Structure-Gas Transport Property Relationships of Poly(dimethylsiloxane-urethane) Nanocomposite Membranes

Reddy, Boreddy S. R.; Gnanasekar, D.

doi:10.5772/14718

Cited by 3 publications

(3 citation statements)

References 28 publications

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“…This behavior is likely associated with the existence of two types of charged species in doped PANI: (1) polaron/bipolaron systems that are mobile along the chain and 2) other bound charge distributions (e.g., dipoles) with restricted mobility accounting for strong polarization in the system. , When the frequency of the applied field is increased, the dipoles cannot reorient as rapidly as the applied electric field. This decreases the dielectric constant and increases the number of mobile charges, which results in higher dielectric loss (ε″), whereas the real part (ε′) decreases. ,, The product of angular frequency (ω) and dielectric loss is equivalent to the dielectric conductivity (σ ac , microwave ac conductivity) as follows , σ ac ( ω ) = ω ε ″ = ω ε normalo ε ″ normalr = 2 π f ε normalo ε ″ normalr where ε ο is the free space permittivity, ε r ″ is relative dielectric loss of the medium, and f is the frequency. Higher dielectric loss leads to increasing microwave ac conductivity and the effective conductivity of the medium: − σ e (ω) = σ dc (ω) + σ ac (ω).…”

Section: Resultsmentioning

confidence: 99%

“…To investigate the contributions of absorption and reflection to the total EMI SE, the transmittance ( T coef ), reflectance ( R coef ), and absorbance ( A coef ) coefficients can be correlated to S parameters as follows T coef = false[ E normalT / E normali false] 2 = S 12 2 = S 21 2 R coef = false[ E normalR / E normali false] 2 = S 11 2 = S 22 2 A coef = 1 − T coef − R coef Here, the term A coef is given with respect to the power of the incident EM wave. If the effect of multiple reflections between both interfaces of the material is negligible, the relative intensity of the effectively incident EM wave inside the shielding layer after reflection is based on the value of (1 – R coef ). Therefore, the effective absorbance can be described as follows A eff = 1 − T coef − R coef 1 − R coef ...…”

Section: Theory Of Electromagnetic Interference Shieldingmentioning

confidence: 99%

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Comparison of Electromagnetic Shielding with Polyaniline Nanopowders Produced in Solvent-Limited Conditions

Tantawy

Aston

Smith

et al. 2013

ACS Appl. Mater. Interfaces

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Nanoparticle synthesis (~10-50 nm) of HCl-doped polyaniline elucidates the impact of limiting solvent (water) and oxidizing agent (ammonium peroxydisulfate) on morphology (XRD and TEM), chemical structure (FTIR), conductivity (two-point DC) and electromagnetic shielding effectiveness (SE) in microwave frequencies (i.e., X-band S-parameter measurements). Detailed comparison of these properties with respect to three distinct polymerization environments indicate that a solvent-free or limited solvent polymerization accomplished through a wet grinding solid-phase reaction produces superior conductivity (27 S/cm) with intermediate crystallinity (66%) for the highest EM shielding-an order of magnitude improvement over conventional polymerization with respect to EM power transmission reduction for all loadings per shielding area (0.04 to 0.17 g/cm(2)). By contrast, the classic oxidation of aniline in a well-dispersed aqueous reaction phase with an abundance of available oxidant in free solution yielded low conductivity (3.3 S/cm), crystallinity (54%), and SE, whereas similar solvent-rich reactions with limiting oxidizer produced similar conductivity (2.9 S/cm) and significantly lower SE with the highest crystallinity (72%). This work is the first to demonstrate that limiting solvent and oxidizer enhances electromagnetic interactions for shielding microwaves in polyaniline nanopowders. This appears connected to having the highest overall extent of oxidation achieved in the wet solid-phase reaction.

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Section: Resultsmentioning

confidence: 99%

Section: Theory Of Electromagnetic Interference Shieldingmentioning

confidence: 99%

Comparison of Electromagnetic Shielding with Polyaniline Nanopowders Produced in Solvent-Limited Conditions

Tantawy

Aston

Smith

et al. 2013

ACS Appl. Mater. Interfaces

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“…These POSS are commonly referred to as T 8 R 8 since, in the nomenclature used for siloxane polymers, T denotes a silicon atom bonded to three oxygen atoms, in turn connected to other silicons, and the fourth bond is with the pendant R group of the relatively rigid eight-corner Si 8 O 12 cage. Their versatility has led to several hundred different T 8 R 8 compounds being prepared. ,, They can be included as components in polymer blends to improve tensile properties, impact strengths, heat stabilities, gas barrier properties, and rheological properties …”

Section: Introductionmentioning

confidence: 99%

The Stability of Amino-Functionalized Polyhedral Oligomeric Silsesquioxanes in Water

et al. 2015

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Octa(aminopropylsilsesquioxane) Si8O12[(CH2)3NH2]8 is a very important precursor for many other hybrid organic/inorganic polyhedral oligomeric silsesquioxanes (POSS) because of the reactivity of its primary amine groups. Unfortunately, it is unstable in water, which can lead to the cleavage of its siloxane cage. In the present work, such a degradation was confirmed using solid-state (29)Si NMR spectroscopy, and the molecular features at the basis of this instability were studied using molecular dynamics simulations (MD). It was also investigated whether replacing the primary amine end groups by secondary amines or by amides with long aliphatic chains could lead to an improvement in the water stability of the Si/O framework. In the pure bulk models, all POSS interdigitate with their pendant organic arms intertwined. Upon insertion of isolated molecules into water, the dimensions of the primary amine POSS remain close to those of the bulk, while the secondary amine and the amide POSS favor conformations that optimize the intramolecular chain-chain interactions. When there are several POSS molecules in water, they cluster with each other through both intra- and intermolecular chain-chain interactions. This tendency for the organic chains to intertwine whenever possible provides some protection to the siloxane cages from water, but also leaves some of the siloxane O exposed. As such, the latter are accessible to form transient hydrogen bonds with the water molecules, which could be a precursor step to hydrolysis and thus cage breakage. In the molecular models, a better protection was obtained in the amide POSS for two reasons: its chains tended to wrap efficiently around its cage, and its ketone O kept water from getting close to the siloxanes. The molecular modeling characterizations were found to agree very well with experimental evidence.

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Identifying the meta, para and ortho isomers in octa(aminophenyl)silsesquioxane (OAPS) from joint experimental characterizations and theoretical predictions of the IR and NMR spectra

Salimi

Radmanesh

Benes

et al. 2022

Journal of Molecular Structure

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Structure-Gas Transport Property Relationships of Poly(dimethylsiloxane-urethane) Nanocomposite Membranes

Cited by 3 publications

References 28 publications

Comparison of Electromagnetic Shielding with Polyaniline Nanopowders Produced in Solvent-Limited Conditions

Comparison of Electromagnetic Shielding with Polyaniline Nanopowders Produced in Solvent-Limited Conditions

The Stability of Amino-Functionalized Polyhedral Oligomeric Silsesquioxanes in Water

Identifying the meta, para and ortho isomers in octa(aminophenyl)silsesquioxane (OAPS) from joint experimental characterizations and theoretical predictions of the IR and NMR spectra

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