In situ atomic force microscopy measurement of the dynamic variation in the elastic modulus of swollen chitosan/gelatin hybrid polymer network gels in media of different pH

The surface morphology and elastic modulus of chitosan/gelatin hybrid polymer network (CS/GLN HPN) gels was investigated by in situ atomic force microscopy (AFM). The surface domains of hydrogel varied from irregular clumps to sponge-like patterns with increasing swelling time. The vertical height and width of the surface domains observed in alkali medium are smaller than in acidic medium. The indentation of the gels caused by the AFM tip increased with time and the elastic modulus of the gels estimated by the Hertz model decreased sharply compared with that of xerogel. In alkali medium, due to the reassociation of hydrogen bondings between networks, the elastic modulus increased slightly. © 1999 Society of Chemical Industry     

Microwave preparation and adsorption properties of EDTA‐modified cross‐linked chitosan

A novel chitosan‐based adsorbent (CCTE) was synthesized by the reaction between epichlorohydrin O‐cross‐linked chitosan and EDTA dianhydride under microwave irradiation (MW). The chemical structure of this new polymer was characterized by infrared spectra analysis, thermogravimetric analysis, and X‐ray diffraction analysis. The results were in agreement with the expectations. The static adsorption properties of the polymer for Pb²⁺, Cu²⁺, Cd²⁺, Ni²⁺, and Co²⁺ were investigated. Experimental results demonstrated that the CCTE had higher adsorption capacity for the same metal ion than the parent chitosan and cross‐linked chitosan. In particular, the adsorption capacities for Pb²⁺ and Cd²⁺ were 1.28 mmol/g and 1.29 mmol/g, respectively, in contrast to only 0.372 mmol/g for Pb²⁺ and 0.503 mmol/g for Cd²⁺ on chitosan. Kinetic experiments indicated that the adsorption of CCTE for the above metal ions achieved the equilibrium within 4 h. The desorption efficiencies of the metal ions on CCTE were over 93%. Therefore, CCTE is an effective adsorbent for the removal and recovery of heavy metal ions from industrial waste solutions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Formation of a DNA/N‐dodecylated chitosan complex and salt‐induced gene delivery

An N‐dodecylated chitosan (CS‐12) was synthesized from dodecyl bromide and chitosan and was assembled with DNA to form a polyelectrolyte complex (DNA/CS‐12 PEC). UV was used to examine the thermal stability of DNA embedded in PEC. The results indicate that the incorporation of dodecylated chitosan can enhance the thermal stability of DNA. The analysis of AFM image shows that PEC develops a globule‐like structure composed of 40–115 DNA molecules. Dissociation of PEC was investigated by the addition of low molecular weight electrolytes. The added small molecular salts dissociate the PEC, inducing DNA to release. The ability of Mg²⁺ to dissociate PEC is greater compared to that of Na⁺ and K⁺. From AFM images, it can be visualized that DNA remains intact and undamaged due to the protection from DNase offered by alkylated chitosan. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3391–3395, 2001     

Atomic force microscopy of cellulose membranes prepared from the N‐methylmorpholine‐N‐oxide/water solvent system

Cellulose membranes were obtained by solutions of cellulose being cast into a mixture of N‐methylmorpholine‐N‐oxide (NMMO) and water under different processing conditions. Atomic force microscopy (AFM) was used to investigate the surface structures of the membranes. The AFM method provided information on both the size and shape of the pores on the surface, as well as the roughness of the skin, through a computerized analysis of AFM micrographs. The results obtained showed that the surface morphologies were intrinsically associated with the permeation properties. For the cellulose membranes, increasing the NMMO concentration and the temperature of the coagulation bath led to higher fluxes and lower bovine serum albumin rejection. These were always correlated with higher values of the roughness parameters and larger pore sizes of the membrane surfaces. When the cellulose concentration of the casting solution was 11 wt %, the membrane showed a nodular structure with interconnected cavity channels between the agglomerated nodules. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3389–3395, 2002     

