Interaction of pulsed laser radiation with a polycarbonate-based composite

Abstract—The interaction of pulsed laser radiation with foil-clad polycarbonate containing diffraction gratings is studied. It is found that the laser beam reflected from diffraction gratings is selffocused in polycarbonate bulk and becomes a seed for changing the polycarbonate structure, which leads to the glass transition and growth of ordered structures with symmetry features, which gives rise to the light dispersion effect in composites. A probable formation mechanism of ordered structures in polycarbonate during irradiation is proposed.     

The effect of supercritical carbon dioxide on secondary relaxation transitions in polysulfone and polycarbonate: The method of conformational probes

The method of FT-IR spectroscopy of conformational probes was used to study the local molecular mobility of polysulfone and polycarbonate before and after treatment by supercritical carbon dioxide. The temperature and the nature of secondary relaxation transitions have been determined. The influence of the supercritical fluid treatment on the temperature of secondary relaxation transitions and the enthalpy differences of the conformations of the probes has been analyzed.     

Iodine swelling of polyacrylonitrile I. Effect of orientation and evidence for a three-phase structure

The swelling of polyacrylonitrile (PAN) film in aqueous I₂/KI (or I₃ ^?) solutions of different concentrations up to 2.0 molal has been investigated, using both biaxially oriented and unoriented film. The absorption curve (equilibrium absorption vs concentration) for oriented film shows three distinct steps, at concentrations of 0.25, 0.65, and 1.6 molal, leading to weight increases of the sample of approximately 250%, 2000%, and 3200%, respectively. In unoriented film, smooth progressive increases of absorption are observed in place of the first and third steps; only the second abrupt step remains. A significant difference in desorption behavior is seen in extraction experiments carried out above and below the second step. It is hypothesized that the first and third steps of swelling correspond to the penetration of two different “amorphous” phases in the polymer, which together with a crystalline phase would indicate a three-phase structure for PAN. The second step of swelling may represent a conformational transition of the molecules in the phase penetrated in the first step. The effects of iodine swelling and extraction on the dynamic mechanical spectrum of PAN were also investigated, and it seems possible to associate the swelling in the region of the first and third steps with the two peaks (or transitions) in the tan δ curve of PAN, which might be regarded as glass transitions of the two amorphous phases. An unusual behavior of sample length vs temperature was observed during the dynamic mechanical measurements in the temperature region of these two transitions. Stress-strain curves were also measured on samples containing different amounts of absorbed iodine.     

Multilayer polymeric mode and polarization filters for integrated optics

We demonstrate theoretically as well as experimentally that a four-layer polymeric waveguide structure can be used to produce a mode and a polarization filter. Various optical properties such as refractive index, birefringence and propagation constant of polycarbonate, polystyrene and a commercially available photoresist (from Shipley) are presented. The thin film structures consisting of glass/polycarbonate/polystyrene/air are used for demonstrating polarization filter action and glass/photoresist/polystyrene/air structure for mode filter. Expressions for the electric field intensity spatial distribution for the structure are used to calculate the intensity profiles to support the observed behavior. The experimental values were in good agreement with the one obtained theoretically.     

Glass transitions in quasi-two-dimensional suspensions of colloidal ellipsoids

We observed a two-step glass transition in monolayers of colloidal ellipsoids by video microscopy. The glass transition in the rotational degree of freedom was at a lower density than that in the translational degree of freedom. Between the two transitions, ellipsoids formed an orientational glass. Approaching the respective glass transitions, the rotational and translational fastest-moving particles in the supercooled liquid moved cooperatively and formed clusters with power-law size distributions. The mean cluster sizes diverge in power law as they approach the glass transitions. The clusters of translational and rotational fastest-moving ellipsoids formed mainly within pseudonematic domains and around the domain boundaries, respectively.     

Study of secondary relaxation transitions in polysulfone and polycarbonate by a method of conformational probes

The local molecular mobility of polysulfone and polycarbonate was studied using a method of conformational probes. Freezing temperatures of conformational equilibria of probe molecules in these polymers were determined using FTIR spectroscopy. The obtained temperatures of relaxation transitions were assigned to the types of conformational mobility of benzene rings of the main polymer chain.     

