Effect of nanoscale confinement on glass transition of polystyrene domains from self-assembly of block copolymers

Abstract

The understanding of size-dependent properties is key to the implementation of nanotechnology. One controversial and unresolved topic is the influence of characteristic size on the glass transition temperature (T(g)) for ultrathin films and other nanoscale geometries. We show that T(g) does depend on size for polystyrene spherical domains with diameters from 20 to 70 nm which are formed from phase separation of diblock copolymers containing a poly(styrene-co-butadiene) soft block and a polystyrene hard block. A comparison of our data with published results on other block copolymer systems indicates that the size dependence of T(g) is a consequence of diffuse interfaces and does not reflect an intrinsic size effect. This is supported by our measurements on 27 nm polystyrene domains in a styrene-isobutylene-styrene triblock copolymer which indicate only a small T(g) depression (3 K) compared to bulk behavior. We expect no effect of size on T(g) in the limit as the solubility parameters of the hard and soft blocks diverge from each other. This strongly segregated limiting behavior agrees with published data for dry and aqueous suspensions of small polystyrene spheres but is in sharp contrast to the strong influence of film thickness on T(g) noted in the literature for free standing ultrathin polystyrene films.

Segmental dynamics and the correlation length in nanoconfined PMMA

“…This means the enthalpic barrier to mixing is negligible, and since the interfacial thickness varies inversely with interfacial energy [35,36], the interphase in these samples is quite extended (as much as a few nm [37e39]). Robertson et al [40] found that in polystyrene block copolymers, a small solubility parameter difference caused very large changes in T g , several tens of K, while a large solubility parameter difference has been found to result in negligible changes in T g [41]. Herein, the presence of the PC within the interfacial region slows down the segmental dynamics of PMMA, significantly increasing its T g .…”

Glass transition properties of PMMA thin shells deposited on rodlike calcium carbonate particles

“…10 Ultrathin films of polysulfone exhibits no size dependence of T g down to 10 nm, 27 and styrene-isobutylene block copolymer shows weak size dependence. 11 As for the latter, the observed T g variation has been attributed to diffuse interface. Figure 5 shows T g and x(T g ) for the shells with similar thicknesses (17-23 nm) with respect to the degree of crosslink X c .…”

“…From a practical point of view and for fundamental research on soft matter, it is becoming important to understand the origin of the anomalous dynamics of nano-sized and nano-confined polymers, which differ considerably from the bulk materials. 1 Investigations to clarify the mechanism of such anomalous dynamics have been extensively performed, especially for the glass transition temperature, T g , of ultrathin films, 2-7 and of confined liquids in nanopores, 8,9 spheres 10 and phase separated polymers, 11 but the subject still seems to be a controversial issue. T g depends on various factors including size, status of the interface, geometry and experimental method (sample preparation and observation).…”

“…In addition, some systems show very weak or no size dependence of T g even below 100 nm. 6,7,[10][11][12] Researchers have been trying to understand the mechanism of glass transition in terms of the cooperatively rearranging region (CRR), 13,14 of which the size increases with decreasing temperature toward an underlying thermodynamic transition point, leading to a drastic increase in relaxation time. The segmental relaxation time is supposed to be a function of the configurational entropy of the smallest CRR s c * .…”

Preparation and glass transition of crosslinked poly(vinyl acetate) thin shells on the surface of a calcium carbonate core

“…These factors may interact with one another, increasing the complexity of the mechanism that is not yet fully understood. In addition, the size effect on T g has been studied for systems with geometries other than thin film, for example, polymer spheres, 11,12 microphase-separated systems 13 and glass-forming liquids confined in nanopores. 6 In general, the observed T g behaviors for such systems do not necessarily coincide qualitatively with those of thin films, suggesting certain geometry effects on the T g in nanosized materials.…”