Functionalization of chitosan membranes through phosphorylation: Atomic force microscopy,wettability, and cytotoxicity studies

Grafting negatively charged groups such as phosphates is a well‐known strategy for inducing the deposition of apatite‐like layers under simulated physiological conditions. In this investigation, chitosan was phosphorylated in an attempt to enhance its osteoconduction. Chitosan membranes were phosphorylated at 30°C with the H₃PO₄/Et₃PO₄/P₂O₅/butanol reaction system for periods up to 48 h. This method is an alternative to the phosphoric acid/urea/dimethylformamide phosphorylation method, which involves the use of much higher temperatures. In this study, the effects of the phosphorylation reaction time on the surface morphology and surface free energy of phosphorylated membranes were investigated with atomic force microscopy and static‐contact‐angle measurements, respectively. In addition, the modified membranes were evaluated with respect to their cytotoxicity toward bone cells through the incubation of human osteoblastic cells with extracts of the materials for two different periods: 24 and 120 h. The results revealed a reduction of the average surface roughness at the nanometer scale with increasing phosphorylation reaction time. Wettability studies showed an increase in the polar component of the surface free energy with increasing reaction time as a result of the increase in the phosphate surface concentration. Cytotoxicity studies revealed no cytotoxic effect of phosphorylated membranes on osteoblastic cells, regardless of the incubation period. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 276–284, 2006     

The interaction between bovine serum albumin and the self-aggregated nanoparticles of cholesterol-modified O-carboxymethyl chitosan

The interaction between bovine serum albumin (BSA) and self-aggregated nanoparticles of cholesterol-modified O-carboxymethyl chitosan (CCMC) with different degrees of substitution (DS) of cholesterol moiety was studied by transmission electron microscopy (TEM), fluorescence quenching method and circular dichroism (CD) measurement. This interaction was started at the disaggregation of CCMC self-aggregated nanoparticles and reached equilibrium after 3-4 h. The apparent quenching constant (K_q) between BSA and CCMC self-aggregated nanoparticles calculated by the modified Stern-Volmer plot increased from 4.14 × 10⁴ to 1.95 × 10⁵ M⁻¹ with DS of cholesterol moiety increasing from 3.2% to 9.8%, whereas the fraction of tryptophan residues in BSA molecule involved in the interaction decreased at the same time. Compared with free BSA, the relative α-helix content of BSA decreased and the unfolding of BSA by a denaturant such as urea was largely suppressed upon interaction with CCMC self-aggregated nanoparticles. DS of cholesterol moiety significantly affected the interaction between BSA and CCMC self-aggregated nanoparticles.     

Pervaporation of tertiary butanol/water mixtures through chitosan membranes cross‐linked with toluylene diisocyanate

Membranes made from 84% deacetylated chitosan biopolymer were cross‐linked by a novel method using 2,4‐toluylene diisocyanate (TDI) and tested for the separation of t‐butanol/water mixtures by pervaporation. The unmodified and cross‐linked membranes were characterized by Fourier transform infra red (FTIR) spectroscopy, X‐ray diffraction (XRD) studies and sorption studies in order to understand the polymer–liquid interactions and separation mechanisms. Thermal stability was analyzed by differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA) while tensile strength measurement was carried out to assess mechanical strength. The membrane appears to have good potential for breaking the aqueous azeotrope of 88.2 wt% t‐butanol by giving a high selectivity of 620 and substantial water flux (0.38 kg m^?2 hr^?1). The effects of operating parameters such as feed composition, membrane thickness and permeate pressure on membrane performance were evaluated. Copyright © 2005 Society of Chemical Industry     

Photo‐oxidative degradation in polyisoprene: surface characterization and analysis by atomic force microscopy

