Block copolymer melts copolymers

Fraai]e J G E M 1993 Dynamic density functional theory for micro-phase separation kinetics of block copolymer melts J. Chem. Phys. 99 9202... 

Fraaije, J.G.E.M., Van Vlimmeren, B.A.C., Maurits, N.M., Postma, M., Evers, O.A., Hoffmann, C., Altevogt, P., Goldbeck-Wood, G. The dynamic mean-field density functional method and its application to the mesoscopic dynamics of quenched block copolymer melts. J. Chem. Phys. 106 (1997) 4260-4269. 

K. Binder. Phase transitions in polymer blends and block copolymer melts some recent developments. Adv Polym Sci 772 181-299, 1994. 

Here, the chains are expected to be stretched, as indicated by the 2/3-power dependence of L on N, but less strongly than in solvent. The experimental evidence available to examine this argument is discussed in the section on block copolymer melts. 

Block Copolymer Melts 5.1 Bulk Block Copolymers... 

The impenetrability of assemblies of tethered chains has broad implications. Some of these are discussed in more detail in the sections on interactions, on dynamics and on block copolymer melts. Examples of phenomena that have been... 

Binder, K. Phase Transitions in Polymer Blends and Block Copolymer Melts Some Recent Developments. VoL 112, pp. 115-134. 

The mean-field SCFT neglects the fluctuation effects [131], which are considerably strong in the block copolymer melt near the order-disorder transition [132] (ODT). The fluctuation of the order parameter field can be included in the phase-diagram calculation as the one-loop corrections to the free-energy [37,128,133], or studied within the SCFT by analyzing stability of the ordered phases to anisotropic fluctuations [129]. The real space SCFT can also applied for a confined geometry systems [134], their dynamic development allows to study the phase-ordering kinetics [135]. 

These concentration fluctuations are pivotal to the phase transitions in block copolymer melts and are dynamic in nature. They lead to a renormahzation of the relevant interaction parameters and are thought to be responsible for the induction of the first-order nature of the phase transition [264,265]. Such fluctuations are better studied in dynamic experiments. Thus, one can observe an increasing interest in diblock copolymer dynamics. These dynamic properties are being analysed through experimental, theoretical [266,267] and computer simulation approaches [268,269] with the aim of determining the main featirres of diblock copolymer dynamics in comparison to homopolymer dynamics. There are three main issues ... 

The combination of careful chemical synthesis with NSE and SANS experiments sheds some light on the fast relaxation processes observed in the collective dynamics of block copolymers melts. The results reveal the existence of an important driving force acting on the junction points at and even well above the ODT. Modelling the surface forces by an expression for the surface tension, it was possible to describe the NSE spectra consistently. The experimental surface tension agrees reasonably well with the Helfand predictions, which are strictly valid only in the strong-segregation hmit. Beyond that, these data are a first example for NSE experiments on the interface dynamics in a bulk polymer system. 

The structure of block copolymer melts, solids, solutions and blends... 

The dynamics of block copolymers melts are as intriguing as their thermodynamics leading to complex linear viscoelastic behaviour and anisotropic diffusion processes. The non-linear viscoelastic behaviour is even richer, and the study of the effect of external fields (shear, electric. ..) on the alignment and orientation of ordered structures in block copolymer melts is still in its infancy. Furthermore, these fields can influence the thermodynamics of block copolymer melts, as recent work has shown that phase transition lines shift depending on the applied shear. The theoretical understanding of dynamic processes in block copolymer melts is much less advanced than that for thermodynamics, and promises to be a particularly active area of research in the coming years. 

The structure of block copolymer melts is usually trapped upon vitrification. The mechanisms underlying the glass transition are similar to those of the constituent homopolymers. Thus there is little distinct physics associated with the formation of solid phases by glassy block copolymers. 

NMR has not been widely employed to study dynamics in block copolymer melts, although field gradient NMR can provide a wealth of information on the diffusion of block copolymer chains (Fleischer et al. 1993). The orientation of a deuterated homopolymer in a lamellar diblock copolymer (in a glassy state) was determined using 2H NMR by Valic et al. (1994,1995). Other applications of NMR to probe polymer chain dynamics and details of experimental protocols are described by Bovey and Jelinksi (1989). 

Thin films of block copolymer melts, and block copolymers adsorbed at the liquid-liquid interface, have been investigated using specular reflectivity (largely neutron reflectivity due to the ability to vary the scattering contrast). Off-specular reflection is, in principle, a powerful method for determining in-plane structure in block copolymer films but is not yet widely used. 

The properties of ordered structures in block copolymer melts have yet to be fully exploited, but the structural and rheological anisotropy is likely to lead to applications not all of which can be envisaged yet. The precision self-assembly of block copolymers into ordered structures for thin film and interfacial applications has enormous potential. Other applications such as nanoscale templates, membranes and filters could exploit the self-assembly of block copolymers into domains with periods 10-100 nm. The possibilities are limited only by the molecular engineer s imagination. 

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