High‐Performance Solar Steam Device with Layered Channels: Artificial Tree with a Reversed Design

Solar steam generation, combining the most abundant resources of solar energy and unpurified water, has been regarded as one of the most promising techniques for water purification. Here, an artificial tree with a reverse‐tree design is demonstrated as a cost‐effective, scalable yet highly efficient steam‐generation device. The reverse‐tree design implies that the wood is placed on the water with the tree‐growth direction parallel to the water surface; accordingly, water is transported in a direction perpendicular to what occurs in natural tree. The artificial tree is fabricated by cutting the natural tree along the longitudinal direction followed by surface carbonization (called as C‐L‐Wood). The nature‐made 3D interconnected micro‐/nanochannels enable efficient water transpiration, while the layered channels block the heat effectively. A much lower thermal conductivity (0.11 W m^?1 K^?1) thus can be achieved, only 1/3 of that of the horizontally cut wood. Meanwhile, the carbonized surface can absorb almost all the incident light. The simultaneous optimizations of water transpiration, thermal management, and light absorption results in a high efficiency of 89% at 10 kW m^?2, among the highest values in literature. Such wood‐based high‐performance, cost‐effective, scalable steam‐generation device can provide an attractive solution to the pressing global clean water shortage problem.     

Nature‐Inspired Tri‐Pathway Design Enabling High‐Performance Flexible Li–O2 Batteries

Trees have an abundant network of channels for the multiphase transport of water, ions, and nutrients. Recent studies have revealed that multiphase transport of ions, oxygen (O₂) gas, and electrons also plays a fundamental role in lithium–oxygen (Li–O₂) batteries. The similarity in transport behavior of both systems is the inspiration for the development of Li–O₂ batteries from natural wood featuring noncompetitive and continuous individual pathways for ions, O₂, and electrons. Using a delignification treatment and a subsequent carbon nanotube/Ru nanoparticle coating process, one is able to convert a rigid and electrically insulating wood membrane into a flexible and electrically conductive material. The resulting cell walls are comprised of cellulose nanofibers with abundant nanopores, which are ideal for Li⁺ ion transport, whereas the unperturbed wood lumina act as a pathway for O₂ gas transport. The noncompetitive triple pathway design endows the wood‐based cathode with a low overpotential of 0.85 V at 100 mA g^?1, a record‐high areal capacity of 67.2 mAh cm^?2, a long cycling life of 220 cycles, and superior electrochemical and mechanical stability. The integration of such excellent electrochemical performance, outstanding mechanical flexibility, and renewable yet cost‐effective starting materials via a nature‐inspired design opens new opportunities for developing portable energy storage devices.     

Plasmonic Wood for High‐Efficiency Solar Steam Generation

Plasmonic metal nanoparticles are a category of plasmonic materials that can efficiently convert light into heat under illumination, which can be applied in the field of solar steam generation. Here, this study designs a novel type of plasmonic material, which is made by uniformly decorating fine metal nanoparticles into the 3D mesoporous matrix of natural wood (plasmonic wood). The plasmonic wood exhibits high light absorption ability (≈99%) over a broad wavelength range from 200 to 2500 nm due to the plasmonic effect of metal nanoparticles and the waveguide effect of microchannels in the wood matrix. The 3D mesoporous wood with numerous low‐tortuosity microchannels and nanochannels can transport water up from the bottom of the device effectively due to the capillary effect. As a result, the 3D aligned porous architecture can achieve a high solar conversion efficiency of 85% under ten‐sun illumination (10 kW m^?2). The plasmonic wood also exhibits superior stability for solar steam generation, without any degradation after being evaluated for 144 h. Its high conversion efficiency and excellent cycling stability demonstrate the potential of newly developed plasmonic wood to solar energy‐based water desalination.     

Ultrafine polysaccharide nanofibrous membranes for water purification

Ultrafine polysaccharide nanofibers (i.e., cellulose and chitin) with 5-10 nm diameters were employed as barrier layers in a new class of thin-film nanofibrous composite (TFNC) membranes for water purification. In addition to concentration, the viscosity of the polysaccharide nanofiber coating suspension was also found to be affected by the pH value and ionic strength. When compared with two commercial UF membranes (PAN10 and PAN400), 10-fold higher permeation flux with above 99.5% rejection ratio were achieved by using ultrafine cellulose nanofibers-based TFNC membranes for ultrafiltration of oil/water emulsions. The very high surface-to-volume ratio and negatively charged surface of cellulose nanofibers, which lead to a high virus adsorption capacity as verified by MS2 bacteriophage testing, offer further opportunities in drinking water applications. The low cost of raw cellulose/chitin materials, the environmentally friendly fabrication process, and the impressive high-flux performance indicate that such ultrafine polysaccharide nanofibers-based TFNC membranes can surpass conventional membrane systems in many different water applications.     