Surface adhesion and surface mechanical properties of natural rubber cast films have been investigated by atomic force microscopy (AFM) before and after UV irradiation. Analysis in the force versus distance (F–d) mode probed changes in tip‐to‐surface adhesion. Adhesion was observed to increase as a result of exposure, in accord with the prediction that generation of polar groups in the surface should promote a hydrophilic transition. The hydrophilicity also gives rise to a stronger adhesive contribution from a meniscus force, as demonstrated by comparison of results obtained in air for irradiated and as‐received samples. Calculated values of work of adhesion, based on the Johnson–Kendall–Roberts model, reflected the changes in surface chemistry and the effects of the fluid environment. The outcomes of F–d analyses revealed both tip indentation and polymer extension; the former was fitted to expressions derived from the Snedden formalism, followed by calculation of an effective Young's modulus. Good agreement was obtained for as‐received surfaces with bulk measurements. The photochemistry predicts chain scission events which are likely to account for the observed softening of the polymer. © 2001 Society of Chemical Industry     

Preparation of pH and temperature dual‐sensitive molecularly imprinted polymers based on chitosan and N‐isopropylacrylamide for recognition of bovine serum albumin

pH and temperature dual‐sensitive protein imprinted microspheres with high absorption capacity have been successfully synthesized on the surface of SiO₂ using chitosan grafted N‐isopropylacrylamide (CS‐g‐NIPAM) as the pH and temperature sensitive monomer, with acrylamide as comonomer, N,N′‐methylenebisacrylamide as the crosslinking agent and bovine serum albumin (BSA) as the template protein. The pH and temperature dual‐sensitivity was also investigated. The results showed that the adsorption capacity and imprinting factor improved slowly with increasing incubation pH from 4.6 to 7.0, and then decreased sharply in alkaline conditions due to the reduction of non‐specific binding from electrostatic and hydrogen bonding interactions. Fourier transform infrared spectroscopy, thermogravimetric analysis and transmission electron microscopy were used to characterize the polymers. The as‐prepared SiO₂@BSA molecularly imprinted polymers were also found to have high adsorption capacity (119.88 mg g^?1) within 2 h, an excellent imprinting factor (α = 2.25), specific selectivity and good reusability. © 2019 Society of Chemical Industry     

Studies on the electrostatic self‐assembly of polyelectrolytes and organic dyes with atomic force microscopy

An ultrathin film was formed by the electrostatic self‐assembly of polyelectrolyte poly‐N‐ethyl‐N,N‐dimethyaminoethyl methacrylate (PDMAEB) and the organic dye metanil yellow (MY) on a smooth glass sheet. An atomic force microscope was used to study the topography and the phase of the two samples and the ultrathin film (PDMAEB–MY). The dynamic course of the surface structure was researched by atomic force microscopy also. It is illustrated that the existence of electrostatic interactions between PDMAEB and MY made MY arrange in order on the polyelectrolyte surface. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1029–1033, 2003     

Adhesion interactions between poly(vinyl alcohol) and iron‐oxide surfaces: The effect of acetylation

Atomic force microscopy with chemically functionalized colloidal probes was used to study “acid–base” interactions between poly(vinyl alcohol) (PVA) and a metal surface. By using well‐defined model surfaces, we have studied the adhesion forces between a hydroxylated surface and cantilever tips with varying hydroxyl content. Decreasing the amount of available hydroxyl groups dramatically reduced the observed adhesion force. The calculated bond energy for each cantilever tip was found to be in the range of typical hydrogen bond energies, i.e., 10–40 kJ/mol, suggesting that the acid–base interactions are predominately hydrogen bonding. Similarly, the force versus distance curves using PVA functionalized colloidal probes showed a strong dependence on the chemical functionality of the tip and the degree of acetylation of the intervening PVA. It was observed that, with an increase in the acetyl content of the PVA, the adhesion force decreased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3528–3534, 2006     

