Polyacrylamide Films Research Articles

Capillary-Assisted Assembly of Polymer Gel-Supported Lipid Bilayers.

The polymer-supported lipid bilayer represents an attractive supramolecular assembly in numerous biophysical and bioanalytical applications. The assembly of polymer-supported membranes with a polymer layer thickness of just a few nanometers is now well-established, but bilayer properties in such a membrane architecture are still influenced by the nearby solid substrate. Polymer-supported lipid bilayer systems with a several micrometers thick polymer layer will overcome this shortcoming. However, formation of a fluid lipid bilayer on a fully hydrated, micrometer thick polymer film using traditional methods (e.g., vesicle fusion and lipid monolayer deposition techniques) remains a challenging task due to the rather unfavorable interfacial conditions for bilayer formation in such a system. Here, we report for the first time on the facile capillary-assisted formation of a lipid bilayer on the surface of a fully hydrated, several micrometers thick polyacrylamide (PAA) gel, in which forced molecular crowding of lipids at the air-water interface of the capillary results in monolayer instability and collapse, thereby forming a lipid bilayer on the top of the polymer gel inside the capillary. Stable bilayer attachment on the surface of the polymer gel can be achieved via physisorption or specific chemical linkages (tethering) on both cross-linked and non-cross-linked PAA films. Unlike the traditional solid-supported lipid bilayer (SLB), the lipid lateral diffusion in the polymer gel-supported lipid bilayer is not anymore perturbed by a solid substrate. Instead, more like a plasma membrane, it is mainly influenced by the properties of the underlying polymer and the nature/distribution of polymer-bilayer attachments. Polymer gel-supported lipid bilayers built using the capillary-assisted assembly approach show attractive self-healing properties, resulting in superior long-term stability relative to the SLB. We hypothesize that the described capillary-assisted assembly method can be applied to a wide range of polymeric materials and lipid compositions, opening exciting opportunities as an advanced model membrane system.

Polymer-Based Long-Lived Phosphorescence Materials over a Broad Temperature Based on Coumarin Derivatives as Information Anti-Counterfeiting.

The development of new polymer-based room-temperature phosphorescence materials is of great significance. By a special molecule design and a set of feasible property-enhancing strategies, coumarin derivatives (CMDs, Ma-Mf) were doped into polyvinyl alcohol (PVA), polyacrylamide (PAM), corn starch, and polyacrylonitrile (PAN) as information anti-counterfeiting. CMDs-doped PVA and CMDs-doped corn starch films showed long-lived phosphorescence emissions up to 1246 ms (Ma-PVA) and 697 ms (Ma-corn starch), reaching over 10 s afterglow under naked eye observation under ambient conditions. Significantly, CMDs-doped PAM films can display long-lived phosphorescence emissions in a wide temperature range (100-430 K). For example, the Me-PAM film has a phosphorescence lifetime of 16 ms at 430 K. The use of PAM with the strong polarity and rigidity has expanded the temperature range of long-life polymer-based phosphorescent materials. The present long-lived phosphorescent systems provide the possibility for developing new polymer-based organic afterglow materials with robust phosphorescence.

Notable electrical and mechanical properties of polyacrylamide (PAM) with graphene oxide (GO) and single-walled carbon nanotubes (SWCNTs)

Abstract In the present investigation, a polyacrylamide (PAM) – graphene oxide (GO)-single-walled carbon nanotubes (SWNTs) composite has been prepared through a cost effective solution cast method and physical properties (electrical and mechanical) measurements have been carried out. The GO sheets contain oxygen functional groups which enhance the interfacial adhesion with the polymer matrix, while the SWNTs act as wires joining the GO together in the composite matrix. This interconnected network creates a conducting path, lowering film resistance and improving PAM films’ electrical, mechanical, and thermal properties. Raman study demonstrated that carbon nanofiller (SWNTs, GO) and polymer PAM have good interfacial bonding. The electrical conductivity and mechanical characteristics (hardness and elastic modulus) of these composite films were enhanced at a loading of 15 wt% GO and 15 wt% SWNTs in PAM matrix. Electrical conductivity of GO (15 wt%) – SWNTs (15 wt%)-PAM composite film was found to be 2.8 × 10−2 S/cm, which is five orders of magnitude higher than that of the PAM polymer. In comparison to pure PAM polymer, the elastic modulus and hardness are found to be 1.14 and 65 times higher, respectively.

