ABSTRACT
Graphene oxide (GO) membranes, which form from the lamination of GO sheets, attract much attention due to their unique nanochannels. There is much interest in controlling the nanochannel structures and improving the aqueous stability of GO membranes so they can be effectively used in separation and filtration applications. This study employed a simple yet effective method of introducing trivalent aluminum cations to a GO sheet solution through the oxidation of aluminum foil, which modifies the nanochannels in the self-assembled GO membrane by increasing the inter-sheet distance while decreasing intra-sheet spacing. The Al3+ modification resulted in an increase in membrane stability in water, methanol, ethanol, and propanol, yet decreased membrane permeability to water and propanol. These changes were attributed to strong interactions between Al3+ and the membrane oxygenated functional groups, which resulted in an increase in membrane hydrophobicity and a decrease in the intra-sheet spacing as supported by surface tension, contact angle, atomic force microscopy, and X-ray photoelectron spectroscopy measurements. Our approach for forming Al3+ modified GO membranes provides a method for improving the aqueous stability and tailoring the permeation selectivity of GO membranes, which have the potential to be implemented in vapor separation and fuel purification applications.
ABSTRACT
The masticatory loading regime of lateral transverse bending (wishboning) is hypothesized to be instrumental in the evolution of symphyseal form among primates. The biomechanics of wishboning have largely been inferred by assuming that the mandible behaves as a curved beam under this load; however, the characterization of stress and strain in the anthropoid symphysis has been interpretively challenging. This is due, in part, to both limitations of sampling strain in an in vivo context and the incongruence of beam theory assumptions on the one hand, and the anatomical complexity of mandibular morphology on the other. Utilizing three-dimensional (3D) Digital Image Correlation (DIC), we employ an in vitro approach to characterize the strain field in a sample of colobine mandibles under simulated wishboning loads in order to assess the utility of idealized curved beam models for characterizing strain gradients in symphyseal bone. Conventional theory of curved beams suggest that colobine mandibles should exhibit reduced disparity of labial and lingual stresses relative to papionin primates given differences in overall mandibular architecture. This prediction is borne out by our analysis: whereas macaques experience lingual:labial strain disparities of 3.5:1, the colobine mandibles exhibit ratios on the order of 2-3:1. However, despite the fact that wishboning loads represent a case of asymmetric bending, details of the wishboning strain field do not conform to expected stress distribution under this model.
