pH-Dependent Thermal Transitions in Hydrated Layer-by-Layer Assemblies Containing Weak Polyelectrolytes

Solvent-Responsive Glass Transition Behavior of Polyelectrolyte Complexes

Polyelectrolyte complexes (PECs) have attracted considerable attention owing to their unique physicochemical properties and potential applications as smart materials. Herein, the glass transitions of PECs solvated with varying alcohols are investigated in poly(diallyldimethylammonium)/poly(acrylic acid) (PDADMA/PAA) complexes by using modulated differential scanning calorimetry (MDSC). Solvents with one or two hydroxyl groups are selected to examine the effect of PAA-solvent interactions on the glass transition temperature (T g). Except for glycerol, all alcohol solvents yield PECs with detectable T g's and plasticization behavior. Furthermore, a linear relationship for 1/T g and the natural logarithm of the number of hydroxyl groups to intrinsic ion pair ratio [ln(n hydroxyl/n intrinsic-ion-pair)] is found. This result is significant because prior work demonstrated the relationship only for water and no other solvents. All-atom molecular dynamics (MD) simulations analyze the ability of the solvent to form hydrogen bonds via the solvent's OH groups to the PAA, revealing that the solvent molecule size and available hydroxyl groups govern the change in the glass transition. Overall, the clear dependence of a PEC's glass transition on the solvent's chemical structure provides a simple guideline for predicting their relationship.

A Perspective on the Glass Transition and the Dynamics of Polyelectrolyte Multilayers and Complexes

Polyelectrolyte multilayers (PEMs) or polyelectrolyte complexes (PECs), formed by layer-by-layer assembly or the mixing of oppositely charged polyelectrolytes (PEs) in aqueous solution, respectively, have potential applications in health, energy, and the environment. PEMs and PECs are very tunable because their structure and properties are influenced by factors such as pH, ionic strength, salt type, humidity, and temperature. Therefore, it is increasingly important to understand how these factors affect PECs and PEMs on a molecular level. In this Feature Article, we summarize our contributions to the field in the development of approaches to quantify the swelling, thermal properties, and dynamic mechanical properties of PEMs and PECs. First, the role of water as a plasticizer and in the glass-transition temperature (Tg) in both strong poly(diallyldimethylammonium)/poly(sodium 4-styrenesulfonate) (PDADMA/PSS) and weak poly(allylamine hydrochloride)/poly(acrylic acid) (PAH/PAA) systems is presented. Then, factors influencing the dynamics of PECs and PEMs are discussed. We also reflect on the swelling of PEMs in response to different salts and solvent additives. Last, the nature of water's microenvironment in PEMs/PECs is discussed. A special emphasis is placed on experimental techniques, along with molecular simulations. Taken together, this review presents an outlook and offers recommendations for future research directions, such as studying the additional effects of hydrogen-bonding hydrophobic interactions.

Electroconvective Flow in Liquid Electrolytes Containing Oligomer Additives

Metal electrodeposition in batteries is fundamentally unstable and affected by different instabilities depending on operating conditions and electrolyte chemistry. Particularly, at high charging rates, a hydrodynamic instability loosely termed electroconvection sets in, which complicates all electrochemical processes by creating a nonuniform ion flux and preferential deposition at the electrode. Here, we isolate and study electroconvection by experimentally investigating how oligomer additives in liquid electrolytes interact with the hydrodynamic instability at a cation selective interface. From electrochemical measurements and direct visualization experiments, we find that electroconvection is delayed and suppressed at all voltages in the presence of oligomers. The underlying mechanism is revealed to involve formation of an oligomer ad-layer at the interface, which in response to perturbation is believed to exert an opposing body force on the surrounding fluid to preserve the ad-layer structure and in so doing suppresses electroconvection. Our results therefore reveal that in battery electrolytes without obvious sources of bulk elasticity, surface forces produced by adsorbed polymers can be used to advantage for suppressing instability.

