Diblock copolymer interaction parameter

Although being qualitatively in agreement with experimental results, disagreements between experiment and theory remain. Besides the composition, /a, and the total degree of polymerization, N, all theoretical works refer to the segmental interaction parameter x This parameter can be estimated from a relationship to the solubility parameters. The ODT as a thermodynamic measure of the incompatibility was used to compare a set of symmetrically composed diblock copolymers from different hydrocarbons, polydimethyl-siloxane and poly(ethylene oxide) (PEO) [33]. While the behaviour of hydrocarbon diblock copolymers was successfully described by a consistent set of solubility parameters, this procedure failed for systems containing PEO. The... 

Fig. 51 Phase diagram for PS-PI diblock copolymer (Mn = 33 kg/mol, 31vol% PS) as function of temperature, T, and polymer volume fraction, cp, for solutions in dioctyl ph-thalate (DOP), di-n-butyl phthalate (DBP), diethyl phthalate (DEP) and M-tetradecane (C14). ( ) ODT (o) OOT ( ) dilute solution critical micelle temperature, cmt. Subscript 1 identifies phase as normal (PS chains reside in minor domains) subscript 2 indicates inverted phases (PS chains located in major domains). Phase boundaries are drawn as guide to eye, except for DOP in which OOT and ODT phase boundaries (solid lines) show previously determined scaling of PS-PI interaction parameter (xodt

An example of the incorporation of an external component on the crystallization behavior of triblock copolymers was given by Schmalz et al. [126]. They obtained PS-fo-poly(ethylene-co-propylene)-fo-PE (PS-fo-PEP-fr-PE) triblock copolymers from the hydrogenation of PS-fr-PI-fo-PB. PS-fo-PEP-fr-PE triblock copolymers have the peculiarity that PEP and PE have an interaction parameter of 0.007 at 120 °C therefore, they form a homogeneous melt, which is segregated from the PS block and can be considered as an intermediate case between diblock and triblock copolymers. The crystallization of the PE block occurs at about 60 °C and the authors evaluated the influence of the incorporation of a solvent during the crystallization and segregation processes under... 

The micellization behavior of copolymers containing two hydrophobic blocks, or double-hydrophobic block copolymers, has been shown to be mainly controlled by the solvent and its interaction with the copolymer blocks. It is thus possible to tune the micellization of these copolymers by changing the organic solvent. In this respect, large differences in Z, i h, Rc, etc. are expected whenever the interaction parameter between the polymer and the solvent is varied. This is illustrated by, e.g., the work of Pit-sikalis et al. [87] for PS-PSMA diblock copolymers dissolved in either ethyl-or methylacetate. The effect of temperature has been studied by Quintana et al. [88,89], who have clearly shown that CMC decreases with increasing temperature for PS-PEB copolymers in alkanes. 

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 ... 

In mean field theory, two parameters control the phase behavior of diblock copolymers the volume fraction of the A block /A, and the combined interaction parameter xTak- V. where Xab is the Flory-Huggins parameter that quantifies the interaction between the A and B monomers and N is the polymerization index [30], The block copolymer composition determines the microphase morphology to a great extent. For example, comparable volume fractions of block copolymer components result in lamella structure. Increasing the degree of compositional asymmetry leads to the gyroid, cylindrical, and finally, spherical phases [31]. 

In contrast to swollen homopolymer films, only a limited number of studies on thin films of block copolymers have been reported in which the degree of the film swelling has been directly accessed. In situ SE has been used to evaluate the polymer-solvent interaction parameters [144], to construct phase diagrams of surface structures [49, 51], and to control the mechanism of lamella reorientation in thick swollen films [118, 163, 164], Spectroscopic reflectometry combined with real-time GISAXS has been used to follow structural instabilities in swollen lamella films [165], Recently, it was demonstrated that swelling of diblock copolymer films in organic selective and non-selective solvents follows the same physical behavior as in thin films of homopolymers [119]. 

A BT is the interaction energy between the block and the exterior pore surface. Those interaction energy parameters suggest that the interaction between blocks and B is repulsive, the surface has strong attractive interaction with block A and strong repulsive interaction with block B. The volume concentration of the A5B5 diblock copolymer is 90%. 

Block copolymer phase separation has first and foremost been studied in bulk. The mesoscale structure is determined by molecular parameters such as chain length (N), volume fractions of the components, interaction between the blocks (x) and temperature (Figure 2.6). In this Chapter, we will be concerned mainly with diblock copolymers,... 

Fig. 10. Schematic phase diagram of a semi-infinite block copolymer melt for the special case of a perfectly neutral surface (Hj=0). Variables chosen are the surface interaction enhancement parameter (-a) and the temperature T rescaled by chain length (assuming X l/T the ordinate hence is proportional to %c/%). While according to the Leibler [197] mean-field theory a symmetric diblock copolymer transforms from the disordered phase (DIS) at Tcb oc n in a second-order transition to the lamellar phase (LAM), according to the theory of Fredrickson and Helfand [210] the transition is of first-order and depressed by a relative amount of order N 1/3. In the second-order case, the surface orders before the bulk at a transition temperature T (oc l / ) as soon as a is negative [216], and the enhancement...

Consider a spherical micelle made out of/diblock copolymers. The insoluble block consists of Aa monomers of size a and its Flory interaction parameter with the solvent is x, ... 

The full relation for the chemical potential of the copolymers in the bulk Pbmsh can be obtained from the Flory-Huggins energy of mixing between diblock copolymers A-N and homopolymers P [259, 260], when interaction parameters %AP> %AN, and % (% =%np) are specified. In most experiments brush N-mers and homopolymer P-mers are microstructurally identical and differ only in the isotopic status. Related isotopic interaction parameter % is usually much smaller than parameters yAP and %AN. Assuming [254] Xan=X,m<+X, and neglecting volume fraction of the anchor moieties in the bulk, the expression for pbulk is obtained in the form... 

Critical micelle concentration ( >cmc is expected to decrease strongly with diminished diblock asymmetry rc as low rc values favor easier creation of highly curved micelle interfaces. Theory of micelle formation [231,260] also indicates that the overall copolymer degree of polymerization Nc, as well as the anchor -homopolymer interaction parameter %AP have to be considered to explain properly the onset of micelle segregation as observed by Shull et al. [260]. Using this theory, experimenters are able to choose systems where only individual copolymers segregate. 

---