The rate of self-adhesion development between optical quality thin films of Poly(Urethane) (PU) b... more The rate of self-adhesion development between optical quality thin films of Poly(Urethane) (PU) block copolymers has been investigated. The dramatic increase in self-adhesion relative to adhesion to an impenetrable substrate(Mylar{reg_sign} or glass), is evidence for inter-diffusion in this system. The interfaces were found to remain relatively narrow by neutron reflection, even after long annealing times, because the interpenetration of the mobile blocks is strongly limited by the physical cross-links. The advantage of thin, smooth films for peel tests is that measurements can be made at early times when the interface strengths are very low, and visco-elastic dissipation effects can be reduced. Visco-elastic dissipation is also seen to be reduced by the highly elastic nature of PU, explaining the very weak adhesion to Mylar{reg_sign}. Because the films are smooth, the results are independent of pressure. The time dependence of the peel strength for self-adhesion between very thin f...
Author Institution:Polarization ratios (circular/linear) for excitation of two-photon forbidden (... more Author Institution:Polarization ratios (circular/linear) for excitation of two-photon forbidden (ungerade) electronic band origins are reported for centrosymmetric aromatic compounds in neat liquid and solutions at room temperature and 77K. The ratios are compared with those of allowed tow-photon excitations in these and related, non-centrosymmetric compounds. The effect of solvent environment on intensity and polarization ratio is discussed
... Ian Andrews, Jian Cui, Jimmy DaSilva, Leo Dudin, Peter Dunn, John Hayler, BillHinkley, David ... more ... Ian Andrews, Jian Cui, Jimmy DaSilva, Leo Dudin, Peter Dunn, John Hayler, BillHinkley, David Hughes, Bernard Kaptein, Kurt Lorenz, Suju Mathew, Thomas Rammeloo, Lijun Wang, Andrew Wells, Timothy White, Fuyao Zhang. ...
The method of molecular tribometry is described. Ultrathin films of liquids are confined between ... more The method of molecular tribometry is described. Ultrathin films of liquids are confined between parallel plates, usually of atomically smooth muscovite mica, such that the apparent area of contact equals the true area of contact. This paper consists of 5 sections. First, the phenomenon of solid lubrication by liquids is described. Second, the alternative viscous response of ultrathin liquid lubricants is described; the microviscosity is considerably enhanced over that of the isotropic liquid. Third, the critical shear strength is shown to have an extreme dependence on the normal pressure. Fourth, the materials requirements for molecular tribometry are discussed. Finally, a discussion is offered of the strengths and limitations of this new tool.
... JOHN VAN ALSTEN and STEVE GRANICK (Member STLE) University of Illinois Urbana, Illinois 61801... more ... JOHN VAN ALSTEN and STEVE GRANICK (Member STLE) University of Illinois Urbana, Illinois 61801 ... The thin sheets of mica used in these experiments were unsupported, however, so that interpretation of measurements was complicated by elastic deformation of the flexible ...
... JOHN VAN ALS1'EN and STEVE GRANICK (Member, STLE) Department of Materials Science and En... more ... JOHN VAN ALS1'EN and STEVE GRANICK (Member, STLE) Department of Materials Science and Engineering University of Illinois Urbana ... thin fi lms of the nonpolar liquids cyclohexane and octamethylcyclo-tetra-siloxane (OMCTS), confined between parallel sheets of mica (1 ...
A technique is described for micropositioning a surface forces apparatus with low mechanical and ... more A technique is described for micropositioning a surface forces apparatus with low mechanical and thermal drift. The technique is less exacting and more stable than competing ones.
The design, calibration, and performance are described of an apparatus to study the shear respons... more The design, calibration, and performance are described of an apparatus to study the shear response of ultrathin liquid films. The device, a modification of the surface forces apparatus, measures the resistance to shear of liquids confined between two atomically smooth solid surfaces. The surfaces are separated by distances on the order of the size of the liquid molecules (liquid film thickness <10 nm). Shear forces with periodic time dependence are applied to one surface while the second is held fixed, and any motion so induced is analyzed to determine the behavior of the liquid film. The frequency and amplitude of the shear forces applied can be varied over a wide range (0.03–60 Hz frequency and 0.1–1000 nm amplitude) to achieve different values for the magnitude of the shear rate. The dynamic response of the device is linear in the applied force at a given frequency; nonetheless, nonlinear dependence of the liquid’s shear resistance on the shear rate, net normal pressure, and f...
Diffusion coefficients of sodium and zinc ions have been measured in bilayers of commercial, part... more Diffusion coefficients of sodium and zinc ions have been measured in bilayers of commercial, partially neutralized poly(ethylene-co-methacrylic acid). The diffusion behavior shows a break at the melting temperature of the resin, suggesting that chain backbone motion is intimately related to ionic transport. The ionic diffusion coefficients are orders of magnitude greater than those of the chain backbone, which suggests that metal ion pairs are transported along the contour of the polymer network via exchange with protons of neighboring acid groups. Interfacial strength development in welded films of ionomers is primarily determined by the melting behavior of the bulk resin. Ionic diffusion rates do not correlate with the strength development behavior. This observation, along with melting and chain center of mass diffusion information, suggests that strength development is dependent on chain interdiffusion like that of many other thermoplastics.
