-Rotation Tests. When pain provocation was used as the indicator of a positive test during palpation of the cervical facet joints, moderate to substantial levels of reliability (κ range: 0.53–0.76) were observed. When patients were instructed not to provide feedback to the clinicians about pain provocation during facet joint palpation and clinicians relied solely on their qualitative assessment of segmental mobility, the level of reliability was lower (κ range: 0.45–0.53). Due to 100 % prevalence of negative findings, Kappa values could not be calculated for the Sharp-Purser test or the Unilateral C2 Spinous Kick Test. Conclusions Most physical examination procedures examined in this study demonstrated moderate to excellent levels of inter-examiner reliability. Palpation for segmental mobility without pain provocation demonstrated a lower level of reliability compared to palpation for pain provocation. Correlation with clinical findings is necessary to establish validity and the applicability of these procedures in clinical practice.

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Tropism of Sub-Axial Cervical Facet Joints Is Not Related to Segmental Movement during Active Movement or Therapist-Perceived Symptomatic Locations

Symmetry ◽

10.3390/sym13050739 ◽

2021 ◽

Vol 13 (5) ◽

pp. 739

Author(s):

Neil Tuttle ◽

Kerrie Evans ◽

Clarice Sperotto dos Santos Rocha

Keyword(s):

Cervical Spine ◽

Neck Pain ◽

Active Movement ◽

Facet Joints ◽

Segmental Mobility ◽

Limited Mobility ◽

Translational Movement ◽

The Difference ◽

Cervical Facet ◽

The Relationship

Tropism, or asymmetry, of facet joints in the cervical spine has been found to be related to degenerative changes of the joints and discs. Clinicians often assume that differences in segmental mobility are related to tropism. The aims of this study were to determine the relationship between asymmetry of facet joints in the sub-axial cervical spine and (1) segmental mobility and (2) spinal levels perceived by therapists to have limited mobility. Eighteen participants with idiopathic neck pain had MRIs of their cervical spine in neutral and at the end of active rotation. Angular movement and translational movement of each motion segment was calculated from 3D segmentations of the vertebrae. A plane was fitted to the facet on each side. Tropism was considered to be the difference in the orientation of the facet planes and ranged from 1 to 30° with a median of 7.7°. No relationships were found between the extent of tropism and either segmental movement or locations deemed to be symptomatic. Tropism in the sub-axial cervical spine does not appear to be related to segmental mobility in rotation or to levels deemed to be symptomatic.

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Plasticizer effect on dielectric properties of poly(methyl methacrylate)/titanium dioxide composites

Polymers and Polymer Composites ◽

10.1177/09673911211014757 ◽

2021 ◽

pp. 096739112110147

Author(s):

Ufuk Abaci ◽

H Yuksel Guney ◽

Mesut Yilmazoglu

Keyword(s):

Dielectric Constant ◽

Titanium Dioxide ◽

Dielectric Properties ◽

Methyl Methacrylate ◽

Pure Pmma ◽

Segmental Mobility ◽

Scanning Calorimetry ◽

Poly Methyl Methacrylate ◽

Casting Technique ◽

Lcr Meter

The effect of plasticizer on dielectric properties of poly(methyl methacrylate) (PMMA)/titanium dioxide (TiO2) composites was investigated. Propylene carbonate (PC) was used as plasticizer in the samples which were prepared with the conventional solvent casting technique. Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis (SEM-EDX) and Differential scanning calorimetry (DSC) analyses and LCR Meter measurements (performed between 300 K and 400 K), were conducted to examine the properties of the composites. With the addition of plasticizer, the thermal properties have changed and the dielectric constant of the composite has increased significantly. The glass transition temperature of pure PMMA measured 121.7°C and this value did not change significantly with the addition of TiO2, however, 112°C was measured in the sample with the addition 4 ml of PC. While the dielectric constant of pure PMMA was 3.64, the ε′ value increased to 5.66 with the addition of TiO2 and reached 12.6 with the addition of 4 ml PC. These changes have been attributed to increase in amorphous ratio that facilitates polymer dipolar and segmental mobility.

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Tracer diffusivity of Si31 in CaO-SiO2 melts at 1600°C

Metallurgical Transactions B ◽

10.1007/bf02662556 ◽

1979 ◽

Vol 10 (4) ◽

pp. 551-554 ◽

Cited By ~ 29

Author(s):

Helmut Keller ◽

Klaus Schwerdtfeger

Keyword(s):

Tracer Diffusivity

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Effect of Temperature on Ozone Cracking of Rubbers

Rubber Chemistry and Technology ◽

10.5254/1.3544871 ◽

1966 ◽

Vol 39 (3) ◽

pp. 643-650

Author(s):

A. N. Gent ◽

J. E. McGrath

Keyword(s):

Polymer Chains ◽

Effect Of Temperature ◽

Ozone Molecule ◽

Segmental Mobility ◽

Network Chain ◽

Styrene Copolymers ◽

Rates Of Growth ◽

Rate Controlling Step ◽

Limiting Value ◽

Butadiene Styrene

Abstract The rates of growth of single ozone cracks have been measured for vulcanizates of a series of butadiene—styrene copolymers, over a temperature range from − 5° C to 95° C. The rates appear to be determined by two mechanisms. At low temperatures, near the glass transition temperature, they are quantitatively related to the segmental mobility of the polymer. The principal rate-controlling step in this case is concluded to be movement of the polymer chains after scission to yield new surface. At high temperatures the rate approaches a limiting value of 10−3 cm/sec/mg of ozone/1. This is about 1/1000 of the maximum possible value when instantaneous reaction of one incident ozone molecule causes scission of one network chain.

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