Tuning of the properties of polyvinyl alcohol/ polyacrylamide film by phytic acid and gamma radiation crosslinking for food packaging applications

ABSTRACT Polyvinyl alcohol/polyacrylamide/phytic acid (PVA/PAAm/PA) film was prepared using gamma radiation. The strength, tensile stress, and elongation of PVA/PAAm/PA are higher than PVA/PAAm. The contact angle was enhanced in the presence of PA and by increasing the irradiation dose. PVA/PAAm/PA film has antimicrobial activity against gram-positive and gram-negative bacteria. Solubility and water uptake highly decreased by incorporating PA and were supported by exposure to gamma irradiation. A completely insoluble (PVA/PAAm/PA) film was obtained at 20 kGy. The results revealed that the synergistic effect of PA and gamma radiation in enhancing the properties of the prepared films.

Tunable alignment of liquid crystals between anisotropic polyacrylamide thin layer

We report uniform liquid crystal (LC) alignment on a polyacrylamide (PAM) film via ion beam (IB) treatment. The IB incidence angle is adjusted from 15° to 75°. Physicochemical modifications caused by the IB process are investigated by atomic force microscopy and x-ray photoelectron spectroscopy. Low IB incidence results in biased and bumpy surfaces, whereas high IB incidence forms isotropic and smooth surfaces; both of these are unsuitable for uniform LC alignment. The 45° IB incidence induces anisotropic surface chemical reformations, and these modifications induce van der Waals forces between the LCs and modified PAM, thereby leading to uniform LC alignment. The LC alignment state is verified by polarized optical microscopy and pretilt angle. The electro-optical characteristic of the modified PAM showed excellent switching performance in twisted-nematic LC system. Thus, the IB-treated PAM film is a good candidate for LC alignment layers and suitable for LC device applications.

Physicochemically modified anisotropic polyacrylamide thin film via ion‐beam treatment for liquid crystal system

AbstractWe investigated ion‐beam (IB)‐treated polyacrylamide (PAM) film as a liquid crystal (LC) alignment layer. Polarized optical microscopy and pretilt angle analysis show the uniform LC alignment status. Atomic force microscopy shows the IB etching effect, and X‐ray photoelectron spectroscopy indicates the formation of carbon–oxygen bonds on the surface, which ensured the uniform alignment of LC molecules via van der Waals forces interaction. The reformed PAM films also had good thermal budgets and optical transparency for the LC system. The IB‐treated PAM films demonstrated stable electro‐optical performances in a twisted nematic LC system. Hence, IB treatment can be an effective method to apply several polymer materials to the LC alignment layer, and IB‐irradiated PAM films have remarkable potential for use in the LC system.

Orientation-induced properties of anisotropic polyacrylamide thin layer via plasma treatment in liquid crystal system

Uniform liquid crystal (LC) alignment was achieved on a polyacrylamide (PAM) film treated by a plasma ion beam (IB), and the alignment status of the LCs was confirmed by polarized optical microscopy and pretilt angle analysis using antiparallel LC cells assembled using the IB-treated PAM (IB-PAM) layer. Physically modified characteristics on the PAM surface caused by the IB treatment were observed by atomic force microscopy. Etching with the IB caused roughness reduction and smoothing on the surface with increased irradiation time. Chemical modifications on the surface were investigated by X-ray photoelectron spectroscopy, whose results demonstrated stoichiometric changes causing formation of CO bonding and polarity on the surface. The IB incident at 40° drives the surface polarity anisotropy and van der Waals interactions with the LC molecules, thereby achieving uniform LC alignment. Thermal endurance tests of the IB-PAM layer showed maintenance of the uniform LC alignment status up to 120 °C. Twisted-nematic cells based on the IB-PAM layer showed suitable electro-optical performance with low operating characteristics. The IB-PAM films also showed high and stable optical transparencies. Thus, IB treatment on polymer layer is deemed suitable for the LC alignment process, and IB-PAM film is an excellent choice for next-generation LC systems.