Suppressing the Hofmeister Anion Effect by Thermal Annealing of Thin-Film Multilayers Made of Weak Polyelectrolytes

Thin films made of weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) have been fabricated on silicon wafers using the layer-by-layer (LbL) method. To study the influence of counteranion type on the growth and properties of PAH/PAA multilayers, the nature of the supporting sodium salt was varied from cosmotropic to chaotropic anions (F^–, Cl^–, and ClO₄^–). Results of ellipsometry and AFM measurements indicate that the film thickness and surface roughness systematically increase on the order F^– < Cl^– < ClO₄^–. Furthermore, we found that the hydrophobicity of the PAH/PAA multilayer also follows the described trend when a polycation is the terminating layer. However, the heating of PAH/PAA multilayers to 60 °C during the LbL assembly suppressed the influence of background anions on the multilayer formation and properties. On the basis of the obtained results, it could be concluded that thermal annealing induces changes at the polymer–air interface in the sense of reorientation and migration of polymer chains.

Structure and Hydration of Asymmetric Polyelectrolyte Multilayers as Studied by Neutron Reflectometry: Connecting Multilayer Structure to Superior Membrane Performance

Porous membranes coated with so-called asymmetric polyelectrolyte multilayers (PEMs) have recently been shown to outperform commercial membranes for micropollutant removal. They consist of open support layers of poly(styrene sulfonate) (PSS)/poly(allylamine) (PAH) capped by denser and more selective layers of either PAH/poly(acrylic acid) (PAA) or PAH/Nafion. Unfortunately, the structure of these asymmetric PEMs, and thus their superior membrane performance, is poorly understood. In this work, neutron reflectometry (NR) is employed to elucidate the multilayered structure and hydration of these asymmetric PEMs. NR reveals that the multilayers are indeed asymmetric in structure, with distinct bottom and top multilayers when air-dried and when solvated. The low hydration of the top [PAH/Nafion] multilayer, together with the low water permeance of comparable [PAH/Nafion]-capped PEM membranes, demonstrate that it is a reduction in hydration that makes these separation layers denser and more selective. In contrast, the [PAH/PAA] capping multilayers are more hydrated than the support [PSS/PAH] layers, signifying that, here, densification of the separation layer occurs through a decrease in the mesh size (or effective pore size) of the top layer due to the higher charge density of the PAH/PAA couple compared to the PSS/PAH couple. The [PAH/PAA] and [PAH/Nafion] separation layers are extremely thin (∼4.5 and ∼7 nm, respectively), confirming that these asymmetric PEM membranes have some of the thinnest separation layers ever achieved.

Emerging trends in the dynamics of polyelectrolyte complexes

Polyelectrolyte complexes (PECs) are highly tunable materials that result from the phase separation that occurs upon mixing oppositely charged polymers. Over the years, they have gained interest due to their broad range of applications such as drug delivery systems, protective coatings, food packaging, and surface adhesives. In this review, we summarize the structure, phase transitions, chain dynamics, and rheological and thermal properties of PECs. Although most literature focuses upon the thermodynamics and application of PECs, this review highlights the fundamental role of salt and water on mechanical and thermal properties impacting the PEC's dynamics. A special focus is placed upon experimental results and techniques. Specifically, the review examines phase behaviour and salt partitioning in PECs, as well as different techniques used to measure diffusion coefficients, relaxation times, various superpositioning principles, glass transitions, and water microenvironments in PECs. This review concludes with future areas of opportunity in fundamental studies and best practices in reporting.

Recent progress in the science of complex coacervation

Complex coacervation is an associative, liquid-liquid phase separation that can occur in solutions of oppositely-charged macromolecular species, such as proteins, polymers, and colloids. This process results in a coacervate phase, which is a dense mix of the oppositely-charged components, and a supernatant phase, which is primarily devoid of these same species. First observed almost a century ago, coacervates have since found relevance in a wide range of applications; they are used in personal care and food products, cutting edge biotechnology, and as a motif for materials design and self-assembly. There has recently been a renaissance in our understanding of this important class of material phenomena, bringing the science of coacervation to the forefront of polymer and colloid science, biophysics, and industrial materials design. In this review, we describe the emergence of a number of these new research directions, specifically in the context of polymer-polymer complex coacervates, which are inspired by a number of key physical and chemical insights and driven by a diverse range of experimental, theoretical, and computational approaches.

Ionic conductivity of solid polyelectrolyte complexes with varying water content: application of the dynamic structure model

We present a systematic study of the dc conductivity of solid polyelectrolyte complexes (PEC) of type x_PSS PSS·(1 − x_PSS) PDADMA as a function of temperature, and of PSS and water content, respectively. The data are discussed in the framework of the dynamic structure model.