ON THE CAUSE OF THE INFLUENCE OF IONS ON THE RATE OF DIFFUSION OF WATER THROUGH COLLODION MEMBRANES. II

1. It had been shown in previous publications that when pure water is separated from a solution of an electrolyte by a collodion membrane the ion with the same sign of charge as the membrane increases and the ion with the opposite sign of charge as the membrane diminishes the rate of diffusion of water into the solution; but that the relative influence of the oppositely charged ions upon the rate of diffusion of water through the membrane is not the same for different concentrations. Beginning with the lowest concentrations of electrolytes the attractive influence of that ion which has the same sign of charge as the collodion membrane upon the oppositely charged water increases more rapidly with increasing concentration of the electrolyte than the repelling effect of the ion possessing the opposite sign of charge as the membrane. When the concentration exceeds a certain critical value the repelling influence of the latter ion upon the water increases more rapidly with a further increase in the concentration of the electrolyte than the attractive influence of the ion having the same sign of charge as the membrane. 2. It is shown in this paper that the influence of the concentration of electrolytes on the rate of transport of water through collodion membranes in electrical endosmose is similar to that in the case of free osmosis. 3. On the basis of the Helmholtz theory of electrical double layers this seems to indicate that the influence of an electrolyte on the rate of diffusion of water through a collodion membrane in the case of free osmosis is due to the fact that the ion possessing the same sign of charge as the membrane increases the density of charge of the latter while the ion with the opposite sign diminishes the density of charge of the membrane. The relative influence of the oppositely charged ions on the density of charge of the membrane is not the same in all concentrations. The influence of the ion with the same sign of charge increases in the lowest concentrations more rapidly with increasing concentration than the influence of the ion with the opposite sign of charge, while for somewhat higher concentrations the reverse is true.     

Cellulose extraction from wood chip in an ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl)

In the present study, 1-allyl-3-methylimidazolium chloride (AmimCl), an ionic liquid (IL), was used to extract cellulose from pine, poplar, Chinese parasol, and catalpa wood chips. Results show that pine is the most suitable wood species for cellulose extraction with ILs. Its cellulose extraction rate can reach as high as 62% under optimized conditions and its cellulose content is as high as 85% when DMSO/water is used as the precipitant. The dissolution process can be clearly observed by hot stage optical microscopy, and the reaction time can be significantly reduced by microwave irradiation. ¹³C CP/MAS NMR, FTIR, XRD, and SEM were used to analyze the cellulose-rich extracts of pine. Results show that IL dissolves pine wood by destroying inter and intramolecular hydrogen bonds between lignocelluloses. The major component of pine extract is cellulose with a homogeneous and dense structure. After extraction, AmimCl can be easily recycled and reused.     

Conversion of Japanese red pine wood (Pinus densiflora) into valuable chemicals under subcritical water conditions

A comparative study on the decomposition of Japanese red pine wood under subcritical water conditions in the presence and absence of phosphate buffer was investigated in a batch-type reaction vessel. Since cellulose makes up more than 40-45% of the components found in most wood species, a series of experiments were also carried out using pure cellulose as a model for woody biomass. Several parameters such as temperature and residence time, as well as pH effects, were investigated in detail. The best temperature for decomposition and hydrolysis of pure cellulose was found around 270 °C. The effects of the initial pH of the solution which ranged from 1.5 to 6.5 were studied. It was found that the pH has a considerable effect on the hydrolysis and decomposition of the cellulose. Several products in the aqueous phase were identified and quantified. The conditions obtained from the subcritical water treatment of pure cellulose were applied for the Japanese red pine wood chips. As a result, even in the absence of acid catalyst, a large amount of wood sample was hydrolyzed in water; however, by using phosphate buffer at pH 2, there was an increase in the hydrolysis and dissolution of the wood chips. In addition to the water-soluble phase, acetone-soluble and water-acetone-insoluble phases were also isolated after subcritical water treatment (which can be attributed mainly to the degraded lignin, tar, and unreacted wood chips, respectively). The initial wood:acid ratio in the case of reactions catalyzed by phosphate buffer was also investigated. The results showed that this weight ratio can be as high as 3:1 without changing the catalytic activity. The size of the wood chips as one of the most important experimental parameters was also investigated.     

