Glass Transition Behavior of Clay Aerogel/Poly(vinyl alcohol) Composites

Abstract

In polymer/clay nanocomposites, the size and morphology of the dispersed clay are crucial in determining the macroscopic composite properties. Clay can be converted into an aerogel structure through a freeze-drying process which results in a reduction of its density from 2.35 to 0.05 g/cm 3 . The morphology of these clay aerogels resembles a house of cards structure. Low weight fraction (0.5-4 wt %) composites of clay and clay aerogel with a poly(vinyl alcohol) (PVOH) matrix polymer were prepared. Glass transition temperature (T g ) behaviors of clay/PVOH composites were investigated as a function of size, loading, and dispersion of clay and clay aerogel in the polymer matrix. The trends in T g measured from both dynamic mechanical analysis and differential scanning calorimetry are similar, exhibiting a maximum value at 1 wt % loading for both clay and clay aerogel and then decreasing with additional filler content. Although the trends are similar, the drop in T g at 4 wt % clay composite is considerably larger than that for a similar loading of clay aerogel. In comparison with the mesoscale clay aerogel, the nanoscale clay shows better dispersion and higher interfacial interaction with the polymer, which enhances polymer crystallinity at lower weight fractions and increases polymer free volumes at higher weight fractions. The relative changes in T g are proposed to be the result of two competing effects: (i) surface interaction which strengthens the interface (decreasing chain mobility) and (ii) enhanced interfacial free volume due to the lower bulk crystallinity of polymer chains (increasing chain mobility).

Investigation of correlation between dielectric parameters and nanostructures in aqueous solution grown poly(vinyl alcohol)-montmorillonite clay nanocomposites by dielectric relaxation spectroscopy

“…Recently, Wang et al [20,21] investigated the dielectric properties of solution intercalated polystyrene-MMT clay and poly(methyl methacrylate)-MMT clay nanocomposite films within the frequencies of 100 Hz-1 MHz and found that loading of 1 wt% MMT clay significantly reduces the ε′ values as compared to the pure polymer film, which is mainly due to reduction in the number of aligned dipolar groups in the presence of randomly distributed exfoliated clay nanoplatelets in the polymer matrix. In PVA-MMT clay nanocomposites, the intercalation of PVA in clay galleries and exfoliation of MMT clay nanoplatelets occur simultaneously [13][14][15][16][17]. The XRD, TEM and DSC studies established that in aqueous solution grown PVA-MMT clay nanocomposites up to 10 wt% MMT clay loading have well dispersed MMT nanoplatelets throughout the PVA matrix, i.e., nanocomposites formed are mostly exfoliated hybrids [14].…”

“…The MMT clay concentration at which ε s decreases, τ increases and vice versa is in good agreement with the above discussed correlation between the ε s values and the amount of exfoliated clay structures in the solution grown PVA-MMT clay nanocomposites. Recently, Bandi and Schiraldi [17] have investigated the glass transition temperature T g of solution intercalated PVA-MMT clay films as a function of clay size, concentration and dispersion in the PVA matrix. They observed that T g exhibits a maximum value at 1 wt% concentration of MMT clay and for higher concentration its value decreases anomalously.…”

“…For the preparation of poly(vinyl alcohol) (PVA)-layered silicate nanocomposite, montmorillonite (MMT) clay is the most commonly used, which has hydrophilic property, and 2:1 phyllosilicate laminar structure. Synthesis of PVA-MMT clay nanocomposites by solution casting technique and their structural characterization have been subject of several investigations [13][14][15][16][17]. Structural and morphological studies of PVA-MMT clay nanocomposite materials investigated by X-ray diffraction (XRD), Fourier transform infra-red (FTIR) spectroscopy, differential scanning calorimetry (DSC), atomic force microscopy (AFM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) have established the high degree intercalation and exfoliation behaviour of MMT clay in the PVA matrix, which improves their thermal, mechanical and permeability properties.…”

Effect of Silica Nanoparticles on the Local Segmental Dynamics in Poly(vinyl acetate)

“…12 Constraints from nanoparticles may affect segmental mobility, at least of chains near the particle surface, and it has been proposed that immobilization of such interfacial chains induces glassy behavior at temperatures above the bulk T g . [13][14][15][16] Relatedly, there have been various reports of increases in the glass transition temperature, T g , due to the presence of reinforcing fillers; [17][18][19][20][21][22] however, other investigators found no effect of carbon black, silica, and other particles on T g . 23,24 The effect of nanoconfinement on the polymer dynamics, seen in thin films and porous structures, [25][26][27] may have an influence for layered fillers such as clay platelets.…”

Avaliação comparativa entre os nanocompósitos de argila motmorilonita/LLDPE e com Hexaniobato de Potássio/LLDPE: Caracterização das propriedades mecânicas e de transporte

“…Porém existem alguns fatores que influenciam esse processo. No caso da solubilidade (S) ela é afetada com a facilidade de condensação do gás no interior do polímero, a presença de volume livre [3] e a polaridade relativa do trio gás/matriz polimérica/carga. O processo de difusão (D), por sua vez, é afetado, também, pela presença de volume livre, pelo grau de cristalinidade da matriz polimérica, uma vez que a difusão ocorre exclusivamente na fase amorfa do polímero [4] .…”