Segregation strength

In conclusion, it can be suggested that the lamellar spacing of miktoarm-star copolymers is controlled by two parameters (i) the molecular weight of the corresponding AB diblock, which also controls the segregation strength, and (ii) the functionality of the central core. 

Weakly segregated systems, Todt > Tc < Tg with hard confinement. In this case, the crystallization of the semicrystalline block can overwhelm the microphase segregation of the MD structures even though the amorphous block is glassy at the crystallization temperature, because of the weak segregation strength [19]. 

Several additional phases are observed experimentally, but are not thermodynamically stable [13]. Moreover, the synthetic nature of the copolymers implies some heterogeneity in the polymer structure and molecular weight distribution. An excellent review has recently been published [97], and the main conclusion is that the polydispersity index (PDI) influences all aspects of the self-assembly. For example, upon an increase of the PDI of one block, the lattice constant of an ordered structure or the size of microphase-separated domains increases, interfacial thickness increases, and phase transitions may be induced. In addition, macrophase-separation may occur as the PDI is increased at certain compositions and segregation strengths. 

By scaling the entropy term by a factor of N the model accounts for the fact that the monomers are covalently bonded in groups of N, preventing the independent dispersion on lattice sides. Therefore, blend phase behavior is controlled by the product xN, the segregation strength, capturing the two opposing enthalpic and entropic contributions [5]. 

As in the case of macrophase separation, the two competing terms of enthalpic and entropic nature govern the thermodynamics of block copolymers. Similar to binary polymer bends the phase behavior of diblock copolymer melts is primarily controlled by the segregation strength and the volume fractions /a and /b = 1 - /a of the two blocks. Being covalently bonded, repulsive blocks are prevented from separating on a macroscopic level. Hence, the segregation into A- and B-rich domains... 

Ren, Y., Lodge, T.P., Hillmyer, M.A. Effect of selective perfluoroalkylation on the segregation strength of polystyrene—1,2-polybutadiene block copolymers. Macromolecules 35, 3889 (2002)... 

From the Flory-Huggins equation, the free energy of the homogeneous mixture (denoted as the disordered state) of binary blends in parallel to diblock copolymers is AFm W, while the free energy of microphase-separated state (denoted as the ordered state) is AF,n Here yr is normally called the segregation strength. 

Fig. 9.13 Illustration of the disordered state and the ordered state separated by the critical segregation strength...

Why do diblock copolymers ( 10.5) contain the larger critical segregation strength than the symmetric polymer blends (=2)7... 

Temperature dependence of interfacial tension of demixed polystyrene/poly (dimethylsiloxane) melts was studied by Nose (1997) using the sessile drop technique. The results were described as a scaled relation of reduced interfacial tension versus reduced segregation strength. The scaled relation was discussed on the basis of the mean-field theory, and a semiempirical expression has been presented for the scaled relation covering a wide temperature range. 

These block copolymers are usually miscible or weakly segregated in the melt (depending on their segregation strength, a function of the average molecular weight of each block time the Flory-Huggins interaction... 

In this chapter, we have introduced the area of the assembly of BCPs both in the bulk and in dilute solution. This area is highly active and complex. In the bulk, phase separation is relatively weU understood and related to the segregation strength of the two chemically distinct polymer components. Phase diagrams have been generated to allow the accurate prediction of the nanostructures adopted on phase separation. Complications arise if one of the blocks is a rod as opposed to a coil, but the assembly is still relatively well understood. 

Conceptually, it is useful to consider two regimes of polymer-solvent blends. In the first one, the copolymers comprise a small fraction of the system, typically 5% volume fraction or less. In these systems, which are considered in Section X, the polymers often form small isolated domains called micelles. In the second regime, considered in this section, the polymers are a major, even majority, component. Experimentally, mixing copolymer with solvent provides access to a far greater range of segregation strength than can be achieved by neat copolymer, particularly if the so-called dilution approximation holds. 

There are of course some problems associated with the use of block copolymers for bit-patterned media. The first lies with the traditionally used block copolymer for most studies to date, PS-fc-PMMA. The relatively weak segregation strength of PS-( -PMMA (x = 0.06) (Russell etfll., 1990) means that an Lq of 20nm (Mn 30000g/mol) is the smallest critical dimension possible before the polymer will fail the condition > 10.5, meaning the polymer... 

TABLE S3 Possible Morphologies of a Linear Diblock Copolymer with One Crystallizable Block Depending on the Segregation Strength and and Values... 

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