Investigation of morphologies and nanostructures of polymer blends by tapping mode phase imaging

Abstract

Tapping mode atomic force microscopy (TMAFM) measurements were carried out for blends of a triblock copolymer, poly(styrene)-block-poly(ethene-co-but-1-ene)-block-poly(styrene) (SEBS), with isotactic polypropylene (i-PP). Our TMAFM work on SEBS/i-PP blends show that phase imaging is an important and competitive tool for studying the microphase separation of polymers, and that the use of the film-glass interface is relevant in learning about the bulk morphology of polyolefinic samples by TMAFM.Poly(styrene)-block-poly(ethene-co-but-1-ene)-block-poly-(styrene) (SEBS) is a thermoplastic triblock copolymer composed of a rigid segment, polystyrene (PS), and a compliant rubbery segment, poly(ethene-co-but-1-ene) (PEB) (Fig. 1). SEBS has a microphase domain structure consisting of the rigid PS component arranged in the flexible PEB matrix [1]. SEBS is often used as a compatibilizer for polymer blends which have one component compatible with the PEB block, and another component compatible with the PS block. SEBS reduces the interfacial tension at the interface of different components and hence improves mechanical properties [2][3][4]. Investigation of the blending behavior of SEBS with isotactic polypropylene (i-PP) is of special interest because PEB is expected to show good compatibility with i-PP [5] and because PEB is miscible with i-PP under certain conditions [6].The nanometer-scale properties and morphologies of polymer blends have mainly been studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Atomic force microscopy (AFM) [7] proFig. 1. Structure of poly(styrene)-block-poly(ethene-co-but-1-ene)-blockpoly(styrene) (SEBS). The polymer described in our work contains 29 wt% of PS and 71 wt% of random PEB copolymer vides a new method of investigations for the morphology, structure and chain order of polymer surfaces on the nanometer scale [8-13]. Tapping mode AFM (TMAFM) [14] is one of the most popular force microscopy techniques because it minimizes lateral forces and sample damage during scanning.In TMAFM the amplitude of the oscillating cantilever is reduced when the tip is brought close to the sample surface, and this amplitude damping is used for imaging. By detecting changes in the phase angle of vibration [15,16], TMAFM has greatly enhanced image contrast. Height and phase TMAFM images of heterogeneous surfaces depend in a complex way on the experimental parameters, i.e. the driving amplitude A 0 and the set-point-amplitude A sp . Nevertheless, it has been shown that under certain circumstances the image contrast is related to variations in the local surface stiffness or local attractive force [17][18][19][20][21]. In the present work we examine the morphologies and nanostructures of several SEBS/i-PP blends by TMAFM. Our work demonstrates that TMAFM phase imaging is an important and competitive tool for studying the microphase separation of polymers. ExperimentalSome chemical and physical properties of the materials used in this study are listed in Table 1. SEBS/i-PP blend...

Structural and electronic properties of pentacene-fullerene heterojunctions

“…[57][58][59] AFM phase imaging can provide high contrast due to variations in local attractive forces and stiffness and can therefore be used as tool to discriminate between areas covered by different chemical compounds in blended films. [60][61][62] The phase image in Fig. 7͑f͒ reveals comparably the same phase angle values ͑ ͒ in the meandered lamellae ͑1͒ and the round islands ͑2͒, however, with high contrast to the surrounding smooth matrix in ͑2͒ ͓white areas in Fig.…”

Investigation of Morphologies of One- and Two-Phase Blends of Isotactic Poly(propene) with Random Poly(ethene-co-1-butene)

“…Phase detection allows one to detect shifts in phase angles of vibration when the oscillating cantilever interacts with the sample surface . Phase imaging (i.e., image contrast related to the phase shifts) has been shown to provide enhanced image contrasts, especially for heterogeneous surfaces. − The contrasts of tapping mode AFM height and phase images depend in a complex way on the driving amplitude A 0 and the set-point ratio r sp = A sp / A 0 of the cantilever. ,− For large A 0 , moderate and small r sp , the tip−sample interaction becomes repulsive so that the phase image contrast is related to the variation of the local surface stiffness on the sample surface. In this case, a larger stiffness leads to a more positive phase shift and thus to a brighter contrast in the phase image.…”

From Images to Interactions: High-Resolution Phase Imaging in Tapping-Mode Atomic Force Microscopy

“…Simultaneously recording the topography and the phase shift of the cantilever oscillation relative to the driving signal as reference allows mapping of interaction properties of a heterogeneous sample. This phase imaging has been applied to explore various material properties, e.g., adhesion and viscoelastic properties (Winkler et al, 1996;Tamayo and García, 1997;Magonov et al, 1997;Noy et al, 1998;Thomann et al, 1998;Chen et al, 1998;San Paulo and García, 2000), capillary forces and wetting (Van Noort et al, 1997;Gil et al, 2000), and even detection of surface charges . As recently shown, the phase shift is related to energy dissipated in the tip-sample contact (Cleveland et al, 1998;García et al, 1999;Anczykowski et al, 1999).…”