Amphiphilic Films Research Articles

Taking another look with fluorescence microscopy: Image processing techniques in Langmuir monolayers for the twenty-first century

Fluorescence microscopy has become a powerful and standard complementary technique in the study of amphiphilic films at the air-water interface. For nearly three decades the coupling of traditional thermodynamic measurements with direct visualization has provided a better understanding of self-assembled Langmuir monolayers and their application in the study of the physical properties of membranes and interfaces. As an introduction we provide a brief overview of this established technique and demonstrate its continued utility in the recent observation of novel phase behavior in monolayers of 25-hydroxycholesterol (25-OH) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). We then focus our review on new analysis techniques which take advantage of the ability to store, process, and analyze large sets of images. We pay particular attention to efforts measuring the line tension between coexisting two dimensional fluid phases in the Langmuir monolayer. Using non-perturbative methods, we can measure fundamental mechanical properties of these two dimensional systems. Finally, we highlight the use of Model Convolution Microscopy as a new tool to provide insight on the experimental limits in these studies.

Synthesis, characterization, and antibacterial activity of metal nanoparticles embedded into amphiphilic comb-type graft copolymers

The synthesis, spectroscopic characterization, and antimicrobial efficiency of gold and silver nanoparticles embedded in novel amphiphilic comb-type graft copolymers having good film-forming properties have been described. Amphiphilic comb-type graft copolymers were synthesized by the reaction of chlorinated polypropylene (PP) (M w = 140,000 Da) with polyethylene glycol (PEG) (M n = 2,000 Da) at different molar ratios. Metal nanoparticles embedded graft copolymers were prepared by reducing solutions of the salts of silver or gold and the copolymer in tetrahydrofuran. The optical properties of the metal nanoparticle embedded copolymers were determined by using UV–visible spectroscopy. Surface plasmon resonance (SPR) of the gold and silver nanoparticle embedded copolymers in toluene was observed at a maximum wavelength (λmax) of 428 and 551 nm in the UV–VIS absorption spectra, respectively. The average particle diameters of the gold and silver nanoparticles were found to be 50 nm from the high resolution scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Amphiphilic polymer films containing silver and gold nanoparticles were found to be highly antimicrobial by virtue of their antiseptic properties to Escherichia coli and Staphylococcus aureus.

Temperature dependence of CO 2 concentration gradient within polymer films as determined by reactive templating

The swelling of thin polymer films by supercritical carbon dioxide has been shown to exhibit an anomalous maximum in the sorption isotherms. This swelling maximum occurs when the activity of the fluid phase approaches unity and the extent of the swelling increases as the critical temperature is approached. Using an in situ selective reactive templating approach based upon silica condensation within hydrophilic domains of an amphiphilic polymer film, the CO 2 distribution within the polymer film is elucidated from the pore sizes generated by hydrophobic domains upon removal of the amphiphile. The origin of the maximum in the swelling of the thin films is demonstrated to be concentration gradients that extend from both interfaces of the film; as the temperature approaches the critical temperature, the local swelling at both interfaces increases progressively. However, the pressure range over which gradients in CO 2 concentration occurs decreases as the critical temperature for CO 2 is approached.

Amphiphilicity in homopolymer surfaces reduces nonspecific protein adsorption.

Amphiphilic homopolymer films have been immobilized onto substrates to study the interactions of these polymers with proteins. X-ray photoelectron spectroscopy (XPS) was utilized to measure the amount of protein adsorption. Amphiphilic homopolymers have been shown to reduce protein adsorption, despite the high affinity of the hydrophobic or hydrophilic functional groups by themselves toward proteins. This protein-resistant property seems to arise from the unique molecular-scale alternation of incompatible functionalities. The combination of incompatible functionalities with a predefined alternating pattern within a monomer could provide a potential design for nonfouling materials.

