Blends, thin films of

Acknowledgement is made to the donors of Petroleum Research Fund administered by the American Chemical Society for partial support of this research under the PRF Research Grant No. 8285AC6C. Thanks are expressed to the NSF for partial support under the Grant DMR-75-17397. 

Shibaev, V.P., Freidzon, J.S., and Plate, N.A., Dokl. Acad. Nauk. USSR, (1976) 1412. 

Influence of Mesomorphic Order on the Physical Properties of Poly(/)-Biphenyl Acrylate) and Related Polymers 

Department of Mechanics and Materials Science, Rutgers, The State University, 

Universita di Pisa, Istituto di Ghimica Industrial ed Applicata, 56100 Pisa, Italy 

---

In a large part of what we have discussed above, we considered binary polymer mixtures. However, the situation is somewhat different, if instead of polymer blends, thin films of block copolymers are investigated. Due to the molecular connectivity of the different blocks, the inherent length scale is now determined by the size of the molecules. Early experiments focussed on the thin film morphology in symmetric diblock copolymers, where surface interactions tend to orient the block copolymer lamellae parallel to the boundary surfaces. In contrast to most bulk specimens, the planar interfaces lead to the formation... 

Akhtar, S. Morphology and Physical Properties of Thin Films of Thermoplastic Elastomers from Blends of Natural Ruhher and Polyethylene, Rubber Chem. Technol. 61, 599-583, 1988. 

A similar one-step process was employed successfully [66] to prepare well-crystallized CdS thin films of optical quality on Au(lll) from an aqueous solution of CdSOa, EDTA, and Na2S at room temperature. A phase transition from cubic (zinc blende) to hexagonal (wurtzite) CdS structure was observed with decreasing pH below 5, while highly preferential orientation along [11.0] directions for the... 

Bruder and Brenn (1992) studied the spinodal decomposition in thin films of a blend of deuterated polystyrene (dPS) and poly(styrene-co-4-bromostyrene) (PBrxS) by TOF-ERDA. They examined the effect of different substrates on the decomposition process. In one series of experiments, a solution of the polymers in toluene was spread on a silicon wafer to form a film of thickness 550 nm which was then heated in vacuum at 180°C for various times. 

The second example, a blend sample consists of 80% PA 6.6, 18% PTFE and 2% silicone oil. From the relative concentrations, it can be seen that PA forms the matrix and provides the necessary stability to the bearing. PTFE acts as an incorporated lubricant. The two main components are not chemically linked. Therefore, silicone oil has been added to work as a boundary lubricant during the break-in phase of the bearing. Due to its liquid nature, it quickly migrates to the surface when pressure is applied and prevents abrasion at the first stage. Shortly after, a thin film of PTFE forms at the interface between the thermoplastic bearing and the counter part. 

Microdomains of block copolymer/ homopolymer blends 25-A-diameter Pd clusters Metal-ion precursors, introduced into cast thin films of polymer microdomains, are reduced by high pressure hydrogen 60,61... 

Thin films of block copolymer/homopolymer blends... 

Thin films of blends of block copolymer with two homopolymers... 

Fig. 6.52 Interfarial excess in thin films of blends of a dPS-P2VP diblock (A PS = 391, jVP2Vp = 68) with PS homopolymer (NK = 6440) (Dai et al. 1992). Since the homopolymer is much longer than the diblock, the diblock forms a dry brush. The circles are the results from forward recoil spectrometry, the lines correspond to theoretical calculations. The dashed line was computed using the theory of Leibler (1988), and the solid line is from the self-consistent mean field calculation of Shull and Kramer (1990).

Thin films of blends containing two block copolymers... 

The bilayer morphology of thin asymmetric films of may be unstable. A regularly corrugated surface structure of the films was ascribed to spinodal transition into a laterally phase separated structure, where the surface morphology depended on the polymer incompatibility and the interfacial interactions [347, 348]. Recently, the phase separation and dewetting of thin films of a weakly incompatible blend of deuterated PS and poly(p-methylstyrene) have been monitored by SFM [349, 350]. Starting from a bilayer structure, after 454 h at T= 154 °C the film came to the final dewetting state where mesoscopic drops of... 

Blending different polymers and thereby conserving their individual properties in the blend is an extremely attractive way to obtain new bulk materials [33,34] or to coat surfaces by functional films [35-40], Thin films of such blends provide micron-sized surface structures that are well adapted to a large variety of applications where the emphasis is not on nano-structures as, for example, in optics [6,41,42], The resulting structures are mainly determined by the used blending ratio and solvent interaction [43-45],... 