A novel manifestation at optical leaky waveguide modes for sensing applications

We report a very simple biosensor based on the direct observation of leaky waveguide (LW) modes as exponentially decaying interference fringes in the reflectivity curve. This phenomenon was only observed when the refractive index contrast between the waveguide and sample was low (0.002–0.005) and the LW was illuminated with a range of angles of incidence simultaneously. The LW acts as a phase object in angle space, resulting in Fresnel diffraction and formation of interference fringes for each waveguide mode. We present theory, a qualitative explanation and a mathematical model governing the formation of these fringes. The binding of an analyte to recognition elements immobilised in the LW changes its refractive index and thus the angular position of the fringes, which provides the biosensing mechanism. The reported LWs comprised a film of polyacrylamide and copolymers on glass slides, and provided high sensitivity, mass manufacturability and simple instrumentation.

Poroelasticity of highly confined hydrogel films measured with a surface forces apparatus.

The influence of poroelasticity on the contact mechanics of thin polyacrylamide films was investigated with a surface forces apparatus (SFA). A model based on a thin film approximation described compression forces for hydrated gels; polymer scaling theory explained the effects of gel dehydration. The results demonstrate that fluid flow dictates the apparent stiffness of highly confined poroelastic films.

Разработка полиакриламидных композиций, наполненных клиноптилолитовыми породами для адсорбционной очистки воды от нефтепродуктов

Синтезированы композиционные материалы с улучшенными нефтесорбционными свойствами на основе наполненного клиноптилолитовыми породами полиакриламида. Полученные композиты изучены методами оптической микроскопии, инфракрасной спектроскопии, дифференциальной сканирующей калориметрии и термогравиметрии. Рассмотрены вероятные варианты взаимодействий между активными центрами наполненной полимерной системы с участием молекул воды. Определены оптимальные содержания дисперсного наполнителя и концентрация водного раствора полиакриламида для получения материала с максимальной экспертной оценкой и степенью очистки морской воды от нефти и дизельного топлива.

Probing molecular interactions between humic acid and surface-grafted polyacrylamide using quartz crystal microbalance with dissipation and atomic force microscopy: implications for environmental remediation

Environmental contextPolyacrylamide and its derivatives may enter the natural environment as a consequence of their wide use in various industrial applications. This study demonstrates the application of a quartz crystal microbalance and atomic force microscopy to study the molecular interactions between polyacrylamides and humic acids under various solution chemistries. The knowledge obtained can be used to understand and predict the environmental behaviour of polyacrylamides. AbstractA fundamental understanding of the environmental behaviour of polyacrylamide (PAM) is of importance for guiding environmental remediation. We create a framework for understanding the molecular interactions between PAM and a major constituent present in all natural waters and soil, humic acid (HA), using a quartz crystal microbalance with dissipation (QCM-D) and an atomic force microscope (AFM). A thin film of PAM was grafted on a silica surface silanised with 3-(trimethoxysilyl)propyl methacrylate and the resulting surface was characterised by X-ray photoelectron spectroscopy for the chemical bonds and composition, secondary ion mass spectrometry for the composition and molecular weight, water contact angle measurements for the hydrophilicity, AFM for the morphology, and ellipsometry for the thickness. Surface-grafted PAM was used to study its interactions with HA in aqueous solutions at different pH (2, 7, and 10) and NaCl salt concentrations (1, 10, and 100 mM, within the range of salt concentrations of fresh water) using QCM-D. QCM-D measurements showed that compared with bare silica, the adsorption of HA by PAM-coated silica was greatly reduced at all pHs and salt concentrations, and the adsorption of HA on PAM-coated silica depended on the solution chemistry including solution pH and salt concentration. Hydrogen bonding between PAM and HA is the major driving force for HA to adsorb on PAM. AFM force measurements showed that adhesion between PAM and HA was observed only at acidic conditions. The knowledge obtained from this study will benefit the prediction of the environmental behaviour of PAMs under different conditions in natural/engineered environments and provide guidance for the design of remediation technologies for water and soil.

