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Enthalpy Relaxation and Morphology Evolution in Polystyrene‑b‑poly(methyl methacrylate) Diblock Copolymer
journal contribution
posted on 2018-09-14, 14:49 authored by Mingchao Ma, Yage Huang, Yunlong GuoDesirable
patterns formed by microphase separation in block copolymers make
these materials attractive for miniaturization of functional devices
in which formation of nanostructures is highly demanded. The microphase
separation forms microdomains under three-dimensional confinement
for each component and thus substantially changes physical properties
such as structural relaxation of the polymer blocks. In this article,
we report enthalpy relaxation and morphology evolution in polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA)
during isothermal physical aging, measured by calorimetry and atomic
force microscopy (AFM). Under nanoconfinement formed by microphase
separation, the PS blocks have higher relaxation rate and amount of
relaxed enthalpy compared with the corresponding homo-PS, while the
PMMA blocks have lower relaxation rate and relaxed enthalpy than the
homo-PMMA. The in situ morphology evolution shows
that the characteristic distribution profiles of the AFM phase angle
become lower and wider with increasing aging time for both the blocks,
and the average distance between the central phase angles of the two
blocks increase during aging. As large AFM phase angle of PMMA representing
higher modulus, it demonstrates that the PS blocks under hard confinement
exhibit greater enthalpy change with enhanced relaxation rate from
the bulk. In contrast, PMMA blocks under soft confinement show the
opposite trend.