The conformation of adsorbed polyacrylamide and derived polymers (original) (raw)
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Tailoring the adhesion properties of polyacrylamide-based hydrogels. Application for skin contact
Journal of Adhesion Science and Technology, 2013
This study investigates the effects of monodisperse polystyrene nanoparticle fillers on the network formation, rheological properties and adhesion performance of hydrogel nanocomposites based on polyacrylamide and poly(acrylamide-hydroxyethyl methacrylate). We demonstrated a simultaneous increase in elasticity and tack of these humid composite materials. A 1 H-NMR kinetic study showed quasi-total conversion of these monomers during the polymerization-reticulation process and the formation of inhomogeneities within the hydrogel network structure due to the difference in reactivity ratios of the comonomers: acrylamide (AM) and hydroxyethyl methacrylate (HEMA)(r AM ¼ 0.41 AE 0.01 and r HEMA ¼ 7.4 AE 0.3). The rheological properties of these materials were found to be affected by their chemical composition (HEMA content, presence of nanoparticles and heterogeneities). We investigated the adhesion properties of our materials using a probe test tack. Measurements were carried out on a human skin substitute to compare with metal and investigate the potential use of these hydrogel nanocomposites as dermatological patches. The adhesion energy was found to be related to the chemical composition and rheological properties of the hydrogels, as well as to the surface properties of both the adhesive and the substrate.
Macromolecules, 2004
We have studied the adsorption of a single polyacrylamide chain onto a freshly cleaved mica surface from a good solvent by force spectroscopy using a custom-built force prober. The polymer chain was covalently attached to the AFM tip at one end. The polymer loop lengths were deduced by measuring the distance between desorption events during the retraction of the tip from the surface. The loop length distribution obtained was found to obey a power law characteristic for the semidilute regime. We claim that this is due to the confinement of the polymer chain between the tip and the surface during the adsorption.
Characterization of inhomogeneous polyacrylamide hydrogels
Journal of Polymer Science Part B: Polymer Physics, 1992
The physical and structural properties of acrylamide gels have been characterized by osmotic deswelling, mechanical compression, and x-ray scattering. These properties vary considerably with the concentration of the crosslinking agent bisacrylamide, at fixed total monomers concentration ( 10% wt/wt water). In particular, changes in the properties appear more prominent at a crosslinking level of about 5 6 % ( w t bisacrylamide/wt monomers). The compression modulus of as-prepared and swollen gels passes through a maximum at this level of crosslinking. The swelling pressure curves can be separated into osmotic and elastic contributions of the gel network. The elastic part exhibits similar behavior to the compression modulus. The scaling of the osmotic part with the gel concentration varies with the degree of crosslinking, changing from 2.33 to 3.09. This indicates that the solvent power of water decreases with increasing crosslinking level, towards 0 conditions. The scattering patterns from the gels have been analyzed as arising from additive contributions from a homogeneous gel matrix, and embedded heterogeneities having a higher crosslinking density. These heterogeneities become much more prominent a t the same level of crosslinking about 5-6%. Hysteresis observed in the sorption/desorption behavior of polyacrylamide gel suggests that further irreversible structural changes may occur at water activities lower than probed by osmotic deswelling. 0 1992 John Wiley & Sons, Inc. Keywords: hydrogels, polyacrylamide, characterization of inhomogeneity in polyacrylamide, inhomogeneous hydrogels of gels of polyacrylamide in water, physical and structural characteristics of Sci. .
