Details of surface features in aromatic polyamide reverse osmosis membranes characterized by scanning electron and atomic force microscopy

In the present article, some new events on the surface morphology of the aromatic polyamide thin‐film‐composite (TFC) membranes were demonstrated in conjunction with their inherent chemical nature. In addition, the detailed, quantitative understanding of the microscopic surface features was shown to be essential in controlling the water permeability and eventually developing the high performance membranes. The surface roughness and the surface area were mainly affected by the existence or nonexistence of the crosslinking and/or the free amide groups not pertinent to the formation of the hydrogen bonding, which in turn contributed to the water permeability. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1429–1440, 1999     

Effects of bisphenol monomer structure on the surface morphology and reverse osmosis (RO) performance of thin-film-composite membranes composed of polyphenyl esters

Four reverse osmosis (RO) composite membranes, in which thin-film active layers were polyphenyl esters, were prepared by interfacial polymerization of a series of bisphenol monomers and trimesoyl chloride (TMC). An atomic force microscope (AFM) was used to investigate the surface morphology and RO experiments were carried out to measure the rejection and flux characteristics of the membranes. Correlations between the inherent chemical nature of bisphenols possessing structural variations in the middle of phenyl rings and the surface morphology/RO performance of the membranes were studied. Polarity of the connectors between two phenyl rings of bisphenols played an important role in determining the surface morphology and RO performance. Nonpolar bisphenol gave a morphology of uniform, distinct nodular corrugation and a superior RO rejection but a relatively low flux, while the polar one resulted in an irregular, ambiguous nodule structure and a high flux. The size of the bisphenol connectors was also found to be important; the smaller one was more favorable for the formation of membrane with better salt rejection, while the larger one contributed to higher flux. © 1996 John Wiley & Sons, Inc.     

Surface morphology of polypyrrole core/polyacrolein shell latex by atomic force microscopy (AFM)

 Polypyrrole latex (P(P)), synthesized in Redox polymerization of pyrrole, was used as seed for radical polymerization of acrolein initiated with K₂S₂O₈. In this process the polypyrrole core/polyacrolein shell latex (P(P–A)) was obtained. Morphology of the surface of P(P–A) particles was investigated by atomic force microscopy (AFM). It was found that macromolecules of polyacrolein are not randomly distributed on the surface of polypyrrole but form patches. Apparently, attraction between macromolecules of poly-acrolein in the surface layer is high and the enthalpy of formation of polyacrolein macromolecule clusters is sufficient to compensate, at least, the negative entropy change due to ordering of these macromolecules. Thickness of the polyacrolein layer on the surface of polypyrrole particles, which were covered only partially with polyacrolein, was equal to only 1.6 nm (standard deviation σ= 0.2 nm) and thus, it was reasonable to assume that it corresponded to the monolayer coverage. Received: 30 April 1997 Accepted: 25 August 1997     

Dynamics of a disturbed sessile drop measured by atomic force microscopy (AFM)

A new method for studying the dynamics of a sessile drop by atomic force microscopy (AFM) is demonstrated. A hydrophobic microsphere (radius, r ～ 20-30 μm) is brought into contact with a small sessile water drop resting on a polytetrafluoroethylene (PTFE) surface. When the microsphere touches the liquid surface, the meniscus rises onto it because of capillary forces. Although the microsphere volume is 6 orders of magnitude smaller than the drop, it excites the normal resonance modes of the liquid interface. The sphere is pinned at the interface, whose small (<100 nm) oscillations are readily measured with AFM. Resonance oscillation frequencies were measured for drop volumes between 5 and 200 μL. The results for the two lowest normal modes are quantitatively consistent with continuum calculations for the natural frequency of hemispherical drops with no adjustable parameters. The method may enable sensitive measurements of volume, surface tension, and viscosity of small drops.     