Genetic improvement of the chemical composition of Scots pine (Pinus sylvestris L.) juvenile wood for bioenergy production

Chemical composition is one of the key characteristics that determines wood quality and in turn its suitability for different end products and applications. The inclusion of chemical compositional traits in forest tree improvement requires high‐throughput techniques capable of rapid, non‐destructive and cost‐efficient assessment of large‐scale breeding experiments. We tested whether Fourier‐transform infrared (FTIR) spectroscopy, coupled with partial least squares regression, could serve as an alternative to traditional wet chemistry protocols for the determination of the chemical composition of juvenile wood in Scots pine for tree improvement purposes. FTIR spectra were acquired for 1,245 trees selected in two Scots pine (Pinus sylvestris L.) full‐sib progeny tests located in northern Sweden. Predictive models were developed using 70 reference samples with known chemical composition (the proportion of lignin, carbohydrates [cellulose, hemicelluloses and their structural monosaccharides glucose, mannose, xylose, galactose, and arabinose] and extractives). Individual‐tree narrow‐sense heritabilities and additive genetic correlations were estimated for all chemical traits as well as for growth (height and stem diameter) and wood quality traits (density and stiffness). Genetic control of the chemical traits was mostly moderate. Of the major chemical components, highest heritabilities were observed for hemicelluloses (0.43–0.47), intermediate for lignin and extractives (0.30–0.39), and lowest for cellulose (0.20–0.25). Additive genetic correlations among chemical traits were, except for extractives, positive while those between chemical and wood quality traits were negative. In both groups (chemical and wood quality traits), correlations with extractives exhibited opposite signs. Correlations of chemical traits with growth traits were near zero. The best strategy for genetic improvement of Scots pine juvenile wood for bioenergy production is to decrease and stabilize the content of extractives among trees and then focus on increasing the cellulose:lignin ratio.     

Use of protein charge ladders to study electrostatic interactions during protein ultrafiltration

Recent studies have demonstrated the importance of electrostatic interactions in membrane systems, but there is still controversy about the underlying phenomena. Protein charge ladders, consisting of a set of chemical derivatives of a given protein that differ by single charge groups, were used to quantify the electrostatic interactions during protein ultrafiltration. Myoglobin charge ladders were generated by acylation, with the different derivatives analyzed simultaneously by capillary electrophoresis. Filtration experiments were performed using polyethersulfone and composite regenerated cellulose membranes, with the membrane charge determined from the streaming potential. As expected, the rejection increased as the protein became more heavily charged due to the increase in electrostatic repulsion. However, the transmission of the weakly charged myoglobin species increased dramatically at very low ionic strength. This increase in transmission was attributed to a shift in pH within the pore caused by hydrogen ion partitioning into the charged membrane. The sieving data were in good agreement with theoretical calculations accounting for the effects of this pH shift on the electrostatic interactions.     

Hierarchically Porous N‐Doped Carbon Fibers as a Free‐Standing Anode for High‐Capacity Potassium‐Based Dual‐Ion Battery

Potassium‐based dual‐ion batteries (KDIBs) have emerged as a new generation of rechargeable batteries, due to their high cell voltage, low cost, and the natural abundance of potassium resources. However, the low capacity and poor cycling stability largely hinder the further development of KDIBs. Herein, the fabrication of hierarchically porous N‐doped carbon fibers (HPNCFs) as a free‐standing anode for high‐performance KDIBs is reported. With a free‐standing hierarchical structure (micro/meso/macropores and nanochannels) and high‐content of nitrogen doping, the HPNCFs not only provide intrinsic electron pathways and efficient ion transport channels, but also afford sufficient free space to tolerate the volume change during cycling. Consequently, the KDIBs made from a graphite cathode and an optimized HPNCFs anode deliver a high reversible capacity of 197 mAh g^?1 at a specific current of 50 mA g^?1, and excellent cycling stability (65 mAh g^?1 after 346 cycles at a specific current of 100 mA g^?1, the capacity calculation of the KDIBs is based on the mass of the anode). These results indicate that the properly designed HPNCFs can effectively improve the capacity and cycling stability of the KDIBs, indicating a great potential for applications in the field of high‐performance energy‐storage devices.     

