An associated solvent theory of polymer solutions
Association model theory for thermodynamic properties of nonpolar polymer mixtures with polar solvent
THERMODYNAMIC PROPERTY↗
SEARCH · Search NASA
Results for “polymer theory”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Polymer-degradation theory of pressure- sensitive hybrid combustion
Polymer thermal degradation theory of pressure sensitive hybrid combustion, calculating linear regression rates
Kumar, R. N.↗
Solid Rocket Fuel Constitutive Theory and Polymer Cure
Solid Rocket Fuel is a complex composite material for which no general constitutive theory, based on first principles, has been developed. One of the principles such a relation would depend on is the morphology of the binder. A theory of polymer curing is required to determine this morphology. During work on such a theory an algorithm was developed for counting the number of ways a polymer chain could assemble. The methods used to develop and check this algorithm led to an analytic solution to the problem. This solution is used in a probability distribution function which characterizes the morphology of the polymer.
Ream, Robert↗
Deformation-Induced Anisotropy of Polymers
New theory calculates anisotropies induced by large deformations in polymers. Theory was developed primarily for calculating anistropy of thermal expansivity, but is also applicable to thermal conductivity, elastic moduli and other properties. Theory assumes that in isotropic state, long polymer chains are randomly coiled and not oriented in particular direction. They acquire an orientation when material is deformed. As average molecular orientation increases with deformation, properties of bulk material exhibit averaging of the microscopic anistropies of the oriented molecular segments.
Peng, S. T. J.↗
Thermal Expansion and Swelling of Cured Epoxy Resin Used in Graphite/Epoxy Composite
The thermal expansion and swelling of resin material as influenced by variations in temperature during moisture absorption is discussed. Comparison measurements using composites constructed of graphite fibers and each of two epoxy resin matrices are included. Polymer theory relative to these findings is discussed and modifications are proposed.
Adamson, M. J.↗
Viscoelasticity and plasticity considerations in the fracture of glasslike high polymers.
Fracture theory for amorphous high polymers below glass transition temperature, considering viscoelastic effects on structural defect stress concentration
CRACK PROPAGATION↗
Theory of Transport of Long Polymer Molecules through Carbon Nanotube Channels
A theory of transport of long chain polymer molecules through carbon nanotube (CNT) channels is developed using Fokker-Planck equation and direct molecular dynamics (MD) simulations. The mean transport or translocation time tau is found to depend on the chemical potential energy, entropy and diffusion coefficient. A power law dependence tau approx. N(sup 2)is found where N is number of monomers in a molecule. For 10(exp 5)-unit long polyethylene molecules, tau is estimated to be approx. 1micro-s. The diffusion coefficient of long polymer molecules inside CNTs, like that of short ones, are found to be few orders of magnitude larger than in ordinary silicate based zeolite systems.
Wei, Chenyu↗
Communications and control for electric power systems
The first section of the report describes the AbNET system, a hardware and software communications system designed for distribution automation (it can also find application in substation monitoring and control). The topology of the power system fixes the topology of the communications network, which can therefore be expected to include a larger number of branch points, tap points, and interconnections. These features make this communications network unlike any other. The network operating software has to solve the problem of communicating to all the nodes of a very complex network in as reliable a way as possible even if the network is damaged, and it has to do so with minimum transmission delays and at minimum cost. The design of the operating protocols is described within the framework of the seven-layer Open System Interconnection hierarchy of the International Standards Organization. Section 2 of the report describes the development and testing of a high voltage sensor based on an electro-optic polymer. The theory of operation is reviewed. Bulk fabrication of the polymer is discussed, as well as results of testing of the electro-optic coefficient of the material. Fabrication of a complete prototype sensor suitable for use in the range 1-20 kV is described. The electro-optic polymer is shown to be an important material for fiber optic sensing applications. Appendix A is theoretical support for this work. The third section of the report presents the application of an artificial neural network, Kohonen's self-organizing feature map, for the classification of power system states. This classifier maps vectors of an N-dimensional space to a 2-dimensional neural net in a nonlinear way preserving the topological order of the input vectors. These mappings are studied using a nonlinear power system model.
Kirkham, H.↗
Thermal conductivity of high polymers.
Thermal conductivity theory based on molecular structure model to study linear amorphous high polymers, specifically polyethylene
MOLECULAR STRUCTURE↗
Temperature Dependence Of Elastic Constants Of Polymers
Two papers extend theory of elastic constants of disordered solids to finite temperatures below glass-transition temperatures. First paper, entitled "Elastic Constants of Disordered Solids II: Temperature Dependence," applies to cryogenic temperatures. Second paper, entitled "Theory of Thermoelastic Properties for Polymer Glasses," develops unified treatment for static compressional and elongational properties at temperatures up to glass-transition temperatures.