Role of membrane surface morphology in colloidal fouling of cellulose acetate and composite aromatic polyamide reverse osmosis membranes

Laboratory-scale colloidal fouling tests, comparing the fouling behavior of cellulose acetate and aromatic polyamide thin-film composite reverse osmosis (RO) membranes, are reported. Fouling of both membranes was studied at identical initial permeation rates so that the effect of the transverse hydrodynamic force (permeation drag) on the fouling of both membranes is comparable. Results showed a significantly higher fouling rate for the thin-film composite membranes compared to that for the cellulose acetate membranes. Addition of an anionic surfactant (sodium dodecyl sulfate, SDS) to mask variations in chemical and electrokinetic surface characteristics of the cellulose acetate and aromatic polyamide membranes resulted in only a small change in the fouling behavior. The higher fouling rate for the thin-film composite membranes is attributed to surface roughness which is inherent in interfacially polymerized aromatic polyamide composite membranes. AFM and SEM images of the two membrane surfaces strongly support this conclusion. These surface images reveal that the thin-film composite membrane exhibits large-scale surface roughness of ridge-and-valley structure, while the cellulose acetate membrane surface is relatively smooth.     

In-situ atomic force microscopy (AFM) imaging: influence of AFM probe geometry on diffusion to microscopic surfaces

The effect of AFM probe geometry on diffusion to micrometer-scale reactive (electrode) interfaces is considered. A disk-shaped substrate electrode was held at a potential to reduce a species of interest (aqueous Ru(NH 3) 6 (3+)) at a diffusion-controlled rate and the current response during AFM imaging provided information on local mass transport to the interface. This approach reveals how the AFM probe influences diffusion to a reactive surface, which is of importance in more clearly delineating the conditions under which in-situ AFM can be treated as a noninvasive probe of surface processes involving mass transport (e.g., electrode reactions and crystal dissolution and growth). An assessment has been made of three types of probes: V-shaped silicon nitride contact mode probes; single beam silicon probes; and batch-fabricated scanning electrochemical-atomic force microscopy (SECM-AFM) probes. Two disk electrodes, (6.1 microm and 1.6 microm diameter) have been considered as substrates. The results indicate that conventional V-shaped contact mode probes are the most invasive and that the batch-fabricated SECM-AFM probes are the least invasive to diffusion at both of the substrates used herein. The experimental data are complemented by the development of simulations based on a simple 2D model of the AFM probe and active surface site. The importance of probe parameters such as the cantilever size, tip cone height, and cone angle is discussed, and the implications of the results for studies in other areas, such as growth and dissolution processes, are considered briefly.     

Surface structure and phase separation mechanism of polysulfone membranes by atomic force microscopy

Atomic force microscopy (AFM) was used to investigate the surface of polysulfone (PSf) membranes. The AFM method provides information on both size and shape of pores or cavities on the surface as well as the roughness of the skin. The pore sizes obtained from AFM observation were found to be more accurate than those obtained from scanning electron microscopy (SEM) since the potential of altering the pore structure of the membrane during sample preparation was eliminated. It was observed that two different modes of phase separation existed during the formation of PSf membrane when the coagulation conditions were varied.     

Surface characteristics of glass fibres covered with an aluminum layer after a chemical modification process using secondary ion mass spectrometry (SIMS) and atomic force microscopy (AFM)

Results show investigations of surface of modified glass fibres (before and after chemical modification of their surface), which are candidates for future original matrix-less reference material for volatile ethene analytes (C₂H₄). Used analytical methods are secondary ion mass spectrometry and atomic force microscopy. The investigations were aimed at observation of changes and processes which occurred on the surface of glass fibres covered with an aluminum layer and constituting an ethane carrier.The paper describes the procedure of chemical modification of the surface of 3 cm segments of glass fibres covered with an aluminum layer (660/680 μm, external diameter of quartz/external Al diameter), a surfactant constituting a source of ethene. Ethene (a measured constituent) in a standard gas mixture is obtained during the process of controlled thermal decomposition of a surface compound in a stream of rarefied gas (such kind of mixture is called matrix-less reference material).     

Aspects of the physical chemistry of polymers, biomaterials and mineralised tissues investigated with atomic force microscopy (AFM)

Beyond being merely a tool for measuring surface topography, atomic force microscopy (AFM) has made significant contributions to various scientific areas dealing with physical chemistry processes. This paper presents aspects of the physical chemistry at surfaces and interfaces of polymers, biomaterials and tissues investigated with AFM. Selected examples presented include surface induced self-assembly of polymer blends, copolymer interfacial reinforcement of immiscible homopolymers, protein adsorption on biomaterials and erosion of mineralised human tissues. In these areas, AFM is a useful and versatile tool to study structural or dynamic sample properties including thermodynamically driven surface evolution of polymer surfaces, lateral surface composition of interfaces, adsorption processes, and the metrology of demineralisation phenomena.     