Impact of thickness on CO2 concentration profiles within polymer films swollen near the critical pressure

Abstract The isothermal swelling of polymer thin films by a supercritical fluid does not increase monotonically with increasing chemical potential (pressure), but rather a maximum in swelling is generally observed near the critical pressure. A reactive templating approach utilizing the condensation of silica within hydrophilic domains of a swollen amphiphilic polymer film enables visualization of the qualitative concentration profile of CO2 by the changes in the size of hydrophobic domains (pores) with cross sectional TEM microscopy; specifically, isothermal swelling of poly(ethylene oxide-propylene oxide-ethylene oxide) films by CO2 at 60 °C is examined. Films that contain thickness gradients are used to avoid any uncertainties in the impact of thickness due to variations in the temperature or pressure during the silica modification. A uniform pore size (local swelling) is observed for all film thicknesses when the pressure is outside of the anomalous maximum in the film swelling, except for a small increase at the buried interface due to preferential adsorption of CO2 to the native silicon oxide surface of the substrate. However at this swelling maximum, a gradient in the pore size is observed at both interfaces. These swelling gradients at interfaces appear to be responsible for the anomalous maximum in thin films. As the film thickness increases beyond 350 nm, there is a decrease in the maximum swelling at the free interface.

Localized Drug Delivery System For The Treatment Of Cancer

Localized drug delivery can provide better treatment for residual cancer tumors. Our research proposes a “package within a package” drug delivery system which results in an effective controlled release of the drug to the targeted site and also reduces its toxic effects to other parts of the body. The first part of the system is a non-ionic surfactant vesicle or niosome and the second a biodegradable and temperature sensitive crosslinked hydrogel. The vesicle is prepared by hydration of amphiphilic films with a PBS buffer solution and a fluorescent marker, 5,6-carboxyfluorescein. We chose to encapsulate this particular marker to imitate and test the release rate of the chemotherapy drug from the vesicle interior. After hydration, the vesicles were extruded to constrict their size distribution. Unentrapped dye was removed using ultracentrifugation and gel exclusion chromatography. The dye encapsulated vesicles were placed in a semi-permeable cellulose membrane and immersed in a solution of either PBS or Milli-Q water. The environment in the PBS solution would closely mimic the vesicle's behavior in the hydrogel and the water environment would closely follow the behavior near a residual cancer site, where the pH tends to be lower compared to blood. Diffusion of the dye through the membrane was determined at different time intervals by using fluorescence spectroscopy and its release rate was determined. The maker encapsulated niosomes will then be embedded into the hydrogel network which will begin to degrade with time exposing the niosomes to a different pH that will cause them to rupture. The thermal sensitive hydrogel is a polymer, chosen to be Chitosan. Chitosan is a biomaterial obtained abundantly in nature. This system will then have antibodies to provide specificity. Using this methodology, we hope to provide a better treatment technique for cancer patients.

Amphiphilic Block Copolymer Films: Phase Transition, Stabilization, and Nanoscale Templates

A morphological transition of asymmetric poly(styrene-b-acrylic acid) (PS-b-PAA) films is observed by in situ scanning probe microscopy (SPM) in aqueous media. Upon initial exposure to buffer solution at pH 7.4, spherical PAA domains swell through a glassy PS surface layer to form negatively charged mushroom caps. With further exposure, the PAA caps coalesce to produce a smooth, highly wettable surface. However, if films are exposed to a buffer solution containing 3-aminopropyltriethoxysilane (APTES) for 1 h, the PAA domain swelling is greatly reduced and the mushroom caps stabilize at a diameter of 33 nm. This stabilization results from a cross-linking reaction between PAA and APTES, which also converts the PAA domains from a net negative to net positive charge. By varying molecular weights of PAA block in PS-b-PAA, the feature size and spacing can be tuned. To demonstrate an application for this template with positively charged domains, a cytoskeletal filament, F-Actin with a net negative charge, is org...

Direct electrochemistry and electrocatalysis of hemoglobin immobilized in an amphiphilic diblock copolymer film

A well-defined amphiphilic diblock copolymer, poly [ N-(2-methacryloyloxyethyl) pyrrolidone]- block-poly [glycidyl methacrylate] (PNMP- b-PGMA), was applied to immobilize hemoglobin (Hb) in a simple procedure. The characterization of PNMP- b-PGMA/Hb film was demonstrated by ultraviolet–visible (UV–vis) spectra, atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS). The electrochemical behaviors of Hb in PNMP- b-PGMA film have been investigated and a pair of well-defined and nearly reversible cyclic voltammetric peaks for the protein heme Fe(III)/Fe(II) redox couples were observed at about −0.409 V (vs. SCE) in pH 7.0 phosphate buffer solution (PBS). The results showed that the PNMP- b-PGMA film improved the protein loading with the retention of bioactivity and greatly promoted the direct electron transfer between Hb and electrode surface. This PNMP- b-PGMA/Hb film modified electrode also exhibited high electrocatalytic effects towards reduction of nitric oxide (NO). These results indicated the potential applicability of the films as new types of third-generation biosensors or bioreactors based on direct electrochemistry of the proteins.

