A theory is developed to account for the restricted swelling in solvents of crosslinked elastomers containing reinforcing fillers. Assuming swelling to be completely restricted at the filler‐rubber interface due to adhesion, the following relation is obtained: where vr is the volume fraction of rubber in the swollen rubber phase, Vro is the same quantity referred to on otherwise analogous, unfilled vulcanizate, Φ is the volume fraction of filler, and c a parameter depending on the filler, but independent of Φ and Vro. This equation is shown to hold for a large volume of experimental data on carbon blacks, involving four rubbers, several sulfur vulcanizing systems, five solvents, and a wide range of crosslinking. Conformance with the theory indicates that carbon blacks are firmly bonded to the rubber and that, in the sulfur crosslinking systems investigated, they have no significant effect on the stoichiometry of vulcanization (although they may affect the rate of vulcanization). Illustrative examples of applications of the theory to problems in filler reinforcement and vulcanization are shown.

The three-body breakup 6 He→ 4 Heϩnϩn is studied experimentally, using a secondary 6 He ion beam of 240 MeV/nucleon incident on carbon and lead targets. Integrated cross sections for one-and two-neutron knockout and differential cross sections d/dE* and d/d for inelastic nuclear or electromagnetic excitations into the 6 He continuum are presented. The E1-strength distribution is deduced from electromagnetic cross sections and is found to exhaust (10Ϯ2)% of the energy-weighted Thomas-Reiche-Kuhn sum rule or (40Ϯ8)% of the cluster sum rule for excitation energies below 5 MeV. Both the energy-weighted and non-energy-weighted dipole cluster sum rules are almost exhausted integrating the strength up to 10 MeV, a fact from which the root-mean-square distance between the ␣ core and the two valence neutrons of r ␣Ϫ2n ϭ(3.36Ϯ0.39) fm is derived. The known I ϭ2 ϩ ͑1.80 MeV͒ resonance in 6 He is observed in nuclear inelastic scattering; model-dependent values of the quadrupole deformation parameter ␦ 2 ϭ(1.7Ϯ0.3) fm or B(E2,0 ϩ →2 ϩ )ϭ(3.2Ϯ0.6)e 2 fm 4 are derived. No clear signature could be obtained for predicted higherlying 2 ϩ resonances, but low-lying continuum strength of multipolarity other than dipole, likely of monopole and quadrupole multipolarity, is indicated by the data. Two-body correlations in the decaying 4 Heϩnϩn system are investigated. The astrophysical relevance of the data with regard to the two-neutron capture process 4 He(2n,␥) 6 He is briefly discussed.

The reinforcement of elastomers by carbon black is governed by the morphology of the black and its physical and chemical interactions with the polymer. The latter are strongly affected by graphitization and surface oxidation. In modern rubber-grade carbon blacks strong bonding of the polymer to the carbon black surface is effected by several mechanisms, but surface chemical differences between blacks are relatively small, so that the dominant characteristic becomes the morphology. This is determined by the average size and size distribution of the particles which are fused together to form primary aggregates resembling branched random coils, the spatial arrangement of the particles in these aggregates, and the number of particles per aggregate and its distribution. This highly complex morphology can, to a first approximation, be represented by the specific surface area accessible to rubber and some, usually indirect, measure of the volume pervaded by the primary aggregates (“structure”). Important mechanical properties of reinforced rubbers depend to different degrees on these two characteristics, often in rather complex manner. Their effects on viscoelastic and failure properties are described. Additionally, some very recent observations on the effects of carbon black on network structure and the influence of the breadth of the aggregate size distribution on viscoelastic behavior are discussed.

Abstract. The longitudinal momentum distribution of ZBe was measured after the break-up reaction of s B in C, A1, and Pb targets at 1471 A.MeV. We observed a narrow distribution with a FWHM of (814-6) MeV/c in all targets. The experimental results indicate an extended spatial distribution of the loosely bound proton in s B, and agree with QRPA calculations. PACS: 27.20+n; 21.10.Ft; 29.30_h; Pioneering experiments with secondary nuclear beams [1, 2] produced via projectile fragmentation at relativistic energies have lead to the discovery of neutron-halo nuclei. These first experiments at relativistic energies (790 A.MeV) have demonstrated that nuclear structure information can be deduced from the total interaction cross sections of halo nuclei, and from the momentum distributions of the break-up products. It was shown [3,4] that the longitudinal momentum distribution which results from the fragmentation of weakly-bound light projectiles is insensitive to the break-up interaction and provides a reliable probe of the internal momentum wavefunction of the system. The nucleus SB has an extemely low binding energy (137 keV) for the valence proton and is considered to be a proton halo candidate. However, the existence of nuclei with a proton halo is controversial based on present experimental and theoretical results [5,6,7,8]. Inspired by the lack of a consistent picture we launched an experiment to investigate this nucleus by'mcasuring the longitudinal momentum distribution of ~'Be created in the break-up reaction at relativistic energies in different target materials. were used at the central and at the final focalplane for momentum an, d cross-section measurements, respectively. The fields of the first t#vo dipole stages of the FRS were set to select SB. The SB nuclei were identified by a combination of their magnetic rigidity (Bp) and energy loss measured by a position sensitive scintillation detector located in front of the secondary target at the central focal plane. In order to measure the parallel momentum distribution of 7Be fragments the FRS was operated as an energy-loss spectrometer [9]. The incident phase space of the SB ions was reduced by slits at the dispersive first focal plane and at the entrance of the FRS in order to reduce transmission losses for the break-up products. The FRS magnets behind the secondary target were set to transmit ZBe nuclei produced from SB break-up. A valid SB identification at the central focal plane was required in coincidence with a ZBe ion at the final focal plane. Targets of 4.40 g/cm 2 C, 5.45 g/cm 2 A1, and 8.00 g/crn 2 Pb were used. The particle identification of ZBe was performed by coincident time-of-flight and energy-deposition measurements combined with the Bp analysis deduced from position measurements (x) at the final focal plane. The Z-identification and the position measurement at the final focal plane were done with two ionisation chambers (ICI,IC2). The peculiar situation that both neighboring isotopes of SB and ;'Be are particle unstable allowed reaction cr...

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Inelastic proton scattering to the first excited 2+ state of the doubly magic ' Ni nucleus was investigated in inverse kinematics, using a secondary beam of radioactive Ni nuclei. At an incident energy of 101 MeV/nucleon, a value B(E2, 0+ 2+) = 600~120 e~fm4 was measured. This result completes the set of experimental data for the first excited 2+ states in the 1f 2p shell with a closed shell of neutrons or protons. These data are compared to recent shell-model calculations.

synopsisThe effect of monomer sequence on physical properties was investigated for butadienestyrene solution copolymers made by organolithium initiation. The polymers varied from random copolymers of uniform composition along the polymer chain to ideal block polymers of specific block sequence arrangement and included rubbers of intermediate degrees of randomness. Uniform composition random copolymers exhibit a single glaw transition temperature and a very narrow dynamic loss peak corresponding to this transition. The glass transition can be predicted from the styrene content and the microstructure of the butadiene portion of the rubber. Random copolymers in which compe sition varies along the polymer chain, and to some extent between molecules, exhibit a single glass transition, but the dynamic loss peak is broadened. The extent of this broadening is shown to be compatible with the sequence distribution, polymer segments of various compositions losing mobility a t different temperatures. This indicates a tendency for association between segments of different temperatures. This indicates a tendency for association between segments of different chains which are similar in composition. Block copolymers display two transitions, corresponding to T, for each type of block. The position and width of the dynamic loss peaks are related to block length and compositional purity of the blocks. 1581