PA Phase Research Articles

Improved compatibility between polyamide and polypropylene by the use of maleic anhydride grafted SEBS

Blends containing equal weight fractions of polypropylene (PP) and polyamide (PA-6 and PA-6.6) and up to 25% of a compatibilizing thermoplastic elastomer, either polystyrene- block-poly(ethylene- stat-butylene)- block-polystyrene (SEBS) or SEBS modified by maleic anhydride (SEBS-MA), were prepared by melt mixing. In all these blends, PP formed the continuous matrix phase. Even at high concentrations, unmodified SEBS was found to be a poor compatibilizer, affecting mainly the properties of the matrix. The graft copolymer formed, by reaction between SEBS-MA and polyamide during melt mixing, strongly influenced the blend morphology, by forming an interphase, separating the PA phase domains from the matrix. The crystallization behaviour of PP indicated that full coverage required between 3% and 5% SEBS-MA at the intense mixing conditions used. Above this level, the total surface area of the polyamide domains seemed to increase in direct proportion to the concentration of SEBS-MA. The thickness of the interphase layer was estimated to be about 15 nm. At high concentrations of SEBS-MA, the PA domains agglomerated and formed extended structures held together by the interphase polymer. This was reflected by the stress–strain and rheological behaviour of the blends. In blends with PA domains of small volume, crystallization of PA was delayed. The rate of water absorption was very low in blends containing SEBS-MA, much lower than in corresponding blends containing SEBS.

Anisotropy in Thermal and Electronic Properties of Single Crystal GeSe2 Obtained by the Photoacoustic Method

Anisotropy in the thermal and electronic properties for two directions of a thermal wave propagation in GeSe2 single crystal was investigated using the photoacoustic frequency transmission technique. First, the electric field of an incident polarized light beam was adjusted to be perpendicular to the “c” axis (El⊥c), and then parallel to it (El//c) . It is shown that there is an obvious difference in the PA amplitude and phase spectra of the same sample, for cases when El//c and El⊥c axis. The results for thermal diffusivity DT obtained by fitting procedure for these two orientations of the electric field with regard to the “c” axis, are calculated: DT//=1.1×10-2 and DT⊥=1.7×10-3 cm2/s, e.g. their ratio is 6.6. The electronic transport parameters are also given: the carrier ambipolar diffusion coefficient D//=1.5 cm2/s and D⊥=2.5 cm2/s.

Graft formation and chain scission in blends of polyamide‐6 and ‐6.6 with maleic anhydride containing polymers

The in situ formation of a compatibilizer, consisting of a copolymer of PA grafted onto a maleic anhydride (MA) containing polymer, is essential for the morphology and properties of the corresponding PA blends. In this study four blends, containing PA-6 or PA-6.6 and EPDM-g-MA or poly(styrene-co-maleic anhydride) (SMA; 28 wt % MA), were prepared and characterized. Chemical analyses showed that the amount of PA graft is independent of the blend composition. Going from EPDM-g-MA to SMA the MA content of the original MA-containing polymer increases, which in the corresponding blends results in an increase in the number of PA grafts and a decrease in the length of the PA grafts. In the SMA blends the number averaged molecular weight of the grafted PA is only about 200 g/mol. It is postulated that the water molecule, released upon imide formation at the PA/(MA-containing polymer) interface, hydrolyses a PA amide group, resulting in a new amine end group, which in its turn reacts with the MA-containing polymer, etc. Differential scanning calorimetry shows that the degree of crystallinity of the PA phase is decreased only when the size of the PA phase between the MA-containing polymer domains approaches the PA crystalline lamellar thickness. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 179–188, 1998

Graft formation and chain scission in blends of polyamide-6 and -6.6 with maleic anhydride containing polymers

The in situ formation of a compatibilizer, consisting of a copolymer of PA grafted onto a maleic anhydride (MA) containing polymer, is essential for the morphology and properties of the corresponding PA blends. In this study four blends, containing PA-6 or PA-6.6 and EPDM-g-MA or poly(styrene-co-maleic anhydride) (SMA; 28 wt % MA), were prepared and characterized. Chemical analyses showed that the amount of PA graft is independent of the blend composition. Going from EPDM-g-MA to SMA the MA content of the original MA-containing polymer increases, which in the corresponding blends results in an increase in the number of PA grafts and a decrease in the length of the PA grafts. In the SMA blends the number averaged molecular weight of the grafted PA is only about 200 g/mol. It is postulated that the water molecule, released upon imide formation at the PA/(MA-containing polymer) interface, hydrolyses a PA amide group, resulting in a new amine end group, which in its turn reacts with the MA-containing polymer, etc. Differential scanning calorimetry shows that the degree of crystallinity of the PA phase is decreased only when the size of the PA phase between the MA-containing polymer domains approaches the PA crystalline lamellar thickness. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 179–188, 1998

Evaluation of Solid-Phase Microextraction for Analysis of Volatile Metabolites Produced by Staphylococci.

