The Role of Interfacial Energy and Specific Interactions on the Behavior of Poly(propylene glycol) Derivatives under 2D Confinement

Abstract

The effect of the chemical modification of poly­(propylene glycol) (PPG) end groups on the molecular dynamics under 2D confinement and the polymer/matrix interactions (including interfacial energies) was investigated by a combination of differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS), surface tension and contact angle measurements. The replacement of −OH groups in native PPG allowed to modify the interactions with the hydroxyl groups attached to the pore walls of nanoporous aluminum oxide (AAO) membranes of various pore diameter. It was found that the observed reduction in the glass transition temperature (T g) of the core polymers correlates well with a general trend (the higher the solid–liquid interfacial tension, γSL, the lower T g,confined) reported earlier. Moreover, we demonstrated that although the interfacial solid–liquid energy seems to be almost the same for each studied herein material, a clear change in the crossover temperature (T c), related to the vitrification of the polymers adsorbed to the pore walls, is noted. Interestingly, the shift in T c with respect to the glass transition temperature of the bulk polymer scales well according to the decreasing ability in the formation of H bonds in the order PPG–OH → PPG–NH2 → PPG–OCH3 for the constant γSL. One can add that no such effect is found for the glass transition of the core polymers, where a similar shift of the T g was recorded. This finding has been discussed in the context of various sensitivity of the studied materials to the density fluctuations, equilibration phenomena occurring below T c, etc. We believe that our finding will help in a better understanding of an interplay between interfacial and core molecules and contribute significantly to the discussion on the impact of interfacial interactions on the molecular dynamics of polymers under 2D confinement.

Segmental Dynamics Govern the Cold Crystallization of Poly(lactic acid) in Nanoporous Alumina

“…The lower T g locates at ~ 308 K (13 K lower than the bulk T g ), and the higher T g locates at almost the same temperature of the bulk PDLLA. As a lower T g indicates higher segmental mobility, the results lead to a natural explanation of a two-layer model, where the lower T g comes from a "mobile" interface layer and the higher T g is caused by the bulk-like core polymer, similar to the previous reports 17,18,24,25 . To investigate in more detail the segmental dynamics of PDLLA, frequency scans were carried out.…”

“…Three T g s were observed for infiltrated PMMA within larger pores (300 nm), and a three-layer model was further proposed. 18 Similar two T g s were found in PPG 24,25 , the times for segmental relaxation and normal mode increased below a crossover temperature.…”

“…Similar treatments have been reported previously. 25,37 The obtained τ should be regarded as an average of all the segments within the system. If the sample is re-measured during heating right after the measurement following the protocol P2, the relaxation times are the same for the two measurements ( Figure S2, Supporting Information).…”

Interfacial Interactions During In Situ Polymer Imbibition in Nanopores

“…S3, Supplemental Material [12]) where 2R g =d ∼ 0.14, the imbibition process has also two regimes with enhanced viscosity than in bulk, however, stage II has now the higher viscosity. In addition, part of the findings could be attributed to changes in glass temperature, T g , under confinement [28][29][30][31][32][33]. Having this in mind we studied the segmental dynamics following the in situ imbibition (by cooling and subsequent heating runs (see Fig.…”

“…S5, Supplemental Material [12]) for a range of PI molecular weights and degrees of confinement. Changes in T g under confinement have been discussed in terms of increasing interfacial energy for a number of different polymers [28,29].…”