O. V. Arzhakova

Oxygen-Sensitive Phosphorescent Nanomaterials Produced from High-Density Polyethylene Films by Local Solvent-Crazing

Discrete solid-state phosphorescent oxygen sensors produced by local solvent-crazing of high density polyethylene films are described. The simple spotting of dye solution followed by tensile drawing of the polymer substrate provides uniform nanostructures with good spatial control, effective encapsulation of dye molecules, and quenchability by O2. The dye-polymer composite sensors prepared using toluene as a solvent and stabilized by annealing at high temperature, show moderate optical signals, near-optimal sensitivity to O2 (RSD at 21 KPa 1.9%), and reproducible phosphorescence lifetime readings. Calibration experiments performed over 0-25 kPa O2 and 10-30 °C temperatures ranges reveal linear Stern-Volmer plots and temperature dependences and minimal effect of humidity on sensor calibration. The high degree of lateral and in-depth homogeneity of these O2-sensitive materials was confirmed by high-resolution atomic force and wide-field optical microscopy, including 2D and 3D phosphorescence lifetime imaging.

STRUCTURE OF POLYMER BLENDS BASED ON SOLVENT-CRAZED POLYMERS

Abstract Blends based on polymers (PET, HDPE) prepared by deformation via the mechanism of classical and delocalized solvent crazing are described. The second component of polymer blends may be represented by various polymers such as PMMA, PS, PBMA, PEG, polyaniline, etc. The above polymers are characterized by a high level of mutual dispersion of components. Structure and mechanical properties of the blends are studied.

Phosphorescent oxygen sensors produced by spot- crazing of polyphenylenesulfide films

Phosphorescent oxygen sensors based on PtBP and PdBP dyes encapsulated in polyphenylenesulfide (PPS) films by the spot-crazing method are described. The new polymer matrix enables simple, one-step production of discrete, high-performance O2 sensors using a low toxicity solvent 2-butanone, low overall strain (8%), low amounts of solvent and precise spatial control. The resulting nano-structured sensor materials display markedly enhanced brightness, high photo-, mechanical and chemical stability. Their structural and physico-chemical properties were characterized by differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), optical microscopy and phosphorescence lifetime imaging microscopy (PLIM). The PPS sensors show a high degree of lateral and in-depth homogeneity on the micro- and macro-scale, as revealed by confocal microscopy, linear Stern–Volmer plots and single-exponential decays. Operating in phosphorescence lifetime mode, optimised sensors show stable O2 calibrations in the range of 0.1–100 kPa O2, low temperature dependence (linear in the range 10–50 °C), low cross-sensitivity to humidity and high reproducibility (RSD 1.5% at 21 kPa and 0.5% at zero O2). This technology facilitates the production of low-cost disposable O2 sensors and their integration in large scale industrial applications such as packaging.

Preparation method for noble metal-polymer matrix nanocomposites

A method is described for the preparation of new nanocomposites based on poly(ethylene terephthalate), poly(vinyl chloride), and polypropylene on the one hand and on noble metals (Ag and Pt) on the other. The method comprises the formation of nanoporous polymer matrices by crazing the polymers with simultaneous incorporation of noble metal precursors (AgNO3 or H2PtCl6) into the matrices. Subsequent in situ reduction of the precursors yields the metal-polymer nanocomposites. Prospects for the practical application of the developed method for the production of metal-polymer nanocomposites are discussed.

Development of a stable open-porous structure in the solvent-crazed high-density polyethylene

It is demonstrated that the tensile drawing of high-density polyethylene (HDPE) films in the presence of physically active media via the mechanism of delocalized crazing results in the development of an open-porous structure in the polymer. Depending on tensile strain, overall volume porosity can reach ∼55%. Here, the parameters of the porous structure (pore and fibril diameters) are in the nanometer range. It is also demonstrated that the nanoporous structure with a highly developed surface formed via delocalized crazing is thermodynamically unstable and the related relaxation processes result in the reduction or complete elimination of porosity. Efficient ways of stabilization and preservation of open porosity and parameters of the porous structure of deformed samples of polyethylene are related to complete removal of the liquid medium from the polymer samples and annealing. This approach makes it possible to obtain open-porous materials based on polyolefins with stable characteristics, which is of a significant practical interest.