Simha, Robert↗
Effects of physical aging on long-term behavior of composites
The HSCT plane, envisioned to have a lifetime of over 60,000 flight hours and to travel at speeds in excess of Mach 2, is the source of intensive study at NASA. In particular, polymer matrix composites are being strongly considered for use in primary and secondary structures due to their high strength to weight ratio and the options of property tailoring. However, an added difficulty in the use of polymer based materials is that their properties change significantly over time, especially at the elevated temperatures that will be experienced during flight, and prediction of properties based on irregular thermal and mechanical loading is extremely difficult. This study focused on one aspect of long-term polymer composite behavior: physical aging. When a polymer is cooled to below its glass transition temperature, the material is not in thermodynamic equilibrium and the free volume and enthalpy evolve over time to approach their equilibrium values. During this time, the mechanical properties change significantly and this change is termed physical aging. This work begins with a review of the concepts of physical aging on a pure polymer system. The effective time theory, which can be used to predict long term behavior based on short term data, is mathematically formalized. The effects of aging to equilibrium are proven and discussed. The theory developed for polymers is then applied first to a unidirectional composite, then to a general laminate. Comparison to experimental data is excellent. It is shown that the effects of aging on the long-term properties of composites can be counter-intuitive, stressing the importance of the development and use of a predictive theory to analyze structures.
Brinson, L. Catherine↗
Viscoelastic Properties of Polymer Blends
Viscosity, shear modulus and other viscoelastic properties of multicomponent polymer blends are predicted from behavior of individual components, using a mathematical model. Model is extension of two-component-blend model based on Rouse-Bueche-Zimm theory of polymer viscoelasticity. Extension assumes that probabilities of forming various possible intracomponent and intercomponent entanglements among polymer molecules are proportional to relative abundances of components.
Hong, S. D.↗
Chemoviscosity modeling for thermosetting resins, 2
A new analytical model for simulating chemoviscosity of thermosetting resin was formulated. The model is developed by modifying the Williams-Landel-Ferry (WLF) theory in polymer rheology for thermoplastic materials. By assuming a linear relationship between the glass transition temperature and the degree of cure of the resin system under cure, the WLF theory can be modified to account for the factor of reaction time. Temperature dependent functions of the modified WLF theory constants were determined from the isothermal cure data of Lee, Loos, and Springer for the Hercules 3501-6 resin system. Theoretical predictions of the model for the resin under dynamic heating cure cycles were shown to compare favorably with the experimental data reported by Carpenter. A chemoviscosity model which is capable of not only describing viscosity profiles accurately under various cure cycles, but also correlating viscosity data to the changes of physical properties associated with the structural transformations of the thermosetting resin systems during cure was established.
Hou, T. H.↗
Studies on chemoviscosity modeling for thermosetting resins
A new analytical model for simulating chemoviscosity of thermosetting resins has been formulated. The model is developed by modifying the well-established Williams-Landel-Ferry (WLF) theory in polymer rheology for thermoplastic materials. By introducing a relationship between the glass transition temperature Tg(t) and the degree of cure alpha(t) of the resin system under cure, the WLF theory can be modified to account for the factor of reaction time. Temperature dependent functions of the modified WLF theory constants C sub 1 (t) and C sub 2 (t) were determined from the isothermal cure data. Theoretical predictions of the model for the resin under dynamic heating cure cycles were shown to compare favorably with the experimental data. This work represents progress toward establishing a chemoviscosity model which is capable of not only describing viscosity profiles accurately under various cure cycles, but also correlating viscosity data to the changes of physical properties associated with the structural transformation of the thermosetting resin systems during cure.
Bai, J. M.↗
Modeling Thermodynamics Of Charring Of A Polymer
Improved method of predicting and of nondestructively analyzing pyrolytic effects in, and thermomechanical properties of, polymers combines theories and techniques from several engineering and scientific disciplines. Evolved in effort to understand charring and erosion of carbon phenolic ablative material in nozzle of rocket engine. Also applicable to other polymers and particularly to nondestructive engineering analysis of specimens heated, charred, or burned.
Funaro, Gregory V.↗
Chemoviscosity modeling for thermosetting resin systems, part 3
A new analytical model for simulating chemoviscosity resin has been formulated. The model is developed by modifying the well established Williams-Landel-Ferry (WLF) theory in polymer rheology for thermoplastic materials. By introducing a relationship between the glass transition temperature (T sub g (t)) and the degree of cure alpha(t) of the resin system under cure, the WLF theory can be modified to account for the factor of reaction time. Temperature-dependent functions of the modified WLF theory parameters C sub 1 (T) and C sub 2 (T) were determined from the isothermal cure data. Theoretical predictions of the model for the resin under dynamic heating cure cycles were shown to compare favorably with the experimental data. This work represents a progress toward establishing a chemoviscosity model which is capable of not only describing viscosity profiles accurately under various cure cycles, but also correlating viscosity data to the changes of physical properties associated with the structural transformations of the thermosetting resin systems during cure.
Hou, T. H.↗
Formulating propellants for fully case-bonded end-burning motors
Low modulus solid propellants family for low thrust-to-mass ratio fully case bonded end-burning motors, using polymer network theory for binder formulation
Marsh, H. E., Jr.↗
A time dependent theory of crazing behavior in polymers
The development of crazing is not only a function of stress, but also a function of time. Under a simple state of tension, a craze opening displacement is closely associated with the viscoelastic behavior of the original bulk polymer medium in which individual crazes initiate and develop. Within each craze region, molecular orientation takes place when conditions permit, and a new phase of rearranged molecules governs its local behavior. Based upon a time-dependent viscoelastic two-dimensional model, using a computer program the craze opening displacement field has been calculated, time-dependent craze length was also computed by taking into consideration the molecular orientation mechanism and large deformations in the craze region. Examples are given for simple viscoelastic media with simplified stress distributions. It is interesting to find out that the occurrence of crazing may be interpreted in terms of the stability or instability of the constitutive behavior of the bulk polymer.
Chern, S. S.↗