Formation of silver nanoparticles created in situ in an amphiphilic block copolymer film

AbstractIn this work, silver nanoparticles were synthesized with an amphiphilic diblock copolymer, polystyrene‐block‐poly(1‐vinyl‐2‐pyrrolidone) (PS‐b‐PVP), as a template film. First, microphase‐separated amphiphilic PS‐b‐PVP (70 : 30 wt %) was synthesized through atom transfer radical polymerization. The self‐assembled block copolymer film was used to template the growth of silver nanoparticles by the introduction of a silver trifluoromethanesulfonate precursor and an ultraviolet irradiation process. The in situ formation of silver nanoparticles with an average size of 4–6 nm within the block copolymer template film was confirmed with transmission electron microscopy, ultraviolet–visible spectroscopy, and wide‐angle X‐ray scattering. Fourier transform infrared spectroscopy also demonstrated the selective incorporation and in situ formation of silver nanoparticles within the hydrophilic poly(1‐vinyl‐2‐pyrrolidone) domains, which were mostly due to the stronger interaction strength of the silver with the carbonyl oxygens of poly(1‐vinyl‐2‐pyrrolidone) in the block copolymer. This work provides a simple route for the in situ synthesis of silver nanoparticles within a polymer film. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Templated synthesis of Ag–Au bimetallic nanoparticles by amphiphilic PVC- g-PSSA graft copolymer film

Amphiphilic comb-like copolymer consisting of a poly(vinyl chloride) (PVC) backbone and poly(styrene sulfonic acid) (PSSA) side chains, i.e. PVC- g-PSSA at 68:32 wt.% was synthesized via atom transfer radical polymerization (ATRP). This self-assembled graft copolymer film was used to template the growth of Ag–Au bimetallic nanoparticles in the solid state by introducing NaBH 4 as a reducing agent. The in situ formation of Ag–Au bimetallic nanoparticles in the graft copolymer film was confirmed by UV–visible spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). High resolution TEM picture showed the formation of spherical Ag-Au core-shell nanoparticles. To the best of our knowledge, this is the first report on the solid-state synthesis of Ag–Au bimetallic core-shell nanoparticles using amphiphilic comb-like copolymer film.

Phase-separated structures of mixed LB films of silane-coupling agents with polymerization initiating groups and amphiphilic carboxylic acids

We studied the structures of mixed LB films of silane-coupling agents with polymerization initiating groups (SCA-PIGs) and conventional amphiphiles such as long-chain fatty acid and hybrid carboxylic acid having both perfluoroalkyl and alkyl moieties. We used (2-bromo-2-methyl)propionyloxyundecyltriethoxysilane (BUE) and (2-bromo-2-methyl)propionyloxyhexyltriethoxysilane (BHE) as SCA-PIGs. Surface pressure–area isotherms of mixtures of SCA-PIGs and conventional amphiphiles were measured. Additivity rule was found to be held in all the mixed systems studied. Mixed LB films of SCA-PIGs and conventional amphiphiles were fabricated. When SCA-PIGs were mixed with long-chain fatty acids, the fatty acids formed circular domains with diameters on the micrometer length scale in the mixed LB films. In contrast, when SCA-PIGs were mixed with hybrid carboxylic acids, nanostructures were found. The difference in morphology can be due to the difference in homo and hetero intermolecular interactions, affecting the balance between the line tension and dipole–dipole interaction. Optimized conditions for the nanowire formation were obtained for mixed LB films of SCA-PIGs and hybrid carboxylic acids.