Hydration and Temperature Response of Water Mobility in Poly(diallyldimethylammonium)-Poly(sodium 4-styrenesulfonate) Complexes

The combination of all-atom molecular dynamics simulations with differential scanning calorimetry (DSC) has been exploited to investigate the influence of temperature and hydration on the water distribution and mobility in poly(diallyldimethylammonium) (PDADMA) and poly(sodium 4-styrenesulfonate) (PSS) complexes. The findings show that the vast majority of the water molecules hydrating the polyelectrolyte complexes (PECs) with 18-30 wt % hydration are effectively immobilized due to the strong interactions between the PE charge groups and water. Temperature and hydration were found to decrease similarly the fraction of strongly bound water. Additionally, at low hydration or at low temperatures, water motions become dominantly local vibrations and rotations instead of translational motion; translation dominance is recovered in a similar fashion by increase of both temperature and hydration. DSC experiments corroborate the simulation findings by showing that nonfreezing, bound water dominates in hydrated PECs at comparable hydrations. Our results raise attention to water as an equal variable to temperature in the design and engineering of stimuli-responsive polyelectrolyte materials and provide mechanistic explanation for the similarity.

Rheological characterization of liquid-to-solid transitions in bulk polyelectrolyte complexes

Polyelectrolyte complexation has long been known to result in both liquid and solid complexes. However, the exact nature of the liquid-to-solid transition remains an open question. We have used rheology to explain this phenomenon for the model system of poly(4-styrenesulfonic acid, sodium salt) (PSS) and poly(diallyldimethyl ammonium chloride) (PDADMAC) in the presence of potassium bromide (KBr). The use of a time-salt superposition allows for a detailed analysis of changes in the linear viscoelastic response for both liquid complex coacervates and solid polyelectrolyte complexes as a function of salt concentration, and facilitates unambiguous determination of the mechanism for this phase transition. Decreasing salt concentration, and the commensurate decrease in the water content of PSS/PDADMAC/KBr complexes is shown to lead to the formation of a physical gel due to the development of a network with trapped electrostatic crosslinks that percolates the sample at a critical salt concentration.

Multilayer Nanofilms via Inkjet Printing for Stabilizing Growth Factor and Designing Desired Cell Developments

Biologically versatile basic fibroblast growth factor (bFGF), well known for roles of signaling molecules between cells and regulating various cellular processes, has been proven to utilize specific functionalities. However, the remarkable functions are inclinable to dwindle with decrease of bFGFs' activity. In nanoscale, developing thin films with intrinsic characteristics of building molecules can facilitate handling various materials for desired purposes. Fabricating nanofilm and handling sensitive materials without detriment to activity via highly productive manufacturing are significant for practical uses in the field of biomedical applications. Herein, a multilayered nanofilm fabricating system is developed by inkjet printing to incorporate bFGF successfully. It is demonstrated that water mixed with glycerol as biological ink maintains stability of bFGFs through simulation and experimental study. With highly stable bFGFs, the proliferation of human dermal fibroblast is enhanced and the undifferentiated state of induced pluripotent stem cell is maintained by the controlled release of bFGF.

Tuning cell adhesive properties via layer-by-layer assembly of chitosan and alginate

Understanding the mechanisms controlling cell-multilayer film interactions is crucial to the successful engineering of these coatings for biotechnological and biomedical applications. Herein, we present a strategy to tune the cell adhesive properties of multilayers based on marine polysaccharides with and without cross-linking and/or coating with extracellular matrix proteins. Chemical cross-linking of multilayers improved mechanical properties of the coatings but also elicited changes in surface chemistry that alter the adhesion of human umbilical vein endothelial cells. We evaluated a strategy to decouple the mechanical and chemical properties of these films, enabling the transition from cell-adhesive to cell-resistant multilayers. Addition of chitosan/alginate multilayers on top of cross-linked films decreased endothelial cell adhesion, spreading, and proliferation to similar levels as uncross-linked films. Our findings highlight the key role of surface chemistry in cell-multilayer film interactions, and these engineered nanocoatings represent a tunable model of cell adhesive and non-adhesive multilayered films.

STATEMENT OF SIGNIFICANCE

Multilayered films based on marine-derived polysaccharides were obtained by layer-by-layer (LbL). Biological tests with human umbilical vein endothelial cells (HUVECs) showed the potential of these films to tailor cell adhesion, spreading and proliferation. These multilayered films promise to be versatile and tunable model of cell adhesive and non-adhesive films.

