Rheology of the Lower Critical Ordering Transition

Abstract

Linear viscoelastic dynamic rheological measurements were performed on symmetric diblock copolymers of deuterated polystyrene and poljKn-butyl methacrylate), denoted P(d-S-ó-nBMA). Isothermal frequency sweep data were time-temperature superposed. A transition from a disordered to ordered morphology was found with increasing temperature as a function of molecular weight. P(d-S-b-nBMA) with molecular weights less than 6.8 104 were always disordered, as evidenced by the scaling of the storage and loss moduli with frequency at low frequencies, G' = 2 and G' °= . Copolymers with molecular weights above 9.9 104 were always ordered, exhibiting very long relaxation times and appearing almost solidlike in the low-frequency limit. Mixtures of the 6.8 104 and 9.9 104 copolymers, however, showed a transition from fluid to solidlike behavior as the temperature was increased. This rheological data is consistent with the existence of a lower critical ordering temperature, LCOT, where a transition from a disordered to ordered state occurs with increasing temperature.

Phase Behavior and Photoresponse of Azobenzene-Containing Polystyrene-block-poly(n-butyl methacrylate) Block Copolymers

“…All these observed phenomena are similar to the general behaviors of their parent PS-b-PnBMA BCPs. PS-b-PnBMA BCP melts are wellknown to exhibit an hourglass-shaped phase diagram, resulting from the simultaneous appearance of a UDOT and a LDOT, in accordance with numerous experimental observations [30][31][32][33][34][35] and compressible RPA calculations. 29,[36][37][38][39][40][41][42][43][44][45][46] More intriguing, Yeung et al, who combined equation-of-state theory with standard descriptions of the order-to-disorder transition (ODT) in di-BCPs, have theoretically predicted the temperature dependence of χ eff N. Upon heating, χ eff N increases when the PS-b-PnBMA BCP is close to LDOT, whereas χ eff N decreases when the PS-b-PnBMA BCP is close to UODT.…”

“…As mentioned in the Introduction, by applying the photocombing method via a reversibly photocontrollable ordering process comparable to the classic zone refinement, long-range ordered arrays of BCP microdomains could be created over a microscopic distance without touching samples. Moreover, it is wellknown that PS-b-PnBMA BCP is also a representative baroplastic; [30][31][32]44,49 that is, the LDOT is very sensitive to pressure so that an ordered BCP can be transformed into a disordered state simply by applying hydrostatic pressure. [62][63][64][65][66] Most recently, this pressure-dependent property has been exploited for applications in data storage by using a scanning probe tip to apply a localized pressure.…”

Dynamical mechanical behavior of copolymers made of styrene and methyl methacrylate: Random, alternate and diblock copolymers

“…In general, block copolymers present an ordered phase at low temperatures which becomes disordered above a composition dependent order-disorder temperature, T OD . The equilibrium properties and phase diagram of diblock copolymers formed by styrene and an n-alkyl methacrylate (n being the number of carbon atoms of the lateral chain) have been studied in detail because of their departure from the classical behaviour [5][6][7]. While the copolymer with methyl methacrylate, and with nO5 show an order-disorder transition when the temperature is increased, those with 2%n%4 are unusual because the transition takes place when the temperature is decreased.…”

Dielectric and molecular dynamics study of the secondary relaxations of poly(styrene-co-methylmethacrylate) copolymers: Influence of the molecular architecture

“…These conclusions were qualitatively confirmed by Molecular Dynamics simulations that also showed an unusual behavior in the short time range and yielded a semi-quantitative agreement with the experimental data. In recent years the equilibrium properties and phase diagram of diblock copolymers formed by styrene and an nalkyl methacrylate (n being the number of carbon atoms of the lateral chain) have been studied in detail because of their departure from the classical behaviour [12][13][14]. While the copolymers with methyl methacrylate and with n > 5 present an order-disorder transition when the temperature is increased, those with 2 ≤ n ≤ 4 are unusual because the transition takes place when the temperature is decreased.…”