The Impact of Molecular Weight on the Behavior of Poly(propylene glycol) Derivatives Confined within Alumina Templates

Abstract

In this paper, we explored the influence of both the variation in the molecular weight (M n = ∼400, 2000, 4000 g/mol) and the terminal groups (hydroxyl, amino, and methoxy) on the molecular dynamics of poly­(propylene glycols) confined within anodic aluminum oxide membranes of different pore diameters. All confined samples revealed the presence of two glass transition temperatures related to the vitrification of two, core and interfacial, fractions of polymers. As found, the glass transition temperature of PPG adsorbed on the pore walls increases with a decrease in polymer M n and scales with the H-bonding ability of a given material. Surprisingly, the glass transition temperature of the core macromolecules decreases with respect to the bulk sample with increasing M n. To gain insight into the observed quite unexpected anti-correlated behavior of both T g values, we performed the additional contact angle and surface tension measurements together with the annealing experiments. As shown, there were no differences in wettability, surface tension, and interfacial energy between studied materials. However, performed time-dependent measurements revealed that the polymer molecular weight significantly affects the density equilibration and adsorption–desorption processes occurring at the interface. This finding seems to be consistent with the annealing experiments carried out on thin polymer films as well as with the recent studies on the kinetics of infiltration of macromolecules into nanochannels (so-called imbibition process). We believe that the presented data might be important in a better understanding of the chain and segmental dynamics in polymers characterized by various functionalities and molecular weights under confinement.

Unique Behavior of Poly(propylene glycols) Confined within Alumina Templates Having a Nanostructured Interface

“…As noted above, T g,modul-AAO ∼ T g,bulk , while for const-AAO, T g,interfacial > T g,bulk > T g,core . The results described above are interesting considering data reported to date for various PPGs (irrespective of molecular weight and terminal group) infiltrated within both alumina 27 − 29 and silica 30 , 31 pores that revealed deviations of τ α from those measured for the bulk sample. Although a different interpretation of this finding has been proposed, previously such variation in the dynamics of confined PPGs has been assigned to the vitrification of the material adsorbed at the interface.…”

“…One can recall that T g,interfacial corresponds well to the higher endothermic event (glass transition) detected in the collected thermograms (Figure ). − It should be noted that because of additional interactions of the substrate and adsorbed molecules, there is some heterogeneity in terms of density and mobility of the confined materials. Thus, there are at least two fractions of molecules (core and interfacial), characterized by various dynamics and glass transition temperatures ( T g,core and T g,interfacial , respectively) for liquid infiltrated in pores .…”

On the Segmental Dynamics and the Glass Transition Behavior of Poly(2-vinylpyridine) in One- and Two-Dimensional Nanometric Confinement

“… 106 Table 1 shows the γ Total , γ LW , and γ P values for P2VP, Al, alumina, and SiO 2 calculated from the contact angle values available in the literature. 58 , 107 , 108 One can estimate the interfacial energy between two materials, in our case, the polymer ″P″ and the substrate ″S″, as follows: 109 …”

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

“…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).…”