Double Glass Transition Temperatures of Poly(methyl methacrylate) Confined in Alumina Nanotube Templates

Abstract

Recently, confinement of polymers with different geometries has become a research hotspot. Here, we report the dramatic deviation of glass transition behaviors of poly(methyl methacrylate) (PMMA) confined in cylindrical nanopores with diameter significantly larger than chain’s radius of gyration (R g ). Fast cooling a PMMA melt in the nanopores results in a glass with one single glass transition temperature (T g). But two distinct T gs are detected after slow cooling the melt. The deviation in T g could be as large as 45 K. This phenomenon is interpreted by a two-layer model. During vitrification under slow cooling two distinct layers are formed: a strongly constrained interfacial layer showing an increased T g as compared to that of the bulk polymer and a core with a decreased T g. By thermal annealing experiments, we find that these two T gs are inherently correlated. In addition, the deviation of T g for PMMA confined in nanopores reveals a dependence on molecular weight.

Hard and soft confinement effects on the glass transition of polymers confined to nanopores

“…For the hard wall confinement, the strong attractive interaction between wall and polymer induces slow polymer dynamics near the wall and thus increases local T g , while the weak attractive interaction between wall and polymer leads to a relatively enhanced monomer mobility, which results in a reduced value of local T g . These behaviors are consistent with previous experiments and simulations, in which the confinement is realized by planar hard walls [28,29,48,50,54e56] and hard nanopores [10,57,58]. Clearly, the magnitude of the change in surface-layer dynamics of polymers is dependent on the interactions of the monomers with the surface as compared to those among monomers.…”

“…However, our simulated polymeric glass former has no polar groups, thus more realistic (atomistic) models should be used to test the idea of a break in cooperativity at the coreeshell boundary. We also notice that the physical or mechanical interlocking effects [61] and slow cooling rate unaccessible in simulations [58] may be other factors that lead to two-T g scenario. Moreover, with the same interaction strength ε pew ¼ 0.8, we can see the large influence of mobile boundary on the T g of confined polymer: Mobile boundary gives rise to much lower T g than the bulk system.…”

The Effect of Surface Chemistry on the Glass Transition of Polycarbonate Inside Cylindrical Nanopores

“…Upon fast cooling a single T g was detected, while slow cooling resulted in two T g 's. 25 To our knowledge, there exists a lack of knowledge on the effect of surface chemistry on the T g of the cylindrically confined amorphous polymer. On the other hand, silanemodified AAO membranes have been previously used to study the effect of confinement on polymer crystallization.…”

Effects of Al3+, W6+, Nb5+ and Pb2+ on the structure and properties of borotellurite glasses

“…This is due to differences in bond dissociation energies of metal oxides; Al-O bond enthalpy is 512 kJ mol − 1 which is higher than Te-O bond enthalpy (391 kJ mol − 1 ), hence the average single bond energies of glasses and hence the glass transition temperature increases with the addition of alumina [33,34]. Two glass transitions are observed at 379°C and 440°C in the glass having 10-mol% of Al 2 O 3 (Sample: 10Al20BTe) that indicates amorphous-amorphous phase separation in the sample [20,24,35,36].…”