The characterization of high generation poly(amidoamine) G9 dendrimers by atomic force microscopy (AFM)

Scanning force microscopy (AFM) has been employed to characterize the generation‐9 (G9) poly(amidoamine) (PAMAM) dendrimer packing on a mica surface under various conditions. Well ordered 2‐D arrays from hexagonally packed particles of PAMAM (G9) dendrimers (11.4nm in diameter) were deposited on the mica surface. This may be one of the smallest regular monolayer arrays ever observed. The mechanism considered to be responsible for this 2‐D array packing is the interaction of forces between the dendrimer and the mica surface and between dendrimer molecules as well. Other factors such as molecular interpenetrating and the rigidity of the branch structure obviously play an important role in the 2‐D array formation.     

Characterization of atomic force microscopy (AFM) tip shapes by scanning hydrothermally deposited ZnO thin films

Direct observation of tip shapes by atomic force microscopy (AFM) has been achieved using spike-like crystallites in ZnO thin films deposited on microscope glass slides by the hydrothermal deposition technique. Three types of AFM tips, e.g. standard Si(3)N(4) tips, a broken silicon supertip and a noncontact silicon tip were examined and the acquired images for these tips show that ZnO crystallites are good samples to image commonly used AFM tips. The most obvious characteristic of this method is that it is easy for every chemical laboratory to access.     

Studies on the morphology and structure of aromatic polyester films

Oriented films of an aromatic polyester containing a triad ester mesogenic group and a decamethylene flexible spacer were studied by polarized light microscopy, small-angle light scattering, and polarized infrared spectroscopy to determine the nature of the alignment of the polymer chains, induced by shearing, which is responsible for the banded or striped morphology observed. The stripes are apparently composed of fibrils arranged in a zigzag manner containing polymer chains packed in a highly ordered, parallel alignment at an angle of ±26° to the shearing direction.     

Correlating polymer structure,dynamics, and function with atomic force microscopy

Since its development, atomic force microscopy (AFM) has become an indispensable tool for investigating fundamental and technological applications of polymer materials. The versatility of AFM imaging modes and operating conditions allows for nanoscale characterization of a range of dynamic processes, such as crystallization, phase separation, self assembly, and electronic transport. Advances in AFM technology, particularly high-speed and high-resolution imaging, enable investigation of polymer structure, function, and dynamics in real world conditions and across a range of relevant spatial and temporal scales. In this perspective, we highlight a collection of recent polymer studies that utilize AFM to correlate the function and structure of polymer films, with focus on its multiparametric imaging capabilities. As the complexity of polymer materials and morphologies continues to increase, AFM is well poised to meet the accompanying demand for nanoscale imaging and characterization.     

Stability and transport characteristics of reverse osmosis membranes using cyanide rinse waters

The recovery of cyanide rinse water using commercially available membranes (DESAL 3, MS10, SW30HR) is the objective of this work. Accordingly, flux, rejection, pretreatment and stability studies were carried out with these thin-film, composite, reverse osmosis membranes. The transport properties of membrane sections were tested using both cyanide rinse waters and NaCl solutions for flux and rejection on a flat-sheet test module after long term exposure to copper cyanide solutions. While SW30HR exhibited good chemical stability, DESAL3 and MS10 were not stable after exposure to high pH solutions for up to 6 months. Pretreatment studies were carried out on SW30HR membranes for flux enhancement in order to improve the recovery of the reverse osmosis system. SW30HR pretreated with ethanol exhibited a five-fold increase in water flux accompanied by an increase in ion rejection. Similar high fluxes and high rejection of principal bath constituents were exhibited by the SW30HR membrane when copper cyanide rinse water solutions were employed as the feed. These results indicate that this type of pretreated reverse osmosis membranes may have significant utility for reprocessing of copper cyanide rinse waters.     

