Polymer dynamics, measurement

A considerable number of experimental extensions have been developed in recent years. Luckliam et al [5] and Dan [ ] review examples of dynamic measurements in the SFA. Studying the visco-elastic response of surfactant films [ ] or adsorbed polymers [7, 9] promises to yield new insights into molecular mechanisms of frictional energy loss in boundary-lubricated systems [28, 70]. 

Some viscoelasticity results have been reported for bimodal PDMS [120], using a Rheovibron (an instrument for measuring the dynamic tensile moduli of polymers). Also, measurements have been made on permanent set for PDMS networks in compressive cyclic deformations [121]. There appeared to be less permanent set or "creep" in the case of the bimodal elastomers. This is consistent in a general way with some early results for polyurethane elastomers [122], Specifically, cyclic elongation measurements on unimodal and bimodal networks indicated that the bimodal ones survived many more cycles before the occurrence of fatigue failure. The number of cycles to failure was found to be approximately an order of magnitude higher for the bimodal networks, at the same modulus at 10% deformation [5] ... 

An instrument designed to follow hysteresis losses in polymers by measuring the resistance to the rolling of small balls over the surface of the test piece it can investigate transitions in polymers to as low a temperature as -120 °C. Superseded by modem dynamic mechanical thermal analysis equipment. 

This reasoning also means that we were not really describing a thermodynamic measurement of the glass transition in a polymer melt but instead a macroscopic determination of the temperature dependence of volume-related internal relaxation processes, i.e., a dynamic measurement in the disguise of a thermodynamic measurement. 

In the systems that I have examined, I can satisfy the dynamic requirements with a ten second pulse delay. The longest methyl T] may be 3 seconds. In general, the longer the side chain, the longer will be the methyl Tj. We will hear more about this subject later on. We need not be too concerned about NOE factors because they are usually full under the experimental conditions (T = 120-130°C) used for polymer quantitative measurements. The Tj problem can be handled, even under non-equilibrium conditions, by utilizing resonances from the same types of carbon atoms in a quantitative treatment. Such an approach can sometimes lead to more efficient quantitative NMR measurements. Adequate pulse spaclngs will have to be used whenever one wishes to utilize all of the observed resonances. Quantitative measurements in branched polyethylenes are very desirable because this is one of the best applications of analytical polymer C-13 NMR. 

We report herein on high-resolution NMR studies of cuticles from limes (7) and of suberized cell walls from potatoes. Measurements include identification and quantitation of magnetically distinct carbon moieties, determination of site-specific polymer dynamics on both MHz and kHz timescales, and delineation of the interactions among polyester, wax, and cell-wall components. 

Polymer Dynamics. 13C spin-lattice relaxation times (Ti) were determined with either an inversion-recovery sequence (16) (for carbons observed by direct polarization) or with a modified cross-polarization experiment (17). 13C rotating-frame relaxation times (Tip(C)) were derived from measurements of the carbon signal that remained after a Tjp(C) hold time of... 

Although crosslinked polymers and polymer gels are not soluble, the spectra of swollen, low crosslink density networks exhibit reasonably narrow C-13 NMR line widths, sufficiently resolved to reveal details of microstructure 13S). Thus, recording the spectra under scalar low power decoupling yields characterization information and some dynamic measurements, concerning T, T2 (line widths) and nuclear Overhauser enhancement (NOE) for lightly crosslinked polymers. 

Dynamic Measurements. A Vibron direct reading viscoelastometer (Toyo Measuring Instruments Co., Ltd., Tokyo, Japan) was used to determine viscoelastic properties. This instrument and its operation have been described in detail by Takayanagi and Yoshino (II, 14). All polymers and blends were examined at a standard frequency of 110 cps. In a few selected examples measurements were also made at 3.5 cps. 

Dynamic Measurements. Figures 1 and 2 show the dynamic storage and loss moduli E and E" at 110 cps for the six component polymers, A to F. The position of the loss maximum is plotted as Tm 1 vs. styrene content in Figure 3. A good straight line is obtained which passes through the expected values for pure polybutadiene (15% vinyl) and polystyrene... 

Steady shear viscosities can be measured with two different instruments. The System IV can measure polymer viscosities from about 0.001 to 10 sec 1 while the Gottfert Capillary Rheometer is capable of obtaining viscosities from 0.1 to 100,0001/s. In steady shear, the strains are very large as opposed to the dynamic measurements that impose small strains. In the capillary rheometer, the polymer is forced through a capillary die at a continuously faster rate. The resulting stress and viscosity are measured by a transducer mounted adjacent to the die. A schematic of the system is illustrated in Figure 5. 