DSC and X-ray study of structure and phase transitions of low molecular compounds incorporated into crazes

Orientation, phase composition and phase transitions of a series of long chain low molecular weight compounds (LMC), such as heneicosane, cetyl alcohol, normal fatty acids, introduced into porous structure (crazes) of polymeric matrices oriented in liquid medium have been studied by means of DSC and SAXS techniques. Different types of LMC crystallites orientation in crazes of polymeric matrices have been observed. LMC phase state in crazes is shown to be characterized by higher stability of high-temperature polymer midifications. LMC melting temperature in crazes usually decreases as well as melting enthalpy (heat) and entropy. The origin of LMC properties changes observed is high dispersity (40–100nm) of LMC particles in crazes resulting in a marked growth of polymer/LMC interface influence on principal thermodynamic parameters of the systems studied.ZusammenfassungMittels DSC- uns SAXS-Techniken wurden die Orientierung, Phasenzusammensetzung und Phasenumwandlungen einer Reihe von langkettigen niedermolekularen Verbindungen (LMC) wie z.B. Heneikosan, Zetylalkohol und normalen Fettsäuren untersucht, die in porösen Strukturen (Haarrissen) von in flüssigem Medium ausgerichteten polymeren Matrizen eingebracht wurden. Es konnten verschiedene LMC-Kristallit-TVpen in Haarrissen von polymeren Matrizen beobachtet werden. Es wurde gezeigt, daß der LMC-Phasenzustand in Haarrissen durch eine höhere Stabilität der Hochtemperatur-Polymermodifikationen charakterisiert ist. Die LMC Schmelztemperatur in Haarrissen nimmt im allgemeinen ab, genauso wie die Schmelzenthalpie (Wärme) und die Entropie. Der Grund für die beobachteten Veränderungen der LMC-Eigenschaften liegt in der großen Dispersität (40–100 nm) der LMC-Partikel in den Haarrissen, woraus sich ein sichtbarer Anstieg der Polymer/LMC Grenzflächeneinwirkung auf die grundlegenden thermodynamischen Parameter des untersuchten Systemes ergibt.

Oligomer-polymer blends based on solvent-crazed polymers

The feasibility of preparation of oligomer-polymer blends by means of the solvent crazing technique is considered. An analysis of the mechanical behavior of polymers and porosity of deformed films led to the conclusion that polyethylene glycol and polypropylene glycol in their liquid state are adsorption-active environments effective toward PET and HDPE. The stretching of PET and HDPE in these environments follows the mechanisms of classical and delocalized solvent crazing, respectively. The blends based on PET and HDPE containing polyethylene glycol 400, polypropylene glycol 400, and polypropylene glycol 3000 with an amount of the hydrophilic component of 25–45% were prepared. Most blends retained their stability with time. The exception is the PET-PEG 400 blend, which exhibited a sustained release of the liquid component.

The effect of preliminary orientation of polymers via tensile drawing at elevated temperature on solvent crazing

We studied how the preliminary orientation of an amorphous glassy PET via its uniaxial tensile drawing above the glass transition temperature affects the deformation behavior during subsequent tensile drawing in the presence of adsorptionally active environments. The tensile drawing of the preoriented PET samples with a low degree of preliminary orientation (below 100%) in the presence of liquid environments proceeds via the mechanism of solvent crazing; however, when a certain critical tensile strain is achieved (150% for PET), the ability of oriented samples to experience crazing appears to be totally suppressed. When the tensile drawing of preoriented samples is performed at a constant strain rate, the craze density in the sample increases with increasing degree of preliminary orientation; however when the test samples are stretched under creep conditions, the craze density markedly decreases. This behavior can be explained by a partial healing and smoothening of surface defects during preliminary orientation and by the effect of entanglement network. The preliminary orientation of polymers provides an efficient means for control over the craze density and the volume fraction of fibrillar polymer material in crazes.

Crazing of Polymers in a Supercritical Carbon Dioxide Fluid

ISSN 00125008, Doklady Chemistry, 2009, Vol. 428, Pa rt 2, pp. 238–241.

Phosphorescent Oxygen and Mechanosensitive Nanostructured Materials Based on Hard Elastic Polypropylene Films

It is well known that sensitivity of quenched-phosphorescence O2 sensors can be tuned by changing the nature of indicator dye and host polymer acting as encapsulation and quenching mediums. Here, we describe a new type of sensor materials based on nanostructured hard elastic polymeric substrates. With the example of hard elastic polypropylene films impregnated with Pt-benzoporphyrin dye, we show that such substrates enable simple one-step fabrication of O2 sensors by standard and scalable polymer processing technologies. In addition, the resulting sensor materials show prominent response to tensile drawing via changes in phosphorescence intensity and lifetime and O2 quenching constant, Kq. The mechanosensitive response shows reversibility and hysteresis, which are related to macroscopic changes in the nanoporous structure of the polymer. Such multifunctional materials can find use as mechanically tunable O2 sensors, as well as strain/deformation sensors operating in a phosphorescence-lifetime-based detection mode.