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Alignment of lamellar diblock copolymer phases under shear: insight from dissipative particle dynamics simulations


, : Alignment of lamellar diblock copolymer phases under shear: insight from dissipative particle dynamics simulations. Langmuir 23(9): 4809-4818

Sheared self-assembled lamellar phases formed by symmetrical diblock copolymers are investigated through dissipative particle dynamics simulations. Our intent is to provide insight into the experimental observations that the lamellar phases adopt parallel alignment at low shear rates and perpendicular alignment at high shear rates and that it is possible to use shear to induce a transition from the parallel to perpendicular alignment. Simulations are initiated either from lamellar structures prepared under zero shear where lamellae are aligned into parallel, perpendicular, or transverse orientations with respect to the shear direction or from a disordered melt obtained by energy minimization of a random structure. We first consider the relative stability of the parallel and perpendicular phases by applying shear to lamellar structures initially aligned parallel and perpendicular to the shear direction, respectively. The perpendicular lamellar phase persists for all shear rates investigated, whereas the parallel lamellar phase is only stable at low shear rates, and it becomes unstable at high shear rates. At the high shear rates, the parallel lamellar phase first transforms into an unstable diagonal lamellar phase; and upon further increase of the shear rate, the parallel lamellar phase reorients into a perpendicular alignment. We further determine the preferential alignment of the lamellar phases at low shear rate by performing the simulations starting from either the initial transverse lamellar structure or the disordered melt. Since the low shear-rate simulations are plagued by the unstable diagonal lamellar phases, we vary the system size to achieve the natural spacing of the lamellae in the simulation box. In such cases, the unstable diagonal lamellar phases disappear and lamellar phases adopt the preferential alignment, either parallel or perpendicular. In agreement with the experimental observations, the simulations show that the lamellar phase preferentially adopts the parallel orientation at low shear rates and the perpendicular orientation at high shear rates. The simulations further reveal that the perpendicular lamellar phase has lower internal energy than the parallel lamellar phase, whereas the entropy production of the perpendicular lamellar phase is higher with respect to the parallel lamellar phase. Values of the internal energy and entropy production for the unstable diagonal lamellar phases lie between the corresponding values for the parallel and perpendicular lamellar phases. These simulation results suggest that the relative stability of the parallel and perpendicular lamellar phases at low shear rates is a result of the interplay between competing driving forces in the system: (a) the system's drive to adopt a structure with the lowest internal energy and (b) the system's drive to stay in a stationary nonequilibrium state with the lowest entropy production.

US$19.90

PMID: 17375943

DOI: 10.1021/la063095c


Other references

Agarwal, L.P.; Malik, S.R., 1957: Diamox (acetazoleamide) in cataract surgery. Ophthalmologica. Journal International D'ophtalmologie. International Journal of Ophthalmology. Zeitschrift für Augenheilkunde 133(3): 153-159

Hamilton, S.J.; McMahon, R.F.T., 2002: Sudden death and suicide: a comparison of brain weight. Recent evidence suggests that the brain weight of individuals over the age of 60 who commit suicide is significantly higher than in those who die of natural causes. To ascertain whether brain weight is different in people of a younger age who comm...

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Bagaturiya, N.L.; Eliava, I.Y., 1966: Mesodorylaimus vulvapapillatus n.sp. (Nematoda: Dorylaimoidea) from eastern Georgian SSR. Mesodorylaimus vulvapapillatus n.sp. is described and figured from Sphagnum sp. from eastern Georgian SSR. One female, one male and 2 larvae were found. The following measurements are given: female, length 1.4 mm., a=31.2, b=4.4, c=17.2, V=53; mal...

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Gadrat, J.; Grimoud, M.; Quercy, J.; Andre, I.Ard, J.; Bernadet, P., 1959: Pediculated adenoma of the small intestine expressed by an intermittent melena and an extreme anemia with leukoblastic reaction. Archives des Maladies de L'appareil Digestif et des Maladies de la Nutrition 48: 1456-1458

Tong, L.Chu.B.; Rudomina, D.; Rekhtman, N.; Lin, O., 2015: Impact of touch preparations on core needle biopsies. Touch preparations (TPs) can be performed for on-site adequacy assessment of core needle biopsies (CNBs). Although TPs can play a role in decreasing the number of nondiagnostic core biopsies, the impact of TPs on CNB has not been extensively evalu...

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