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  • 1
    Electronic Resource
    Electronic Resource
    The scaling exponents of polyacrylamide and acrylamide-sodium acrylate copolymer gels (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7108-7114 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ratio of bulk modulus to shear modulus, Ke/Ge, of polyacrylamide (PAAM) gels was studied. This ratio is directly related to a scaling exponent, δ, which is related to the concentration dependence of both bulk modulus and shear modulus. It was found that δ depends on the details of chemical ingredients and process. It increases as the crosslinker or monomer concentration increases. The behavior of acrylamide/sodium acrylate gel was found to be dramatically different from the nonionic gels. As sodium acrylate (SA) concentration increases from zero to 2 mol %, δ decreases from 2.09 to 1.08. Further increase of SA results in the formation of surface pattern and the value of δ increases slightly, eventually reaching a plateau around 1.25.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465429
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  • 2
    Electronic Resource
    Electronic Resource
    Polymer gel as thermally responsive attenuator for ultrasonic waves (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2233-2235 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The ultrasonic attenuation in N-isopropylacrylamide (NIPA) gel has been measured as a function of temperature at various frequencies. It is found that at room temperature, the attenuation of a longitudinal ultrasonic wave in the gel is small and close to that of pure water. However, as the temperature increases above the spinodal phase transition point of the gel, the attenuation increases drastically. This change of the attenuation is completely reversible and due to the microdomains formed in the NIPA gel above its phase transition temperature. The increase of attenuation at 15 MHz from 26 to 45 °C is about 26 dB/cm. The attenuation varies within 5 min after the temperature change is made for a sample with diameter 1 cm and height 0.8 cm. The results reported here may have potential applications from ultrasonic assisted drug release to a switch for ultrasonic signals. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123811
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  • 3
    Electronic Resource
    Electronic Resource
    Bending of N-isopropylacrylamide gel under the influence of infrared light (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 551-555 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A CO2 infrared laser has been used to irradiate a straight cylindrical N-isopropylacrylamide gel. It is found that the infrared laser not only induces the volume phase transition in the gel, but also causes the gel to bend toward the laser beam. When the laser is blocked, the gel becomes straight again. The transition between the straight and the bending gel is fully reversible. The maximum bending strain of the gel is comparable to that obtained for poly(vinyl alcohol)–poly(sodium acrylate) copolymer gel under the influence of an electric field. The bending effect has been systematically studied as a function of CO2 laser power, time, and the sample cell temperature. The relaxation behavior for the gel restoring its original shape after blocking the infrared irradiation follows an exponential form. It is suggested that the bending effect is caused by a temperature gradient which produces an osmotic pressure difference between the front surface area of the gel and the remainder of the gel. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469434
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  • 4
    Electronic Resource
    Electronic Resource
    Temperature and time dependencies of surface patterns in constrained ionic N-isopropylacrylamide gels (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 4645-4652 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Surface patterns in ionic N-isopropylacrylamide (N-IPA) gels have been investigated under external constraint. Hexagonal, grain, and bubble patterns have been observed at temperatures below, near, and above the phase transition temperature Tc. It is found that the behavior of these patterns depends not only on temperature, time, and external constraint, but also on the thermal path. The time dependence of the gel thickness has revealed that there is a plateau period and that the end of the plateau period corresponds to the onset of the bubble pattern. This observation is in agreement with previous measurements of free spherical N-IPA beads. The experiments show that each hexagonal cell evolves into a bubble for N-IPA gels, while a bubble can be present in the middle of a hexagonal cell for acrylamide gels. The mechanism for the shrinking patterns will be also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466247
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  • 5
    Electronic Resource
    Electronic Resource
    Pattern formation of constrained acrylamide/sodium acrylate copolymer gels in acetone/water mixture (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 4637-4644 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Pattern formation and evolution in constrained acrylamide/sodium acrylate (PAAM/SA) gels have been investigated in acetone/water mixture. The constraint is achieved by cross linking the gel slabs onto a rigid substrate. All samples are initially kept in water with the hexagonal pattern develop on the surface before being immersed in the acetone/water mixture. Depending on the solvent composition and ionic strength of the sample, different patterns, i.e., hexagonal, grains, and bubbles, have been observed. These patterns are formed at acetone concentration below, near, and above the concentration at which the gel volume phase transition occurs. The wavelengths of hexagonal and bubble patterns are found to be the same, while that of the grain pattern is four times smaller. It is suggested that the shrinking patterns are formed due to the dense gel surface produced during the shrinking process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466296
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  • 6
    Electronic Resource
    Electronic Resource
    Bending of bi-gels (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 3794-3800 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The bending of bi-gels has been studied as a function of temperature, acetone concentration, and NaCl concentration. The bi-gels consist of acrylamide on one side, and the interpenetrating polymer networks of acrylamide and N-isopropylacrylamide on the other side. The maximum bending strain achieved by the bi-gel is about 0.85. The bending mechanism of the bi-gels reported here is due to the engineered structure heterogeneity, in contrast with previous homogeneous gel bending which is induced by external gradient fields. The kinetic behavior of the bi-gel is discussed. A theoretical model is used to estimate the collective diffusion coefficient Dc of the IPN side of the bi-gels in pure water and in salt solution. The results agree with those obtained by the light-scattering method. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472200
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  • 7
    Electronic Resource
    Electronic Resource
    Turbidity Study of Spinodal Decomposition of an N-Isopropylacrylamide Gel (1995)
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 4194-4197 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00116a021
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  • 8
    Electronic Resource
    Electronic Resource
    Polymer gels with engineered environmentally responsive surface patterns (1998)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 393 (1998), S. 149-152 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The polymer gels called hydrogels may be induced to swell or shrink (taking up or expelling water between the crosslinked polymer chains) in response to a variety of environmental stimuli, such as changes in pH or temperature, or the presence of a specific chemical substrate. These gels are ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/30205
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  • 9
    Electronic Resource
    Electronic Resource
    Kinetics of ion-induced gelation in carrageenan gels under physiologic conditions (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 60 (1996), S. 221-224 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The kinetics of gelation of an ungelled carrageenan solution exposed to a gel-inducing ionic solution was studied using a turbidity technique. Alkali metal ions were allowed to diffuse through a dialysis membrane into the solution of biopolymer. Optical transmission was measured as a function of distance away from the membrane. In the early stage of 12 h, the transmission increases with distance. After 96 h, the transmission is independent of distance. This indicates that gelation is completed everywhere inside the gel and the gel's structure is homogeneous, in agreement with previous results. Time-dependent transmission indicates the presence of two relaxation processes occurring during ion-induced gelation: a primary relaxation process related to the gelling zone movement, and a secondary relaxation process related to local diffusion of polymer, bound ions, and water molecules. © 1996 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New method for measuring poisson's ratio in polymer gels (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 50 (1993), S. 1107-1111 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A new method for measuring the Poisson's ratio of polymer gels has been proposed and has been experimentally demonstrated. The method is based on different swelling behaviors of free and constrained gels. The Poisson's ratio of polyacrylamide gel, as a function of crosslinker concentration, has been measured using this method and has been found to be sensitive to the amount of polymerization initiator. The results are compared with results determined by other methods. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1993.070500619
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