Interfacial aspects of adhesion in polymer nanocomposite thin‐film devices

Nanoscale polymeric composites are important in many new electronic technologies, including lightweight and flexible devices and sensors. The influence of surface chemical treatments, which particularly affect the adhesion properties of carbon–polyimide nanocomposite thin films, was studied with infrared spectroscopy, electron microscopy, atomic force microscopy, and contact angle measurements with respect to corresponding polyimide thin films. The contact angles showed that the inclusion of carbon initially increased the hydrophilicity, whereas a potassium hydroxide treatment increased the hydrophilicity of the pure polyimide film and the polyimide component of the nanocomposite surface without increasing the hydrophilicity of the carbon nanoparticle component. Friction‐force atomic force microscopy was shown to be a powerful technique for confirming the relative wetting characteristics at the nanoscale. The lower hydrophilicity and activity of the carbon nanoparticles during adhesion reactions reduced the load at break, and this suggests that this conventional modification used for polyimides is less effective for their nanocomposite counterparts. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Atomic force microscopy study on structure and properties of irradiation grafted silica particles in polypropylene‐based nanocomposites

Nanosilica particles treated by irradiation grafting polymerization can effectively improve the strength and toughness of a thermoplastic polymer at a rather low filler content. A detailed investigation on the modified nanoparticles in the absence and presence of a polypropylene matrix is carried out by using atomic force microscopy. The results indicate that the loosen agglomerates of the untreated SiO₂ became more compact due to the linkage between the nanoparticles offered by the grafting polymer. In addition, the molecules of the polypropylene matrix are able to diffuse into the modified nanoparticle agglomerates during the melt processing. Entanglement between the molecules of the grafting polymer and the matrix is thus available, which in turn facilitates a strong particle–matrix interfacial interaction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2218–2227, 2001     

Preparation and characterization of hyaluronan/chitosan scaffold cross‐ linked by 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide

A novel biocompatible scaffold was prepared by cross‐linking hyaluronan (HA) and chitosan (CS). The carboxyl groups of HA were activated by 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide (EDC) and then cross‐linked with amino groups of CS by forming amide bonds. The HA/CS scaffold thus prepared was characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and differential scanning calorimetry. FTIR spectra showed that the absorbance of the amide (1550 cm^?1) and carbonyl (1633 cm^?1) bond in the cross‐linked scaffold was stronger than that in HA or CS. SEM micrographs showed that the cross‐linked scaffold produced at low EDC concentration had an intertwisted ribbon‐like microstructure, while the product prepared at higher EDC concentration had a porous structure. The concentration of EDC in the reaction system greatly affected the structure and properties of the HA/CS scaffold. The prepared scaffold could strongly resist degradation by hyaluronidase, free radicals in vitro and stress. Copyright © 2007 Society of Chemical Industry     

Effect of some substituted anilines‐formaldehyde polymers on mild steel corrosion in hydrochloric acid medium

The influence of linear copolymer of amines and formaldehyde namely poly(aniline‐formaldehyde) (Inh1), poly(o‐toluidene‐formaldehyde) (Inh2), and poly(p‐chloroaniline‐formaldehyde) (Inh3) on corrosion of mild steel in hydrochloric acid was evaluated by weight loss measurements, linear polarization, Tafel polarization, and electrochemical impedance spectroscopy. These polymers showed very high inhibition efficiency at very low concentrations. Results obtained showed that all inhibitors are mixed inhibitors and participate in reaction probably in the form of metal inhibitor complex on metal surface. Atomic force microscopic studies reveal that the surface of metal is quite unaffected after use of inhibitor in hydrochloric acid solution. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of hydroxyl‐terminated polybutadiene additives on the poly(ether sulfone) ultra‐filtration membranes