In situ polymerization of supramolecular nanorods assembled from polymerizable perylene bisimide

Dimethacryl amide functionalized perylene bisimide monomer was synthesized, in-situ free radical polymerization was then performed in the organized state to maintain the assembly structures.

Development of the modern theory of polymeric complex coacervation

Oppositely charged polymers can undergo the process of complex coacervation, which refers to a liquid-liquid phase separation driven by electrostatic attraction. These materials have demonstrated considerable promise as the basis for complex, self-assembled materials. In this review, we provide a broad overview of the theoretical tools used to understand the physical properties of polymeric coacervates. In particular, we discuss historic theories (Voorn-Overbeek, Random Phase Approximation), and then describe recent developments in the field (Field Theoretic, Counterion Release, Molecular Simulation, and Polymer Reference Interaction Site Model methods). We provide context for these methods, and map out the patchwork of theoretical models that are used to describe a diverse array of coacervate systems. We use this review of the literature to clarify a number of important theoretical challenges remaining in our physical understanding of complex coacervation.

Biomimetic Extracellular Environment Based on Natural Origin Polyelectrolyte Multilayers

Surface modification of biomaterials is a well-known approach to enable an adequate biointerface between the implant and the surrounding tissue, dictating the initial acceptance or rejection of the implantable device. Since its discovery in early 1990s layer-by-layer (LbL) approaches have become a popular and attractive technique to functionalize the biomaterials surface and also engineering various types of objects such as capsules, hollow tubes, and freestanding membranes in a controllable and versatile manner. Such versatility enables the incorporation of different nanostructured building blocks, including natural biopolymers, which appear as promising biomimetic multilayered systems due to their similarity to human tissues. In this review, the potential of natural origin polymer-based multilayers is highlighted in hopes of a better understanding of the mechanisms behind its use as building blocks of LbL assembly. A deep overview on the recent progresses achieved in the design, fabrication, and applications of natural origin multilayered films is provided. Such films may lead to novel biomimetic approaches for various biomedical applications, such as tissue engineering, regenerative medicine, implantable devices, cell-based biosensors, diagnostic systems, and basic cell biology.

Effect of Assembly pH on Polyelectrolyte Multilayer Surface Properties and BMP-2 Release

The effect of solution pH during layer-by-layer assembly of polyelectrolyte multilayer (PEM) coatings on properties relevant to orthopedic implant success was investigated. Bone morphogenetic protein 2 (BMP-2), a potent osteoconductive growth factor, was adsorbed onto the surface of anodized titanium, and PEM coatings prepared from solutions of poly-l-histidine and poly(methacrylic acid) were built on top of the BMP-2. High levels of BMP-2 released over several months were achieved. Approximately 2 μg/cm(2) of BMP-2 were initially adsorbed on the anodized titanium and a pH-dependent release behavior was observed, with more stable coatings assembled at pH = 6-7. Three different diffusion regimes could be determined from the release profiles: an initial burst release, a sustained release regime, and a depletion regime. BMP-2 was shown to maintain bioactivity after release from a PEM and the presence of a PEM was shown to preserve BMP-2 structure. No visible change was observed in surface roughness as the assembly pH was varied, whereas the surface energy decreased for samples prepared at more basic pH. These results indicate that the initial BMP-2 layer affects PEM surface structure, but not the functional groups exposed on the surface.

The Effect of Temperature Treatment on the Structure of Polyelectrolyte Multilayers

The study addresses the effect of thermal treatment on the internal structure of polyelectrolyte multilayers (PEMs). In order to get insight into the internal structure of PEMs, Neutron Reflectometry (NR) was used. PEMs with a deuterated inner block towards the substrate and a non-deuterated outer block were prepared and measured in 1% RH and in D₂O before and after a thermal treatment. Complementarily, PEMs with the same number of layers but completely non-deuterated were investigated by ellipsometry. The analysis for the overall thickness (d), the average scattering length density (SLD) and the refractive index (n) indicate a degradation of the PEM. The loss in material is independent of the number of layers, i.e., only a constant part of the PEM is affected by degradation. The analysis of the internal structure revealed a more complex influence of thermal treatment on PEM structure. Only the outermost part of the PEM degenerates, while the inner part becomes denser during the thermal treatment. In addition, the swelling behavior of PEMs is influenced by the thermal treatment. The untreated PEM shows a well pronounced odd-even effect, i.e., PDADMAC-terminated PEMs take up more water than PSS-terminated PEMs. After the thermal treatment, the odd-even effect becomes much weaker.

