Ultrasonic force microscopy on poly(vinyl alcohol)/SrTiO3 nano-perovskites hybrid films

Abstract

Atomic Force Microscopy (AFM) and Ultrasonic Force Microscopy (UFM) have been applied to the characterization of composite samples formed by SrTiO3 (STO) nanoparticles (NPs) and polyvinyl alcohol (PVA). The morphological features of the STO NPs were much better resolved in UFM than in contact-mode AFM topography. For high STO concentrations the individual STO NPs formed nanoclusters, which gathered in microaggregates. The STO aggregates, covered by PVA, exhibited no AFM frictional contrast, but were clearly distinguished from the PVA matrix using UFM. Similar aggregation was observed for NPs in the composite samples than for NPs deposited on top of a flat silicon substrate from a milliQ water solution in the absence of polymer. In the hybrid films, most STO nanoparticles typically presented a lower UFM contrast than the PVA matrix, even though stiffer sample regions such as STO should give rise to a higher UFM contrast. STO NPs with intermediate contrast were characterized by an UFM halo of lower contrast at the PVA/STO interface. The results may be explained by considering that ultrasound is effectively damped on the nanometer scale at PVA/ STO interfaces. According to our data, the nanoscale ultrasonic response at the PVA/STO interface plays a fundamental role in the UFM image contrast.KEYWORDS. Atomic Force Microscopy. Ultrasonic Force Microscopy. Poly(vinyl alcohol). Stroncium Titanate. Nanoparticles. Nanocomposites. 1-IntroductionUltrasonic Force Microscopy (UFM) is a powerful technique to investigate the elastic and adhesive response of materials on the nanoscale [1,2]. The procedure is capable to provide material contrast in both soft and hard samples, bringing additional advantages when compared with other Scanning Probe Microscopy (SPM) approaches [3][4][5][6]. Here, UFM is applied to the characterization of composite samples formed by SrTiO3 (STO) nanoparticles (NP) and poly(vinyl alcohol) (PVA). We intend to further explore the capability of the technique to provide subsurface information, to characterize the nanostructures formed by STO NP in the PVA hybrid films, and to gain inside into the mechanisms of ultrasound propagation on the nanoscale and the origin of the UFM contrast.The insertion of ceramics nanoparticles into polymer matrix has led to the generation of novel hybrid materials with improved electrical and thermo-mechanical properties. In titanate-polymer composites, the titanates contribute with a high capacitance, and the polymers are typically easy to process. Hence, the composite films appear very attractive for the fabrication of integrated circuits [7,8]. Composites of STO with polymeric materials have been considered for microwave applications [9,10]. The dielectric properties of PVA mixed with PbTiO3 show promise for their application as supercapacitors and humidity sensors [11]. STO nanoparticles are being tested for the development of thin film transistors [8], batteries [12], photodiodes [13], and solar cells [14]. Also, they may exhibit photocatalytic activity [15][16...

PVA-Based Films with Strontium Titanate Nanoparticles Dedicated to Wound Dressing Application

“…The increase in the maximum tensile strength simultaneously with a decrease in elastic modulus of a film containing 10%STO indicates a corresponding significant increase in the ultimate strain. The positive effect of various nanoparticles on the mechanical properties of modified materials was previously confirmed [ 11 ]. According to previous UFM results, the PVA/STO interface interactions are very weak; ultrasound is effectively damped at the matrix/nanoparticle interface regions.…”

“…nanoparticles on the mechanical properties of modified materials was previously firmed [11]. According to previous UFM results, the PVA/STO interface interactions very weak; ultrasound is effectively damped at the matrix/nanoparticle interface regi However, it is strongly related to both the concentration, type, and size of nanopart and their distribution in the matrix [33][34][35].…”

“…Recent studies have demonstrated that PVA-SrTiO 3 nanocomposite films can be prepared with a significant flexoelectric response [10]. The properties of the nanocomposite films have proved to be highly dependent on the nanoparticle concentration, aggregation within the matrix, and the nanoparticle/matrix interface interactions [11]. SrTiO 3 nanoparticle incorporation in PVA matrices has been considered to improve its dielectric properties [12] and to prepare proton exchange membranes for microbial fuel cells [13] Many scientists are fascinated by the technology of multilayer titanium dioxide nanotubes.…”

Nanostructural Arrangements and Surface Morphology on Ureasil-Polyether Films Loaded with Dexamethasone Acetate

“…The images in Figure 5 a,b were simultaneously recorded over a (5000 × 5000) nm surface area. Figure 5 a is the surface topography, and Figure 5 b is the ultrasonic force microscopy (UFM) image, which allows us to distinguish nanoscale regions with different stiffness and/or adhesion [ 7 , 32 ]. The surface morphology in Figure 5 a is markedly different from that of the unloaded u-PPO surface ( Figure 3 b); after loading with DMA, clusters of different sizes can be distinguished on the film surface.…”

“…Interestingly, in UFM, sample regions with distinctly darker contrast are clearly noticeable. Even though, in principle, darker contrast in UFM should indicate softer areas, in polymer nanocomposites, depending on the filler/matrix interface properties, the locations of the filler appear with a darker contrast in UFM due to ultrasound scattering at the interface regions [ 32 ]. The morphology in those regions ( Figure 5 a) is characterized by rounded clusters or dots of ~100 nm in diameter, which appear aligned along a well-defined direction, indicated by a dashed white arrow in Figure 5 a.…”