Xyloglucan and xyloglucan endo-transglycosylases (XET): Tools for ex vivo cellulose surface modification

Wood fibres constitute a renewable raw material for the production of novel biomaterials. The development of efficient methods for cellulose surface modification is essential for expanding the properties of wood fibres for increased reactivity and compatibility with other materials. By combining the high affinity between xyloglucan and cellulose, the unique mechanistic property of xyloglucan endo-transglycosylases (XET, EC 2.4.1.207) to catalyze polysaccharide-oligosaccharide coupling reactions, and traditional carbohydrate synthesis, a new system for the attachment of a wide variety of functional groups to wood pulps has been generated. An overview of recent developments is presented in the context of the structure, physical properties, and historical applications of xyloglucan.     

Xyloglucan and xyloglucan endo-transglycosylases (XET): Tools for ex vivo cellulose surface modification

Wood fibres constitute a renewable raw material for the production of novel biomaterials. The development of efficient methods for cellulose surface modification is essential for expanding the properties of wood fibres for increased reactivity and compatibility with other materials. By combining the high affinity between xyloglucan and cellulose, the unique mechanistic property of xyloglucan endo-transglycosylases (XET, EC 2.4.1.207) to catalyze polysaccharide-oligosaccharide coupling reactions, and traditional carbohydrate synthesis, a new system for the attachment of a wide variety of functional groups to wood pulps has been generated. An overview of recent developments is presented in the context of the structure, physical properties, and historical applications of xyloglucan.     

Review on modelling and control of desalination system using reverse osmosis

Dissolved salts in seawater or brackish water are reduced to a potable level through separation techniques, like, distillation, multiple effect vapor compression, evaporation, or by membrane processes such as electro-dialysis reversal, nano-filtration, and reverse osmosis (RO). RO is the most widely used desalination process. Recent advances in RO technology has led to more efficient separation and now is the most cost effective process to operate. The performance of the reverse osmosis process is dependent on concentration of dissolved solids in the feed-water, feed-water pressure, and the membrane strength to withstand system pressure, membrane solute rejection, membrane fouling characteristics, and the required permeate solute concentration. RO is a promising tool that uses cellulose acetate (or) polyamide membrane and is widely chosen as the cost of production is reduced by the use of energy efficient and process control techniques. This paper presents a review on modelling, identification of parameters from single input-outputs and multi input/output lumped systems, dynamic modelling and control of desalination systems in the past twenty years by collecting more than 60 literatures.     

Low-Friction Graphene Oxide-Based Ion Selective Membrane for High-Efficiency Osmotic Energy Harvesting

Graphene-based laminate membranes with selective ion-transport capability show great potential in renewable osmotic energy harvesting. One of the great challenges is to reduce the overall energy barriers while remain the high ion selectivity in the transmembrane ion transport process. Here, a strategy is proposed to break the trade-off between ion selectivity and permeability in laminar nanochannels using amphiphilic molecules as modifier, which enhances the surface charge density of nanochannel by loading more ion polymer with polar head and lows the frictional force of ion transport with hydrophobic tail. The conversion efficiency can reach to 32% in osmotic energy harvesting (0.5 m /0.01 m concentration gradient) after adopting this modifier. During the process of mixing real river water and seawater, the maximum power density can reach to 13.38 W m⁻². The amphiphilic molecules also bind adjacent nanosheets, endowing the membrane's strong mechanical strength and high stability in aqueous solution. This work can open up a new way to regulate the transmembrane ion transport in 2D laminate membranes.     

Model films from native cellulose nanofibrils. Preparation, swelling, and surface interactions

