The solidification of low molecular weight materials from their melts (in the absence of temperature fields) generally leads to a product with no preferred orientation, independent of the extent or rate of deformation of the melt. The solidification of polymers from a highly deformed melt or solution nearly always leads to a product with preferred molecular orientation. Further, the rate of solidification can be significantly increased by melt deformation. The change in rate, relative to that in a quiescent melt or solution, can be several orders of magnitude [1]. These differences, relative to small-molecule systems, arise from the degree to which orientation and local strain can be maintained in the melt. Due to the long-range connectivity within a polymer molecule, it is possible to impart large extensions to these molecules in the molten state, and significant time is often required for the molecules to relax back to their undistorted, coiled state. If crystallization or glass formation occurs before the chain can relax, an extended molecular configuration can be retained. Thus in the solidification of oriented polymers there exists a competition between the “freezing” of the molecular orientation and the relaxation (re-coiling) of the molecules.

In the early theories of rubber elasticity, the retractive force and change in free energy of a stretched specimen were calculated from the deformation of the polymer chains of which the rubber network was formed. The mean chain deformation was presumed to be the same as that of the macroscopic specimen, an assumption which seemed reasonable, but could not be confirmed experimentally. Small angle neutron scattering (SANS) made measurement of chain dimensions possible, and it was soon discovered [1], [2] that the actual relation between dimensional changes of the polymer chain and deformation of the specimen was not at all what had been assumed.

SANS studies of carefully prepared elastomeric networks provide the most direct experimental information required for a molecular theory of rubber elasticity, and have stimulated many new developments.

Aqueous suspensions of charged polymer latex particles exhibit several forms of ordered structure, the particular form depending on the size, number density and charge of the latex particles, and on the ionic strength of the aqueous medium. At low ionic strength, the inter-particle potential may become sufficiently long-ranged to generate crystalline order, which usually shows bcc symmetry at low density and becomes fcc above about 3% volume fraction of latex in the system. As the ionic strength increases, the crystalline structure melts, and ordered liquid structures develop. Light scattering may be used to study these structures at low density, but at higher density, where the opacity of the suspensions renders optical techniques intractable, neutron scattering must be used.

This paper will review some of the recent small-angle neutron scattering experiments on polymer latex suspensions, in the light of new theoretical methods which permit in situ analysis of the particle size and charge. The discussion will also encompass new experimental methods for studying latex structures under dynamic shear conditions.

Atactic glassy polystyrene has been deformed by shear banding. The influence of the macroscopic shear stress down to a scale smaller than the dimensions of the macromolecules has been investigated by small-angle neutron scattering. The chemical resolution has been improved by using isotopic labelling on different parts of the monomer unit. The analysis of the experimental scattering curves has been made according to the thin thread model with a superimposed thickness. On the other hand, the contrast variation method has been applied in order to determine both the structure factor of the phenyl rings and that of the backbone part of the chain. This allows us to precise the influence of non-elastic deformation on the local structure of the chain.

Amorphous Polymethylmethacrylate/Polyethyleneoxide blends deformed by solid-state coextrusion exhibit anomalous anisotropic Small Angle Neutron scattering patterns in the low q range. It is shown that upon drawing the samples have undergone phase separation to some extent. The resulting structure of the system is characterized by combining scattering techniques with Differential Scanning Calorimetry.

SANS studies on the relaxation of an amorphous polymer melt is reported. Just after the uniaxial elongation the chains deform affinely. Shortly thereafter the SANS results give evidence of chain contraction. Some randomization is observed long before the reptation time is reached.

A double rotation goniometer has been mounted in the neutron beam in order to characterize the molecular deformation in polymers subjected to various strain conditions.

The results provide a direct verification of the fiber symmetry in solid state coextruded polymethylmethacrylate (PMMA) and polypropylene (PP) homopolymers.

In the case of the shear banding phenomenon, we have been able to test the validity of the simple shear assumption: it also provides a direct estimate of the finite shear strain involved in the process. As a last illustration ofthe method, we also consider the biaxial deformation of PP and PMMA squeezed under various temperature and strain-rate conditions.