Evaluation of polycarbonate substrate hologram recording medium regarding implication of birefringence and thermal expansion

In this paper, we evaluate photopolymer media using a polycarbonate (PC) substrate. In holographic data storage medium, substrates that sandwich the photopolymer material are needed to protect the photopolymer material against exogenous shock and open air. An optical glass such as BK-7 is normally used as a substrate, but a PC substrate has a cost advantage and is easy to fabricate compared with optical glass. For holographic recording and reading, however, the high birefringence and high thermal expansion of a PC substrate are significant problems. First, we analyze the degree of degradation of output power by the polarization change and estimate the threshold value of birefringence to record hologram normally. Next, we estimate the temperature tolerance of hologram readout with polycarbonate substrate hologram medium. These analyses results indicate the possible usage of the PC substrate as holographic recording media.     

Four layer polymeric mode polarization filter for integrated optics

We report on our systematic study of fabrication and characterization of four-layer polymer waveguides. Various optical properties (such as refractive index, birefringence, and propagation loss) of polycarbonate and polystyrene waveguides are presented. The thin film structure consisting of glass/polycarbonate/polystyrene/air has been used for demonstrating polarization filter action because the two polymers are quite different with respect to their optical anisotropy. Modal electric field plots for both TE and TM are generated to support the observed behavior. It is also observed that the four-layer lightguide exhibits relatively low loss values compared to the monolayer configuration.     

Stability and mobility of the endohedral metallofullerene of La@C<Subscript>82</Subscript> in polycarbonate polymer films

An La@C₈₂-doped polymer (bisphenol-A polycarbonate) was prepared. EPR spectra of La@C₈₂ in a solid polymer film and in a polycarbonate solution in o-dichlorobenzene were studied. The EPR spectrum shape of La@C₈₂ was shown to be sensitive to the phase state of the polymer. La@C₈₂ in the film was found to have a high chemical stability below the glass formation temperature, thus permitting one to use the polymer for the storage and study of endohedral metallofullerenes.     

Multi-walled carbon nanotube-based transparent conductive layers deposited on polycarbonate substrate

We characterize 10-nm outer diameter multi-walled carbon nanotubes (powder and dispersion), which will be used for the preparation of conductive layers on polycarbonate (PC) substrates. The optical, electrical, and mechanical characterization of the spin-coated deposited layers is shown and compared with results obtained for layers deposited in borosilicate glass substrates. In both glass and plastic, the layers have shown transmittance higher than 78% in the visible range and have passed the tape and pencil standard tests for adherence and hardness, respectively. However, the sheet resistance presented by layers deposited on PC is still much superior to that of layers deposited on glass and sintered at higher temperatures. Nevertheless, the results obtained still allow the use of such layers in antistatic applications.     

Reentrant spin glass behavior in Cr-doped perovskite manganite

The magnetic and transport properties of the Cr-doped manganites La(0.46)Sr(0.54)Mn(1-y)Cr(y)O3 ( 0 < or = y < or = 0.08) with the A-type antiferromagnetic structure were investigated. Upon cooling, we find multiple magnetic phase transitions, i.e., paramagnetic, ferromagnetic (FM), antiferromagnetic (AFM), and spin glass in the y = 0.02 sample. The low temperature spin glass state is not a conventional spin glass with randomly oriented magnetic moments but has a reentrant character. The reentrant spin glass behavior accompanied by the anomalous multiple magnetic transitions might be due to the competing interactions between the FM phase and the A-type AFM matrix induced by the random Cr impurity.     

Granular packing as model glass formers

Static granular packings are model hard-sphere glass formers. The nature of glass transition has remained a hotly debated issue. We review recent experimental progresses in using granular materials to study glass transitions. We focus on the growth of glass order with five-fold symmetry in granular packings and relate the findings to both geometric frustration and random first-order phase transition theories.     

On the potential energy landscape of supercooled liquids and glasses

The activation-relaxation technique (ART), a saddle-point search method, is applied to determine the potential energy landscape around supercooled and glassy configurations of a three-dimensional binary Lennard-Jones system. We show a strong relation between the distribution of activation energies around a given glassy configuration and its history, in particular, the cooling rate used to produce the glass and whether or not the glass was plastically deformed prior to sampling. We also compare the thermally activated transitions found by ART around a supercooled configuration with the succession of transitions undergone by the same supercooled liquid during a time trajectory simulated by molecular dynamics. We find that ART is biased towards more heterogeneous transitions with higher activation energies and more broken bonds than the MD simulation.     