Tuning Mechanical Properties of Mesoporous Silicas Using Associating Homopolymers/Block Copolymer Blends as Templates

Ordered mesoporous films are synthesized from the vapor-phase condensation of tetraethyl orthosilicate within preformed amphiphilic template films consisting of a blend of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (Pluronic F127) and poly(4-hydroxystyrene) (PHOSt). By modification of the Pluronic F127:PHOSt ratio in the template film, the long range order of the synthesized mesoporous silica can be tuned with the largest grains observed at approximately 15 wt % PHOSt. This increase in ordering and orientation of the mesopores is accompanied by a narrowing of the pore size distribution, a slight increase in the average mesopore radius, and a substantial increase in the Young's modulus of the film. Deviations from this 15 wt % PHOSt composition to higher or lower PHOSt loadings result in a decay in the long range ordering and subsequently a decrease in the film modulus. The modulation in the mechanical properties through modification in the PHOSt concentration (1−50 wt %) is nearly 1 order of magnitude without significantly altering the porosity. Moreover, samples with nearly indistinguishable morphology as determined through TEM micrographs can exhibit a difference in modulus by a factor of 3. This work demonstrates the importance of long range order for fabricating mechanically robust porous films.

Selective Doping of Lead Ions into Normally Aligned PEO Cylindrical Nanodomains in Amphiphilic Block Copolymer Thin Films

Abstract Hexagonally arranged nanocylindrical arrays of polymer-complexed multivalent metallic ions were fabricated by performing template process with amphiphilic diblock copolymer consisting of poly(ethylene oxide) and liquid crystalline poly(methacrylate) with azobenzene mesogen (PEO-b-PMA(Az)). The block copolymer exhibits PEO hexagonal cylindrical microdomains perpendicular to the substrate. Lead ions were selectively diffused into the PEO microdomains to generate the lead-doped nanocylinder array, of which size, shape, and alignment can be controlled by the block copolymer thin film as a template.

In situ formation of silver nanoparticles within an amphiphilic graft copolymer film

AbstractSilver nanoparticles were prepared by UV irradiation from silver salts, such as AgBF4 or AgNO3, when dissolved in an amphiphilic film of poly((oxyethylene)9 methacrylate)‐graft‐poly((dimethyl siloxane)n methacrylate), POEM‐g‐mPDMS. The in situ formation of silver nanoparticles in the graft copolymer film was confirmed by transmission electron microscopy (TEM), UV‐visible spectroscopy, and wide angle X‐ray scattering (WAXS). The results demonstrated that the use of AgBF4 yielded silver nanoparticles with a smaller size (∼5 nm) and narrower particle distribution when compared with AgNO3. The formation of silver nanoparticles was explained in terms of the interaction strength of the silver ions with the ether oxygens of POEM, as revealed by differential scanning calorimetry (DSC) and X‐ray photoelectron spectroscopy (XPS). It was thus concluded that a stronger interaction of silver ions with the ether oxygens results in a more stable formation of silver nanoparticles, which produces uniform and small‐sized nanoparticles. DSC and small angle X‐ray scattering (SAXS) data also showed the selective incorporation and in situ reduction of the silver ions within the hydrophilic POEM domains. Excellent mechanical properties of the nanocomposite films (3–5 × 105 dyn/cm2) were observed, mostly because of the confinement of silver nanoparticles in the POEM chains as well as interfaces created by the microphase separation of the graft copolymer film. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1283–1290, 2007

Design and Interfacial Assembly of a New Series of Gemini Amphiphiles with Hydrophilic Poly(ethyleneamine) Spacers

A new series of gemini amphiphiles containing two Schiff base moieties linked by the poly(ethyleneamine) with different lengths were designed, and their interfacial assemblies were investigated. Condensed monolayers were obtained on nearly neutral subphase where the hydrophilic spacers were found to immerse into the subphase. On strong alkaline and acidic subphase, the headgroup and the spacer of the gemini amphiphiles underwent dissociation and protonation, respectively, resulting in the enlargement of the molecular areas. Flat and uniform domains were obtained for the monolayers from nearly neutral subphase; flower-like or dendritic domains were observed for the films transferred from strong acidic subphase. On the other hand, when an anionic tetrakis(4-sulfonatonphenyl)porphine (TPPS) was added into an acidic subphase, an in situ complex formation between the gemini amphiphiles and TPPS occurred. The complex monolayers were transferred onto solid substrate and TPPS existed predominantly as J-aggregate in the complex films. Due to the multisited positive charges in the spacer on acidic subphase, the complex films of gemini amphiphiles with TPPS appeared as short fiber or nanorod structures and formed two-dimensional (2D) conglomerate chiral domains.