Mechanism and dynamics of the ordering process in oriented crystallization of polymers were investigated by time-resolved small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXS). As a model system for the oriented crystallization, a cross-linked polybutadiene rubber with a high cis-1,4-linkage was chosen, and the structure evolution during the isothermal crystallization was investigated under constant elongations by real time and in situ analyses of the microscopic observables such as long spacing, crystallite size, SAXS integrated intensity, WAXS crystallinity and WAXS line width as well as a macroscopic observable such as stress. The isothermal ordering processes were explored in three different crystallization regimes: crystallization from (i) unoriented melts, (ii) weakly-to-moderately oriented melts and (iii) highly oriented melts.

Small angle scattering has been used to study the mechanical fatigue of crazes in polystyrene. The high radiation intensity obtainable from a synchrotron has permitted the examination of the processes that occur during the fatigue in real time. Both the short term changes that occur within a single cycle and the long term changes that occur over many cycles have been observed.

Most of the craze growth, as measured by the scattering invariant obtained at peak deformation, occurred in the first cycle of fatigue. However the craze fibril diameter, obtained by Porod analysis, doubled over 250 cycles. As the volume of craze was not growing during during the fatigue this fibril diameter increase was believed to occur by change, that is coalescence, of the preexisting fibrils.

The SAXS patterns obtained at a number of different deformations within a single cycle were compared with calculated patterns obtained assuming that the fibrils bend in a sinusoidal manner. Good qualitative agreement was obtained so it was concluded that the craze fibrils showed considerable deformation as the craze was unloaded and then straightened out again on reloading. When the ratio of minimum to maximum deformation was decreased from 0.9 to 0.5 the fibril deformation (contraction) increased to 10% with the fibrils remaining straight. As the minimum deformation was decreased below this the craze stress tends to zero and fibril buckling was evident. The main changes in fatigue lifetime occurred over the regions where there fibrils were straight, perhaps because buckling involves relatively small deformations.

The fracture toughness and the craze shape of a propagating single crack/craze in polymethylmethacrylate has been measured in a very low pressure toluene gas environment by means of optical interferometry. Below a velocity of 0.01 mm/s the craze size increases up to 4 times the craze size in air, whereas the fracture toughness remains identical to the toughness in air. Above 0.01 mm/s the crack/craze behaves like a crack/craze in air.

One of the basic problems in the field of mechanical properties of polymers is the observation of the sequence of deformation events and the changes in microstructure associated with them during deformation at relatively high rates. Typically, well characterized polymer-samples are subjected to mechanical impact, and then various microscopy techniques are used to determine the deformation events (i.e., crazing, shear banding, cavitation) post mortem. Real time small angle X-ray scattering (RTSAXS) techniques, however, make possible the direct observation of scattering from crazes and voids while the deformation is in process. In this paper we report RTSAXS measurements, performed using intense synchrotron X-ray radiation, from a high impact polystyrene (HIPS) and an acrylonitrile butadiene styrene (ABS) copolymer during tensile impact. At a deformation rate of 4.2 cm/sec, (100 in./min), the ABS was found to absorb over ten times the impact energy of a HIPS sample. RTSAXS studies indicated: (1) that the ABS has a larger average craze fibril diameter than the HIPS (12.2nm vs. 8.7nm), (2) that localized shear occurs before crazing in the ABS, and (3) that the ABS sample generated 3.8 times the craze volume compared to the HIPS. The increase in craze volume alone, however, does not account for the greater toughness of the ABS, indicating the importance of the contribution of localized shear deformation to impact behavior.

Linear triblock copolymers of styrene and isoprene with isoprene as the centre block are microphase separated elastomers in the solid state. The styrene blocks form domains of regular morphology 1arranged on a paracrystalline lattice with considerable long range order. Domain symmetry is chiefly determined by the composition of the block copolymer; only cylindrical domain geometry is dealt with here. Three levels of organisation can be recognised.

The recent renewal of interest in the time dependent response of complex material systems stems both from their increasing importance and from recent advances in theoretical tools and concepts. This paper describes one of these advances, the coupling model of relaxation. The coupling model proposes a view of how relaxation proceeds in time in which a primitive relaxation mode is coupled to its complex surroundings. Examples of the coupling model predictions for terminal relaxations, primary-segmental relaxations including physical aging, and secondary relaxations in polymers are described. It is able to confront and quantitatively explain several long-standing problems and anomalies for which traditional approaches, in their present form, such as distributions of relaxation times, free volume, configuration entropy and reptation are not successful. The coupling model response function is also appropriate for structural nonequilibrium and its predictions for volume recovery are described. The same coupling model response function is used as a timedependent kernal in a constitutive equation to discuss nonlinear viscoelasticity. The model incorporates the strain history dependence and allows for the evolution of material structure. Using information from strain-tickle experiments on polycarbonate and polyetherimide, we show that the coupling model reproduces the essential features observed experimentally for a variety of strain histories.

