Hydroxyl functionalized multi-walled carbon nanotubes (MWCNTs) were blended with Polyacrylonitrile (PAN) to prepare ultrafiltration membranes by a phase inversion process. Three different concentrations of MWCNTs were used in PAN, i.e. 0.5, 1 and 2 wt%. The water flux of the membranes increased by 63% at 0.5 wt% loading of MWCNTs compared to neat PAN membranes. The water flux decreased upon further increase in the concentration of MWCNTs, but at 2 wt% loading it was still higher compared to pure PAN membranes. The surface hydrophilicity of the membranes was enhanced upon the addition of MWCNTs, as observed by contact angle measurements. The increased hydrophilicity might have an impact on the improved water flux. All the membranes showed a molecular weight cut off (MWCO) of approximately 50 Kg/mol. Surface pore size analysis by scanning electron microscopy (SEM) showed no significant difference in the mean pore size of the nanocomposite membranes compared to the neat membranes. The cross section morphology was influenced by the introduction of MWCNTs where less but enlarged macrovoids were observed, particularly prominent at a loading of 2 wt% MWCNTs. The membranes containing 2wt% MWCNTs showed 36% improvement in resistance against compaction compared to neat membranes. Furthermore, the tensile strength of the membranes at 2wt% MWCNTs loading increased over 97% compared to neat ones.

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Atomic force microscopy (AFM) has proven to be a valuable instrument to characterize quantitatively the mechanical and morphological properties of soft materials. For medium and hard samples (E41 MPa), the nanomechanical accuracy of AFM is well established and ascertained. However, for soft samples, the experimental setup and data analysis for AFM are not yet firmly established. A calibration obtained for homogeneous samples with a Young's modulus ranging from 100 Pa to a few kPa will prove its usefulness for nanomechanical AFM investigations of soft biological specimens, such as living cells and extracellular matrices. For this purpose, poly(N-isopropylacrylamide) (PNIPAM) hydrogels were synthesized in different methanol − water mixtures to produce a series of homogeneous samples with finely tunable mechanical properties. These samples allowed the comparison and validation of AFM force spectroscopy results using macroscopic and rheological techniques. In AFM measurements, the geometry of the indenter is fundamental to the model used for data interpretation; therefore, experiments were carried out using spherical micrometric and standard pyramidal sharp probes. Moreover, a PNIPAM gel embedded with hard microspheres was analyzed, which showed the capability of AFM for measuring the local mechanical properties of heterogeneous samples.

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