Native cellulose model films containing both amorphous and crystalline cellulose I regions were prepared by spin-coating aqueous cellulose nanofibril dispersions onto silica substrates. Nanofibrils from wood pulp with low and high charge density were used to prepare the model films. Because the low charged nanofibrils did not fully cover the silica substrates, an anchoring substance was selected to improve the coverage. The model surfaces were characterized using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The effect of nanofibril charge density, electrolyte concentration, and pH on swelling and surface interactions of the model film was studied by quartz crystal microbalance with dissipation (QCM-D) and AFM force measurements. The results showed that the best coverage for the low charged fibrils was achieved by using 3-aminopropyltrimethoxysilane (APTS) as an anchoring substance and hence it was chosen as the anchor. The AFM and XPS measurements showed that the fibrils are covering the substrates. Charge density of the fibrils affected the morphology of the model surfaces. The low charged fibrils formed a network structure while the highly charged fibrils formed denser film structure. The average thickness of the films corresponded to a monolayer of fibrils, and the average rms roughness of the films was 4 and 2 nm for the low and high charged nanofibril films, respectively. The model surfaces were stable in QCM-D swelling experiments, and the behavior of the nanofibril surfaces at different electrolyte concentrations and pHs correlated with other studies and the theories of Donnan. The AFM force measurements with the model surfaces showed well reproducible results, and the swelling results correlated with the swelling observed by QCM-D. Both steric and electrostatic forces were observed and the influence of steric forces increased as the films were swelling due to changes in pH and electrolyte concentration. These films differ from previous model cellulose films due to their chemical composition (crystalline cellulose I and amorphous regions) and fibrillar structure and hence serve as excellent models for the pulp fiber surface.     

Enhanced cellulose degradation using cellulase-nanosphere complexes

Enzyme catalyzed conversion of plant biomass to sugars is an inherently inefficient process, and one of the major factors limiting economical biofuel production. This is due to the physical barrier presented by polymers in plant cell walls, including semi-crystalline cellulose, to soluble enzyme accessibility. In contrast to the enzymes currently used in industry, bacterial cellulosomes organize cellulases and other proteins in a scaffold structure, and are highly efficient in degrading cellulose. To mimic this clustered assembly of enzymes, we conjugated cellulase obtained from Trichoderma viride to polystyrene nanospheres (cellulase:NS) and tested the hydrolytic activity of this complex on cellulose substrates from purified and natural sources. Cellulase:NS and free cellulase were equally active on soluble carboxymethyl cellulose (CMC); however, the complexed enzyme displayed a higher affinity in its action on microcrystalline cellulose. Similarly, we found that the cellulase:NS complex was more efficient in degrading natural cellulose structures in the thickened walls of cultured wood cells. These results suggest that nanoparticle-bound enzymes can improve catalytic efficiency on physically intractable substrates. We discuss the potential for further enhancement of cellulose degradation by physically clustering combinations of different glycosyl hydrolase enzymes, and applications for using cellulase:NS complexes in biofuel production.     

THE INFLUENCE OF ELECTROLYTES ON THE ELECTRIFICATION AND THE RATE OF DIFFUSION OF WATER THROUGH COLLODION MEMBRANES

1. When pure water is separated by a collodion membrane from a watery solution of an electrolyte the rate of diffusion of water is influenced not only by the forces of gas pressure but also by electrical forces. 2. Water is in this case attracted by the solute as if the molecules of water were charged electrically, the sign of the charge of the water particles as well as the strength of the attractive force finding expression in the following two rules, (a) Solutions of neutral salts possessing a univalent or bivalent cation influence the rate of diffusion of water through a collodion membrane, as if the water particles were charged positively and were attracted by the anion and repelled by the cation of the electrolyte; the attractive and repulsive action increasing with the number of charges of the ion and diminishing inversely with a quantity which we will designate arbitrarily as the "radius" of the ion. The same rule applies to solutions of alkalies. (b) Solutions of neutral or acid salts possessing a trivalent or tetravalent cation influence the rate of diffusion of water through a collodion membrane as if the particles of water were charged negatively and were attracted by the cation and repelled by the anion of the electrolyte. Solutions of acids obey the same rule, the high electrostatic effect of the hydrogen ion being probably due to its small "ionic radius." 3. The correctness of the assumption made in these rules concerning the sign of the charge of the water particles is proved by experiments on electrical osmose. 4. A method is given by which the strength of the attractive electric force of electrolytes on the molecules of water can be roughly estimated and the results of these measurements are in agreement with the two rules. 5. The electric attraction of water caused by the electrolyte increases with an increase in the concentration of the electrolyte, but at low concentrations more rapidly than at high concentrations. A tentative explanation for this phenomenon is offered. 6. The rate of diffusion of an electrolyte from a solution to pure solvent through a collodion membrane seems to obey largely the kinetic theory inasmuch as the number of molecules of solute diffusing through the unit of area of the membrane in unit time is (as long as the concentration is not too low) approximately proportional to the concentration of the electrolyte and is the same for the same concentrations of LiCl, NaCl, MgCl₂, and CaCl₂.     

