Polymer bulk composites

Researchers have performed experiments on CNT-polymer bulk composites at the macroscale and observed the enhancements in mechanical properties (like elastic modulus and tensile strength) and tried to correlate the experimental results and phenomena with continuum theories like micro-mechanics of composites or Kelly Tyson shearing model [105,115-120]. 

In a molded polymer blend, the surface morphology results from variations in composition between the surface and the bulk. Static SIMS was used to semiquan-titatively provide information on the surface chemistry on a polycarbonate (PC)/polybutylene terephthalate (PBT) blend. Samples of pure PC, pure PBT, and PC/PBT blends of known composition were prepared and analyzed using static SIMS. Fn ment peaks characteristic of the PC and PBT materials were identified. By measuring the SIMS intensities of these characteristic peaks from the PC/PBT blends, a typical working curve between secondary ion intensity and polymer blend composition was determined. A static SIMS analysis of the extruded surface of a blended polymer was performed. The peak intensities could then be compared with the known samples in the working curve to provide information about the relative amounts of PC and PBT on the actual surface. 

For the calculation of AhP we must count contacts within the surface layer, and between the surface layer and the neighbouring layer (which has bulk composition). This calculation is simplified very much if we assume that at the critical point the surface is almost saturated with displacer (i.e. g 1), since not only the polymer, but also the still more weakly adsorbing solvent will have been almost completely displaced. Before exchange, we have a displacer molecule at the surface, and a segment in the solution, giving contributions to the mixing energy h = X Jx 0 and ... 

Every segment in the polymer chain is solvated by two solvent molecules. Those molecules of solvents 1 and 3 in the solvated sheath which correspond to the bulk composition of 1 1 are disregarded. Only those molecules of solvent 1 in the solvated sheath in excess of this 1 1 ratio constitute what may be regarded as the complex with the polymer. In this particular example the value of is 1 mol of solvent-1 per mol of segment. If the molar volumes of liquid-1 and polymer segment were equal, the coefficient of selective adsorption could also be expressed here as 1 ml of liquid-1 per ml of monomer units. 

The interface region thus formed has a substantial thickness, and its chemical, physical and mechanical properties are different from those of either the bulk fiber and the matrix (i.e., the interphase as opposed to the interface of zero thickness). The interphase is found to be significantly softer than the bulk matrix material in polymer matrix composites (Williams et al., 1990 Tsai et al., 1990). For example,... 

This paper reviews the results of investigations into low-frequency mechanical and high-frequency (ultrasonic) vibration effects upon flowable polymeric systems, primarily, on molten commercial thermoplastics. We tried to systematize possible techniques to realize vibration in molding of polymers. Theoretical and experimental corroboration is provided for major effects obtained at cyclic (shear and bulk) strains of molten polymers and compositions based thereon. It is demonstrated that combined stress of polymeric media is attained under overlapping vibrations and this results in a decreased effective viscosity of the melts, a drop i the pressure required to extrude them through molding tools, increased critical velocities of unstable flow occurrence and a reduced load on the thrust elements of extruder screws. 

The most obvious requirement, of course, is that the specimen be cut to size. The size depends on the microscope and could range from a few centimeters in a normal SEM to a few inches in a specially designed SEM. In TEM, of course, since the thickness is extremely low and the sample needs to be on a grid or support, the specimen is normally a few millimeters in size. Ductile metals are sometimes rolled into sheets before cutting into the desired size. It needs to be kept in mind that this process itself will lead to defect creation and microstructural changes that need to be annealed out [11], Some polymers and composites are easily available as sheets anyway, so this step is not of any concern. In the large variety of bulk materials that it is not possible to form into sheets, sectioning the sample to a thin slice is the only way to start. 

Several applications of scanning force microscopy (SFM) and related techniques in polymer science have been given in the above sections. The reviewed results were gathered from surfaces of cross-sectioned bulk polymers, polymer-matrix composites, and polymer blends as well as free surfaces of polymer samples such as films, or surfaces prepared by means of replica techniques. The materials contrasts reported on range from several mechanical ones via thermal to electrical ones. 

Electrodeposition — Electrodeposition is the process of forming a film or a bulk material using an electrochemical process where the electrons are supplied by an external power supply. It is an important surface finishing procedure and in the broadest sense comprises the deposition of metals, alloys, oxides, polymers, and composites. 

Table I - Bulk. Compositions, Solvents and Synthesis References for Polymer Systems Studied...

In the blends, the concentration of PS at the polymer-air interface is higher than the bulk concentration of PS. However, the surface excess of PS in the polyblends is less than that found in the diblock copolymers of comparable bulk composition. 

Non-Aqueous Processes. Dispersions of composite particles in non-aqueous media (12) have been prepared. The particles were sterically stabilised to prevent flocculation and aggregation. This was achieved by physical absorption of amphipathic graft or block copolymer (13,14) or by covalent attachment of diluent-soluble oligomer or polymer chains (15) at the particle surface so that by definition different polymers were situated at the surface and in the bulk of the particles, even for single-polymer particles. Composite particles were prepared by slow addition of the second monomer which was fully miscible with the diluent phase, obviating a monomer droplet phase further monomer-soluble initiation and amphipathic graft stabiliser was included as appropriate so that the process comprised continued dispersion... 

One can see that G-band is characterized with the highest intensity in the spectra (Fig. 7.6a). It should be noted as well that the SWCNT 2vd band is noticeably higher in intensity in comparison with the main D band, which can be seen from the lower curve 1. Broadband noise is typically not strong in Raman spectra of SWCNT but became more noticeable for the bulk systems (graphite and polymer-SWCNT composite, curves 2 and 3 in the Fig. 7.6a). SWCNT possess also a low-frequency vibration mode at Vrbm 160 cm corresponding to radial oscillations of carbon atoms in plane of the cross section, which exhibits a strong variation with nanotube diameter [7]. The SWCNT vibration spectra show a sum harmonic signal Vg+Vrbm with a spectral shape, which will be discussed below. 

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