Journal of Applied Polymer Science, 2006
Hydrophobically modified polyacrylamide (HMPAM), with a molecular weight of 10 4 g/mol, was studied using a range of rheological methods and dynamic light scattering (DLS). DLS measurements indicate that the association of the modified polymer begins at low concentration. The modified polymer with high substitution forms transient networks below the critical concentration, but the networks are disrupted by the micelles formed by the polymer itself, and the networks do not contribute to viscosity enhancement. The modified polymers exhibited surface activity, so they may be regarded as non-ionic polymeric surfactants rather than thickeners. On the other hand, HMPAM is shown to interact with the surfactant SDS while PAM is inert to SDS. In the hydrophobic domains, it undergoes a surfactant-induced association process; in the hydrophobe-surfactant transition regions, the surfactant binds to the polymer in a non-cooperative way, and forms a polymer-surfactant complex. Contracted polymer chains begin to extend due to electrostatic repulsion, which can overcome the association at surfactant domains. The conformation of HMPAM polymer chains could be controlled by adding a certain amount of surfactant.
Journal of the Brazilian Chemical Society, 2013
Poli(acrilamida-co-dihexilacrilamida) (PAHM-0) e poli(acrilamida-co-acrilato de sódio-co-dihexilacrilamida) (PAHM-21) foram estudadas por espalhamento de raios-X a baixos ângulos (SAXS), espalhamento de luz (LS) e reologia. Os resultados de SAXS ressaltaram o caráter polieletrolítico da PAHM-21, com uma conformação altamente estendida em solução aquosa devido às repulsões entre as cargas, enquanto a PAHM-0 tem uma conformação em novelo aleatório. As medidas de LS indicaram que a PAHM-0 forma aglomerados intermoleculares em solução, na presença e na ausência de sal, mesmo com um conteúdo hidrofóbico menor que o descrito na literatura para poliacrilamidas associativas. Contudo, os resultados reológicos mostraram que, apesar de haver associação hidrofóbica, não há um aumento da viscosidade. Os resultados de LS da PAHM-21 sugerem que esse polímero forma, predominantemente, associações intramoleculares na presença de sais. Além disso, as medidas viscosimétricas mostram que a sua viscosidade diminui com a blindagem das cargas pela adição de sais. Poly(acrylamide-co-dihexylacrylamide) (PAHM-0) and poly(acrylamide-co-sodium acrylate-co-dihexylacrylamide) (PAHM-21) were studied through small-angle X-ray scattering (SAXS), light scattering (LS) and rheology. SAXS results highlighted the polyelectrolyte character of PAHM-21, with highly extended conformation in aqueous solution owing to charge repulsion, while the PAHM-0 has a coil conformation. LS measurements indicated that PAHM-0 makes intermolecular clusters in solution, in presence and absence of salt, even with a lower hydrophobic content than that described in the literature to the associative polyacrylamides. However, the rheological results showed that there is not an enhancement of the viscosity although hydrophobic association takes place. LS results for PAHM-21 suggest that this polymer makes intramolecular associations mainly in the presence of salts. Furthermore, the viscosity measurements show that its viscosity decreases due to screening of the charges by the addition of salts.
Journal of the Brazilian Chemical Society, 2011
Uma poliacrilamida hidrofobicamente modificada e dois dos seus derivados parcialmente hidrolisados, contendo grupos hidrofóbicos e carboxila, foram preparados por polimerização micelar e pós-hidrólise. A massa molar, o segundo coeficiente do virial e o raio de giração foram determinados por espalhamento de luz estático (SLS). O espalhamento de luz dinâmico (DLS) e o espalhamento de raios-X a baixos ângulos (SAXS) foram utilizados respectivamente para determinar a formação de agregados e o tipo de empacotamento das cadeias em regime semi-diluído. O comportamento das soluções, em regime diluído e semi-diluído foi estudado por viscosimetria e reologia. A poliacrilamida modificada hidrofobicamente apresentou tendência à formação de agregados devido aos grupos hidrofóbicos, mas essa agregação não foi suficiente para aumentar a viscosidade aparente. Embora os derivados parcialmente hidrolisados não apresentassem a mesma tendência para agregação, eles apresentaram um comportamento anisotrópico devido à introdução de densidade de carga sobre a cadeia polimérica, a qual levou a uma conformação mais alongada da macromolécula e maior viscosidade. A hydrophobically-modified polyacrylamide and two partially hydrolyzed derivatives containing hydrophobic and carboxylic groups were prepared by micellar polymerization and posthydrolysis. The molecular weight, second virial coefficient and radius of gyration were determined by static light scattering (SLS). Dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) were employed to determine the aggregate formation and type of chain packing in the semidilute regime, respectively. The behavior of solutions in dilute and semidilute regimes was also studied by viscometry and rheology. The hydrophobically-modified polyacrylamide showed a tendency to form aggregates due to the hydrophobic groups, but not enough to increase apparent viscosity. The partially hydrolyzed derivatives did not show the same aggregate-forming tendency. Rather, they exhibited anisotropic behavior, due to the charge density introduced into the polymer chain, which led to a more elongated macromolecular conformation and higher viscosity.