The evaluation of solid-phase microextraction (SPME) for analysis of flavor compounds produced by bacteria has been studied. First, it was necessary to determine the optimal conditions to extract the different volatile compounds in dilute aqueous solutions. For this, the effects of salt, headspace, and liquid samplings and two coating phases [poly(dimethylsiloxane) (PDMS) and poly(acrylate) (PA)] were tested. The addition of salt enhanced SPME absorption of all the compounds. Ethyl ester was better extracted in liquid sampling with PDMS phase, whereas all of the other compounds were better extracted in headspace sampling at 80 degrees C with PA phase. The SPME technique was applied to the analysis of bacterial metabolites. It has been shown that Staphylococcus xylosus (16) and Staphylococcus carnosus (833) were able to produce esters and to catabolize leucine and that S. carnosus (833) limited the oxidation of free fatty acids.

Studies of the killing kinetics of benzylpenicillin, cefuroxime, azithromycin, and sparfloxacin on bacteria in the postantibiotic phase

Most antibiotics are known to be incapable of killing nongrowing or slowly growing bacteria with few exceptions. Bacterial cell division is inhibited during the postantibiotic phase (PA phase) after short exposure to antibiotics. Only scarce and conflicting data are available concerning the ability of antibiotics to kill bacteria in the PA phase. The aim of the present study was to investigate the killing effect of four different antibiotics on bacteria in the PA phase. A postantibiotic effect (PAE) was induced by exposing Streptococcus pyogenes and Haemophilus influenzae to 10x MICs of benzylpenicillin, cefuroxime, sparfloxacin, and azithromycin. The bacteria were thereafter reexposed to a 10x MIC of the same antibiotic used for the induction of the PAE at the beginning of and after 2 and 4 h in the PA phase. Due to a very long PAE, the bacteria in PA phase induced by azithromycin were also exposed to 10x MICs after 6 and 8 h. A previously unexposed culture exposed to a 10x MIC was used as a control. The results seem to be dependent on both the antibiotic used and the bacterial species. The antibiotics exhibiting a fork bactericidal action gave significantly reduced killing of the bacteria in PA phase (cefuroxime with S. pyogenes, P < 0.01, and sparfloxacin with H. influenzae, P < 0.001), which was restored at 4 h for cefuroxime with S. pyogenes. There was a tendency to restoration of the bactericidal activity also with sparfloxacin and H. influenzae, but there was still a significant difference in killing between the control and the test bacteria in PA phase at 4 h. However, in the combinations with a lesser bactericidal effect (benzylpenicillin with S. pyogenes and sparfloxacin with S. pyogenes), there was no difference in killing between the control and the test bacteria in PA phase. Azithromycin induced long PAEs in both S. pyogenes and H. influenzae and exhibited a slower bactericidal action on both the control and the bacteria in PA phase especially at the end of the PAE, when the killing was almost bacteriostatic. Our findings in this study support the concept that a long interval (> 12 h) between doses of azithromycin, restoring full bactericidal action, may be beneficial to optimize efficacy of this drug but is not necessary for the other antibiotics evaluated, since the bactericidal effect seems to be restored already at 4 h.

Theory of X-ray photoacoustic spectroscopy

PhotoAcoustic Spectroscopy (PAS) in the X-ray region is becoming a new field in PAS research and poses some new problems, such as heat production mechanisms and non-exponential heat distribution due to multi-excitation processes, additional signals caused by escaped fluorescence and electrons, special backing and fronting setup for comparison with absorption experiment, etc. In this paper we treat these problems and include them in an extended theoretical model which can be reduced to the RG model in a special case. The results indicate that the non-exponential heat distribution has no effect on the PA phase. The contribution by gas heating of the escaped electrons can be neglected. The thermally thin gas layers between the sample and the Be windows are sensitive factors to both amplitude and phase. The PA signal generated in the backing gas layer by the backing surface of the sample should be considered to understand the frequency dependence of the PA signal. The expansion of the backing gas layer is the reason for the phase change in PA-EXAFS.

Photoacoustic Spectroscopy of CuxS/CdS Heterojunction

The Cux S/CdS heterojunction interface was studied by photoacoustic spectroscopy (PAS). By changing the modulation frequency of the incident light, the edge absorption of Cux S and CdS layers clearly appeared not only in the PA intensity spectrum but also in the PA phase spectrum. The PA spectrum of the thermally annealed Cux S/CdS heterojunction showed evidence of Cu diffusion into the CdS single crystal.

