Petar R. Dvornic

The thermogravimetric analysis of some polysiloxanes

Thermogravimetric (TG) and differential thermogravimetric analyses (DTG) of some homo- and copolymers of dimethylsiloxane have been performed. The effect of the presence of hydrido-substituents and/or vinyl end-groups on the thermal and thermo-oxidative stability of the examined polysiloxanes was determined. In all cases it was found that these polysiloxanes are thermally less stable than the parent all-methyl polysiloxane.

Recent advances in dendritic polymers

Interest in dendritic polymers has increased nearly exponentially in the past few years. Dendritic polymers are now recognized as a fourth major class of macromolecular architecture. New applications, based on these structure-controlled architectures, have made this area the object of wide interdisciplinary interest. Recent advances in organometallic constructs, dendritic processes, catalysis, electron conduction, gene vectoring and guest—host chemistry have kindled activities in such diverse areas as material, interfacial, supramolecular and life sciences.

Thermal Properties of Polysiloxanes

Thermal properties are among the most characteristic and at the same time the most technologically important properties of polysiloxanes. They embrace a unique combination of pronounced elasticity at unusually low temperatures and high thermal and thermo-oxidative stability at elevated temperatures. These properties are characteristic of polysiloxanes because they directly originate from a specific interplay of some of the most fundamental features inherent to the basic structural building blocks that make up their repeat units, chain segments and entire macromolecules. They are therefore found in more or less all members of this family of polymers. At the same time they are also of outstanding technological importance because not only that they clearly distinguish these unique polymers from their purely organic, -C-C- type counterparts, but they often make polysiloxanes the materials of choice for many applications where performance under extreme service conditions is required and where no other polymer can successfully satisfy the purpose.

Highly stable hollow bifunctional cobalt sulfides for flexible supercapacitors and hydrogen evolution

Hollow structures of NiAs-type cobalt sulfide have been synthesized by a facile hydrothermal method. These hollow structured cobalt sulfides exhibit excellent electrochemical properties for supercapacitor applications (867 F g−1) and respectable hydrogen evolution activity. The symmetrical supercapacitor device fabricated using cobalt sulfide nanostructures showed an areal capacitance of 260 mF cm−2 with good flexibility and high temperature stability. The specific capacitance of the supercapacitor is enhanced over 150%, when the temperature is increased from 10 to 70 °C.

High Per formance and Flexible Supercapacitors based on Carbonized Bamboo Fibers for Wide Temperature Applications

High performance carbonized bamboo fibers were synthesized for a wide range of temperature dependent energy storage applications. The structural and electrochemical properties of the carbonized bamboo fibers were studied for flexible supercapacitor applications. The galvanostatic charge-discharge studies on carbonized fibers exhibited specific capacity of ~510F/g at 0.4 A/g with energy density of 54 Wh/kg. Interestingly, the carbonized bamboo fibers displayed excellent charge storage stability without any appreciable degradation in charge storage capacity over 5,000 charge-discharge cycles. The symmetrical supercapacitor device fabricated using these carbonized bamboo fibers exhibited an areal capacitance of ~1.55 F/cm2 at room temperature. In addition to high charge storage capacity and cyclic stability, the device showed excellent flexibility without any degradation to charge storage capacity on bending the electrode. The performance of the supercapacitor device exhibited ~65% improvement at 70 °C compare to that at 10 °C. Our studies suggest that carbonized bamboo fibers are promising candidates for stable, high performance and flexible supercapacitor devices.