A label-free platform for dopamine biosensing.

This work presents a label-free platform for dopamine (DA) monitoring based on the spectroscopic properties of laccase. Working in batch mode, DA ranging from 25 to 250μM, can be determined without the interference of norepinephrine and epinephrine. Laccase immobilized in a polyacrylamide film is the basis of a platform for the label-free determination of DA. The linear range goes from 100 to 900μM with an RSD of 5.3% and a film lifetime of more than 30 measurements. The biosensors also permit the DA + epinephrine + norepinephrine determination. The method permits the determination of DA and the total concentration of the three neurotransmitters, and could be used for DA monitoring in urine samples.

In-column bonded phase polymerization for improved packing uniformity.

It is difficult to pack chromatographic particles having polymeric-bonded phases because solvents used for making a stable slurry cause the polymer layer to swell. Growth of the polymer inside the column (in situ) after packing was investigated and compared with conventional, ex situ polymer growth. The method of activators generated by electron transfer, along with atom-transfer radical polymerization, enabled polymerization under ambient conditions. Nonporous, 0.62μm silica particles with silane initiators were used. Polyacrylamide films with a hydrated thickness of 23nm in 75:25 water/isopropanol grew in 55min for both in situ and ex situ preparations, and the same carbon coverage was observed. Higher chromatographic resolution and better column-to-column reproducibility were observed for in situ polymer growth, as evaluated by hydrophilic interaction liquid chromatography for the model glycoprotein, ribonuclease B. In situ polymer growth was also found to give lower eddy diffusion, as shown by a narrower peak width for injected acetonitrile in 50:50 acetonitrile/water. When columns were packed more loosely, bed collapse occurred quickly for ex situ, but not for in situ, polymer growth. The higher resolution and stability for in situ polymer growth is explained by packing with hard, rather than soft, contacts between particles.

Investigation of the structure, thermomechanical and sorption properties of crosslinked polyacrylamide films formed under the influence of constant electric field

Investigation of the structure, thermomechanical and sorption properties of crosslinked polyacrylamide films formed under the influence of constant electric field

Inkjet printed nanohydrogel coated carbon nanotubes electrodes for matrix independent sensing.

Polyacrylamide (PA) based hydrogels are used in several applications including polyacrylamide gel electrophoresis and sensing devices. Homogeneous and compact PA films can be prepared based on chemical or photopolymerization processes. However, the accurate and reproducible coating of substrates with nanohydrogel patterns is challenging due to the in situ polymerization and deposition requirements. Herein, we report an inkjet printing (IJP) concept with simultaneously performed UV photopolymerization of a specifically prepared acrylamide/N,N'-methylenebis(acrylamide) containing ink. A prepolymerization step of the hydrogel precursor molecules was implemented in the ink formulation protocol to adjust the viscosity of the ink and to enhance the rate of polymerization during printing. After the optimization of the printing parameters, a nanometer thin PA hydrogel coating with well distributed nanopores was achieved on top of a stand-alone carbon nanotubes (CNTs) pattern. Batches of fully inkjet printed PA/CNT modified electrodes were prepared that showed outstanding improvements for the electrochemical detection of antioxidants in complex matrices such as untreated orange juice and red wine samples thanks to the properties of the PA coating.

