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  • 1
    Electronic Resource
    Electronic Resource
    Phase coexistence of neutral polymer gels under mechanical constraint (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 2289-2296 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the equilibrium diameter of cylindrical poly(N-isopropylacrylamide) (NIPA) gels with submillimeter diameters under a mechanical constraint along the uniaxial direction. The linear swelling curve, diameter vs temperature, was obtained in the vicinity of the volume phase transition temperature under isometric constraint: both ends of the gel were fixed at rest (stress was zero) in a swollen state at 30 °C (a few degrees below the transition temperature). Thereafter, the temperature was gradually changed by keeping the uniaxial length constant (to the fixed length). It was demonstrated that the gel could take a coexistent state at the transition point and remain stable for several days. This time was much longer than the characteristic relaxation time of the phase transition in this tiny gel. The phase coexistence observed here was caused by stress inhomogeneity along the uniaxial direction due to the mechanical constraint. A collapsed to swollen phase transition induced by uniaxial stress at a fixed temperature was also presented. It was shown that the ratio of the swollen portion to the total length could be controlled by the degree of elongation: when the elongation was slightly increased or decreased, the phase boundary between the swollen and collapsed phases was accordingly shifted to increase or decrease the swollen state, respectively. The ratio of the swollen to the collapsed phase in the case of stress-induced coexistence is discussed herein in terms of a phase diagram (diameter vs elongation), and a simple phase selection rule is presented. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477882
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  • 2
    Electronic Resource
    Electronic Resource
    Optical switching in polymer gels (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 131-136 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Soft materials have long been sought after for use in devices such as actuators, artificial muscles, separators, switches, sensors, memories, and so forth. We developed a soft, optically transparent material using polymer gels that can not only be activated by visible light (switched on) but also deactivated (switched off) by altering the local environment using three different means: pH, temperature, and light. This copolymer gel is a covalently cross-linked network of N-isopropylacrylamide, sodium acrylate, and a chromophore, which is found to undergo phase transitions exhibiting large hysteresis in the degree of swelling in response to pH, temperature, and light. In each system, between the transitions for swelling and shrinking, the gel can show either a swollen or a collapsed state, which can be selected according to the history of the variables. It has been established that a thermoresponsive gel with chromophore exhibits a local volume phase transition upon illumination with visible light. By making use of this phenomenon, we have successfully controlled the phase in which a gel exists with visible light: Without light illumination the gel stays in the swollen state. Upon illumination beyond a threshold intensity, however, a volume transition is locally induced, thereby forming a material in which both phases coexist stably for at least several hours after the light source has been removed. The phenomenological stability of the material in the coexistence state is discussed on the basis of the Landau theory. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362768
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  • 3
    Electronic Resource
    Electronic Resource
    Shrinking pattern and phase transition velocity of poly(N-isopropylacrylamide) gel (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 360-367 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have studied the shrinking phase transition of cylindrical poly(N-isopropylacrylamide) gels with submillimeter diameter. The macroscopic conformation change and the phase transition velocity were obtained during the heating process by two different methods. One is a continuous heating process with a constant temperature drift rate, and the other is an isothermal process after a steplike temperature increase beyond the transition point. In the former measurement, the phase transition can be controlled by the nucleation mechanism in the smaller temperature drift rates; at the transition point, after the fine pattern appears and disappears on the surface, for instance, the gel gradually and uniformly shrinks while keeping a smooth surface. On the other hand, at the larger temperature drift rates, the phase transition comes into the unstable region before being completed; after the fine pattern disappears, a coarse pattern appears on the surface, and the entire gel becomes opaque. The gel gradually becomes transparent with time from the surface layer to the core portion. These two processes, characterized by two types of surface pattern as well as the growth of a collapsed surface skin layer, can be clearly observed in the latter measurements, which depend on the degree of super-heating (how far the final temperature is from the transition point). The results are discussed qualitatively on the basis of the classical phase separation model of nucleation and spinodal decomposition, as well as the phase diagram of the present gel system. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479278
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  • 4
    Electronic Resource
    Electronic Resource
    Phase transition in strongly stretched polymer gels (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 5179-5185 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We will present the volume phase transition of cylindrical poly N-isopropylacrylamide (NIPA) gels under large distortion along the uniaxial direction. The neutral and slightly ionized NIPA gels were synthesized in submillimeter diameter. The gel was stretched along the uniaxial direction with the longitudinal deformation ratio, α(parallel) (the ratio of the stretched length to the equilibrium length in the swollen state at 30 °C). By keeping the longitudinal length constant, we have simultaneously measured the equilibrium diameter and the force as functions of temperature. The swelling curves of the neutral NIPA gels including the volume phase transition temperature were obtained for several deformations in the range between α(parallel)=1 and α(parallel)=6. With increasing α(parallel), the transition temperature increased up to 1 °C in the small deformation below α(parallel)∼3.5, and it saturated and slightly decreased in the large α(parallel) above α(parallel)∼4. At the transition temperature on heating, the force to keep the length constant increased discontinuously in the smaller region below α(parallel)∼3.5. The magnitude of this steplike change in the force began to decrease in the vicinity of α(parallel)∼3.5, and hereafter exhibited negative change above α(parallel)∼4. In the case of the slightly ionized NIPA gels, these effects came into play at an earlier stage, that is, at smaller α(parallel), because of the prestretching due to the ionic pressure. The present observations, especially for the strong deformation above α(parallel)∼4, were discussed by the equation of states of strongly stretched hydrophobic gels on the basis of the extended Flory-type free energy taken into account the non-Gaussian effect. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474880