Scanning force microscopy of polyester: surface structure and adhesive properties

Scanning force microscopy has been used to characterize the surface structure and properties of poly(ethylene terephthalate) (PET) films. Two types of biaxially oriented film have been studied: one (Melinex O) is free of additives while the other (Mylar D) contains particulate additives at the surface. Contact mode characterization of both materials provide clear images of the polymer surface and (in the case of Mylar D) the additives. Phase images reveal substantial nanoscale morphological detail, including small features thought to be crystallites. To model the adhesive properties of polymer surfaces, mixed self‐assembled monolayers containing polar and methyl terminated adsorbates were studied using chemical force microscopy. It was found that the strength of the tip‐sample adhesion increased with the fraction of polar terminated adsorbates at the surface when a carboxylic acid terminated tip was employed, while the trend was reversed when a methyl terminated tip was used. Adhesion forces measured for plasma treated PET increased with treatment time, and linearly with the cosine of the water contact angle, illustrating the chemical selectivity of chemical force microscopy. However, friction forces were found to vary in a non‐linear fashion, indicating that changes to the polymer surface mechanical properties following treatment were important.     

Heat-fixation method used in an atomic force microscopy study of cell morphology

In order to overcome the difficulties with existing methods for sample immobilization in imaging Halobacterium salinarum (H. salinarum) living in a highly salty medium by atomic force microscopy (AFM), a heat-fixation method was, for the first time, used to overcome existing problems in preparing samples for AFM. The effect on the cell morphology of the heat-fixation method was studied by MAC mode AFM, and was compared with the drop-and-dry and the polylysine-adhesion methods. It was found that the heat-fixation method can be successfully used for preparing Gram-negative and Gram-positive bacteria samples for AFM studies. Using this method, high-resolution AFM images of H. salinarum were obtained. Round protrusions on the cell surface and horn-like protrusions only at one pole of H. salinarum were observed.     

Investigating the morphology and mechanical properties of blastomeres with atomic force microscopy

Atomic force microscopy (AFM) was used to directly investigate the morphology and mechanical properties of blastomeres during the embryo development. With AFM imaging, the surface topography of blastomeres from two‐cell, four‐cell, and eight‐cell stages was visualized, and the AFM images clearly revealed the blastomere's morphological changes during the different embryo developmental stages. The section measurements of the AFM topography images of the blastomeres showed that the axis of the embryos nearly kept constant during the two‐cell, four‐cell, and eight‐cell stages. With AFM indenting, the mechanical properties of living blastomeres from several embryos were measured quantitatively under physiological conditions. The results of mechanical properties measurements indicated that the Young's modulus of the two blastomeres from two‐cell embryo was different from each other, and the four blastomeres from the four‐cell embryo also had variable Young's modulus. Besides, the blastomeres from two‐cell embryos were significantly harder than blastomeres from four‐cell embryos. These results can improve our understanding of the embryo development from the view of cell mechanics. Copyright © 2013 John Wiley & Sons, Ltd.     

Surface morphology of antifrictional polymer materials: Experience in atomic force and electron microscopy

The morphology of the friction surface of antifrictional charged carbon plastics is investigated by atomic force and scanning electron microscopy. Methodical approaches to composites probe preparing are described, and possibilities of methods for examination of friction surface are shown. On the basis of the obtained results, the role of nanosized modifiers of various chemical natures (used in manufacturing antifrictional materials) is highlighted, and the mechanisms of the processes that occur in carbon plastics on the tribological contact are suggested.     

Preparation,structure characteristics and separation properties of thin-film composite polyamide-urethane seawater reverse osmosis membrane

A novel thin-film composite (TFC) seawater reverse osmosis membrane was developed by the interfacial polymerization of 5-chloroformyloxyisophthaloyl chloride (CFIC) and metaphenylenediamine (MPD) on the polysulphone supporting membrane. The performance of the TFC membrane was optimized by studying the preparation parameters, which included the reaction time, pH of the aqueous-MPD solution, monomer CFIC concentration, additive isopropyl alcohol content in aqueous solution, curing temperature and time. The reverse osmosis performance of the resulting membrane was evaluated through permeation experiment with synthetic seawater, and the structure of the novel membrane was characterized by using SEM, AFM and XPS. Furthermore, the separation properties of the TFC membrane were tested by examining the reverse osmosis performances of various conditions, the boron rejection performance and the long-term stability. The results show that the desired TFC seawater reverse osmosis membrane has a typical salt rejection of 99.4% and a flux of about 35 L/m² h for a feed aqueous solution containing 3.5 wt.% NaCl at 5.5 MPa, and an attractive boron rejection of more than 92% at natural pH of 7–8; that the novel seawater reverse osmosis membrane appears to comprise a thicker, smoother and less cross-linking film structure. Additionally, the TFC membrane exhibits good long-term stability.