High-Performance Flexible Supercapacitors obtained via Recycled Jute: Bio-Waste to Energy Storage Approach

In search of affordable, flexible, lightweight, efficient and stable supercapacitors, metal oxides have been shown to provide high charge storage capacity but with poor cyclic stability due to structural damage occurring during the redox process. Here, we develop an efficient flexible supercapacitor obtained by carbonizing abundantly available and recyclable jute. The active material was synthesized from jute by a facile hydrothermal method and its electrochemical performance was further enhanced by chemical activation. Specific capacitance of 408 F/g at 1 mV/s using CV and 185 F/g at 500 mA/g using charge-discharge measurements with excellent flexibility (~100% retention in charge storage capacity on bending) were observed. The cyclic stability test confirmed no loss in the charge storage capacity of the electrode even after 5,000 charge-discharge measurements. In addition, a supercapacitor device fabricated using this carbonized jute showed promising specific capacitance of about 51 F/g, and improvement of over 60% in the charge storage capacity on increasing temperature from 5 to 75 °C. Based on these results, we propose that recycled jute should be considered for fabrication of high-performance flexible energy storage devices at extremely low cost.

Degradative side reactions in the syntheses of exactly alternating silarylene-siloxane polymers

SummaryFour principal synthetic methods for preparation of exactly alternating silarylene-siloxane polymers: the chlorosilane, the acetoxysilane, the aminosilane and the ureidosilane polymerization reactions, were compared under equivalent experimental conditions. As indicated earlier, polymers with considerably different molecular weights were obtained. The highest molecular weight polymer resulted from the ureidosilane reaction, while the lowest ones were obtained from the chlorosilane and the acetoxysilane routes. Because thorough precautions were taken to ensure equally favorable conditions in all preparations, these results seem to support a hypothesis that the latter two reactions are limited by the occurrence of degradative desilytation side reactions which are inherent to the nature of these polymerization systems.

Colorimetric Biosensors Based on Polydiacetylene (PDA) and Polyamidoamine (PAMAM) Dendrimers

Abstract Biosensing techniques are crucially important in a wide variety of applications from the detection of biological warfare agents to analysis for pesticide residues in crops or determination of freshness of food products. The intense search for better and more accurate biosensors has recently drawn attention to polyamidoamine (PAMAM) dendrimers. The unique properties of globular PAMAM dendrimers, with large numbers of exo-presented functional end-groups, provide a very promising platform for biological sensor elements. Polydiacetylene (PDA), on the other hand, is a macromolecule that exhibits a colorimetric response to a variety of stimuli, and is therefore a strong candidate for sensor elements. Consequently, an ensemble of PAMAM dendrimers and PDA segments provides for a novel type of molecular biosensor, which is expected to have highly pronounced sensitivity and widely applicable versatility. In this article, an overview of recent experimental work and progress achieved on biosensors from PAMAM...

Nanostructured Materials from Radially Layered Copolymeric Amidoamine-Organosilicon (PAMAMOS) Dendrimers

Abstract Radially layered copolymeric poly(amidoamine-organosilicon) (PAMAMOS) dendrimers have been prepared with hydrophilic polyamidoamine (PAMAM) interiors and hydrophobic organosilicon (OS) exteriors. At low degrees of surface derivitization with trimethylsilyl-groups these dendrimers significantly reduce water surface tension. At higher degrees they become insoluble and form spread monolayers on water which on compression can sustain surface pressures of over 50 mN/m due to the strong attraction of the PAMAM core to the water surface. When reactive organosilicon terminating units such as methoxysilyl- groups are incorporated, the copolydendrimers can be crosslinked into networks. These new elastomeric or plastomeric dendritic materials have well-defined, nanoscopic domains with the ability to complex and encapsulate within the PAMAM domains, a wide variety of metal compounds and metal atoms.

General Introduction to Silicone Surfaces

Silicones, particularly polydimethylsiloxane (PDMS), are widely exploited for their surface properties. A quantitative review of relevant properties is presented including liquid surface tension measurements, water contact angle studies and solid surface tension determinations from both contact angle and contact mechanics approaches. The properties are considered in the light of the fundamental characteristics of PDMS and related siloxane polymers in order to establish a structure/property relationship of importance in any examination of the surface science of this family of polymers. The central position of PDMS in silicone science and industry follows inevitably from its structure. The combination of small, low-intermolecular-force methyl groups arrayed along the uniquely flexible siloxane backbone produces a polymer whose low surface energy can be equaled or bettered by relatively few other polymers. There is also the additional benefit of greater thermal and oxidative stability than most comparable organic polymers that is important in many applications.