Dual stimuli-responsive coating designed through layer-by-layer assembly of PAA-b-PNIPAM block copolymers for the control of protein adsorption

In this paper, we describe the successful construction, characteristics and interaction with proteins of stimuli-responsive thin nanostructured films prepared by layer-by-layer (LbL) sequential assembly of PNIPAM-containing polyelectrolytes and PAH. PAA-b-PNIPAM block copolymers were synthesized in order to benefit from (i) the ionizable properties of PAA, to be involved in the LbL assembly, and (ii) the sensitivity of PNIPAM to temperature stimulus. The impact of parameters related to the structure and size of the macromolecules (their molecular weight and the relative degree of polymerization of PAA and PNIPAM), and the interaction with proteins under physico-chemical stimuli, such as pH and temperature, are carefully investigated. The incorporation of PAA-b-PNIPAM into multilayered films is shown to be successful whatever the block copolymer used, resulting in slightly thicker films than the corresponding (PAA/PAH)n film. Importantly, the protein adsorption studies demonstrate that it is possible to alter the adsorption behavior of proteins on (PAA-b-PNIPAM/PAH)n surfaces by varying the temperature and/or the pH of the medium, which seems to be intimately related to two key factors: (i) the ability of PNIPAM units to undergo conformational changes and (ii) the structural changes of the film made of weak polyelectrolytes. The simplicity of construction of these PNIPAM block copolymer-based LbL coatings on a large range of substrates, combined with their highly tunable features, make them ideal candidates to be employed for various biomedical applications requiring the control of protein adsorption.

Thermal Transitions in Polyelectrolyte Assemblies Occur via a Dehydration Mechanism

Hydrated polyelectrolyte (PE) complexes and multilayers undergo a well-defined thermal transition that bears resemblance to a glass transition. By combining molecular simulations and differential scanning calorimetry (DSC) of poly(diallyldimethylammonium) (PDAC) and poly(styrenesulfonate) (PSS) multilayers, we establish for the first time that dehydration drives the thermally induced change in plasticization of the complex and in the diffusion behavior of its components. DSC experiments show that the thermal transition appears when the assemblies are hydrated in water but not in the presence of alcohols, which supports that water is required for this transition. These findings connect PE complexes more generally to thermoresponsive polymers and liquid crystal phases, which bear phase transitions driven by the (de)hydration of functional groups, thus forming a fundamental link toward an integrated understanding of the thermal response of molecular materials in aqueous environments.

The effect of nanoparticle location and shape on thermal transitions observed in hydrated layer-by-layer assemblies

Nanoparticles can have a profound effect on thermal transitions observed in polymer nanocomposites. Many layer-by-layer (LbL) assemblies contain nanoparticles for added functionality, but the resulting effects of nanoparticles on an LbL film's thermal properties are not known. Previously, we have shown that a nanoparticle-free LbL film containing strong polyelectrolytes, poly(diallyldimethylammonium chloride)/poly(styrene sulfonate) (PDAC/PSS), exhibited a single reversible thermal transition much like a glass-melt transition. In the work presented here, nanoparticles of either spherical (SiO2) or platelet (Laponite clay) shape are inserted at varying vertical locations throughout PDAC/PSS LbL films. Temperature-controlled quartz crystal microbalance (QCM-D) and modulated differential scanning calorimetry (MDSC) are applied, for which QCM-D proved to be more sensitive to the transition. All Laponite-containing films possess two thermal transitions. During growth, Laponite-containing films exhibit steady increases in dissipation, which is proposed to arise from mechanically decoupled regions separated by the Laponite nanoparticles. For SiO2-containing films, three transitions are detectable only when the SiO2 nanoparticles are placed in the middle of the film; no transitions are observed for SiO2 placed at the bottom or top, perhaps because of a weakening of the transition. The lowest transition is close in value to that of neat PDAC/PSS LbL films, and was assigned to a "bulk" response. The higher transition(s) is attributed to polymer chains in an interfacial region near the nanoparticle. We propose that nanoparticles restrict segmental mobility, thus elevating the transition temperature in the interfacial region.