Real-time UV-visible spectroscopy analysis of purple membrane-polyacrylamide film formation taking into account Fano line shapes and scattering.

We theoretically and experimentally analyze the formation of thick Purple Membrane (PM) polyacrylamide (PA) films by means of optical spectroscopy by considering the absorption of bacteriorhodopsin and scattering. We have applied semiclassical quantum mechanical techniques for the calculation of absorption spectra by taking into account the Fano effects on the ground state of bacteriorhodopsin. A model of the formation of PM-polyacrylamide films has been proposed based on the growth of polymeric chains around purple membrane. Experimentally, the temporal evolution of the polymerization process of acrylamide has been studied as function of the pH solution, obtaining a good correspondence to the proposed model. Thus, due to the formation of intermediate bacteriorhodopsin-doped nanogel, by controlling the polymerization process, an alternative methodology for the synthesis of bacteriorhodopsin-doped nanogels can be provided.

MISCIBILITY AND INTERACTIONS IN CHITOSAN AND POLYACRYLAMIDE MIXTURES

In the present work, the results of Fourier transform infrared (FTIR) and atomic force microscopy (AFM) studies of films of chitosan acetate (ChA), polyacrylamide (PAM), and their mixtures are presented. The morphology of the ChA and PAM films and their mixtures was studied by tappingmode atomic force microscopy (AFM). The topography images were considered by determining the root mean square (RMS) deviation in the image data. The study of mixtures by AFM showed a completely different morphology when compared with pure components. The roughness of mixtures increases with the increase of ChA content but is significantly reduced after UV exposure. This may indicate a strong interaction between the polymeric components. The FTIR spectroscopy also supports the obtained results. The miscibility of polymer mixtures is related to interactions between the functional groups of the polymeric components.

Effect of electron beam irradiation on physico-chemical properties of polyacrylamide films

High-energy radiation is a well-known technique for the modification of polymers. In this experimental study, the effect of electron beam (EB) radiation on physico-chemical properties of polyacrylamide films has been investigated by ultraviolet–visible (UV–VIS) spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis and differential scanning calorimetric techniques. UV–VIS and FTIR results show that some small structural changes occurring in the polymer depending upon the dose of radiation. SEM micrographs reveal that there is no significant change in the morphology with EB irradiation. Thermal studies indicate that there may be small amount of cross-linking taking place for lower doses of radiation. At higher doses of radiation, however, degradation or chain scission begins to occur. Tensile strength of the films found to be increases upon irradiation at lower doses.

Stratified Polymer Grafts: Synthesis and Characterization of Layered ‘Brush’ and ‘Gel’ Structures

Stratified polyacrylamide films featuring polymer-brush and polymer-gel blocks are fabricated by sequential, surface-initiated, photoiniferter-mediated polymerization. Use of selective solvent mixtures during re-initiation allows the formation of well-defined brush and gel layers with graded properties. Nano-mechanical and tribological characterization by colloidal-probe AFM clarifies the architecture of each layer and determines the film properties under application of normal and lateral forces.

Ultrasensitivity by Molecular Titration in Spatially Propagating Enzymatic Reactions

Delineating design principles of biological systems by reconstitution of purified components offers a platform to gauge the influence of critical physicochemical parameters on minimal biological systems of reduced complexity. Here we unravel the effect of strong reversible inhibitors on the spatiotemporal propagation of enzymatic reactions in a confined environment in vitro. We use micropatterned, enzyme-laden agarose gels which are stamped on polyacrylamide films containing immobilized substrates and reversible inhibitors. Quantitative fluorescence imaging combined with detailed numerical simulations of the reaction-diffusion process reveal that a shallow gradient of enzyme is converted into a steep product gradient by addition of strong inhibitors, consistent with a mathematical model of molecular titration. The results confirm that ultrasensitive and threshold effects at the molecular level can convert a graded input signal to a steep spatial response at macroscopic length scales.