Registration temperature effect in polymers: Physico-chemical aspects

Registration temperature effect in two different polymers - poly(ethylene terephthalate) (PET) and polypropylene (PP) films - is investigated. Temperature effects on track formation are considered in terms of molecular mobility and relaxation transitions. The track eth rate is measured as a function of irradiation temperature in the range of 77 to 373 K. The obtained results are compared with the radical yields, radiothermoluminescence curves and thermally stimulated currents measured with the aim of detecting changes in the mobility of macromolecules and radiolysis intermediates. It is found that the change of the track etch rate with changing registration temperature correlates with γ- and glass transitions in PP and with β-and glass transitions in PET.     

On the behaviour of supercooled liquids and polymers in nano-confinement

ABSTRACT

Size effects play an important role in structural phase transitions, melting transitions, in martensitic materials, glass transitions, etc. Very often the question arises, whether a measured size effect originates from the geometrical confinement itself, or if it appears due to the interaction with the limiting surface. Using dynamic mechanical analysis (DMA) technique we have studied various microphase segregated polymers, molecular glass forming liquids and supercooled water confined in nanoporous silica as well as in biological tissues. Here we show on some selected examples that DMA measurements can be used to study relaxation processes in detail and to disentangle in favourable cases pure pore size effects from effects that are induced by the confining surface.     

Microstructure and rheology near an attractive colloidal glass transition

Microstructure and rheological properties of a thermally reversible short-ranged attractive colloidal system are studied in the vicinity of the attractive glass transition line. At high volume fractions, the static structure factor changes very little but the low frequency shear moduli varies over several orders of magnitude across the transition. From the frequency dependence of shear moduli, fluid-attractive glass and repulsive glass-attractive glass transitions are identified.     

Organic–inorganic nanocomposite films made from polyurethane dispersions and colloidal silica particles

Polyurethane/silica nanocomposites were prepared by solution blending of polyurethane water dispersion (PUD) based on polycarbonate macrodiol with colloidal silica aqueous sol LUDOX TMA. Because of mixing PUDs made from linear polyurethane with the nanofiller, only physical polymer/filler type of interface formed by hydrogen bonds was obtained. As a result the materials were possible to reuse after dissolution in acetone followed by dispersion in water. The effect of colloidal silica content on mechanical, thermal, morphological, and swelling properties of obtained films was tested by tensile test, dynamic mechanical thermal analysis, thermogravimertic analysis, scanning electron microscopy, atomic force microscopy, and swelling analyses. The nanocomposites were classified in three groups differing in the internal structure and functional properties: organic matrix filled with inorganic nanofiller (up to 10 wt% of silica), bicontinous systems (25 and 32 wt% of silica) and inorganic matrix filled with polyurethane (50 and 60 wt% of silica). Only small amount of colloidal silica (up to 10 wt%) improves thermo-mechanical properties, smoothes the materials, and suppresses extent of swelling without changing of the films transparency.     

Force Distributions near Jamming and Glass Transitions

We calculate the distribution of interparticle normal forces P(F) near the glass and jamming transitions in model supercooled liquids and foams, respectively. P(F) develops a peak that appears near the glass or jamming transitions, whose height increases with decreasing temperature, decreasing shear stress and increasing packing density. A similar shape of P(F) was observed in experiments on static granular packings. We propose that the appearance of this peak signals the development of a yield stress. The sensitivity of the peak to temperature, shear stress, and density lends credence to the recently proposed generalized jamming phase diagram.     

Phase transitions in random Potts systems and the community detection problem: spin-glass type and dynamic perspectives

Phase transitions in spin-glass type systems and, more recently, in related computational problems have gained broad interest in disparate arenas. In the current work, we focus on the “community detection” problem when cast in terms of a general Potts spin-glass type problem. As such, our results apply to rather broad Potts spin-glass type systems. Community detection describes the general problem of partitioning a complex system involving many elements into optimally decoupled “communities” of such elements. We report on phase transitions between solvable and unsolvable regimes. A solvable region may further split into “easy” and “hard” phases. Spin-glass type phase transitions appear at both low and high temperatures (or noise). Low-temperature transitions correspond to an “order by disorder” type effect wherein fluctuations render the system ordered or solvable. Separate transitions appear at higher temperatures into a disordered (or an unsolvable) phase. Different sorts of randomness lead to disparate behaviors. We illustrate the spin glass character of both transitions and report on memory effects. We further relate Potts type spin systems to mechanical analogs and suggest how chaotic-type behavior in general thermodynamic systems can indeed naturally arise in hard computational problems and spin glasses. The correspondence between the two types of transitions (spin glass and dynamic) is likely to extend across a larger spectrum of spin-glass type systems and hard computational problems. We briefly discuss potential implications of these transitions in complex many-body physical systems.