Dangling Chains Research Articles

The effect of temperature on the viscoelastic response of rubbery polymers at finite strains

Constitutive equations are derived for the viscoelastic response of rubbery polymers at finite strains. A polymer is thought of as a network of long chains connected to temporary junctions. At random times, chains detach from the junctions, which is treated as transition from their active state to the dangling state. A dangling chain captures a new junction in the vicinity of its free end at a random instant and returns to its active state. Breakage and reformation of long chains are modeled as thermo-mechanically activated processes. Stress-strain relations for a rubbery polymer are developed using the laws of thermodynamics. Adjustable parameters in the model are found by fitting observations in uniaxial tensile tests for a carbon black filled rubber at various temperatures. Fair agreement is demonstrated between experimental data and results of numerical simulation.

Substrate effects of gel surfaces on cell adhesion and disruption.

Substrate effects of hydrogel surfaces prepared on hydrophilic and hydrophobic substrates on the cell adhesion and disruption were studied. The adhesion of tobacco protoplasts onto anionic hydrogels was strongly influenced by the substrates on which the gels were synthesized. In the case of anionic poly(2-acrylamido-2-methylpropanesulfonic acid) gel, more cells adhered on the gel surface prepared on hydrophobic substrates than that prepared on hydrophilic substrates. On the other hand, in the case of cationic quaternized poly-(dimethylaminopropylacrylamide) gel, cell disruption occurred in a few seconds accompanied with an intensive release of cellular contents on the gel surface prepared on the hydrophilic substrates, while the cationic gel synthesized on hydrophobic substrates induced no cell disruption. These different behaviors of the cell have been made in terms of different structures of gel surfaces associated with the presence of flexible dangling chains.

Permeability and diffusional studies on silicone polymer networks with controlled dangling chains

The permeability to oxygen of silicone polymer networks with controlled high-molecular-weight side chains was measured using electrochemical techniques. Networks with controlled amounts of pendent chains were prepared by hydrosilation reactions involving the addition of hydrosilanes from crosslinking molecules to the vinyl end-groups of mono- and difunctional prepolymer molecules. Values of the permeability coefficient P were determined by measuring the steady electric current in an experimental set-up in which several layers of moistened paper were placed between the network and the electrodes. The curve representing the dependence of the permeability coefficient on the molecular weight of the dangling chains, M, shows that, for values of M < 130 000, P is nearly a linear function of M; however, for M > 130 000, the permeability coefficient does not show a noticeable dependence on the molecular weight of the dangling chains. The diffusion coefficient increases with the molecular weight of the side chains, reaching a nearly asymptotic value for M ≈ 170 000.

Dynamic modeling of a trailing wire towed by an orbiting aircraft

A numerical model treating the dynamics of a long trailing wire towed by an orbiting aircraft is described. The dynamics are based on the superposition of a dangling chain model upon the steady-state, no-wind wire equilibrium position. Excitation is due to the wind's nonuniform vertical profile causing a once-per-orbit cycle harmonic aerodynamic input. The model was validated both by analytic methods and by comparison with experimental data.

Dangling polymer networks: Glass transition of PU elastomers

AbstractPolyurethane elastomers possessing dangling chains were prepared by partial substitution of the multifunctional polyol with a monohydroxyl alcohol in the reaction with an isocyanate terminated prepolymer. The dynamic mechanical spectroscopy showed that created dangling segements resulted in a broader glass‐transition region. This indicated material with potentially good energy absorbing properties might be prepared from a ‘dangling polymer’ system. © 1993 John Wiley &amp; Sons, Inc.

A PMR study of collapse in a crosslinked poly(oxyethylene- co-oxypropylene) hydrogel

Collapse of a gel prepared from an oxyethylene-oxypropylene copolymer was studied by measuring the temperature dependences of spin-lattice and spin-spin relaxation times; the copolymer network was prepared by a reaction between thiol end groups of a three-star oligomer. The collapse manifests itself by a sudden drop of the segmental mobility of macromolecules as well as of rotational mobility of water molecules. The observed strong decrease of the self-diffusion coefficient of water is not due to the sudden rise of polymer concentration, but results from a displacement of water into micropores in the collapsed gel. Parameters of the network were evaluated from the measured spin-spin relaxation times of the gel swollen in toluene-d 8: about 9 stars are situated between the crosslinks, the non-reacted arms form the dangling chain ends.

The viscoelastic relaxation of cross-linked polymer networks

Theoretical interpretations of the viscoelastic relaxation behavior of cross-linked elastomers are discussed. The dangling chain retracing mechanisms of deGennes and Pearson-Helfand, which assume that the stress contribution of a dangling chain decreases as it assumes successively lower entropy configurations, are replaced by an alternative relaxation mechanism, based on the hopping model of hindered diffusion.