When we now consider a thin film of thickness D, Eq. (41) must be supplemented by boundary conditions of the same type as in the polymer blend case, Eqs. (7) and (10), i.e. we add a (bare) surface free energy contribution to the free energy that accounts for preferential attraction of one kind of monomers to the walls, missing neighbors in the pairwise interactions, and possible changes in the pairwise interactions near the surface. As in the blend case, this surface contribution is taken locally at the walls only and expanded to second order in the local order parameter /(z). Per unit area of the wall, this free energy is written as... 

As discussed already in the introduction, there is a huge and diverse literature on thin films of polymer blends and block copolymers. The field is rapidly developing, and many phenomena are as yet not fully understood. In this section, we hence cannot attempt to give a fair evaluation of this rich literature, but focus... 

Zinc selenide (yellow) and telluride (brown) have similar stractures to those of the sulfide, both existing in both wurtzite and zinc blende modifications. The selenide is used with zinc sulfide as a phosphor. It has the interesting property that it can act as a bine-green solid state laser bine-green laser action in solids is rare (most solid-state lasers function towards the red end, 635 nm or more, of the spectrum). At room temperature, laser action with the selenide at a wavelength of 525 nm (green) is observed and at -196°C at 495 nm (bine). Unfortunately the laser is relatively short-lived. Zinc telluride is a wide band gap semicondnctor whose electron transport properties in the form of thin films of stoichiometric and nonstoichiometric forms have been mnch studied. Its applications in optoelectronics, for example, as an optical recording material, have been reviewed. ... 

Suspensions of polyacetylene were prepared as burrs or fibers (46) by using a vanadium catalyst. When the solvent was removed, films of polyacetylene were formed with densities greater than that prepared by the Shirakawa method. These suspensions were mixed with various fillers to yield composite materials. Coatings were prepared by similar techniques. Blends of polypyrrole, polyacetylene, and phthalocyanines with thermoplastics were prepared (47) by using the compounding techniques typically used to disperse colorants and stabilizers in conventional thermoplastics. Materials with useful antistatic properties were obtained with conductivities from 10" to 10" S/cm. The blends were transparent and had colors characteristic of the conducting polymer. For example, plaques containing frans-polyacetylene had the characteristic violet color exhibited by thin films of solid trans-polyacetylene. 

Using the standard TM-AFM procedures (3.2.1), the free surface of the blend thin films can be investigated. Owing to the softness and adherent properties of the PB phase, it is advisable to increase the rms amplitude of the free cantilever oscillation sufficiently. 

Pulsed force mode scans on the thin film of the phase separated blend of P2VP and PtBMA show pronounced contrast in two imaging modes, i.e., height and adhesion, while the stiffness suffers to some extent from artefacts. In a new mode called combined dynamic X mode SFM, these problems are overcome [30]. 

Fig. 4.12 Pulsed force mode measurement on a thin film of a blend of P2VP and PtBMA. The pulsed force mode AFM adhesion image (5x5 pm) clearly distinguishes the PtBMA islands from the surrounding P2VP. (Reprinted with permission from [30]. Copyright 2000. American Institute of Physics.)...

Thin films of a blend of poly(sebaic acid) and PLA (Polysciences) on glass are prepared by spin-coating from 1 w/v % solutions in chloroform onto cleaned glass slides. The glass slides are glued with epoxy to the metallic sample holder disc. 

J. Spadavecchia, G. Ciccarella, P. Siciliano, S. Capone, R. Rella, Spin-coated thin films of metal porphyrin-phthalocyanine blend for an optochemical sensor of alcohol vapors. Sen. Actuators, B, Chem 100, 88-93 (2004). 

Fig. 1.6 TEM image of a RuOi-stained thin film of an atactic polystyrene/Kraton G1650 blend containing 30% polystyrene. Swollen styrene domains can be seen within the block copolymer together with the larger phase-separated polystyrene regions.

Samples for transmission electron microscopy were prepared in the following manner. A 50/50 blend was potted in an acrylic resin (London Resin Co. Ltd.) and subsequently microtomed in thin films of approximately 600 angstrom thickness and transferred onto electron microscope grids. These sections were then doped with iodine vapor (stained) and were ready for transmission electron microscopy. The blends of other compositions were not examined in this manner for reasons discussed later. 

---