T. Inoue, H. Hayashihara, H. Okamoto, and K. Osaki, Birefringence of amorphous polymers. I. Dynamic measurements on polystyrene, Macromolecules, 24, 5670 (1991) T. Inoue, H. Okamoto, and K. Osaki, Birefringence of amorphous polymers, I. Dynamic measurement and relaxation measurement, J. Polym. Sci. Part B. Polym. Phys., 30,409 (1992). 

T. Inoue, H. Okamoto, and K. Osaki, Birefringence of amorphous polymers. I. Dynamic measurements of polystyrene, Macromolecules, 24, 5670 (1991). 

Inoue T, Okamoto H, Osaki K (1991) Birefringence of amorphous polymers. 1 Dynamic measurements on polystyrene. Macromolecules 24 5670—5675 Isayev AI (1973) Generalised characterisation of relaxation properties and high elasticity of polymer systems. J Polym Sci A-2 116 2123—2133 Ito Y, Shishido S (1972) Critical molecular weight for onset of non-Newtonian flow and upper Newtonian viscosity of polydimethylsiloxane. J Polym Sci Polym Phys Ed 10 2239— 2248... 

FIG. 25 Coefficients of static and dynamic friction between the bladder membrane and the polymer surface measured during in vitro friction testing. The square and circle symbols denote the nonlubricated and the lubricated surface, respectively. The open and closed symbols denote coefficients of static and dynamic friction, respectively. The coefficients of friction were measured after pre-loading. (From Ref. 87.)... 

Intercalated compounds offer a unique avenue for studying the static and dynamic properties of small molecules and macromolecules in a confined environment. More specifically, layered nanocomposites are ideal model systems to study small molecule and polymer dynamics in restrictive environments with conventional analytical techniques, such as thermal analysis, NMR, dielectric spectroscopy and inelastic neutron scattering. Understanding the changes in the dynamics due to this extreme confinement (layer spacing < Rg and comparable to the statistical segment length of the polymer) would provide complementary information to those obtained from traditional Surface-Force Apparatus (SFA) measurements on confined polymers (confinement distances comparable to Rp [36]. 

The absorption spectrum studies presented above merely reflect the electronic environment of the molecule and do not give specific information about the type of interaction. The data which must be accounted for in considering a physical mode for the binding process can be derived from several different approaches. Hydro-dynamic measurements on the DNA-drug complex are of interest, since Lerman58, S9 has established that an increase in the intrinsic viscosity of DNA and a decrease in the sedimentation coefficient of the polymer are two criteria for intercalation of ring systems between base pairs of a double-helical DNA. 

Fytas et al. [18[ observed polymer dynamics associated with height fluctuations of PEO-PS copolymers attached to glass in toluene. Some of the measured normalized autocorrelation functions are shown in Fig. 8. The data was well represented by a single exponential function with a decay constant that exhibited minimal dependence on q. There is no calculation of the structure factor for such a system, but it is possible to rationalize the dependence of the decay constant on the 5/3 power of the chain density and the cube of the number of monomers in the PS segment. 

Yandrasits, M.A. et al.. Dynamics of PFSA polymer hydration measured in situ by SAXS, ECS Trans., 3, 915, 2006. 

Thus, in the case of polymer solutions. Synchrotron excited FAD leads to results consistent with previous experimental data and with the most recent theoretical expectations. Moreover, this technique is able to measure the OACF with a precision unavailable previously, and gives access to new information on polymer dynamics. These observations support the use of this technique in the newer field of local dynamics in bulk polymers. 

Polarized fluorescence arises from a different optical interaction with matter than does Raman scattering, but as in Raman scattering, the wavelength of the emitted light differs from that of the incident light. Also like Raman scattering, fluorescence polarization also allows one to measure both second and fourth moments of the orientation of specific bonds in a molecule. Monnerie (1987) has pioneered the application of fluorescence polarization methods to polymer dynamics. 

Dynamic mechanical tests have been widely applied in the viscoelastic analysis of polymers and other materials. The reason for this has been the technical simplicity of the method and the low tensions and deformations used. The response of materials to dynamic perturbation fields provides information concerning the moduli and the compliances for storage and loss. Dynamic properties are of considerable interest when they are analyzed as a function of both frequency and temperature. They permit the evaluation of the energy dissipated per cycle and also provide information concerning the structure of the material, phase transitions, chemical reactions, and other technical properties, such as fatigue or the resistance to impact. Of particular relevance are the applications in the field of the isolation of vibrations in mechanical engineering. The dynamic measurements are a... 

In this paper we will concentrate on the diffraction techniques (SANS and reflectometry), and hence static measurements. However, it should be pointed out that through inelastic scattering, aspects of polymer dynamics are accessible. In particular, it has been possible to access single chain dynamics in bulk systems, deformation and relaxation of polymer melts under shear, shed new light on viscoelasticity in polymer melts, and obtain direct information on polymer reputation and particle fluctuations. 

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