The dielectric, mechanical and volumetric relaxation data, and stress-strain data in tension, shear and uniaxial compression for polymeric glasses are compared. The relaxation phenomenon is viewed as a thermodynamically irreversible response to a perturbation in the configurational state. The relaxation behavior is apparently linear only in the limit of a very small perturbation, but otherwise generally nonlinear. Adam-Gibbs' entropy equation [1] has previously been shown to describe the dielectric and volumetric relaxation data better than Doolittle's free volume equation [2]. The temperature and the structure, i.e., history, dependence of mechanical relaxation time is shown to agree with the A-G theory better Than the Doolittle theory, in that the former predicts an Arrhenius type dependence on the temperature when the structural parameter, in this case the entropy, is fixed, while the latter predicts the temperature independence if the fractional free volume is fixed in the glassy state. The temperature dependence of the distribution of relaxation times is shown to agree qualitatively with the dynamic Ising model of Fredrickson and Andersen [3] (F-A model) involving the cooperativity of molecular motions in dense liquids.

Creep and creep rupture of PMMA at high stresses have been characterized and found to be relatable by use of reduced variables, it is shown that when the creep compliances can be correlated by a superposition principle for which the vertical shift is the ratio of the applied stress to a reference stress and when strain at failure is a constant, a commonly used failure criterion (that the product of the strain rate at failure and the time to failure is constant) becomes valid. The reduced variables approach is found to apply to two greatly different thermal histories. Consistent with the concept of physical aging, the response of a quenched sample is simply shifted along the log time axis to shorter times relative to the response of the aged sample.

The nonequilibrium mechanism controlling the viscoelastic response in the glassy state is analyzed in accordance with our multiple hole energy model. The change in the nonequilibrium glassy state defines the Struik physical aging exponent and determines the motion of the relaxation time spectrum, the transition of the global shift factor and the slow decay of the stress relaxation modulus especially at longer times in the glassy state where the Kohlrausch-Williams-Watts function fails. Although the distribution of relaxation times has its time scales shifted with the aging time, the shape of the spectrum remains very much the same which supports the notion of thermo-aging-rheological simplicity in the glassy and transition states.

A Cu/polyimide thin film couple prepared on a thin quartz reed has been used to study interfacial stress relaxation during thermal cycling between room temperature and 400 °C. The polyimide thickness varies from 0 (no polyimide at all) to 10.5μm while the Cu thickness was fixed at 0.53μm. The average copper film stress has been calculated from the curvature of the quartz reed. The information clarifies the relation between the polyimide thickness and the average Cu film stress. The Cu/polyimide interfacial morphology after thermal cycling has also been examined using the cross sectional TEM technique. The results suggest that the interfacial stress is partially released through the deformation of polyimide near the Cu/polyimide interface.

The fracture properties of engineering polymers and composites are strongly affected by two major areas of influence. The first one covers the microstructural parameters of the material, whereas the second one includes the external testing conditions. In this contribution, it is mainly outlined how area one can determine the fracture characteristics. An introductory section illustrates the variety of microstructural details, for example molecular structure and semicrystalline polymer morphology, and filler related factors, such as volume fraction of reinforcing fibers, their orientation etc. In the following part, effects of these parameters on fracture mechanical properties are discussed. It is distinguished between the fracture behavior of unfilled engineering polymers, of short fiber reinforced, injection molded thermoplastics, and of continuous fiber composite laminates. In the latter group, special emphasis is given to the effect of new, high temperature resistant thermoplastic matrices, for instance PEEK, on the interlaminar fracture energy of the composites.

The fracture surface morphology of various polymer specimens, fractured under alternating loading, has been examined by scanning electron microscopy. Illustrations are given of both typical and unusual fracture surfaces and the influence of such variables as composition, molecular weight, presence of a dispersed second phase and induced thermal effects is discussed.

Polymer strength depends on the nature of the constituting elements and their mechanical, thermal, and otherwise physical, but also chemical interaction. Some of these mechanisms are discussed in this paper; special attention is given to disentanglement and chain scission.