Direct evidence of the changing structure of an adsorbed PMMA layer at the solid/solution interfa... more Direct evidence of the changing structure of an adsorbed PMMA layer at the solid/solution interface during early stages of the adsorption is presented
The rate of self-adhesion development between optical quality thin films of Poly(Urethane) (PU) b... more The rate of self-adhesion development between optical quality thin films of Poly(Urethane) (PU) block copolymers has been investigated. The dramatic increase in self-adhesion relative to adhesion to an impenetrable substrate(Mylar{reg_sign} or glass), is evidence for inter-diffusion in this system. The interfaces were found to remain relatively narrow by neutron reflection, even after long annealing times, because the interpenetration of the mobile blocks is strongly limited by the physical cross-links. The advantage of thin, smooth films for peel tests is that measurements can be made at early times when the interface strengths are very low, and visco-elastic dissipation effects can be reduced. Visco-elastic dissipation is also seen to be reduced by the highly elastic nature of PU, explaining the very weak adhesion to Mylar{reg_sign}. Because the films are smooth, the results are independent of pressure. The time dependence of the peel strength for self-adhesion between very thin f...
Author Institution:Polarization ratios (circular/linear) for excitation of two-photon forbidden (... more Author Institution:Polarization ratios (circular/linear) for excitation of two-photon forbidden (ungerade) electronic band origins are reported for centrosymmetric aromatic compounds in neat liquid and solutions at room temperature and 77K. The ratios are compared with those of allowed tow-photon excitations in these and related, non-centrosymmetric compounds. The effect of solvent environment on intensity and polarization ratio is discussed
... Ian Andrews, Jian Cui, Jimmy DaSilva, Leo Dudin, Peter Dunn, John Hayler, BillHinkley, David ... more ... Ian Andrews, Jian Cui, Jimmy DaSilva, Leo Dudin, Peter Dunn, John Hayler, BillHinkley, David Hughes, Bernard Kaptein, Kurt Lorenz, Suju Mathew, Thomas Rammeloo, Lijun Wang, Andrew Wells, Timothy White, Fuyao Zhang. ...
The method of molecular tribometry is described. Ultrathin films of liquids are confined between ... more The method of molecular tribometry is described. Ultrathin films of liquids are confined between parallel plates, usually of atomically smooth muscovite mica, such that the apparent area of contact equals the true area of contact. This paper consists of 5 sections. First, the phenomenon of solid lubrication by liquids is described. Second, the alternative viscous response of ultrathin liquid lubricants is described; the microviscosity is considerably enhanced over that of the isotropic liquid. Third, the critical shear strength is shown to have an extreme dependence on the normal pressure. Fourth, the materials requirements for molecular tribometry are discussed. Finally, a discussion is offered of the strengths and limitations of this new tool.
... JOHN VAN ALSTEN and STEVE GRANICK (Member STLE) University of Illinois Urbana, Illinois 61801... more ... JOHN VAN ALSTEN and STEVE GRANICK (Member STLE) University of Illinois Urbana, Illinois 61801 ... The thin sheets of mica used in these experiments were unsupported, however, so that interpretation of measurements was complicated by elastic deformation of the flexible ...
... JOHN VAN ALS1'EN and STEVE GRANICK (Member, STLE) Department of Materials Science and En... more ... JOHN VAN ALS1'EN and STEVE GRANICK (Member, STLE) Department of Materials Science and Engineering University of Illinois Urbana ... thin fi lms of the nonpolar liquids cyclohexane and octamethylcyclo-tetra-siloxane (OMCTS), confined between parallel sheets of mica (1 ...
A technique is described for micropositioning a surface forces apparatus with low mechanical and ... more A technique is described for micropositioning a surface forces apparatus with low mechanical and thermal drift. The technique is less exacting and more stable than competing ones.
The design, calibration, and performance are described of an apparatus to study the shear respons... more The design, calibration, and performance are described of an apparatus to study the shear response of ultrathin liquid films. The device, a modification of the surface forces apparatus, measures the resistance to shear of liquids confined between two atomically smooth solid surfaces. The surfaces are separated by distances on the order of the size of the liquid molecules (liquid film thickness <10 nm). Shear forces with periodic time dependence are applied to one surface while the second is held fixed, and any motion so induced is analyzed to determine the behavior of the liquid film. The frequency and amplitude of the shear forces applied can be varied over a wide range (0.03–60 Hz frequency and 0.1–1000 nm amplitude) to achieve different values for the magnitude of the shear rate. The dynamic response of the device is linear in the applied force at a given frequency; nonetheless, nonlinear dependence of the liquid’s shear resistance on the shear rate, net normal pressure, and f...
Diffusion coefficients of sodium and zinc ions have been measured in bilayers of commercial, part... more Diffusion coefficients of sodium and zinc ions have been measured in bilayers of commercial, partially neutralized poly(ethylene-co-methacrylic acid). The diffusion behavior shows a break at the melting temperature of the resin, suggesting that chain backbone motion is intimately related to ionic transport. The ionic diffusion coefficients are orders of magnitude greater than those of the chain backbone, which suggests that metal ion pairs are transported along the contour of the polymer network via exchange with protons of neighboring acid groups. Interfacial strength development in welded films of ionomers is primarily determined by the melting behavior of the bulk resin. Ionic diffusion rates do not correlate with the strength development behavior. This observation, along with melting and chain center of mass diffusion information, suggests that strength development is dependent on chain interdiffusion like that of many other thermoplastics.
Direct evidence of the changing structure of an adsorbed PMMA layer at the solid/solution interfa... more Direct evidence of the changing structure of an adsorbed PMMA layer at the solid/solution interface during early stages of the adsorption is presented
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