Traditional dip-assisted layer-by-layer (LbL) assembly produces robust and conformal coatings, but it is time-consuming. Alternatively, spray-assisted layer-by-layer (SA-LbL) assembly has gained interest due to rapid processing resulting from the short adsorption time. However, it is challenging to assemble anisotropic nanomaterials using this spray-based approach. This is because the standard approach for fabricating “ all-polyelectrolyte ” LbL films does not necessarily give rise to satisfactory film growth when one of the adsorbing components is anisotropic. Here, polymers are combined with a model anisotropic nanomaterial via SA-LbL assembly. Specifically, graphene oxide (GO) is investigated, and the effect of anchor layer, colloidal stability, charge distribution along the carbon framework, and concentration of polymer on the growth and the film quality is examined to gain insight into how to achieve pinhole-free, smooth polymer/GO SA-LbL coatings. This approach might be applicable to other anisotropic nanomaterials such as clays or 2D nanomaterials for future development of uniform coatings by spraying.
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Trapping of Antibacterial Agents within Hydrophobic Films of Polyphosphazene Polyelectrolytes
Direct layer-by-layer (LbL) assembly of cationic, small-molecule antibacterial bioactives with water-soluble, ionic polyphosphazenes (PPzs) containing trifluoroethoxy and carboxy substitients is reported. First, influence of PPzs hydrophobicity and antibiotic charge density on LbL assembly was studied via evolution of dry film thickness. We found that the use of fluorinated PPz polyelectrolytes enhanced ionic pairing within LbL coatings, and that increasing charge density of small molecules increased antibiotic uptake. This strategy was successful even in the case of gentamicin, a hydrophilic, small antibiotic with only 3 to 4 positive charges at pH 7.5. Confirmation of antibiotic presence in films was demonstrated via x-ray photoelectron spectroscopy. Importantly, LbL films of fluorinated PPz polyelectrolytes retained antibiotics in physiological conditions due to the enhanced hydrophobic interactions. In contrast, LbL films of non-fluorinated PPzs released antibiotics at low pH and in the presence of salt following the charge renormalization argument. The potential of these coatings with a biomedically relevant bacterial strain, Staphylococcus aureus, is discussed.
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- Award ID(s):
- 1808483
- NSF-PAR ID:
- 10092770
- Date Published:
- Journal Name:
- Abstracts of papers - American Chemical Society
- ISSN:
- 0065-7727
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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ABSTRACT The properties of phosphonium polyelectrolytes (PELs) were evaluated in an effort to assess the influence of both side chain and main chain composition. The influence of side chain was examined by comparing properties of a series of PELs having hydrophobic octyloxy side chains to those of structural analogues lacking the side chains. The influence exerted by backbone flexibility/length of spacer between charges was revealed by comparing properties of two series of polymers with a variable number of methylene units between phosphonium charge‐bearing sites. Side chain composition and spacing between phosphonium units lead to noteworthy influence on thermal stability, glass transition, and crystallinity. The molecular structure of PELs also correlates with trends in film morphology and critical surface energy of PEL dip‐cast films. Sensitivity of morphology to humidity or water in the casting solvent was observed. Supramolecular assembly of films via layer‐by‐layer deposition of PELs alternating with anionic polythiophene derivative layers was also undertaken. The linearity of film growth, amount of material deposited in each bilayer, polycation:polyanion ratio, and film roughness all show noteworthy trends that depend on both the presence/absence of side chains and on spacing between ionic centers. The relationship between side chain and spacer on bactericidal activity against
Staphylococcus aureus andEscherichia coli was assessed. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.2019 , 57, 24–34 -
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Conjugated polyelectrolytes (CPEs) are polymer semiconductors whose properties are affected by the presence of covalently fixed and mobile ions. These structural components lead to interfacial dipoles, electrochemical doping, and mixed ionic and electronic conductivity. While the behavior of ionic carriers is important to a number of CPE applications, it remains difficult to quantify ion transport in films due to interference from electronic carriers; relationships between molecular structure and ion conductivity are thus not well understood. This work demonstrates direct observation of ions in six different CPE films using Kelvin probe force microscopy. Surface potential measurements of thin, planar CPE device structures are used to map the distribution of ions through the simple electrostatic relationship between potential and charge density. The transport of mobile ions within the CPE bulk can be studied through the time‐dependent relaxation of bias‐stressed CPE films, through which the decay of ion populations near each electrode is measured and carefully modeled, leading to estimated values of ionic mobility and effective ionic carrier density. The results show that ion transport is most strongly impacted by the number of ion‐bearing side chains per monomer, which facilitate room temperature ion transport via vibrational motion.
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null (Ed.)This work establishes a correlation between the selectivity of hydrogen-bonding interactions and the functionality of micelle-containing layer-by-layer (LbL) assemblies. Specifically, we explore LbL films formed by assembly of poly(methacrylic acid) (PMAA) and upper critical solution temperature block copolymer micelles (UCSTMs) composed of poly(acrylamide- co -acrylonitrile) P(AAm- co -AN) cores and polyvinylpyrrolidone (PVP) coronae. UCSTMs had a hydrated diameter of ∼380 nm with a transition temperature between 45 and 50 °C, regardless of solution pH. Importantly, micelles were able to hydrogen-bond with PMAA, with the critical interaction pH being temperature dependent. To better understand the thermodynamic nature of these interactions, in depth studies using isothermal titration calorimetry (ITC) were conducted. ITC reveals opposite signs of enthalpies for binding of PMAA with micellar coronae vs. with the cores. Moreover, ITC indicates that pH directs the interactions of PMAA with micelles, selectively enabling binding with the micellar corona at pH 4 or with both the corona and the core at pH 3. We then explore UCSTM/PMAA LbL assemblies and show that the two distinct modes of PMAA interaction with the micelles ( i.e. whether or not PMAA binds with the core) had significant effects on the film composition, structure, and functionality. Consistent with PMAA hydrogen bonding with the P(AAm- co -AN) micellar cores, a significantly higher fraction of PMAA was found within the films assembled at pH 3 compared to pH 4 by both spectroscopic ellipsometry and neutron reflectometry. Selective interaction of PMAA with PVP coronae of the assembled micelles, achieved by the emergence of partial ionization of PMAA at pH 4 was critical for preserving film functionality demonstrated as temperature-controlled swelling and release of a model small molecule, pyrene. The work done here can be applied to a multitude of assembled polymer systems in order to predict suppression/retention of their stimuli-responsive behavior.more » « less
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null (Ed.)This work focuses on the development of nanoparticle-based layer-by-layer (LbL) coatings for enhancing the detection sensitivity and selectivity of volatile organic compounds (VOCs) using on-chip mid-infrared (MIR) waveguides (WGs). First, we demonstrate construction of conformal coatings of polymer/mesoporous silica nanoparticles (MSNs) on the surface of Si-based WGs using the LbL technique and evaluate the coating deposition conditions, such as pH and substrate withdrawal speed, on the thickness and homogeneity of the assemblies. We then use the modified WGs to achieve enhanced sensitivity and selectivity of polar organic compounds, such as ethanol, versus non-polar ones, such as methane, in the MIR region. In addition, using density functional theory calculations, we show that such an improvement in sensing performance is achieved due to preferential adsorption of ethanol molecules within MSNs in the vicinity of the WG evanescent field.more » « less
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Accepted Manuscript1.0
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