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  • 5
    Electronic Resource
    Electronic Resource
    Growth of ZnSe/MgS strained-layer superlattices by molecular beam epitaxy (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2945-2947 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Growth of ZnSe/MgS strained-layer superlattices (SLSs) has been carried out by molecular beam epitaxy. The crystal quality of SLSs degraded with MgS thickness of more than about 3 monolayers. Photoluminescence due to the transition between quantized levels was observed. Photoluminescence peak energies higher than 3.0 eV at 77 K were observed, which are comparable to that of ZnMgSSe quaternary material. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114820
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  • 6
    Electronic Resource
    Electronic Resource
    Fast two-dimensional potential measurement at the thermal barrier region of the tandem mirror Gamma 10 (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 4251-4259 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A gold neutral beam probe system was improved by adopting a multichannel ion detector and adding sweeping functions of beam energy, deflector voltage, and electrode voltage of the analyzer to the system to measure the fluctuations and time evolution of the two-dimensional space potentials with fast resolving time during one shot. Positions of the beam spot on the multichannel detector corresponding to the ionizing points of the beam in the plasma were simulated precisely as a function of the beam energy and the injection angle. A potential derivation formula was determined taking into consideration both the numerical and experimental results, and the reproducibility of the potential profile was checked. Two-dimensional potential profiles were measured in the optimization experiment of the microwave injection angles for formation of the plug potential. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150062
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  • 7
    Electronic Resource
    Electronic Resource
    Pinhole camera imaging of x rays and energetic neutral atoms for hot plasma diagnostics (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 2574-2575 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A compact pinhole camera is found to be useful for observation of a spatial distribution of hot ions by imaging energetic charge-exchange neutral atoms. One can obtain images of neutral atoms and of x rays in the same geometry only by selecting filtering foils at the pinhole opening of a single camera. Easy comparison between the images associated with distributions of ions and electrons is quite beneficial for physical analyses of plasmas. The imaging technique is expected also to be useful to determine space–time-resolved energy spectra of hot ions. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148962
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  • 8
    Electronic Resource
    Electronic Resource
    Direct observation of polymer gel surfaces by atomic force microscopy (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 1751-1757 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report here, for the first time, the direct observation of the submicron structure of gel surfaces in water by using an atomic force microscope (AFM). We present also its change in response to external stimuli; we investigated, among the variables that affect the topography of the gel surface, the effect of the network density of poly(acrylamide) gels and the effect of the temperature change of poly N-isopropylacrylamide gels. Gels were prepared with disklike shape of thickness ranging from 10 to 50 μm, and one of the gel surfaces was chemically adhered onto a glass plate. Spongelike domains of submicrometer scale were found here on the gel surfaces, which was strongly affected by the cross-linking density (nature of the gel network) as well as the osmotic pressure (environmental condition), and also thickness (condition of constraint). The qualitative properties of the surface microscopic structure of gels are discussed in relation to a hypothetical model of two-dimensional gels based on the Flory–Huggins theory. These results disclose that the surface microstructures of polymer gels in solvent as well as the nanometer scale structural changes are associated with the gel phase transition. Moreover, they indicate that the potential for a new technology to control the domain size of the gel surface as well as its function by external stimuli could emerge, which would find a variety of applications in many fields, such as engineering, medicine, and biology. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470760
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  • 9
    Electronic Resource
    Electronic Resource
    Hysteretic behavior and irreversibility of polymer gels by pH change (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4706-4710 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Swelling equilibrium has been studied on N-isopropylacrylamide gel which is randomly but slightly incorporated both by trisodium salt of copper chlorophyllin and by sodium acrylate. An ionic gel with both hydrophobic interaction and hydrogen bonding was found here to display hysteretic behavior in swelling degree with an interesting nature when the pH is cycled between 7 and 12. In the shrinking transition to the collapsed state observed during pH decrease, there are two different processes characterized by the first order phase transitions with different pHs (7.3 and 7.6). These could be selected whether or not the pH had been increased beyond the threshold (pH=9). Namely, in the larger pH region beyond the threshold, the gel can reswell larger than the first swollen state which appeared directly from the collapsed phase. The hysteretic behavior as well as the irreversibility observed in higher pH region than the threshold was attributed to the screening effect on the ionic groups in the gels because of excess Na+ ions from NaOH that is introduced for increasing the solvent pH. A simple theoretical model is presented to qualitatively explain the phenomena on the basis of the Landau theory. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470608
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  • 10
    Electronic Resource
    Electronic Resource
    PROPER MEASUREMENT OF BLOOD PRESSURE AND HEART RATE IN SHRSP AND WKY BY AN INDIRECT VOLUME-OSCILLOMETRIC METHOD (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Clinical and experimental pharmacology and physiology 22 (1995), S. 0 
    Details
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. The effect of environmental temperature on the indirect measurement of rat blood pressure and heart rate was investigated with special reference to the tail arterial blood flow in both strains of SHRSP and WKY.2. Very good correlations (r 〉 0.82, P 〈 0.05; t-test, 10 d.f.) were observed between the two values of systolic blood pressure or heart rate measured by a direct and an indirect method at environmental temperatures between 26 and 38°C in SHRSP, and 34 and 38°C in WKY, respectively.3. When the temperature was elevated by 10°C from 25°C to 35°C, the regional blood flow in the tail artery increased by 52–69%, sufficient to detect a blood flow increase by the indirect method.4. These data showed that the best way to measure the accurate blood pressure and heart rate in both strains of SHRSP and WKY by the indirect volume-oscillometric method was to hold the rats at 34–36°C for 5 min.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1440-1681.1995.tb02923.x
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