2016
Preparation of hydrogels on solid surfaces is of great significance for a number of reasons such as changing the interfacial properties, increasing hydrophilicity, etc. Such films strongly improve mechanical and hydrodynamic properties of the surfaces. Creating nano-layers of hydrogel thin films has been an attractive subject in advanced academic research for past few years. Due to the relatively high water absorption capacity of hydrogels, the hydrogel coatings have critical applications including biological detectors, drug delivery, contact lenses, artificial blood veins, and biocompatible implants such as stents in heart and ears. In this study, free radical polymerization was initiated by electron transfer from a metallic substrate (stainless steel) to a redox-active initiator in NaNO3 containing electrolyte, using electro-polymerization method. The resulted electro-polymerized polyacrylamide hydrogel nano-films with a typical thickness of 30 to 150 nm were examined and globule-like microstructures on the surface were observed in field emission scanning electron microscopy (FE-SEM) images. The formation of these globules in the early stages of reaction could be due to the disproportionate distribution of radicals, disproportionate growth in specific area, local gelation of film, and an increase in propagation rate constant of reaction on nano-film surface. Also many nano-tracks were observed on the surface and it refers to the morphological instability of surface attached hydrogels. Finally, atomic force microscopy (AFM) images were studied and monomer concentration introduced as an effective parameter on average roughness of the nano-film surface.
The Journal of Physical Chemistry B, 2008
The effect of salts on adsorbed polyelectrolyte conformations has been studied extensively over the past three decades. Previous researchers have proposed that increasing salt concentration results in larger loops and tails for weak polyelectrolytes adsorbed on a surface. However, no experimental verification of this theory has been published. In this work, we present experimental verification acquired by "pulling" single molecules of a polyelectrolyte from a mica surface using a scanning probe technique. We also present a new method for analyzing changes in adsorbed polymer tail lengths. We demonstrate that increasing solution salt concentration correlates with both loop and tail lengths of an adsorbed low charge density cationic polyacrylamide on a mica substrate.
New approach to the molecular characterization of hydrophobically modified polyacrylamide
Polymer, 2004
A new approach to the molecular characterization of hydrophobically associating copolymers of acrylamide is developed. It is based on the study of associative properties: the formation of intermolecular aggregates was followed by dynamic and static light scattering (DLS and SLS), while the formation of hydrophobic domains was detected by fluorescence spectroscopy with pyrene as a probe. In aqueous media, hydrophobic aggregation begins at concentrations much lower than the overlap concentration. The addition of co-solvent, acetonitrile, shifts the aggregation to the semi-dilute region. The dissolution of hydrophobic aggregates is controlled both by fluorescence spectroscopy with pyrene as a probe and by DLS and SLS. Absolute M w values are measured by SLS in mixed solvent of optimal composition. Molecular weight distribution (MWD) is characterized by GPC using calibration with secondary standards characterized by SLS. This approach allowed us to follow MWD evolution during a micellar copolymerization of acrylamide, N-nonylacrylamide and acrylic acid. It is found that the molecular weight heterogeneity remarkably growths with the increase of conversion. q