More Like this

1. Two-Dimensional and Three-Dimensional Ultrathin Multilayer Hydrogels through Layer-by-Layer Assembly

   https://doi.org/10.1021/acs.langmuir.2c00630  

   Kozlovskaya, Veronika; Dolmat, Maksim; Kharlampieva, Eugenia (January 2022, Langmuir)

   Stimuli-responsive multilayer hydrogels have opened new opportunities to design hierarchically organized networks with properties controlled at the nanoscale. These multilayer materials integrate structural, morphological, and compositional versatility provided by alternating layer-bylayer polymer deposition with the capability for dramatic and reversible changes in volumes upon environmental triggers, a characteristic of chemically crosslinked responsive networks. Despite their intriguing potential, there has been limited knowledge about the structure−property relationships of multilayer hydrogels, partly because of the challenges in regulating network structural organization and the limited set of the instrumental pool to resolve structure and properties at nanometer spatial resolution. This Feature Article highlights our recent studies on advancing assembly technologies, fundamentals, and applications of multilayer hydrogels. The fundamental relationships among synthetic strategies, chemical compositions, and hydrogel architectures are discussed, and their impacts on stimuli-induced volume changes, morphology, and mechanical responses are presented. We present an overview of our studies on thin multilayer hydrogel coatings, focusing on controlling and quantifying the degree of layer intermixing, which are crucial issues in the design of hydrogels with predictable properties. We also uncover the behavior of stratified “multicompartment” hydrogels in response to changes in pH and temperature. We summarize the mechanical responses of free-standing multilayer hydrogels, including planar thin coatings and films with closed geometries such as hollow microcapsules and nonhollow hydrogel microparticles with spherical and nonspherical shapes. Finally, we will showcase potential applications of pH- and temperature-sensitive multilayer hydrogels in sensing and drug delivery. The knowledge about multilayer hydrogels can advance the rational design of polymer networks with predictable and well-tunable properties, contributing to modern polymer science and broadening hydrogel applications. 

   more » « less
2. Influence of Side Chain Hydrolysis on the Evolution of Nanoscale Roughness and Porosity in Amine-Reactive Polymer Multilayers

   https://doi.org/acs.chemmater.0c02095  

   Carter, Matthew C.; Wong, Matthew S.; Wang, Fengrui; Lynn, David M. (July 2020, Chemistry of materials)

   We report the influence of side chain hydrolysis on the evolution of nanoscale structure in thin films fabricated by the reactive layer-by-layer (LbL) assembly of branched poly(ethylenimine) (PEI) and poly(2-vinyl-4,4-dimethylazlactone) (PVDMA). LbL assembly of PEI and PVDMA generally leads to the linear growth of thin, smooth films. However, assembly using PVDMA containing controlled degrees of side chain hydrolysis leads to the growth of thicker films that exhibit substantial nanoscale roughness, porosity, and have resulting physicochemical behaviors (e.g., superhydrophobicity) that are similar to those of some thicker PEI/PVDMA coatings reported in past studies. Our results reveal that the degree of PVDMA partial hydrolysis (or carboxylic acid group content) influences the extent to which complex film features develop, suggesting that ion-pairing interactions between hydrolyzed side chains and amines in PEI promote the evolution of bulk and surface morphology. Additional experiments demonstrate that these features likely arise from polymer/polymer interactions at the surfaces of the films during assembly, and not from the formation and deposition of solution-phase polymer aggregates. When combined, our results suggest that nanoporous structures and rough features observed in past studies likely arise, at least in part, from some degree of adventitious side chain hydrolysis in the PVDMA used for film fabrication. Our results provide useful insight into molecular-level features that govern the growth and structures of these reactive materials, and provide a framework to promote nanoscale morphology reliably and reproducibly. The principles and tools reported here should prove useful for further tuning the porosities and tailoring the physicochemical behaviors of these reactive coatings in ways that are important in applied contexts. 

   more » « less
3. Effect of polyacid architecture and polycation molecular weight on lateral diffusion within multilayer films

   https://doi.org/10.1063/5.0190377  

   Brito, Jordan; Shah, Parin Purvin; Aliakseyeu, Aliaksei; Sukhishvili, Svetlana A (March 2024, The Journal of Chemical Physics)

   Despite the potential use of polyelectrolyte multilayers for biomedical, separation, and energy applications, their dynamic properties are not sufficiently understood. In this work, center-of-mass diffusion of a weak polyacid—poly(methacrylic acid) (PMAA) of linear and 8-arm architecture (L-PMAA and 8-PMAA, respectively) and matched molecular weight—was studied in layer-by-layer (LbL) assemblies with poly(diallyldimethylammonium) chloride (PDADMAC) of varied molecular weight. The film deposition at low-salt, acidic conditions when PMAA was only partially ionized yielded thicker, more diffused layers with shorter PDADMAC chains, and bilayer thickness decreased for multilayers constructed with longer PDADMAC. The molecular architecture of PMAA had a weak effect on film growth, with bilayer thickness being ∼20% larger for L-PMAA for the films constructed with the shortest PDADMAC (35 kDa) and identical film growth for L-PMAA and 8-PMAA with the longest PDADMAC (300 kDa). The exposure of the multilayer films to 0.2M NaCl triggered a reduction in PMAA ionization and significant lateral diffusivity of fluorescently labeled PMAA molecules (PMAA*), with diffusion coefficients D ranging from 10−13 to 10−12 cm2/s, as determined by the fluorescence recovery after photobleaching technique. For all the films, polymer mobility was higher for star polyacids as compared to their linear counterparts, and the dependence of PMAA diffusion coefficient D on PDADMAC molecular weight (D ∼ M−n) was relatively weak (n < 0.6). However, 8-PMAA demonstrated an approximately doubled power exponent compared to the L-PMAA chains, suggesting a stronger effect of the molecular connectivity of the partner polycation molecules on the diffusion of star polyelectrolytes. 

   more » « less
4. Layer-by-layer assembly of polymers and anisotropic nanomaterials using spray-based approach

   https://doi.org/10.1557/jmr.2020.44  

   De, Souvik; Patel, Anish; Lutkenhaus, Jodie L. (May 2020, Journal of Materials Research)

   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. 

   more » « less
5. Electrodeposition of Polymer Networks as Conformal and Uniform Ultrathin Coatings

   https://doi.org/10.1002/adma.202409826  

   Wang, Wenlu; Resing, Anton_B; Brown, Keith_A; Werner, Jörg_G (October 2024, Advanced Materials)

   Abstract Natural systems, synthetic materials, and devices almost always feature interphases that control the flow of mass and energy or stabilize interfaces between incompatible materials. With technologies transitioning to non‐planar and 3D mesoscale architectures, novel deposition methods for realizing ultrathin coatings and interphases are required. Polymer networks are of particular interest for their tunable chemical and physical properties combined with their structural integrity. Here, the electrodeposition of polymer networks (EPoN) is introduced as a general approach to uniformly coat non‐planar conductive materials. Conceptually, EPoN utilizes electrochemically activated crosslinkers as polymer end groups to confine their network formation exclusively to the material surface upon charge transfer, yielding a passivating and self‐limiting growth of conformal and uniform coatings with tunable submicron thickness on conductive materials. EPoN is found to result in thin functional films of various polymer backbones and side group chemistries as demonstrated for poly(ether) and poly(acrylamide) based polymers as solid electrolyte and thermally responsive interphases, respectively. 

   more » « less