sample-preparation-quartz-crystal-microbalance-measurements-protein

Sample Preparation in Quartz Crystal Microbalance Measurements of Protein Adsorption and Polymer Mechanics

In this study, we present various examples of how thin film preparation for quartz crystal microbalance experiments informs the appropriate modeling of ...

Northwestern University

The electrochemical quartz crystal microbalance (QCM) was used to investigate the deposition of poly(allylamine hydrochloride) (PAH) with molybdate anions under anodic conditions. The PAH-molybdate complex was used as a model system to understand possible deposition criteria which may be relevant to the formation of proteinaceous films on CoCrMo hip implants. Data indicate that PAH deposition will occur above ∼0.60 V vs SCE if molybdate anions are present in the electrolyte above a critical concentration, and if the polymer concentration remains below a critical value. Numerical modeling and dynamic light scattering (DLS) studies were performed to understand the conditions that enable deposition to occur at these potentials. The results indicate that PAH-molybdate complexes form most efficiently when the polyvalent positive charge and polyvalent negative charge in the system are in an optimum range with respect to each other.

Anodic Electrodeposition of a Cationic Polyelectrolyte in the Presence of Multivalent Anions.

Polyelectrolyte complex (PEC) films made from oppositely charged polymer chains have applications as drug-delivery vehicles, separation membranes, and biocompatible coatings. Conventional layer-by-layer techniques for polyelectrolyte coatings are low-throughput and multistep processes that are quite slow for building films on the order of micrometers. In this work, PEC films are electrochemically deposited using a rapid one-pot method, yielding thick (1 μm) films within short experimental time scales (5 min). This rapid electrodeposition is achieved by exploiting the reduction of hydrogen peroxide at mild electrode potentials that avoid water electrolysis yet trigger the pH-responsive self-assembly of a PEC film composed of poly(acrylic) acid and poly(allylamine) HCl. In situ rheology using an electrochemical quartz crystal microbalance quantified the shear modulus-density product of the deposited layer to be on the order of 10 Pa g/cm at a frequency of 15 MHz, with a viscoelastic phase angle of approximately 50°. This electrodeposition scheme furthers the development of PEC coatings for more high-throughput applications, where a fast and efficient single-step approach would be desirable for obtaining coatings.

pH-Controlled Electrochemical Deposition of Polyelectrolyte Complex Films.

In the inertial limit, the resonance frequency of the quartz crystal microbalance (QCM) is related to the coupled mass on the quartz sensor through the Sauerbrey expression that relates the mass to the change in resonance frequency. However, when the thickness of the film is sufficiently large, the relationship becomes more complicated and both the frequency and damping of the crystal resonance must be considered. In this regime, a rheological model of the material must be used to accurately extract the adhered film's thickness, shear modulus, and viscoelastic phase angle from the data. In the present work we examine the suitability of two viscoelastic models, a simple Voigt model ( Physica Scripta 1999, 59, 391-396) and a more realistic power-law model ( Langmuir 2015, 31, 4008-4017), to extract the rheological properties of a thermoresponsive hydrogel film. By changing temperature and initial dry film thickness of the gel, the operation of QCM was traversed from the Sauerbrey limit, where viscous losses do not impact the frequency, through the regime where the QCM response is sensitive to viscoelastic properties. The density-shear modulus and the viscoelastic phase angle from the two models are in good agreement when the shear wavelength ratio, d/λ , is in the range of 0.05-0.20, where d is the film thickness and λ  is the wavelength of the mechanical shear wave at the n harmonic. We further provide a framework for estimating the physical properties of soft materials in the megahertz regime by using the physical behavior of polyelectrolyte complexes. This provides the user with an approximate range of allowable film thicknesses for accurate viscoelastic analysis with either model, thus enabling better use of the QCM-D in soft materials research.

Quantitative Rheometry of Thin Soft Materials Using the Quartz Crystal Microbalance with Dissipation.

Quantitatively understanding the self-assembly of amphiphilic macromolecules at liquid-liquid interfaces is a fundamental scientific concern due to its relevance to a broad range of applications including bottom-up nanopatterning, protein encapsulation, oil recovery, drug delivery, and other technologies. Elucidating the mechanisms that drive assembly of amphiphilic macromolecules at liquid-liquid interfaces is challenging due to the combination of hydrophobic, hydrophilic, and Coulomb interactions, which require consideration of the dielectric mismatch, solvation effects, ionic correlations, and entropic factors. Here we investigate the self-assembly of a model block copolymer with various charge fractions at the chloroform-water interface. We analyze the adsorption and conformation of poly(styrene)--poly(2-vinylpyridine) (PS--P2VP) and of the homopolymer poly(2-vinylpyridine) (P2VP) with varying charge fraction, which is controlled via a quaternization reaction and distributed randomly along the backbone. Interfacial tension measurements show that the polymer adsorption increases only marginally at low charge fractions (<5%) but increases more significantly at higher charge fractions for the copolymer, while the corresponding randomly charged P2VP homopolymer analogues display much more sensitivity to the presence of charged groups. Molecular dynamics (MD) simulations of the experimental systems reveal that the diblock copolymer (PS--P2VP) interfacial activity could be mediated by the formation of a rich set of complex interfacial copolymer aggregates. Circular domains to elongated stripes are observed in the simulations at the water-chloroform interface as the charge fraction increases. These structures are shown to resemble the spherical and cylindrical helicoid structures observed in bulk chloroform as the charge fraction increases. The self-assembly of charge-containing copolymers is found to be driven by the association of the charged component in the hydrophilic block, with the hydrophobic segments extending away from the hydrophilic cores into the chloroform phase.

Article	Year
Anodic Electrodeposition of a Cationic Polyelectrolyte in the Presence of Multivalent Anions. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 27419476	2016
pH-Controlled Electrochemical Deposition of Polyelectrolyte Complex Films. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 28142239	2017
Quantitative Rheometry of Thin Soft Materials Using the Quartz Crystal Microbalance with Dissipation. Analytical chemistry\| PubMed ID: 29473414	2018
Self-Assembly of Charge-Containing Copolymers at the Liquid-Liquid Interface. ACS central science\| PubMed ID: 31041389	2019

Kazi Sadman

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