Investigation of the Surface Glass Transition Temperature by Embedding of Noble Metal Nanoclusters into Monodisperse Polystyrenes

Abstract

Chain mobility in a near surface region at a polystyrene/vacuum interface was investigated by embedding of noble metal nanosized clusters. The embedding process was monitored in situ by X-ray photoelectron spectroscopy. The embedding of nanosized clusters needs long-range chain mobility of the polymer. Therefore, the embedding process is a probe for the glass transition in a near surface region. The clusters used in this study are formed by the dewetting of evaporated noble metals onto the polymer surface. First, methodical influences on the embedding process were investigated. An onset embedding temperature T* was defined. T* increases with a heating rate comparable to T g(bulk) determined with a differential scanning calorimeter. Furthermore, T* increases with nominal metal coverage which results in increasing average cluster radius. The cluster size distribution was investigated by transmission electron microscopy. It is shown that T* is an upper limit for T g in a near surface region with a depth of a few nanometers. With optimized probe conditions, embedding processes were performed on monodisperse polystyrene (M w = 3−1000 kg/mol). The T* values fit quite well with the Fox−Flory relation, but with a saturation temperature of approximately 8 K below the bulk value. ΔT = T g(bulk) − T* increases with molecular weight. This molecular weight dependence of T* will be discussed in terms of several models. The chain end segregation model can be ruled out. To investigate the kinetics of the embedding process, isothermal experiments were performed. From these experiments surface viscosities were derived, which are well below bulk values.

Metal-Polymer Nanocomposites: (Co-)Evaporation/(Co)Sputtering Approaches and Electrical Properties

“…A method, alternative to metals and polymers co-deposition processes, to produce polymer-metal nanocomposite films is based on the embedding phenomenon of metal NPs deposited on the polymers surface [27,30,31,[55][56][57][58][59][60][61][62][63][64][65]. For example, in fact, first the polymer can be spin-coated on a substrate and the thickness of the polymer layer can be controlled by the process parameters (rpm, etc.…”

“…Some research groups have used scanning probe microscopy [58,65], X-ray reflectivity [60,61] and X-ray photoelectron spectroscopy [63] to study the embedding of metal NPs in polymers. Some studies highlighted a complete embedding of the metal NPs in the polymeric layers [55,56,61,62], while others analyses highlighted only partial embedding [58]. Such a difference is related to the dependence of the embedding process on the polymer chain mobility: so, partial or no embedding can be expected at temperatures below the polymer glass-transition temperature Tg, while NP complete embedding is observed at temperatures higher than Tg [62].…”

“…Some studies highlighted a complete embedding of the metal NPs in the polymeric layers [55,56,61,62], while others analyses highlighted only partial embedding [58]. Such a difference is related to the dependence of the embedding process on the polymer chain mobility: so, partial or no embedding can be expected at temperatures below the polymer glass-transition temperature Tg, while NP complete embedding is observed at temperatures higher than Tg [62]. Deshmukh et al [64] studied, using transmission electron microscopy, individual Au NP embedding in a polystyrene melt showing that the NPs near the polymer surface are completely covered by a thin wetting layer of polymer with critical thickness d*.…”

Poly(methyl methacrylate) composites with size-selected silver nanoparticles fabricated using cluster beam technique

“…[3][4][5][6][7] One of the very widely used techniques to fill a polymer with metal is evaporation. [8][9][10] The cohesive energy of metals exceeds the cohesive energy of polymers by typically two orders of magnitude and generally it is expected that metals exhibit a strong tendency to aggregate and form clusters when deposited on the surface of an organic substrate. 11 However, in case of low reactivity metals like Cu, Ag, Au, and Pd, deposited atoms can diffuse toward bulk of a substrate causing subsequent formation of clusters below the surface under certain evaporation conditions.…”

Surface Effect on Mechanical Properties and Atomic Mobility of Ultrathin Polystyrene Films using Molecular Dynamics Simulations

“…Disagreement in the explanation of size dependence still exists on whether there is a liquid like layer near the surface [12,13]. Experimental techniques utilizing nanoindentation [5,14], nanoparticle embedding [15,16] and instable wrinkling [6,17] have been developed to explore the mechanical properties of ultrathin films and coatings. However, these techniques cannot evade the far field effects from the substrate and the indenter5 since these experiments can only be carried out on the substrate-supporting specimens.…”