Functionalized elastomeric compatibilizer in PA 6/PP blends and binary interactions between compatibilizer and polymer

AbstractSuperior impact properties were obtained when maleic anhydride grafted styrene ethylene/butylene styrene block copolymer (SEBS‐g‐MAH) was used as a compatibilizer in blends of polyamide 6 (PA 6) and isotactic polypropylene (PP), where polyamide was the majority phase and polypropylene the minority phase. The optimum impact properties were achieved when the weight relation PA:PP was 80:20 and 10 wt% SEBS‐g‐MAH was added. The blend morphology was systematically investigated. Transmission electron microscopy (TEM) indicated that the compatibilizer forms a cellular structure in the PA phase in addition to acting as an interfacial agent between the two polymer phases. In this cellular‐like morphology the compatibilizer appears to form the continuous phase, while polyamide and polypropylene form separate dispersions. In microscopy, PA appeared as a fine dispersion and PP as a coarse dispersion. The mechanical properties indicated that in fact PA, too, is continuous, and the blend can be interpreted as possessing a modified semi‐interpenetrating network (IPN) structure with separate secondary dispersion of PP. The coarser PP dispersion plays an essential role in impact modification. Binary blends of the compatibilizer and one blend component were also investigated separately. The same cellular structure was observed in the binary PA/SEBS‐g‐MAH blends, and SEBS‐g‐MAH again appeared to form the continuous phase when the elastomer concentration was at least 10 to 20 wt%. By contrast, in PP/SEBS‐g‐MAH only conventional dispersion of elastomeric SEBS‐g‐MAH was observed up to 40 wt% elastomer. Impact strength was improved and the elastic modulus was lowered in both PA/SEBS‐g‐MAH and PP/SEBS‐g‐MAH blends when the elastomer content was increased. The changes in modulus indicate that the semi‐IPN‐like structure is formed in the binary PA/SEBS‐g‐MAH blends as well as in the ternary structure.

Ternary blends of poly(amide‐6)/polycarbonate/poly(ε‐caprolactone)

AbstractBlends of poly(amide‐6) (PA) and poly(ε‐caprolactone) (PCL) prepared by solution casting and screw extrusion have been investigated by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). From the measured melting point (Tm) of the solution‐cast PA/PCL blends, a Tm depression of the PA was observed for the investigated compositions. No Tm depression was found for the extruded PA/PCL blends, however. In the SEM study of the morphology of the solution‐cast PA/PCL blends, phase separation was observed between the PA phase and the PCL phase for all blend compositions. For the extruded PA/PCL blends, however, more pronounced phase separation was observed for all blend compositions. Ternary blends of PA, PCL, and bisphenol‐A polycarbonate (PC) have also been prepared by screw extrusion. From the study of morphology and extrudate swell of the PA/PC binary blends and the extruded PA/PC/PCL ternary blends, it appears that PCL could be used as a compatibilizer for the extruded PA/PC/PCL blends. © 1993 John Wiley &amp; Sons, Inc.

Analysis of Pyroelectric Signal in Photoacoustic Spectroscopy Using a Transparent Transducer

It is shown that a pyroelectric signal from a transparent transducer, Z-cut LiNbO3, depends on the surface state of the measured sample, a Si wafer. The signal of the Si wafer with the native oxide deviates markedly from the normal pyroelectric signal. Also, we develop a three-dimensional theory of 1he transparent pyroelectric transducer method in photoacoustic spectroscopy (PAS). We discuss the cases in which the pump beam illuminates the sample not only directly, but also through the transducer. It is shown that the theoretical calculation results are in good agreement with the experimental data of both PA amplitude and phase signals of Si. This result indicates that the validity of our theoretical model is verified experimentally.

Pharmacodynamic effects of subinhibitory concentrations of beta-lactam antibiotics in vitro

The pharmacodynamic effects of subinhibitory concentrations of different beta-lactam antibiotics were investigated. A postantibiotic effect (PAE) was induced for different bacterial species by exposure to 10x MIC of several beta-lactam antibiotics for 2 h in vitro. The antibiotic-bacterial combinations used in this study were imipenem-Pseudomonas aeruginosa, benzylpenicillin-Streptococcus pneumoniae and -Streptococcus pyogenes, cefcanel-S. pyogenes, ampicillin-Escherichia coli, and piperacillin-E. coli. After the induction of the PAE, the exposed cultures as well as the unexposed controls were washed and diluted. Thereafter, the cultures in the postantibiotic phase (PA phase) and the cultures not previously treated with antibiotics were exposed to 0.1, 0.2, and 0.3x MIC of the relevant drug and the growth curves were compared. When bacteria in the PA phase were exposed to sub-MICs, a substantial prolongation of the time before regrowth was demonstrated, especially in antibiotic-bacterial combinations for which a PAE was found. In contrast, sub-MICs on cultures not previously exposed to suprainhibitory antibiotic concentrations yielded only a slight reduction in growth rate compared with the controls. Thus, it seems important to distinguish the direct effects of sub-MICs on bacteria not previously exposed to suprainhibitory concentrations from the effects of sub-MICs on bacteria in the PA phase.