Cellulose depolymerization to glucose and other water soluble polysaccharides by shear deformation and high pressure treatment

The simultaneous action of shear deformation and high pressure (SDHP) creates changes in the structure of wood and its main components (cellulose, hemicelluloses, lignin). The formation of water and alkali soluble polysaccharides under SDHP action, proceeds in seconds in the solid state, without the use of any reagents and solvents. Therefore, SDHP seems to be a technologically safe method and friendly to the environment. The amorphization of cellulose crystallites and depolymerization of cellulose chains were observed under a wide range of pressures (1–6 GPa), both for cellulose samples and the cellulose part of wood. Similar depolymerization occurs in the hemicellulose part of wood. The decomposition of polysaccharides under SDHP causes the formation of the water soluble part, whose content increases with pressure and the applied shear deformation. A maximum solubility of 40% and 55% was registered at 6 GPa following treatment of cellulose and birch wood samples. A higher output in the case of wood can be explained by a specific role of lignin under SDHP, which acts as a ‘grinding stone’ during cellulose and hemicelluloses destruction. As shown by high-performance size exclusion chromatography, the water soluble fraction obtained from cellulose contained glucose (2.6%), cellobiose (9.6%), cellotriose (16.6%) and other higher water soluble oligomers (71%). Almost complete dissolution (98%) of the treated cellulose sample can be achieved by extraction with 10% NaOH solution. The SDHP treated birch wood was subjected to submerged fermentation (with Trichoderma viride), and a 13% output of proteins was obtained. In this case, the water soluble part played the role of the so called ‘start sugars’. Abbreviations: ASF, alkali soluble fraction; DP, degree of polymerization; EC, energy consumption; HP, high pressure; LMWS, low molecular weight sugars; MC, moisture content; MCC, microcrystalline cellulose; SD, shear deformation, SDHP, shear deformation under high pressure; SS, shear strength; WSF, water soluble fraction This revised version was published online in November 2006 with corrections to the Cover Date.     

An improved method for concentrating rotavirus from water samples

A modified adsorption-elution method for the concentration of seeded rotavirus from water samples was used to determine various factors which affected the virus recovery. An enzyme-linked immunosorbent assay was used to detect the rotavirus antigen after concentration. Of the various eluents compared, 0.05M glycine, pH 11.5 gave the highest rotavirus antigen recovery using negatively charged membrane filtration whereas 2.9% tryptose phosphate broth containing 6% glycine; pH 9.0 was found to give the greatest elution efficiency when a positively charged membrane was used. Reconcentration of water samples by a speedVac concentrator showed significantly higher rotavirus recovery than polyethylene glycol precipitation through both negatively and positively charged filters (p-value <0.001). In addition, speedVac concentration using negatively charged filtration resulted in greater rotavirus recovery than that using positively charged filtration (p-value = 0.004). Thirty eight environmental water samples were collected from river, domestic sewage, canals receiving raw sewage drains, and tap water collected in containers for domestic use, all from congested areas of Bangkok. In addition, several samples of commercial drinking water were analyzed. All samples were concentrated and examined for rotavirus antigen. Coliforms and fecal coliforms (0->1,800 MPN/100 ml) were observed but rotavirus was not detected in any sample. This study suggests that the speedVac reconcentration method gives the most efficient rotavirus recovery from water samples.     

Morphology of modified regenerated model cellulose II surfaces studied by atomic force microscopy: effect of carboxymethylation and heat treatment

Model cellulose II surfaces with different surface charge have been prepared from carboxymethylated wood pulp. AFM tapping-mode imaging in air showed that the introduction of charged groups into the film does not appreciably change the surface morphology. However, after a mild heat treatment (heating at 105 degrees C for 6 h), an irreversible surface structure change, from near spherical-type aggregates to a fibrillar structure, was observed. This might be attributed to the formation of strong hydrogen bonds in the crystalline region of the films while the amorphous regions shrank upon drying. The suitability of these charged cellulose films for surface forces studies was also investigated. At pH below the pK(a) of the carboxyl groups present in the film, the interaction force could be fit by a van der Waals force interaction. At higher pH, the interaction was of a purely electrostatic nature with no van der Waals component observable due to the swelling of the surfaces.