The surface segregation of binary athermal polymer blends confined in a nanoscale thin film was investigated by dissipative particle dynamics. The polymer blend included linear/linear, star/linear, bottlebrush/linear, and rod-like/linear polymer systems. The segregation was driven by purely entropic effects and two different mechanisms were found. For the linear/linear and star/linear polymer blends, the smaller sized polymers were preferentially segregated to the boundary because their excluded volumes were smaller than those of the matrix polymers. For the bottlebrush/linear and rod-like/linear polymer blends, the polymers with a larger persistent length were preferentially segregated to the boundary because they favored staying in the depletion zone by alignment with the wall. Our simulation outcome was consistent with experimental results and also agreed with theoretical predictions - that is, a surface excess dictated by the chain ends for the branch/linear system. These consequences are of great importance in controlling the homogeneity and surface properties of polymer blend thin films.
The phase behavior of an athermal film of a polymer-nanoparticle blend (PNB) driven by depletion attraction is investigated by dissipative particle dynamics for nanospheres and nanocubes. Surface segregation is observed at low nanoparticle concentrations, while bulk aggregation is seen at high concentrations. Surface excess and the aggregation number can be controlled by tuning the nanoparticle concentration. As surface-roughened or polymer-grafted nanoparticles are used, uniform PNBs are acquired due to the lack of depletion. Thus, addition of surface-roughened nanoparticles into PNBs of smooth nanoparticles can be employed to tune the phase characteristics. It is found that bulk aggregation is suppressed for both polymer-nanosphere and polymer-nanocube blends. However, surface segregation is impeded for polymer-nanosphere blend but enhanced for polymer-nanocube blend owing to the distinct influence of the nanoparticle shape on depletion.
Hf 1−x Zr x O 2 (HZO) is a complementary metal−oxide−semiconductor (CMOS)-compatible ferroelectric (FE) material with considerable potential for negative capacitance field-effect transistors, ferroelectric memory, and capacitors. At present, however, the deployment of HZO in CMOS integrated circuit (IC) technologies has stalled due to issues related to FE uniformity. Spatially mapping the FE distribution is one approach to facilitating the optimization of HZO thin films. This paper presents a novel technique based on synchrotron X-ray nanobeam absorption spectroscopy capable of mapping the three main phases of HZO (i.e., orthorhombic (O), tetragonal (T), and monoclinic (M)). The practical value of the proposed methodology when implemented in conjunction with kinetic-nucleation modeling is demonstrated by our development of a T → O annealing (TOA) process to optimize HZO films. This process produces an HZO film with the largest polarization values (P s = 64.5 μC cm −2 ; P r = 35.17 μC cm −2 ) so far, which can be attributed to M-phase suppression followed by low-temperature annealing for the induction of a T → O phase transition.
Surface segregation and bulk aggregation in a thin film of athermal polymer-nanoparticle blends have been investigated by dissipative particle dynamics simulations. The thin film is confined between two athermal walls and the shape of the nanoparticles is spherical or cubic. Both phases are driven purely by the entropic effect, i.e., depletion attraction, which depends significantly on the nanoparticle size. At a specified particle volume fraction, surface segregation dominates for small nanoparticles but bulk aggregation emerges for large ones. The transition between the two phases is a result of the competition between particle-wall and particle-particle depletion attractions. The dominance of the former leads to surface segregation while the control of the latter results in bulk aggregation. Since nanocubes possess more contact areas and thus exhibit stronger depletion attractions than nanospheres do, the crossover from surface segregation to bulk aggregation occurs at smaller particle size for nanocubes.
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