Theoretical Analysis of Photoacoustic Signal on PAS Using a Transparent Transducer

We proposed a new theoretical model for photoacoustic spectroscopy (PAS) using a transparent transducer. Based on the Jackson and Amer model, this takes into account not only a very small air gap as thermal resistance between the sample and the transducer but also the transducer displacement due to its own temperature distribution. It is shown that the theoretical calculations based on our model are more consistent with the experimental data for both PA amplitude and phase signals of GaAs than the conventional model. From these results, the validity of our theoretical model is verified experimentally.

透明トランスジューサを用いた光音響分光法（ＰＡＳ）による半導体の評価

This is a review of Photoacoustic (PAS) measurement using transparent transducer of semiconductor materials. This technique is very sensitive to detect a PA signal because the light is illuminated to the sample surface through a transparent piezoelectric transducer (LiNbO3) and the PA signal is detected directly from the transducer. In this review the generation mechanisms of PA amplitude and phase signals for layered semiconductor materials (GaInP/GaAs) are experimentally clarified. Then, a theoretical analysis of generation mechanism of PA signal is presented and the validity of the theory is clarified by the experimental results. Finally, the thermal conductivity of InP is estimated by using both the theory and the experiment.

Evaluation of Multilayer Structure and Depth Profile by PAS Using a Transparent Transducer

This paper concerns the experimental evaluation of optical properties of a multilayer semiconductor structure by PAS using a transparent transducer method. The sample is a GaxIn1-xP(1.8 µm)/GaAs (380 µm)/Si(530 µm). Optical absorption edges of this sample are evaluated from PA amplitude and phase signals. Between two layers a sharp dip of the PA signal is observed which corresponds to the absorption edge. Generation mechanism of the PA dip is discussed in comparison with the phase delay of two signals.

Kinetics and thermodynamics of calcium-induced lateral phase separations in phosphatidic acid containing bilayers.

The effects of calcium on the mixing of synthetic diacylphosphatidylcholines (PC's) and diacylphosphatidylethanolamines (PE's) with the corresponding phosphatidic acids (PA's) have been examined by high-sensitivity differential scanning calorimetry and by measurements of the fluorescence of labeled PA or PC species in PA-PC bilayers. Calorimetrically derived phase diagrams for dimyristoyl- and dielaidoyl-substituted PA-PC and PA-PE mixtures indicate that these species are readily miscible in the absence of calcium but phase-separate very extensively in the presence of high levels of calcium (30 mM). The limiting solubilities of PA (Ca2+) in liquid-crystalline PC or PE bilayers are less than or equal to 10 and approximately 5 mol %, respectively, while approximately 20 mol % of PC or PE can be introduced into the "cochleate" phase of PA (Ca2+) before a distinct PC-rich (or PE-rich) phase appears. The kinetics of calcium-induced lateral phase separations were examined for dioleoyl- and dielaidoyl-substituted PA-PC unilamellar vesicles labeled with fluorescent (C12-NBD-acyl) PA or PC, whose fluorescence becomes partially quenched upon phase separation. Our results indicate that, for the PA-PC system, lateral phase separation is very rapid (approximately less than 1 s) after calcium addition and develops partially (possibly in only one face of the bilayer) when calcium is present only on one side of the bilayer. Moreover, phase separations can develop at a rate faster than that of vesicle diffusion when calcium is added to dilute suspensions of vesicles, suggesting that interbilayer contacts are not essential to promote phase separations.

Observation of Surface Roughness by PAS using Transparent Transducer and Photothermal Deflection Sepectroscopy (PDS)

This paper is concerned with the experimental study of photoacoustic spectroscopy (PAS) using a transparent transducer and photothermal deflection spectroscopy (PDS). The amplitude and phase of PA and PD signals are observed for differen surface roughness (etched, polished, and roughed) of the example semiconducting CdS. There are no substantial differences between PAS and PDS. Additional signal increase caused by the damaged surface layers is observed at wavelength longer than the absorption edge. The phase signals reflect information of the depth and arc less affected by the noise.

PA-SPECTROSCOPIC INVESTIGATION ON FLOWER PETALS

PA amplitude and phase spectra of intact flower petals are compared with the corresponding scattered transmittance, diffuse reflectance spectra and the solution spectra of pigments.

MODEL OF OSCILLATING INTERFACE AT FIRST ORDER PHASE TRANSITION AND AT GLASS TRANSITION - NONVANISHING AMPLITUDE APPROXIMATION

A theoretical model for PA amplitude and phase angle at first order phase transition is generalized to arbitrary thermal thickness of the sample. It can be applied to second order phase transitions, too. Results of measurements at the melting point of indium and in the glass transition region of polystyrene confirm the model.