Mechanical Properties and Structure of Polymer−Clay Nanocomposite Gels with High Clay Content

Abstract

The mechanical properties and structures of nanocomposite gels (NC gels), consisting of poly-(N-isopropylacrylamide) (PNIPA) and inorganic clay (hectorite), prepared using a wide range of clay concentration (∼25 mol % against water) were investigated. All NC gels were uniform and transparent, almost independent of the clay content, C clay . The tensile modulus (E) and the strength (σ) were controlled without sacrificing extensibility by changing C clay . The E, σ, and fracture energy observed for as-prepared NC gels attained 1.1 MPa, 453 kPa, and 3300 times that of a conventional chemically cross-linked gel, respectively, and σ increased to 3.0 MPa for a once-elongated NC25 gel. From the tensile and compression properties, in addition to optical transparency, it was concluded that a unique organic/inorganic network structure was retained regardless of C clay . The effects of C clay on the tensile mechanical properties on the first and second cycles, the time-dependent recovery from the first large elongation and the optical anisotropy of NC gels, and also the disappearance of the glass transition and the formation of clay-polymer intercalation in the dried NC gel were revealed. Thus, it became clear that the properties and the structure changed dramatically for an NC gel with a critical clay content (C clay c ≈ NC10) or above. The structural models for NC gels with low and high C clay , exhibiting different clay orientation and residual strain, were depicted.

Synthesis and properties of soft nanocomposite materials with novel organic/inorganic network structures

“…6,7,20,26,27 A variety of clay minerals with layered crystal structures and good water swellability can be used as the inorganic component; examples are the smectite-group clays (hectorite, saponite, montmorillonite and so on) and mica-group clays (synthetic fluorine mica). Among these, the synthetic hectorite 'Laponite XLG' (Rockwood Ltd, UK; [Mg 5.34 capacity: 104 mequiv per 100 g), 26,28 which has a 2:1 layered structure (Figure 2), was most effective because of its high degree of swellability and exfoliation, high purity, sufficiently small platelet size and good interaction with PNIPA.…”

“…E and s for NC gels also increased with increasing C p , as shown in Figure 6c, 31 as the number of polymer chains linking neighboring clay platelets increases with C p . Figure 8a shows tensile stress-strain curves for N-NC gels with different C clay (NC5ÀNC25) values, 27 where both E and s increase markedly with C clay , as shown by the arrows. s exceeds 1000 kPa in the N-NC25 gel.…”

Small-angle neutron scattering on polymer gels: phase behavior, inhomogeneities and deformation mechanisms

“…71,72 The mechanical properties can be easily chosen by the composition. 81 The structure-property relationship was extensively investigated by SANS. 74,75,78,82 Because NC gels are three-component systems, the scattering intensity function consists of six partial scattering functions, S ij (q) where i, j¼1, 2 and 3.…”

Synthetic, layered nanoparticles for polymeric nanocomposites (PNCs)

“…149 After drying, the interlayer spacing was measured. The compositions containing < 50 mmol/l were exfoliated, while those at clay content !100 mmol/l were intercalated.…”