Thermal transitions in hydrated layer-by-layer assemblies observed using electrochemical impedance spectroscopy

Layer-by-layer (LbL) assemblies have been of great interest due to their versatile functionality and ease of fabrication, but their response to temperature is not completely understood. It has been recently shown that hydrated LbL assemblies of poly(diallyldimethylammonium chloride) (PDAC) and poly(styrene sulfonate) (PSS) under go a thermal transition much like a "glass-melt" transition. This thermal transition is of great interest because many LbL applications are found in water. Here, we report upon the nature of this thermal transition as probed using electrochemical impedance spectroscopy (EIS) as a function of assembly salt concentration, film thickness, and outermost layer. EIS reveals that the transition is signified by a structural rearrangement of virtual pores, resulting in increased conductivity and decreased surface coverage of the electrode. Two separate thermal transitions are obtained from changes in the film resistance (Ttr,Rf) and the charge transfer resistance (Ttr,Rct). Only Ttr,Rct is strongly dependent on film thickness, salt concentration, and outermost layer, for which values ranging from 50 to 64 °C were observed. As the assembly salt concentration increases from 0.5 M to 1.0 M NaCl, Ttr,Rct increases by about 10 °C. Below 20 layers, deviations of Ttr,Rct with respect to outermost layer appear, in which PSS-capped LbL films tend to show elevated Ttr,Rct values. These results suggest that extrinsic charge compensation plays a large role in the value of Ttr,Rct in which a large degree of extrinsic charge compensation drives Ttr,Rct towards higher values. On the other hand, Ttr,Rf is largely unaffected by assembly parameters, and closer in value to prior reports via calorimetry and quartz crystal microbalance with dissipation.

Layers over layer-by-layer assemblies: silanization of polyelectrolyte multilayers

The functionalization of poly(allylamine hydrochloride)/poly(acrylic acid) (PAH/PAA) polyelectrolyte multilayers by silanes reacted from the gas phase is studied depending on reaction time and temperature, pH of multilayer assembly, and nature of the reacting silane group. Whereas monochlorosilanes only diffuse in the multilayer and graft in limited amount, trichloro- and triethoxysilanes form rapidly a continuous gel layer on the surface of the multilayer, with a thickness of ca. 10-20 nm. The reactivity is lower in the strongly paired regime of the multilayers (neutral assembly conditions) but otherwise is not affected by the pH of multilayer assembly. Silanization considerably broadens the range of possible functionalities for (PAH/PAA) multilayers: hydrophobicity, surface-initiated polymerization, and grafting of fluorescent probes by the formation of disulfide bridges are demonstrated. Conversely, our results also broaden the range of substrates that can be functionalized by silanes, using (PAH/PAA) multilayers as ubiquitous anchoring layers.

Improving the gas barrier property of clay-polymer multilayer thin films using shorter deposition times

Relatively fast exposure times (5 s) to aqueous solutions were found to improve the gas barrier of clay-polymer thin films prepared using layer-by-layer (LbL) assembly. Contrary to the common belief about deposition time (i.e., the longer the better), oxygen transmission rates (OTRs) of these nano-brick-wall assemblies are improved by reducing exposure time (from 1 min to 5 s). Regardless of composition, LbL films fabricated using shorter deposition time are always thicker in the first few layers, which correspond to greater clay spacing and lower OTR. A quadlayer (QL) assembly consisting of three repeat units of branched polyethylenimine (PEI), poly(acrylic acid) (PAA), PEI and montmorillonite (MMT) clay is only 24 nm thick when deposited with 1 min exposure to each ingredient. Reducing the exposure time of polyelectrolytes to 5 s not only increases this film thickness to 55 nm but also reduces the oxygen transmission rate (OTR) to 0.05 cm3/(m2 day atm), which is 2 orders of magnitude lower than the same film made using 1 min exposures. A conceptual model is proposed to explain the differences in growth and barrier, which are linked to polyelectrolyte relaxation, desorption, and interdiffusion. The universality of these findings is further exemplified by depositing clays with varying aspect ratios. This ability to quickly deposit high-barrier nanocomposite thin films opens up a tremendous opportunity in terms of commercial-scale processing of LbL assemblies.

Temperature-triggered shape-transformations in layer-by-layer microtubes

Freely released microtubes in water transform to ellipsoids and spheres at high temperatures, while microtubes bound to the template surface showed periodic voids suggestive of Rayleigh instabilities.