We have studied, by simultaneous force and WAXS measurements, crystallization and melting properties of stretched natural poly cis-isoprene, vulcanized at different rates, in static and dynamic deformations. The overall effects of increasing N C, the number of monomers between cross-link bridges, is to slow the kinetics of crystallization and to decrease the melting temperature, crystallites sizes, crystallinity, and mechanical hysteresis. The origin of these properties is discussed. The morphologies of vulcanized rubbers during static and dynamic deformations are very similar. The process of crystallization (and melting) occurs during these two types of deformation by nucleation (and disappearance) of crystallites with constant sizes. The role of the affine deformation of the cross-link network on the crystallites dimension is pointed out. During cyclic deformations, real time measurements during stretching and recovery permit one to conclude that mechanical hysteresis is due only to the chains crystallization or more exactly to the supercooling (difference between melting and crystallization temperatures). During stress hardening, the form of the stress-strain curve σ ∼ λ 2 is explained following the Flory idea. Each new crystallite formed during stretching is considered as a cross-link. The Flory stress-induced crystallization model is discussed. In the Appendix, we describe the new effect called "inverse yielding" observed in weakly cross-linked rubbers.

We have examined the polymer/surfactant interaction in mixed aqueous solutions of cationic surfactants and anionic polyelectrolytes combining various techniques: tensiometry, potentiometry with surfactant-selective electrodes, and viscosimetry. We have investigated the role of varying polymer charge density, polymer concentration, surfactant chain length, polymer backbone rigidity, and molecular weight on the critical aggregation concentration (Cac) of mixed polymer/surfactant systems. The Cac of these systems, estimated from tensiometry and potentiometry, is found to be in close agreement. Different Cac variations with polymer charge density and surfactant chain length were observed with polymers having persistence lengths either smaller or larger than surfactant micelle size, which might reflect a different type of molecular organization in the polymer/surfactant complexes. The surfactant concentration at which the viscosity starts to decrease sharply is different from the Cac and probably reflects the polymer chain shrinkage due to surfactant binding.

The properties X (stress, crystallinity, melting temperature, crystallite sizes) of stretched filled and unfilled natural rubber (NR) are compared. The measurements have been done during deformation at equilibrium and at room temperature. From each physical property X in static and dynamic experiments one defines for the filled NR an amplification factor A X and a differential amplification factor A * X . From stress and WAXS measurements two regimes are observed:  For λ < λA, the material has not crystallized and the amplification factor A X is independent of λ. A X is on the order of 2 for the sample filled with 20% black carbon (volume concentration). It is shown that the Guth relation fits rather well our data and those of Lee and Donovan on similar filled NRs. For λ > λA, stress-induced crystallization occurs, A X ≈ 1.5−3 is weakly dependent on λ, and the differential amplification factor is constant. The values of determined by the different measurements are of the same order of magnitude. These amplification factors characterize the state of extension of the amorphous chains during the process of stress-induced crystallization.

Stress-induced crystallization, orientation, and crystallinity have been measured by X-ray diffraction around cracks in a cis-1,4-polyisoprene sample drawn at low ratio, λ < 3.5. A zone of maximum crystallinity and a transition zone of varying crystallinity are observed; the dimensions of these semicrystalline zones surrounding the crack tip are measured as a function of the draw ratio, crack length, and cross-link density. An isocrystallinity map is established; this permits one to measure the local draw ratio and then the local stress around the crack tip. The stress distribution around the crack tip is compared with the scaling laws predicted by the linear or nonlinear elasticity theories. Finally, one shows the existence of a relaxed zone between the crack tip, the crack surface, and the lateral sides of the sample. The surface of this zone is comparable to the area of the semicrystalline zone around the crack tip and to the crack opening surface.

Particles in protein therapeutics are undesirable because they may have the potential for causing adverse immunogenicity in patients. Agitation-induced exposure to the air-water interface during manufacturing, shipping, and administration can cause particle formation in therapeutic protein products. We systematically studied how application of surface pressure during periodic interfacial compressions caused a model monoclonal antibody to form particles. Above a critical interfacial compression ratio of 5 we observed a dramatic increase in the rate of protein particle formation. During continuous interfacial compression/dilation cycles, particle numbers increased but the particle size distribution remained unchanged. When cyclic compressions were halted, particles did not nucleate additional particles or grow further in bulk solution suggesting that they are formed only at the airwater interface. In fact, we found that particles in the bulk slowly decreased in number upon standing. The rate of particle formation was only weakly dependent on both the bulk protein concentration and the period of cyclical interfacial compressions. These observations are consistent with the interfacial aggregation of proteins during periods of high surface pressure, followed by collapse of the adsorbed layer and detachment of protein particles from the interface into the bulk.

We report a new class of molecules, linactants, that partition at phase boundaries and reduce the line tension between coexisting two-dimensional phases in molecular monolayers. The line tension between hydrocarbon-rich and fluorocarbon-rich phases was determined by monitoring the relaxation kinetics of deformed domains. Two partially fluorinated linactant molecules (with one and two tails, respectively) were synthesized and tested; the more efficient single-tail variant reduced the line tension by more than 20% at a mole fraction of only 8 x 10(-4).

Stress-induced crystallization and melting of natural and synthetic cis-isoprene are compared by simultaneous Wide Angles X-ray Scattering (WAXS) and mechanical measurements. Natural (NR) and synthetic polyisoprene (SR) rubbers have the same composition and sulfur crosslink density. At fixed elongation and during cyclic deformation, the properties X of the semi crystalline phase are determined as function of draw ratio λ; X being crystallites dimensions and orientation, half-time of crystallization, melting temperature, crystallinity and crystalline zone dimensions around a crack tip. It is shown that all the curves X(λ) of both types of rubber at room temperature can be superposed by a simple translation δλ along the draw ratio axis. This translation factor of the order of 0.5 to 1 does not depend on the property X. These effects are explained by the decrease of the melting and crystallization temperatures due to the presence of chain defects in synthetic rubber.

Real time synchrotron Small‐Angle and Wide‐Angle X‐ray Scattering was performed during the tensile deformation of a high‐density polyethylene copolymer. The changes of the structure in the crystalline and in the amorphous domains were followed during the three characteristic stages of the load‐displacement curves: The elastic stage and the plastic range composed of the stage of the lowering load in the force‐displacement‐curve (yielding) and the strain hardening. Competitive phenomena like crystallite fragmentation and cavitation were found to occur simultaneously in the phase of lowering the load but at different length scale. We prove that the void formation occurs mainly during yielding. During strain hardening there was no further increase of the void volume fraction, only changes in void size.