Hydroxyl‐terminated polybutadiene (HTPB) was blended into a poly(ether sulfone) (PES) casting solution used to prepare ultra‐filtration (UF) membranes via the phase inversion technique. The membranes were then characterized by contact angle (CA) measurements and UF experiments. The CA was increased with the addition of HTPB in the PES membrane and also by lowering the gelation bath temperature. It was observed that the CA was lower for membranes prepared with N‐methyl‐2‐pyrrolidinone (NMP) as the solvent than those using N,N‐dimethylacetamide (DMAc) as solvent. The flux values were higher for membranes made using a 4°C gelation bath when compared with the ambient temperature ((25 ± 1)°C) irrespective of the cast solvents, NMP or DMAc. The flux values were much higher and the solute separations were lower for the HTPB‐based PES membranes than for the pure PES membrane, when the membranes were cast with DMAc as a solvent. On the other hand, both flux and separation values were much lower for the HTPB‐based PES membranes than for the pure PES membrane, when the membranes were cast using NMP. Atomic force microscopy and scanning electron microscopy were used for morphological characterization and the correlation of topography/photography with the performance data was also examined. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2292–2303, 2006     

Quantification of surface forces of thermoplastic elastomeric nanocomposites based on poly(styrene‐ethylene‐co‐butylene‐styrene) and clay by atomic force microscopy

Atomic force microscopy was used for qualitative phase morphological mapping as well as quantitative investigation of surface forces measured at constituting blocks and clay regions of a thermoplastic elastomeric nanocomposite based on triblock copolymer: poly(styrene‐ethylene‐co‐butylene‐styrene) (SEBS) and organically modified nano‐clay. The roughness and power spectral density analyses of surface topography provided the increment in random roughness of the nanocomposite surface compared to pristine SEBS surface. The same surfaces were examined by means of single point force‐distance, and force‐volume measurements. Large adhesive force of 25 nN and contact force of 260 nN were found in soft polyethylene (PEB) segments and higher cantilever deflection of 210 nm was found for clay regions of SEBS‐clay nanocomposite. Mapping of elastic modulus of the glassy and rubbery blocks and clay regions was probed by employing Hertzian and JKR model from respective approaching and retracting parts of force‐distance curves. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Poly(2‐hydroxyethylmethacrylate)/chitosan dye and different metal‐ion‐immobilized interpenetrating network membranes: Preparation and application in metal affinity chromatography

Composite membranes were synthesized with 2‐hydroxyethylmethacrylate and chitosan (pHEMA/chitosan) via an ultraviolet‐initiated photopolymerization technique in the presence of an initiator (α,α′‐azobisisobutyronitrile). The interpenetrating network (IPN) membranes were improved by the immobilization of dye molecules via hydroxyl and amino groups on the membrane surfaces from the IPNs. A triazidine dye (Procion Green H‐4G) was covalently immobilized as a ligand onto the IPN membranes. The protein showed various affinities to different chelated metal ions on the membrane surfaces that best matched its own distribution of functional sites, resulting in a distribution of binding energies. In support of this interpretation, two different metal ions, Zn(II) and Fe(III), were chelated with the immobilized dye molecules. The adsorption and binding characteristics of the different metal‐ion‐chelated dye‐immobilized IPN membranes for the lysozyme were investigated with aqueous solutions in magnetically stirred cells. The experimental data were analyzed with two adsorption kinetic models, pseudo‐first‐order and pseudo‐second‐order, to determine the best fit equation for the adsorption of lysozyme onto IPN membranes. The second‐order equation for the lysozyme–dye–metal‐chelated IPN membrane systems was the most appropriate equation for predicting the adsorption capacity for all the tested adsorbents. The reversible lysozyme adsorption on the dye‐immobilized and metal‐ion‐chelated membranes obeyed the Temkin isotherm. The lysozyme adsorption capacity of the pHEMA/chitosan dye, pHEMA/chitosan dye–Zn(II), and pHEMA/chitosan dye–Fe(III) membranes were 2.54, 2.85, and 3.64 mg cm^?2, respectively. The nonspecific adsorption of the lysozyme on the plain pHEMA/chitosan membrane was about 0.18 mg cm^?2. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1843–1853, 2003