Gas transport through nano and micro composites of natural rubber (NR) and their blends with carboxylated styrene butadiene rubber (XSBR) latex membranes

Stephen, Ranimol; Ranganathaiah, C.; Varghese, Siby; Joseph, Kuruvilla; Thomas, Sabu

doi:10.1016/j.polymer.2005.12.020

Cited by 113 publications

(51 citation statements)

References 53 publications

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“…20.72 has been verified for various glassy polymers [38,41,54] [60]. In polymer nanocomposite systems, there is an additional feature that strongly affects the gas diffusion process: the tortuosity.…”

Section: Diffusion and Free Volumementioning

confidence: 90%

Recent Developments in the Permeability of Polymer Clay Nanocomposites

Choudalakis

Gotsis

2013

Handbook of Polymernanocomposites. Processing, Performance and Application

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Section: Diffusion and Free Volumementioning

confidence: 90%

Recent Developments in the Permeability of Polymer Clay Nanocomposites

Choudalakis

Gotsis

2013

Handbook of Polymernanocomposites. Processing, Performance and Application

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“…However, several PALS studies have reached the opposite conclusion: that the free volume of a polymer matrix decreases when filler particles are added. Thus, Stephen et al [2006] investigated gas transport and free volume in nano and micro composites of natural rubber (NR), carboxylated styrene-butadiene rubber (XSBR), and 70 : 30 NR/XSBR rubber blend membranes, containing 2-phr fillers. The unmodified layered silicates sodium bentonite and sodium fluorohectorite were used as nanofillers, and the conventional microfillers were unmodified clay and silica.…”

Section: Pals As a Probe For Free Volume In Nanocompositesmentioning

confidence: 99%

Positron Annihilation Lifetime Studies of Free Volume in Heterogeneous Polymer Systems

2010

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474 POSITRON ANNIHILATION LIFETIME STUDIES INTRODUCTIONThe theoretical and experimental background related to the positron annihilation lifetime spectroscopy (PALS) technique and its application as a quantitative probe for free volume in polymeric materials have been discussed extensively in Chapters 10 and 11, so we limit ourselves to a brief overview of these issues by way of introduction and commentary. Our principal focus here is to review what evidence has been generated using the PALS technique to provide insight into three topics of current interest, each of which involves probing specific heterogeneities in the amorphous polymeric phase. The first relates to the existence of concentration fluctuations in miscible polymer blends and their effect on materials properties, such as broadening of the glass transition region. The second concerns the fact that to interpret accurately the properties of certain semicrystalline polymers, such as gas transport, it is necessary to invoke a rigid amorphous phase, believed to involve the disordered chain segments that link crystalline lamellae, whose behavior differs from the usual (mobile) amorphous phase that exists far from the crystalline surface. The third topic involves evidence that a similarly rigid amorphous phase exists in polymeric nanocomposites, associated with polymer chains that lie near the surface of the inorganic particles. PALS AS A PROBE FOR FREE VOLUME IN POLYMERSA PALS experiment involves bringing a polymer sample into contact with a source of positrons, typically 22 Na. Energetic positrons emitted into the polymer by the source are slowed through collisions with atoms, creating an ionized radiation track (positron spur). In the last portion of the spur, referred to as the blob, the positron thermalizes, and either annihilates or finds a secondary electron created by the ionization to form a localized positronium atom Byakov, 2003, 2007;Stepanov et al., 2005a Stepanov et al., ,b, 2007. The spin 1 atom, called ortho-positronium (o-Ps), is three times more likely to form than is the spin 0 atom [para-positronium (p-Ps)] and is more stable than the latter, which annihilates within 125 ps. o-Ps has a long lifetime (140 ns in vacuum), which lifetime is determined by interactions with the medium. Typically, o-Ps annihilates via a pickoff mechanism, with the positron "picked off" by an electron of the medium that has opposite spin. Since o-Ps is easily polarizable, and therefore strongly repelled by the medium, it tends to localize in regions of low electron density (holes or free volume). The lifetime of o-Ps is then determined by the electron density and physical size of the hole in which it finds itself, and normally falls in the range of a few nanoseconds.Typically, therefore, a PALS spectrum consists of a minimum of three components: the short-lived p-Ps component with intensity I 1 and lifetime τ 1 = 125 ps; a free positron annihilation component, with intensity I 2 and lifetime τ 2 ; and the o-Ps component, with intensity I 3 and lifetime τ 3 . ...

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“…Fluorohectorite revealed a better swelling ability than bentonite and thus gave a more exfoliated structure [45].…”

Section: Emulsion Blending From a Pristine Claymentioning

confidence: 99%