Effect of Divalent Cations in Langmuir-Blodgett Films on the Protection of Copper against Corrosion

Langmuir-Blodgett films (LB) of hydroxamic amphiphiles were used as coating barriers on metal surface against corrosion. Two long-chain hydroxamic acids [CH3(CH2)16CONHOH] monolayers in the presence of some divalent cations (Ca2+, Mg2+, and Cu2+) have been studied at different pH of the subphase. The monolayer was characterized by surface pressure-area isotherms and visualized by Brewster angle microscope (BAM). Compact Langmuir layers were deposited on copper surface, where the modified surfaces were characterized by contact angle measurement as well as by electrochemical techniques. The morphology of LB coated copper surface was visualized by atomic force microscopy (AFM). The coated copper surfaces were tested in corrosive media at acidic and neutral pH. The results show that the multi-molecular LB films of hydroxamic acid salts form good barriers against copper corrosion. The comparison of these results with copper coated by LB layers without divalent cations shows that the presence of divalent cations in the subphase increases the copper corrosion inhibition. The octadecanoyl hydroxamic acid (C18N) results in better and more stable monolayer with cations in the subphase.

Corrigendum to: Suppression of cell attachment and protein adsorption onto amphiphilic polylactide-grafted dextran films

Corrigendum to: Suppression of cell attachment and protein adsorption onto amphiphilic polylactide-grafted dextran films

Triacylglycerol microemulsions stabilized by alkyl ethoxylate surfactants—A basic study: Phase behavior, interfacial tension and microstructure

As triacylglycerols are the main components of natural fats and oils their solubilization in the form of emulsions or microemulsions was of great interest within the last years. However, systematic studies of their properties along the classical lines of complex fluids science are still missing. In the present paper we focus on the phase behavior, the interfacial tension and the microstructure of systems of type H 2O/NaCl–triacylglycerol–alkylpolyglycolether (C i E j ). The interfacial tension between water and oil σ ab is high in a microemulsion system containing triolein. Thus, one needs high surfactant mass fractions to formulate a single-phase microemulsion. We show that this is not only true for triolein, but also for saturated long-chained triacylglycerols. The determination of the amphiphilicity factor f a and the calculation of the bending rigidities of the amphiphilic film confirm that despite the fact that high surfactant mass fractions and high temperatures are needed to solubilize triolein in a system of type H 2O/NaCl–triacylglycerol–alkylpolyglycolether (C i E j ), this is still a microemulsion in the narrower sense.

Amphiphilic porphyrin film on glass as a simple and selective solid-state chemosensor for aqueous Hg2+

Deposition of amphiphilic porphyrin derivatives occurs spontaneously on silanised glass surfaces, in a controlled fashion. The resulting porphyrin films show appreciable fluorescence emission. This emission can be effectively quenched by immersion of the slides into a diluted solution of Hg(2+) (microM concentration). The initial intensity can be restored by washings with a solution of N,N,N',N'-tetrakis(2-pyridilmethyl)ethylenediammine with no loss of efficiency. A remarkable selectivity is featured toward the detection of Hg(2+) over Cu(2+), Cd(2+), Pb(2+) and Zn(2+) counterparts. This protocol can be extended to a flow-through apparatus. The presented results are of importance for the achievement of a solid-state chemosensor for mercuric ions, at micromolar concentration, in water.

Growth of bimolecular films of three-tailed amphiphiles

The three-tailed amphiphile ferric stearate molecule, which forms a bimolecular layer on water surface with molecules in the lower and upper layers in different conformations, has been studied to understand transfer and growth of bimolecular films on the surface of hydrophilic silicon substrates. This bimolecular film forms a two-dimensional lattice on water with a slightly distorted hexagonal lattice where both the in-plane and out-of-plane domain sizes are small. The film also showed larger microscopic rigidity compared to its macroscopic mechanical response. This asymmetric bimolecular layer was found to be preserved when the film is transferred on the substrates at different values of surface pressures ranging from 1 mN/m to near-collapse (55 mN/m). Both the upper and lower layers become denser and interfaces between these layers become sharper with increase in deposition pressure but the growths have different natures. The lower layer of transferred film is dense from 1 mN/m and, except for a steplike increase between 20 and 30 mN/m, changes slowly in density. The density of the upper molecular layer grows continuously with surface pressure.